Mark D Barton

Interests

Research

My research interests span the general areas of mass and energy transfer in the lithosphere, particularly those involving fluids be they aqueous or melts. These topics are fundamental to undertanding the nature of mineral and energy resources, and how we make the best decisions about how they might (or might not) be used. Given this breadth, my work has tended to follow the greatest demand, particularly where funding (USGS, NSF, industry) was available and driven in part by the interests / needs of my graduate students. My original focus (and continuing interest) is in the fundamental stability of minerals and fluids, beginning with their structural and thermodynamic properties, and with their phase equilbria and geochemistry. Experimental, theoretical, and observational studies have continued with a handful of students who have, for instance, worked on the crystal chemistry and petrology of the tourmaline group (Ana Collins), the geochemistry of thallium (Shelby Rader), and the geochemistry of arsenic (Jenny Dabbs). Similarly, my early (mainly at UCLA) field and petrology focus was on the evolution of magmatism and metamorphism in arcs (contact metamorphism, evolution of Cordilleran magmatism, mass transfer processes in subduction zones). A few recent students have continued with these themes (e.g., James Girardi on Mesozoic magmatism in SW N Am, and coastal Chile), however most UA grad students (and applicants, of which there have been 40-60 per year) have been keen on applications to ore deposit (ore-forming systems) and related geochemical topics. The major themes here have been multi-disciplinary approaches to the study of the geologic systems that generate ore deposits of multiple types. Among these are the evolution or arcs and magmatic hydrothermal systems (e.g., porphyry Cu/Mo/Au), brine-dominated hydrothermal systems (e.g., Fe-oxide copper-gold; sediment-hosted Cu-Co-Ag-U), and precious metal deposits (including Carlin-type Au). These topics allow combination of rigorous field-based research (which appeals to and is needed by many students) with quantitive analytical and theoretical approaches. A corollary of this observation-based approach to mineral resource topics has been the abundance of industry support – partly because they recognize the value of this "basic" research, but more importantly because they are keen to help support rigorous field-related education at the graduate level. The UA is one of very few schools world-wide that does this, and our success with industry and in attracting students reflects that.

Teaching

My teaching interests span much of hard rock geology notably including quantitative chemical and physical approaches (analytical and theoretical) to addressing geologic problems, rigorous field approaches, and applications to problems of mineral and energy resources. My mission is to challenge geology students at all levels become better scientists: both through increased rigor and through a broader appreciation of the breadth and role of the geosciences in addressing societal challenges. I am also committed to broadening education related to use of earth materials (mineral resources among them) to a diverse audience from the general public and K-12 (through LIMR efforts) and through interdisciplinary courses, minors, and professional / continuing educations (including online) at all levels. Specifically, I have taught (and remain interested in teaching) both undergraduate and graduate courses. Undergraduate courses have included, introductory geology, physical geology, mineralogy, introductory petrology, economic geology, and field camp. Graduate courses have included advanced mapping (field course), advanced ore deposits (theory and applications), thermodynamics for geologists, and multiple topical courses including seminars. An important part of my teaching over the last 15 years has involved outreach to the professional community through our extended (10-day) short courses which combine teaching to industry professionals from around the world and our students (mostly graduate, but including a few undergraduate students). These courses, offered through the Lowell Program in Economic Geology (Eric Seedorff, Director), are one of the most geologically visible components of the Lowell Institute for Mineral Resources – to date, there have been about 1,000 participants from several dozen countries and many companies representing 6 contintents.

Courses

Scholarly Contributions

Chapters

• Barton, M. D., & King, C. A. (2022). Contrasting igneous-related Eocene hydrothermal systems of the northern Copper Basin area, Battle Mountain, Nevada. In Vision for Discovery: Geology and Ore Deposits of the Basin and Range. Reno, NV: Geological Society of Nevada.
• Barton, I. F., Barton, M. D., & Thorson, J. P. (2018). Characteristics of Cu and U-V deposits in the Paradox Basin (Colorado Plateau) and associated alteration. In Society of Economic Geologists Guidebook Series 59(pp 73-102). Society of Economic Geologists.
• Barton, M. D., Barton, I. F., & Thorson, J. P. (2018). Paleofluid flow in the Paradox Basin: Introduction. In Society of Economic Geologists Guidebook Series 59(pp 1-12). Society of Economic Geologists.
• Barton, M. D., Barton, I. F., & Thorson, J. P. (2018). Paradox Basin fluids and Colorado Plateau copper, uranium and vanadium deposits: Road log. In Society of Economic Geologists Guidebook Series 59(pp 47-72). Society of Economic Geologists.
• Thorson, J. P., Barton, I. F., & Barton, M. D. (2018). Paleofluid flow in the Paradox Basin: Introduction. In Society of Economic Geologists Guidebook Series 59(pp 1-12).
• Thorson, J. P., Barton, I. F., & Barton, M. D. (2018). Paradox Basin fluids and Colorado Plateau copper, uranium and vanadium deposits. In Society of Economic Geologists Guidebook Series 59(pp 47-72). Society of Economic Geologists.
• Thorson, J. P., Barton, M. D., & Barton, I. F. (2018). Characteristics of Cu and U-V deposits in the Paradox Basin (Colorado Plateau) and associated alteration. In Society of Economic Geologists Guidebook Series 59(pp 73-102).
• Barton, M. D. (2014). Iron Oxide(-Cu-Au-REE-P-Ag-U-Co) Systems. In Ore Deposits (2nd edition): Treatise on Geochemistry, Volume 11(pp 515-541). Elsevier Inc. doi:10.1016/b978-0-08-095975-7.01123-2
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  The Fe oxide(-Cu-Au-REE-P-U) family of Cu, Fe, and/or Au deposits (or IOCG) represents a geochemically coherent but geologically diverse group that formed globally from the Archean to the Holocene. IOCG systems exhibit intense, voluminous Na-Ca-K-Fe(-H) hydrothermal alteration related to flow of moderately to highly saline metal-rich, sulfur-poor brines. These fluids account for the characteristic sulfide-poor, oxide-rich mineralogy and the alkali-rich character of the alteration and for the varied contents of Cu, Au, and other metals. Associated igneous rocks range from mafic to felsic, subalkaline to alkaline. Metal enrichments vary with host-rock type and sulfur availability. Geologic settings are tectonically diverse but commonly have evidence for contemporaneous or older evaporitic environments. Magmatism drives most systems, yet clearly amagmatic examples occur. Geochemical and petrologic studies demonstrate igneous-dominated sources for some solutes and permissive evidence for a connection to magmatic fluids. In many cases, a central role for nonmagmatic saline fluids is evident. The geochemistry of the latter fluids rationalizes the key distinguishing features of the IOCG family. The diversity of the IOCG family parallels that seen in other major families of deposits; their distinctive attributes indicate that they comprise a separate class of (mainly) terrestrial hydrothermal systems. © 2014 Elsevier Ltd. All rights reserved.
• Barton, M. D. (2014). Iron oxide(-Cu-Au-REE-P-Ag-U-Co) systems. In Treatise on Geochemistry(pp 515-541). Oxford: Elsevier.
• Barton, M. D., Dilles, J. H., Girardi, J. P., Haxel, G., Johnson, D. A., Kreiner, D. C., & Seedorff, E. (2011). Jurassic igneous-related metallogeny of southwestern North America. In Great Basin Evolution and Metallogeny(pp 373-376). Reno, Nevada: Geological Society of Nevada.
• Barton, M. D., & Young, S. (2002). Non-pegmatitic deposits of Beryllium: Mineralogy, geology, phase equilibria and origin. In Reviews in Mineralogy and Geochemistry(pp 591-691). De Gruyter Mouton. doi:10.2138/rmg.2002.50.14
• Christiansen, E. H., Kowallis, B. J., & Barton, M. D. (1994). Temporal and Spatial Distribution of Volcanic Ash in Mesozoic Sedimentary Rocks of the Western Interior: An Alternative Record of Mesozoic Magmatism. In Mesozoic Systems of the Rock Mountain Region, USA(pp 73-94). Rocky Mountain Section (SEPM).
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  Abstract The Mesozoic Era of the Western Interior of the United States was dominated by sedimentation in shallow marine and continental settings behind a magmatic arc developed along the western margin of the continent. Part of the history of this magmatism is preserved as altered volcanic ash enclosed in sedimentary rocks. For the Mesozoic of the Western Interior, we have compiled from the literature the ages and locations of discrete volcanic ash beds (mostly bentonites) and ash–rich rocks (e.g., analcime–rich or bentonitic mudstones). These data are plotted on a series of eight paleogeologic maps and compared with the locations of contemporaneous Mesozoic sedimentary and plutonic rocks. From these maps we infer: (1) Most ash was erupted from volcanoes in the arc during plinian eruptions of silicic magma associated with caldera–collapse and emplacement of ignimbrite. The ash was deposited as pyroclastic fall, and then reworked physically and chemically by sedimentary processes. (2) Ash–producing volcanism was intermittent with pulses separated by as few as several million years to as many as forty million years. (3) Major periods of volcanism occurred during the Late Triassic (about 225 Ma), during the Middle Jurassic (about 160 to 140 Ma), and during two periods in the Late Cretaceous, peaking in the Cenomanian (about 95 Ma) and again near the Campanian–Maastrichtian boundary (about 75 Ma). Volcanic quiescence prevailed during the Early and Middle Triassic, from the latest Triassic to the Middle Jurassic, and perhaps during the early Cretaceous. (4) Volcanic episodes correlate closely with the temporal pattern of pluton emplacement in the western United States. (5) The location and extent of the arc plutonic belt and the distribution of ash in each time interval constrain the locations of the volcanoes from which the ash erupted. For example, the bentonitic mudstones of the Late Triassic Chinle Formation contain ash probably erupted from volcanoes in what is now southeastern California, southern Arizona, and northern Mexico. Middle and Late Jurassic ashes probably erupted from near the continental margin from vents in what is now the Sierra Nevada Batholith, whereas Cretaceous ashes erupted from the Idaho and Boulder batholiths as well as the Sierra. As a result of the distribution of these magmatic systems, no volcanic ash is preserved in sedimentary rocks in Montana that are older than Aptian (mid- Cretaceous). (6) Two general types of vent regions may have erupted compositionally distinct ashes. Continental margin regions are typified by the northern or western Sierra igneous suites and the Idaho and Boulder batholiths comprise a continental interior suite. (7) In the Western Interior, Mesozoic sedimentary rocks are not widespread during times of magmatic quiescence. This relationship can be explained if periods of slow sea-floor spreading increased the volume of the ocean basins, caused elevation of the continental margins, and decreased rates of intrusion and volcanism above the slab being subducted beneath the western margin of North America.
• Barton, M. D., Ilchik, R. P., & Marikos, M. (1991). Chapter 7. METASOMATISM. In Reviews in Mineralogy and Geochemistry (v 26)(pp 321-350). De Gruyter. doi:10.1515/9781501509612-010

Journals/Publications

• Bos Orent, E., Barton, M. D., & Kirk, J. D. (2025). Episodic copper mineralization in sedimentary basins: evidence from the Paradox Basin, USA. Earth and Planetary Science Letters, 671(Issue). doi:10.1016/j.epsl.2025.119620
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  Episodicity is common in mineral systems – it is responsible for mineral parageneses that form over timescales from 10 s of kyr to 10 s of Myr. New U-Pb dating of vein carbonate minerals reveals an unexpected epoch of fluid flow and sediment-hosted copper (Cu) mineralization between 18 and 3 Ma across large parts of the evaporite-dominated Paradox Basin. Sulfide-bearing carbonate veins from 9 locations with a mix of geologic settings and metal traps were analyzed by laser ablation inductively coupled mass spectrometry (LA-ICP-MS); of 37 samples examined, 13 from 9 mineral deposits had suitable U-Pb contents. Our results add to previously reported mid-Cretaceous to Oligocene ages for Cu mineralization in some of the same areas, highlighting the long-term and episodic nature of these systems. Cu mineralization requires appreciable fluid flux, yet the new ages mostly precede flow related to rapid exhumation (
• Lucero, D., Bailey, L., Kim, J. H., Voller, V., Hughes, A., Krantz, R., Lingrey, S., Barton, M. D., Barton, I., Reiners, P., McIntosh, J., Neuzil, C., Thorson, J., & Person, M. (2025). Influence of internal fluid driving mechanisms on red bed bleaching in the Paradox Basin (Colorado Plateau, Utah and Colorado, USA). Bulletin of the Geological Society of America, 137(Issue 5-6). doi:10.1130/b37654.1
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  While it has been known for some time that reducing fluids have bleached red beds adjacent to fault zones and regionally across the Colorado Plateau, the volumes of fluids expelled along faults have never been quantified. We have developed and applied a suite of one-dimensional hydrologic models to test the hypothesis that internally generated, reducing fluids migrated up sub-basin bounding faults across the Paradox Basin and bleached overlying red beds. The internal fluid driving mechanisms included are mechanical compaction, petroleum and natural gas generation, aquathermal expansion of water, and clay dewatering. The model was calibrated using pressure, temperature, porosity, permeability, and vitrinite reflectance data. Model results indicate that sediment compaction was the most important pressure generation mechanism, producing the majority of internal fluids sourced during basin evolution. Peak fluid migration occurred during the Pennsylvanian–Permian (325–300 Ma) and Cretaceous (95–65 Ma) periods, the latter being concurrent with simulated peak oil/gas generation (87–74 Ma), which likely played a role in the bleaching of red beds. Batch geochemical advection models and mass balance calculations were utilized to estimate the volume of bleaching in an idealized reservoir having a thickness (∼100 m) and porosity (0.2) corresponding to bleached reservoirs observed in the Paradox Basin. Bleaching volume calculations show that internal fluid driving mechanisms were likely responsible for fault-related alteration observed within the Wingate, Morrison, and Navajo Formations in four localities across the Paradox Basin in the Colorado Plateau, Utah and Colorado, USA. The volume calculation required that 33%–55% of the total basinal fluids, composed of hydrogen-sulfide and paleo-seawater, migrated into an overlying red bed reservoir (0.5 wt% Fe2O3).
• Barton, I., & Barton, M. (2024). Paradox Basin Uranium-Vanadium Deposits: Comparative Mineralogy and Paragenesis. Mining, Metallurgy and Exploration, 41(Issue 6). doi:10.1007/s42461-024-01128-6
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  Broadly similar U(-V) deposits are hosted by Permian to Jurassic sandstones in the Paradox Basin of the Colorado Plateau. Common features of all the Paradox Basin deposits include occurrence in bleached red bed sandstones; accessory barite and/or celestine; authigenic Ti minerals; lack of correlation between mineralization and plant coal distribution; and evidence for or actual traces of hydrocarbons in the rock before and/or during mineralization. All but the structure-hosted Cutler deposits also show a mix of hematite, pyrite, and hypogene U and/or V minerals enclosed under authigenic overgrowths surrounding detrital quartz cores, which are extensively replaced by fringes of vanadian phyllosilicates. In the Entrada-hosted deposits, all but traces of hypogene U and V oxides have been removed to leave mainly the V-phyllosilicate minerals, but otherwise they resemble the mineralogy and paragenesis in the rest of the Paradox Basin U-V deposits. This paper presents and compares the deposit types to each other and to global sandstone-hosted U resources. Deposits hosted in the Jurassic Salt Wash Member of the Morrison Formation mostly form tabular, V-dominated bodies in permeable, trough cross-bedded horizons of bleached former red beds. Common quartz overgrowths entrap pyrite, pitchblende, and montroseite. Pitchblende and montroseite also form interstitial masses in cementing V-phyllosilicates, which corrode and partially replace the quartz overgrowths. Common accessory phases include pyrite (some framboidal), chalcopyrite, ferroselite, clausthalite, galena, sphalerite, and barite, with minor asphalt globules that corrode quartz overgrowths and cores and contain pitchblende and pyrite. Down the stratigraphic section, the Jurassic Entrada hosts minor lenticular deposits in aeolian sandstones just below a capping limestone. Ore minerals consist mainly of roscoelite replacing quartz overgrowths and cementing the sandstone. Except for small vanadiferous pitchblende inclusions trapped under quartz overgrowths, minor U-vanadates are the only U minerals observed. Continuing down-section, U-V deposits in the Triassic Chinle occur in conglomerates and sandstones just above the Chinle-Cutler unconformity in the Big Indian district, and in the basal Chinle in White Canyon. Quartz overgrowths are rarer but also enclose inclusions of hematite and pitchblende, more rarely V minerals. Pitchblende, montroseite, and V-phyllosilicates are the main ore minerals, forming interstitial masses and replacing some of the plant coal in the rocks. Accessory minerals include pyrite, sphalerite, galena, and barite. Secondary fluid inclusions fluoresce bright blue in ultraviolet light, indicating hydrocarbons. Chinle-hosted deposits in the San Rafael Swell occur as uraniferous asphalt that also contains V-Cr-Fe oxide. Roscoelite hosts most of the V and the deposits contain a large suite of accessory minerals, including pyrite, chalcopyrite, Ni-arsenide, sphalerite, galena, realgar, and barite. Where bleached, the coarse sandstone of the underlying Cutler Formation hosts small deposits below or near Chinle orebodies, either along permeable sandstones or along steep faults. Cutler-hosted deposits showing stratigraphic control share most features with the nearby Chinle orebodies, including quartz and rarer feldspar overgrowths enclosing U-V minerals and an assemblage dominated by pitchblende and montroseite with minor V-phyllosilicates. Deposits hosted along faults in the Cutler are highly distinct, mineralized with pitchblende and uraniferous asphalt in the fault cores and V-phyllosilicate in surrounding areas. Alone among the U and V deposits of the Paradox Basin, no quartz overgrowths have been observed in this type. Deposits’ interpreted parageneses are also similar, with bleaching of original red beds during or shortly before the beginning of mineralization, followed by further U-V deposition in the main ore stage. Late in the ore stage, fresh V or V (hydr)oxide minerals back-reacted with silica in quartz overgrowths to form V-phyllosilicates, while accessory base metal sulfides and selenides precipitated along with barite. These similarities of mineralogy and texture imply a similar mechanism of formation for most of the Paradox Basin U-V deposits, corresponding either to a single basinwide ore-forming event or to the same geologic processes independently repeated in different strata at different times. Hydrocarbons were likely a major reductant, with ore precipitating where an oxidized metal-bearing fluid either mixed with hydrocarbons or entered a rock previously reduced by their passage. Lastly, the Paradox Basin deposits’ most remarkable feature is their high V content, which is unique worldwide and makes the area a world-class resource for this critical green energy metal.
• Bos Orent, E., Barton, M. D., & Barton, I. F. (2024).

  Characterization of U(-V) deposits in the La Sal District, UT and CO, and their relationship to Paradox Basin fluid flow

  . Mining, Metallurgy, & Exploration, 41(4), 2693-2721.
• Bos Orent, E., Barton, M. D., & Barton, I. F. (2024). Characterization of U(-V) Deposits in the La Sal District, UT and CO and Their Relationship to Paradox Basin Fluid Flow. Mining, Metallurgy and Exploration, 41(Issue 5). doi:10.1007/s42461-024-01062-7
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  This paper synthesizes new and previous work on the tabular sandstone-hosted uranium and vanadium deposits of the La Sal district, one of the principal U-V districts of the Colorado Plateau. Deposits form a 1–3 km wide, E-W trending 30 km long trend spanning the Utah-Colorado border, approximately orthogonal to the Uravan belt. Ore is hosted in the uppermost fluvial subarkosic sandstones of the Salt Wash Member of the Jurassic Morrison Formation and typically forms channel-parallel, elongate orebodies up to 180 m long, 90 m wide, and 1 m thick. Sandstones are interbedded with silty, muddy, and calcareous units. Principal mineralogical changes include quartz overgrowths accompanied by destruction of early diagenetic hematite. Precipitation of compositionally distinct carbonate cements and clays followed. Bleaching was prior to and/or contemporaneous with mineralization, which is restricted to bleached rocks. Petrography shows that ore minerals (uraninite, coffinite, and montroseite) in part predate growth of authigenic quartz and calcite cements, followed by the formation of ferroan dolomites. Abundant V-rich phyllosilicates may reflect back-reaction of montroseite with quartz and other minerals. New U-Pb dating of ore-hosting calcite (~144 Ma) and K-Ar dating of V-clays (~42–36 Ma) parallel published results for elsewhere on the Plateau. Sedimentary structures (e.g., crossbedding), primary porosity, and the distribution of lithofacies in the local Salt Wash channel system control mineral growth. The thin section- to district-scale observations suggest that mineralization formed either by mixing of two fluids, or alternatively by reaction of oxidized fluids with a reductant earlier introduced during bleaching, as has been suggested in other Plateau deposits.
• Salati, S., Barton, M. D., Neilson, J. W., Richardson, C. A., Orent, E. B., & Riley, D. N. (2024). Abandoned mine lands inventory: Progress, collaboration and challenges in Arizona. Mining Engineering, 76(Issue 4).
• Rader, S. T., King, C. A., Barton, M. D., & Mazdab, F. K. (2023). New constraints on fluid chemistry and elemental mobility during hydrothermal alteration from thallium isotope systematics of the battle mountain district, North-central Nevada. Applied Geochemistry, 156(Issue). doi:10.1016/j.apgeochem.2023.105758
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  The Battle Mountain area is a major porphyry style Au (–Cu) district in northern Nevada, forming one end of the Battle Mountain-Eureka mineral trend. This trend, along with several others in the north-central Nevada region, hosts some of the world's most prolific gold mineralization, which is oftentimes associated with a suite of trace elements including arsenic, antimony, tungsten, and thallium and can be related to or overprinted by hydrothermal alteration. However, determining the extent of control hydrothermal fluids exert on some of the deposits in the region has been difficult to ascertain. One of the associated trace metals in the region, thallium (Tl), is a highly incompatible element and, as such, dominantly resides in the continental crust, where it can be easily remobilized during hydrothermal alteration. While previous work has demonstrated the effects of hydrothermal alteration on Tl distribution and fractionation, the controls responsible for the observed Tl fractionation during hydrothermal alteration are still poorly characterized but may provide insight into fluid behavior. Here, we present new Tl isotope composition and concentration data for a suite of 54 mineral separates obtained from 43 samples from the Battle Mountain area, which range from unaltered intrusive igneous rocks through varying types and degrees of hydrothermally altered rocks. Measured Tl concentrations vary by more than an order of magnitude, from below detection limit (0.2 ppm in this study) to 2.0 ppm, while ε205Tl ranges between −5.0 and +2.2 (ε205Tl is the deviation of the 205Tl/203Tl isotope ratio of a sample from a standard in parts per 104). Thallium concentrations correlate positively with whole-rock potassium (K), thus show strong increases during K alteration, and demonstrate significantly lower ε205Tl values within K-altered samples. Conversely, during later, overprinting Na–Ca alteration, both K and Tl are removed, resulting in a noted decrease in Tl concentrations coupled with a shift to significantly higher ε205Tl values. It appears that during hydrothermal alteration, 203Tl is more easily (re)mobilized and (re)distributed, which reflects: 1) a first-order hydrothermal alteration control that relates to the transport of Tl during the formation of a new, metasomatic mineral assemblage (particularly the breakdown and/or formation of K-bearing minerals) and 2) a second-order mineralogical control, relating to inter-mineral equilibrium, which also results in a small fractionation effect.
• Rader, S. T., King, C., Barton, M. D., & Mazdab, F. K. (2022). Controls on thallium redistribution and stable isotope variations during hydrothermal alteration of the Battle Mountain district, north-central Nevada: A mineralogical approach. Applied Geochemistry.
• Barton, I. F., Gabriel, M. J., Barton, M. D., Lyons-Barral, J., Duplessis, L., & Roberts, C. (2020). Ground- and drone-based hyperspectral remote sensing for mineral mapping in active mine environments – a pilot study in mine-scale geometallurgy. Minerals Engineering.
• Barton, I. F., Gabriel, M. J., Barton, M. D., Lyons-Barral, J., Duplessis, L., & Roberts, C. (2021). Ground- and drone-based hyperspectral remote sensing for mineral mapping in active mine environments – a pilot study in mine-scale geometallurgy. Mining, Metallurgy, & Exploration.
• Can-Sener, S. E., Thomas, V. M., Hogan, D. E., Maier, R. M., Carbjales-Dale, M., Barton, M. D., Karanfil, T., Crittenden, J. C., & Amy, G. L. (2020). Recovery Potential of Critical Minerals and Metals from Aqueous Sources. ACS Sustainable Chemistry and Engineering.
• Kim, J. H., Bailey, L., Noyes, C., Tyne, R. L., Ballentine, C. J., Person, M., Ma, L., Barton, M., Barton, I., Reiners, P. W., Ferguson, G., & McIntosh, J. (2022). Hydrogeochemical evolution of formation waters responsible for sandstone bleaching and ore mineralization in the Paradox Basin, Colorado Plateau, USA. Bulletin of the Geological Society of America, 134(Issue 9-10). doi:10.1130/b36078.1
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  The Paradox Basin in the Colorado Plateau (USA) has some of the most iconic records of paleofluid flow, including sandstone bleaching and ore mineralization, and hydrocarbon, CO2, and He reservoirs, yet the sources of fluids responsible for these extensive fluid-rock reactions are highly debated. This study, for the first time, characterizes fluids within the basin to constrain the sources and emergent behavior of paleofluid flow resulting in the iconic rock records. Major ion and isotopic (δ18Owater; δDwater; δ18OSO4; δ34SSO4; δ34SH2S; 87Sr/86Sr) signatures of formation waters were used to evaluate the distribution and sources of fluids and water-rock interactions by comparison with the rock record. There are two sources of salinity in basinal fluids: (1) diagenetically altered highly evaporated paleo-seawater-derived brines associated with the Pennsylvanian Paradox Formation evaporites; and (2) dissolution of evaporites by topographically driven meteoric circulation. Fresh to brackish groundwater in the shallow Cretaceous Burro Canyon Formation contains low Cu and high SO4 concentrations and shows oxidation of sulfides by meteoric water, while U concentrations are higher than within other formation waters. Deeper brines in the Pennsylvanian Honaker Trail Formation were derived from evaporated paleo-seawater mixed with meteoric water that oxidized sulfides and dissolved gypsum and have high 87Sr/86Sr indicating interaction with radiogenic siliciclastic minerals. Upward migration of reduced (hydrocarbon- and H2S-bearing) saline fluids from the Pennsylvanian Paradox Formation along faults likely bleached sandstones in shallower sediments and provided a reduced trap for later Cu and U deposition. The distribution of existing fluids in the Paradox Basin provides important constraints to understand the rock record over geological time
• Kim, J., Bailey, L., Noyes, C., Tyne, R. L., Ballentine, C. J., Person, M., Ma, L., Barton, M. D., Barton, I. F., Reiners, P. W., Ferguson, G., & Mcintosh, J. C. (2022). Hydrogeochemical evolution of formation waters responsible for sandstone bleaching and ore mineralization in the Paradox Basin, Colorado Plateau, USA. Geological Society of America Bulletin. doi:https://doi.org/10.1130/B36078.1
• Kim, J., Bailey, L., Noyes, C., Tyne, R. L., Ballentine, C. J., Person, M., Ma, L., Barton, M. D., Barton, I. F., Reiners, P. W., Ferguson, G., & Mcintosh, J. C. (2022). Hydrogeochemical evolution of formation waters responsible for sandstone bleaching and ore mineralization in the Paradox Basin. Geological Society of America Bulletin.
• Mazdab, F. K., Lecumberri-Sanchez, P., Steele-MacInnis, M. J., Barton, M. D., Seedorff, C. E., & Runyon, S. R. (2019). Coarse muscovite veins and alteration in porphyry systems. Ore Geology Reviews.
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  Runyon, S. E., Seedorff, E., Barton, M. D., Steele-MacInnis, M. J., Lecumberri-Sánchez, P., and Mazdab, F. K., submitted, Coarse muscovite veins and alteration in porphyry systems: Submitted to Ore Geology Reviews 31 Dec 2018.
• Mcintosh, J. C., Ferguson, G., Reiners, P. W., Barton, I. F., Barton, M. D., Ma, L., Person, M., Ballentine, C. J., Tyne, R. L., Noyes, C., Bailey, L., & Kim, J. (2022). Hydrogeochemical evolution of formation waters responsible for sandstone bleaching and ore mineralization in the Paradox Basin, Colorado Plateau, USA. Geological Society of America Bulletin. doi:https://doi.org/10.1130/B36078.1
• Roberts, C., DuPlessis, L., Barton, M. D., Lyons-Baral, J., Gabriel, M. J., & Barton, I. F. (2019). Ground- and drone-based hyperspectral remote sensing for large-scale mineral mapping in active mine environments – a pilot study. Mining, Metallurgy, & Exploration.
• Steele-MacInnis, M. J., Lecumberri-Sanchez, P., Mazdab, F. K., Barton, M. D., Seedorff, C. E., Nickerson, P. A., & Runyon, S. E. (2019). Sodic-calcic family of alteration in porphyry systems of Arizona and adjacent New Mexico. Economic Geology.
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  Runyon, S. E., Nickerson, P. A., Seedorff, E., Barton, M. D., Mazdab, F. K., Lecumberri-Sánchez, P., and Steele-MacInnis, M. J., submitted, Sodic-calcic family of alteration in porphyry systems of Arizona and adjacent New Mexico: Submitted to Economic Geology 30 June 2018, resubmitted 27 Jan 2019, 15 March 2019.
• Amy, G. L., Barton, M. D., Carbajales-dale, M., Crittenden, J. C., Hogan, D. E., Karanfil, T., Maier, R. M., Sener, S. E., & Thomas, V. M. (2021). Recovery of Critical Metals from Aqueous Sources.. ACS sustainable chemistry & engineering, 9(35), 11616-11634. doi:10.1021/acssuschemeng.1c03005
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  Critical metals, identified from supply, demand, imports, and market factors, include rare earth elements (REE), platinum group metals, precious metals, and other valuable metals such as lithium, cobalt, nickel, and uranium. Extraction of metals from U.S. saline aqueous, emphasizing saline, sources is explored as an alternative to hardrock ore mining. Potential aqueous sources include seawater, desalination brines, oil-and-gas produced waters, geothermal aquifers, and acid mine drainage, among others. A feasibility assessment reveals opportunities for recovery of lithium, strontium, magnesium, and several REE from select sources, in quantities significant for U.S. manufacturing and for reduction of U.S. reliance on international supply chains. This is a conservative assessment given that water quality data are lacking for a significant number of critical metals in certain sources. The technology landscape for extraction and recovery of critical metals from aqueous sources is explored, identifying relevant processes along with knowledge gaps. Our analysis indicates that aqueous mining would result in much lower environmental impacts on water, air, and land than ore mining. Preliminary assessments of the economics and energy consumption of recovery show potential for recovery of critical metals.
• Barton, I. F., Gabriel, M. J., Lyons-Baral, J., Barton, M. D., Duplessis, L., & Roberts, C. (2021). Extending geometallurgy to the mine scale with hyperspectral imaging: a pilot study using drone- and ground-based scanning. Mining, Metallurgy and Exploration, 38(Issue 2). doi:10.1007/s42461-021-00404-z
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  Geometallurgical assessment of orebodies in the mining industry typically relies on bench-scale or lab-based characterization techniques. In this study, we investigate drone- and tripod-based field hyperspectral imaging as a potential addition to the geometallurgy toolkit in multiple applications. This pilot study tests hyperspectral imaging for large-scale mineral mapping in and around the active Lisbon Valley copper mine, including natural exposures, previously producing U-V mines, highwalls, dumps, and leaching sites. Tests include different (supervised and unsupervised) mineral data classification methods, varying mineral spectral reference libraries, comparison with ground-truth geological and spectroscopic mapping and sampling, and integration with LiDAR data. The results show that hyperspectral scans can produce spatially registered maps of the distribution of different spectrally active mineral types over dumps, highwalls, leach pads, and natural outcrops. Clays, other phyllosilicates, carbonates, and sulfates showed up particularly well. The sensor was also able to distinguish dry from lixiviant-saturated areas and map different clay types on the leach pads, and shows promise for differentiating types and health of vegetation. These results suggest that hyperspectral imaging, if coupled with robust ground-truthing, can be a useful complement to existing geometallurgical techniques in the mining industry, such as geological mapping, blast hole sampling and automated mineralogy identifications, and handheld spectrometry. In particular, hyperspectral imaging has promise for mapping the distribution of acid-consuming minerals; mapping the distribution of swelling, sliming, and heap-blinding clays; and pinpointing problem areas on heap leach pad surfaces.
• Can Sener, S. E., Thomas, V. M., Hogan, D. E., Maier, R. M., Carbajales-Dale, M., Barton, M. D., Karanfil, T., Crittenden, J. C., & Amy, G. L. (2021). Erratum: Recovery of Critical Metals from Aqueous Sources (ACS Sustainable Chemistry and Engineering (2021) 9 (35) (11616-11634) DOI: 10.1021/acssuschemeng.1c03005). ACS Sustainable Chemistry and Engineering, 9(Issue 44). doi:10.1021/acssuschemeng.1c06821
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  Several numerical errors were recently discovered in Table 2 of our original perspective (https://pubs.acs.org/doi/10.1021/ acssuschemeng.1c03005). Specifically, several table values were off by a factor of 1000, caused by a units-conversion error. A corrected version of Table 2 appears below. While Table 4 later in the perspective builds upon some of the Table 2 values, Table 4 values are all based on correct Table 2 data or other data and need no correction. (Table Presented).
• Roberts, C., DuPlessis, L., Lyons-Barral, J., Barton, M. D., Gabriel, M. J., & Barton, I. F. (2021). Extending geometallurgy to the mine scale with hyperspectral imaging: a pilot study using drone and ground-based scanning. Mining, Metallurgy, & Exploration, 38(2), 799-818.
• Barton, I. F., Rathkopf, C. A., & Barton, M. D. (2020). Rhenium in Molybdenite: a Database Approach to Identifying Geochemical Controls on the Distribution of a Critical Element. Mining, Metallurgy and Exploration, 37(Issue 1). doi:10.1007/s42461-019-00145-0
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  Molybdenite is the world’s principal source of rhenium (Re), a critical element in multiple high-tech applications. However, the Re contents in molybdenite vary by orders of magnitude on scales ranging from single grains to whole deposits. In order to better understand the systematics of this variation and what geochemical factors control molybdenite Re concentration, and hence overall Re resources, we examine global patterns in molybdenite Re contents through a compilation of > 3000 measurements of Re in molybdenite from > 700 mainly ore-bearing moderate- to high-temperature hydrothermal systems of different types. Our results are similar to but expand on those of earlier studies. Rhenium concentration in molybdenite has a lognormal distribution and varies systematically with type of geologic system, intrusive lithology, and Mo grade. The lowest-Re molybdenite occurs in greisens (geometric mean 1 ppm ± a multiplicative standard deviation of 9), quartz vein-hosted W-Sn deposits (2 ± 5 ppm), unmineralized granites and granodiorites (12 ± 8 ppm), intrusion-related deposits (24 ± 8 ppm), and porphyry W-Sn deposits (16 ± 11 ppm). Rhenium is most enriched in molybdenites from volcanic sublimates (23,800 ± 5 ppm), with skarn Fe and Au (560 ± 5 ppm and 540 ± 3 ppm respectively) and porphyry Cu and Cu-Au deposits next (470 ± 4 and 430 ± 7 ppm respectively). Among porphyries, skarns, and quartz vein-hosted deposits, Re is most highly concentrated in molybdenites from Cu and Au systems and its concentration decreases systematically through Cu-Mo, Mo, Sn, and W deposits. In nearly all cases, molybdenites from systems associated with intermediate igneous rocks contain more Re than molybdenites from systems of the same type with more felsic rock associations. The disparity between Re contents of molybdenite in felsic and intermediate systems is largest for porphyries, quartz vein-hosted, and skarn deposits and is near zero for subeconomic or barren granite and granodiorite Mo systems; felsic intrusion-related deposits have slightly higher molybdenite Re than their equivalents associated with intermediate intrusions. In most systems, molybdenite Re content does not correlate with metal grade, but may have an inverse correlation with Au grade in intrusion-related deposits (based on a small number of data points) and does exhibit a strong inverse correlation with deposit Mo grade. Dilution of Re through larger amounts (higher deposit grades) of molybdenite explains about 40% of this correlation, but the relative enrichment of Re in molybdenite from low-Mo deposits must also reflect some selective enrichment of Re/Mo in porphyry Cu systems compared to porphyry Mo systems. We found no evidence for secular increase or other systematic temporal variation in molybdenite Re content. The data regarding the use of molybdenite Re content as a proxy for mantle influence are ambiguous. Nearly all observed empirical correlations can be traced back to differences in redox state and sulfide concentration, the two geochemical factors identified here and by previous experimental work as the controlling influences on Re mobility under hydrothermal conditions. Hydrothermal systems with reducing conditions (W- and Sn-rich) tend to have low molybdenite Re even though compiled whole-rock data indicate that their source rocks have as much or more Re as those of more oxidized systems (e.g., Cu-rich). Vapor-phase exsolution, crustal assimilation, and mixing with external fluids may all enrich molybdenite Re concentrations in individual deposits and deposit types, but their extent and importance in overall hydrothermal concentration of Re is uncertain. Thus, it appears that the available molybdenite Re resource in an ore deposit largely depends on how the deposit’s redox and sulfidation conditions have varied over time and space during the timespan of hydrothermal activity. Oxidized, high-sulfide conditions tend to concentrate Re in molybdenite, whereas reducing conditions tend to leave Re dispersed at low concentrations in the bulk rock.
• Barton, I. F., Rathkopf, C. A., & Barton, M. D. (2019). Rhenium in molybdenite: A database approach to identifying geochemical controls on the distribution of a critical element. Mining, Metallurgy and Exploration.
• Barton, M. D., & Greig, R. E. (2019). Regional-scale evolution of the Laramide arc and porphyry copper province, southwestern North America. Field Guides, 55, 401-406. doi:10.1130/2019.0055(16)
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  Porphyry copper provinces are time-space clusters of porphyry copper deposits (PCDs) that form in magmatic arcs. The evolution of the Laramide arc of southwestern North America, which hosts the Laramide porphyry copper province - the second-largest in the world - provides insight into factors contributing to its transient and localized metallogenic fertility. Regional-scale patterns are evident based on new and compiled U-Pb geochronological and whole-rock geochemical data, collected as part of an ongoing study. The migration of the locus of PCD formation coupled with shut-off of the magmatic arc and other geological evidence suggest localization of PCD formation near the southern margin of a shallowly subducting portion of the Farallon plate. Trends in increasing maximum size of PCDs and increasing SiO2 content of magmas with time correlate with the duration of arc activity in a given locale. Collectively, these trends suggest a variety of processes, including (1) uncertain ones related to local tectonic configuration, and (2) variations in crustal assimilation and/ or metasomatism, which are correlated to the local duration of arc magmatism, contributed to the richness of the Laramide porphyry copper province.
• Barton, M. D., Downs, R. T., Hiskey, J. B., Schumer, B. N., & Stegen, R. J. (2019). Mineralogical Profile of Supergene Sulfide Ore in the Western Copper Area, Morenci Mine, Arizona. The Canadian Mineralogist, 57(3), 391-401. doi:10.3749/canmin.1800020
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  The intergrowths and compositions of supergene copper sulfide minerals from drill hole MOR-4511 in the Western Copper area of the Morenci mine, Greenlee County, Arizona, have been examined by reflected light microscopy and electron probe microanalysis (EPMA) to better understand the formation of supergene sulfides with implications for hydrometallurgical processing. The supergene copper sulfides occur in three main textures: partial to complete replacement of chalcopyrite, partial replacement of pyrite, and partial to complete replacement of one another. Compositions of copper sulfides vary widely, but (CuþFe):S ratios of 1.80 6 0.05, 1.92 6 0.03, and 1.10 6 0.10 are dominant. No stoichiometric Cu2S was found. At shallower depths in the supergene blanket and near/within faults, high (CuþFe):S phases (with ratios of 1.80 6 0.05 and 1.92 6 0.03) replacing primary chalcopyrite and pyrite or lower (CuþFe):S supergene sulfides are dominant, and near the base of the blanket low (CuþFe):S phases (with ratios of 1.10 6 0.10) replacing primary chalcopyrite or higher (CuþFe):S supergene sulfides gradually become more dominant. This indicates high concentration of Fe3þ, Fe2þ, and Cu2þ, necessary to form high (CuþFe):S phases, at shallower depths and near sources of unreacted fluid, such as faults. Formation of low (CuþFe):S phases directly from chalcopyrite or from high (CuþFe):S phases could be controlled by decreased concentrations of iron species and Cu2þ due to reaction with primary chalcopyrite and pyrite as fluids descend or migrate away from faults, reduced access to supergene fluids, and/or lower pyrite-chalcopyrite ratios. The compositional patterns of supergene copper sulfide minerals observed at Morenci are similar to those observed in other supergene enrichment blankets of porphyry copper systems worldwide and are even more similar to compositions seen in leaching experiments of synthetic copper and copper-iron sulfides.
• Barton, M. D., Maier, R. M., Mazdab, F. K., & Rader, S. T. (2019). Uptake and Fractionation of Thallium by Brassica juncea in a Geogenic Thallium-Amended Substrate. Environmental Science & Technology, 53(5), 2441-2449. doi:10.1021/acs.est.8b06222
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  This study shows thallium (Tl) concentrations in Brassica juncea (Indian mustard) tissue are more than an order of magnitude higher (3830 μg/kg) than that of the substrate (100 μg/kg) and are strongly influenced by the underlying mineralogy; i.e., Tl bioaccessibility depends on the mineral structure: K-feldspar > Mn nodule > hendricksite mica. The majority of Tl for all substrates is contained in edible parts of the plant, i.e., leaves (41% of total Tl, on average) ≥ flower stems (34%) > seed pods (11%) ? stems (10%) > flowers (3%). We also show that Tl isotope fractionation induced by B. juncea is substantial, at nearly 10 ? 205 Tl units, and generates systematic plant-specific patterns. Progressive plant growth strongly fractionates Tl isotopes, discriminating against 205 Tl as the plant matures. Thus, 205 Tl values are systematically higher in the early formed stem (? 205 Tl avg = +2.5) than in plant elements formed later (? 205 Tl avg = ?2.5 to +0.1), which demonstrates the large degree of translocation and the associated effects during plant growth. This study establishes the potential of Tl isotopes as a new tool for understanding heavy metal (re)distribution during anthropogenic and geologic processes and the utility of such information in environmental and health-related planning and in phytomining or bioprospecting.
• Barton, M. D., Rathkopf, C., & Barton, I. F. (2020). Rhenium in molybdenite: A database approach to identifying geochemical controls on the distribution of a critical element. Mining, Metallurgy, & Exploration, 37(1), 21-37. doi:https://doi.org/10.1007/s42461-019-00145-0
• Rader, S. T., Maier, R. M., Barton, M. D., & Mazdab, F. K. (2019). Uptake and fractionation of thallium by brassica juncea in geogenic thallium-amended substrate. Environmental Science and Technology, 53, 2441-2449.
• Richardson, C. A., Favorito, D. A., Runyon, S. E., Seedorff, E., Maher, D. J., Barton, M. D., & Greig, R. E. (2019). Superimposed Laramide contraction, porphyry copper systems, and Cenozoic extension, east-central Arizona: A road log. GSA Field Guides. doi:10.1130/2019.0055(14)
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  This field trip integrates economic geology with structural geology and tectonics, as well as petrology, geochemistry, and regional geology, to examine a segment of the Laramide arc that includes part of the Laramide porphyry copper province of southwestern North America. The province arguably is the second-largest porphyry copper province in the world, hosting six of the world's 25 largest porphyry deposits on the basis of contained copper metal. The Globe-Superior-Ray-San Manuel area includes about a dozen Laramide (Late Cretaceous to early Paleocene) porphyry copper deposits and the related granodioritic to granitic plutons. These plutons and their wall rocks were tectonically dismembered and variably easterly or westerly tilted (locally >90°) during Laramide contraction and subsequent mid-Cenozoic extension. The style of both shortening and extension here remains a subject of debate. Although this trip includes one brief mine visit and examination of drill core at the Resolution deposit, it will principally focus on: (1) different parts of various plutons and the associated alteration aureoles, including review of resultant mineralization, and the original sides, roots, and deep flanks of the hydrothermal systems; and (2) structure in the adjacent wall rocks and the implications for the style and timing of deformation in absolute and relative terms to hypogene ore formation. An increased understanding of the structural geology and the alteration-mineralization zonation of the dismembered hydrothermal aureoles allows an integrated view of the original geometry and size of the porphyry systems, the relationship between porphyry copper mineralization and crustal shortening, and possible origins of deep hydrothermal alteration.
• Runyon, S. E., Nickerson, P. A., Seedorff, E., Barton, M. D., Mazdab, F. K., Lecumberri-Sanchez, P., & Steele-MacInnis, M. (2019). Sodic-calcic family of alteration in porphyry systems of Arizona and adjacent New Mexico. Economic Geology, 114(Issue 4). doi:10.5382/econgeo.4661
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  Sodic-calcic alteration has affected numerous districts with Laramide porphyry systems across Arizona and New Mexico. Previously undocumented Na-Ca alteration has been identified at Charleston, Sycamore Canyon, Silver Bell, and the Ninetysix Hills in Arizona and the Central mining district in New Mexico. These new occurrences are compared to sodic-calcic alteration at the Sierrita-Esperanza deposit (Pima district), the Ajo mining district, the Tea Cup pluton (Kelvin-Riverside district), and the Eagle Pass dike swarm in Arizona. Spatial positions, crosscutting relationships, and mineral assemblages and compositions allow for interpretation of the geochemical conditions of formation and implications for associated hydrothermal processes. Diopside- or andradite-grossular solid solution (Ad68-Ad72)-stable assemblages representative of calcic alteration typically occur in deep and/or distal positions but are less commonly exposed. The sodic-calcic and sodic alteration types, however, occur more proximally to the porphyry orebody. Sodic-calcic assemblages containing Na plagioclase (An10-An33)-Ca amphibole ± epidote are focused along granite cupolas near the base of orebodies, and these grade into shallower sodic assemblages containing albite (An00-An09)-epidote-chlorite. Mineral composition and fluid inclusion data suggest that Na-Ca plagioclase-bearing assemblages form at higher temperatures (360°-470°C+) than later, lower-temperature albite-epidote assemblages (>250°C). Calculated δD isotope compositions of fluids in equilibrium with Na-Ca alteration minerals span a broad range (-46 to -1%) and are consistently less negative than magmatic fluids. Where members of the Na-Ca family of alteration assemblages are present in porphyry systems, many lines of evidence - including isotopic compositions of minerals and the geologic alteration zoning patterns - are consistent with an origin by incursion of saline external fluids. Where Na-Ca alteration is present, it is best developed at relatively deep levels of porphyry systems. Several Laramide systems that are well exposed at comparably deep levels lack Na-Ca alteration, probably because sources of saline fluid were absent or hydrologic conditions were unfavorable for the incursion of saline external fluids. Though similar in temperatures, isotopic compositions, mineral assemblages, and zoning patterns, Na-Ca alteration in Laramide systems is volumetrically smaller than in Jurassic systems documented in the western United States, probably because saline external fluids were much less abundant during the Laramide after a tectonically driven excursion in paleoclimate from arid to humid conditions.
• Runyon, S. E., Seedorff, E., Barton, M. D., Steele-MacInnis, M., Lecumberri-Sanchez, P., & Mazdab, F. K. (2019). Coarse muscovite veins and alteration in porphyry systems. Ore Geology Reviews, 113(Issue). doi:10.1016/j.oregeorev.2019.103045
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  Coarse muscovite veins and alteration occur in porphyry copper and porphyry molybdenum-copper systems within the Laramide arc in Arizona, as well as at the Yerington district in Nevada. This work describes coarse muscovite in veins and altered wall rock in porphyry systems in this region and documents mineral assemblages, mineral compositions, spatial and temporal relationships, and hydrogen isotopic compositions. Coarse hydrothermal muscovite is documented in the roots of porphyry Cu ± Mo systems, as well as in and above the ore bodies in porphyry Mo-Cu systems, and it is compared to coarse hydrothermal muscovite (greisen) in lode Sn-W-Mo systems. Basin and Range extension has exposed coarse hydrothermal muscovite in several Laramide and Jurassic porphyry Cu (±Mo) systems, at paleodepths of ~3 to 12 km: Miami-Inspiration, Sierrita-Esperanza, Copper Basin (Crown King), Granite Mountain (roots of the Ray porphyry system), Gunnison (Texas Canyon stock), Grayback (Kelvin-Riverside district), Sycamore Canyon, the New Cornelia mine (Ajo district), and two systems in the Yerington district. Muscovite is the dominant mica in these coarse muscovite veins and associated alteration, with common K-feldspar and albite (An00-06), common accessory hematite, rutile, pyrite, and apatite, and rare accessory chalcopyrite, fluorite, molybdenite, wolframite, and scheelite. Coarse hydrothermal muscovite yields δD compositions that suggest formation from fluids that are dominantly magmatic-hydrothermal in origin. Whole-rock compositions of coarse hydrothermal muscovite show common gains in K and loss of Ca ± Na. Coarse muscovite veins and alteration in porphyry copper systems postdate mineralized potassic veins and form too deeply to overlap with shallower acidic forms of alteration (sericitic, advanced argillic). Variation in mineral assemblage, mineral compositions, and mineralization of coarse hydrothermal muscovite correlate with the composition of Laramide stocks. Porphyry Mo-Cu systems contain coarse muscovite alteration assemblages with the highest mineral diversity and trace-element enrichment. Coarse muscovite veins and alteration in porphyry Mo-Cu systems related to stocks ranging from quartz monzonite to granite in composition form at shallower paleodepths and occur within and above the associated orebodies. In contrast, coarse muscovite veins and alteration associated with subalkaline porphyry copper systems occur at deeper levels, in some cases overlapping with the bottom of potassic alteration and the ore body but extending well into the roots of the system in the underlying granitoid cupola. In these latter systems, zones of coarse muscovite alteration typically are poorly mineralized and mineral assemblages are less varied. These characteristics suggest that coarse muscovite-forming fluids are predominately of magmatic-hydrothermal origin and exsolved from late-stage, fractionated magmas of the larger pluton that sourced porphyry stocks and dikes responsible for porphyry copper mineralization. In some instances, however, the exposed coarse muscovite alteration is associated with a petrologically unrelated, commonly more felsic, later intrusion, rather than being related to late exsolution of fluid from the same crystallizing stock or batholith.
• Runyon, S. R., Nickerson, P. A., Seedorff, C. E., Barton, M. D., Mazdab, F. K., Lecumberri-Sanchez, P., & Steele-MacInnis, M. J. (2019). Sodic-calcic family of alteration in porphyry systems of Arizona and adjacent New Mexico. Economic Geology.
• Runyon, S. R., Seedorff, C. E., Barton, M. D., Steele-MacInnis, M. J., Lecumberri-Sanchez, P., & Mazdab, F. K. (2019). Coarse muscovite veins and alteration in porphyry systems. Ore Geology Reviews.
• Schumer, B. N., Stegen, R. J., Barton, M. D., Hiskey, J. B., & Downs, R. T. (2019). Mineralogical profile of supergene sulfide ore in the Western Copper area, Morenci mine, Arizona. Canadian Mineralogist.
• Seedorff, E., Barton, M. D., Gehrels, G. E., Valencia, V. A., Johnson, D. A., Maher, D. J., Stavast, W. J., & Marsh, T. M. (2019). Temporal evolution of the Laramide arc: U-Pb geochronology of plutons associated with porphyry copper mineralization in east-central Arizona. GSA Field Guides. doi:10.1130/2019.0055(15)
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  We describe the time-space evolution of a segment of the Laramide arc in eastcentral Arizona that is associated with porphyry copper mineralization, as constrained by U-Pb zircon geochronology conducted by laser ablation-multicollector-inductively coupled plasma-mass spectrometry. Mid-Cenozoic normal faulting dismembered and tilted many of the plutons and the associated porphyry copper deposits and produced a wide range in depths of exposure. The study area reconstructs to a 75-km-long slice along the arc, with exposures from 10 km depth. The copper deposits are related to granodioritic to granitic plutons that exhibit variable magmatic sources and locally severe degrees of zircon inheritance. U-Pb zircon ages of plutons in the study area range from 75 to 61 Ma, with dioritic rocks at the older end of the range. The age range of magmatism and mineralization in a cluster of deposits near the Schultze Granite, including the Globe-Miami, Pinto Valley, and Resolution deposits, is from ca. 69-61 Ma. To the south in the Tortilla and Dripping Spring Mountains, the porphyry systems range from ca. 74 Ma at Kelvin- Riverside to ca. 69 Ma at Ray and ca. 65 Ma at Christmas. At several localities where geologic constraints exist, mineralizing plutons were emplaced following Laramide shortening. The ages of the inherited zircon cores correspond fairly closely to the ages of basement rocks in the immediate vicinity of sample sites, implying that similar basement ages and lithologies contributed to the source areas of magmas that produced Laramide porphyry deposits. The U-Pb results on hypabyssal rocks are typically 1-5 m.y. older than previous K-Ar ages, and U-Pb ages on more deeply emplaced plutonic rocks are as much as 5-10 m.y. older. These results are consistent with predictions from thermal modeling and suggest that temporal evolution of the entire Laramide arc needs revision. For this segment of the arc, magmatism was stagnant for ~15 m.y., with minimal migration over time and mineralization occurring episodically over most of that lifespan. There is no simple geographic progression in ages along or across the strike of the arc. Thus, it is difficult to call upon time-specific far-field or plate margin triggers for magmatism or mineralization. The intrusive flux of the Laramide arc appears to be similar to that of the Sierra Nevada arc during the Mesozoic during its "background"periods, rather than during episodes of flare-up. The wide compositional diversity of the Laramide arc is more akin to northeastern Nevada during the onset of extension in the mid-Cenozoic than to the Mesozoic of the Sierra Nevada.
• Seedorff, E., Richardson, C. A., Favorito, D. A., Barton, M. D., & Greig, R. E. (2019). Crustal shortening and porphyry copper mineralization in the Laramide arc and superimposed extension: Introduction and themes. GSA Field Guides. doi:10.1130/2019.0055(13)
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  The Laramide continental arc formed in southwestern North America at about the same time the Sierra Nevadan arc was shutting down, and the Laramide arc was active concurrent with the progress of the Laramide orogeny, from ca. 80 Ma to ca. 45 Ma. East-central Arizona offers an excellent opportunity to explore aspects of tectonics, structural geology, magmatism, and hydrothermal systems in a segment of the Laramide arc that is exceptionally well endowed with porphyry copper deposits. The structure of this region is especially complicated, with multiple generations of normal faults commonly superimposed on originally moderate-angle reverse faults with associated fault-propagation folds. A large new porphyry copper deposit, Resolution, was discovered near Superior in the mid-1990s. The discovery started a new round of development in the mining life cycle at the Resolution deposit; in the region, it contributed to copper exploration again becoming vigorous in the last decade. In the years since discovery of Resolution, important new scientific insights have been gained, including at the regional scale. Post-ore crustal extension exposed multiple levels of Laramide and older igneous and hydrothermal systems at the surface where they can be more easily mapped and sampled, and palinspastic reconstructions of post-mineral normal faulting permit the exposures to be restored to their original positions. The porphyry-related products that are observed at higher levels include local advanced argillic alteration and Cordilleran-style veins and associated mantos, such as at the Magma mine, Resolution deposit, and Old Dominion mine in the shallowest levels of the Superior- Globe-Miami area. Most porphyry copper ore bodies were developed at intermediate depths, where porphyry intrusions exhibit sericitic and potassic alteration and carbonate rocks were converted to skarn, such as in the heart of the Miami-Inspiration, Resolution, Ray, and Christmas deposits. Plutonic rocks are exposed at deeper paleodepths, where pegmatites, quartz veins, and greisen muscovite are locally observed, especially directly beneath porphyry copper orebodies, as in the Schultze and Granite Mountain plutons. Likewise, sodic-calcic alteration may be developed on the deep flanks of porphyry systems, such as adjacent to the Tea Cup pluton. Subsequent Cenozoic extension variously buried or exhumed the hypogene portions of these hydrothermal systems, leading to the development of various supergene products, both in situ and exotic.
• Rader, S. T., Mazdab, F. K., & Barton, M. D. (2018). Mineralogical thallium geochemistry and isotope variations from igneous, metamorphic, and metasomatic systems. Geochimica et Cosmochimica Acta, 243(Issue). doi:10.1016/j.gca.2018.09.019
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  This study presents new thallium (Tl) concentration and isotopic composition data for potassium feldspar (K-feldspar), micas, sulfides, and other minerals using solution multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS). The samples studied represent a diverse set of igneous, metamorphic, and metasomatic rock types. Purified separates of minerals anticipated to be Tl-bearing were analyzed; in many cases coexisting minerals were measured to examine the distribution of Tl and its isotopes between coexisting phases. This study is the first of its kind to document mineralogical controls on Tl chemical and isotopic fractionation. Thallium contents in rock-forming minerals and common sulfides vary from below detection limit (here, approximately 0.2 ppm Tl in the mineral utilizing an IsoProbe MC-ICP-MS) to 3200 ppm. In this present study, mica and feldspar samples can reach Tl concentrations well over 20 ppm, compared to only 0.7 ppm in average crust. In contrast, only 14 of 38 common sulfide samples contain Tl at levels above the detection limit. Measured Tl isotope ratios, reported as ε205Tl relative to the NIST 997 standard solution, range from −12.1 ± 0.6 to +18.0 ±1.4 (2σ). Most samples analyzed fall within the published range of ε205Tl (−20 to +15) (Nielsen et al., 2017). Although most sulfides show limited Tl enrichment, they display the highest ε205Tl values among coexisting minerals, with Fe-rich micas having the lowest ε205Tl values. The patterns in enrichment are best interpreted to reflect crystal chemical differences and the incompatible, dominantly lithophile nature of Tl. In turn, isotopic fractionation also reflects control by the bonding environment as well as redox conditions. The preferential distribution of Tl into micas and K-feldspar found here is consistent with the similarity in charge and ionic radius of Tl+ and K+. The higher ε205Tl values in sulfides agree with previous observations and theoretical studies showing the tendency of covalent bonds, high bond strengths, and high oxidation states to favor heavy isotopes. This work highlights important areas for future research regarding the natural weathering of Tl-bearing substrates, understanding regional cycling of Tl, and potential bioremediation of Tl contamination.
• Rader, S. T., Mazdab, F. K., & Barton, M. D. (2018). Thallium geochemistry and isotope variations in igneous, metamorphic, and metasomatic systems. Geochimica et Cosmochimica Acta, 243, 42-65.
• Stegen, R. J., Barton, M. D., & Waegli, J. A. (2018). Cerro Verde-Santa Rosa porphyry copper-molybdenum deposits, Peru: Magmatic, hydrothermal, and supergene evolution of adjacent systems. SEG Special Publication, 21, 293-319.
• Kreiner, D. C., & Barton, M. D. (2017). Sulfur-poor intense acid hydrothermal alteration: A distinctive hydrothermal environment. Ore Geology Reviews, 88(Issue). doi:10.1016/j.oregeorev.2017.04.018
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  A fundamentally distinct, sulfide-poor variant of intense acid (advanced argillic) alteration occurs at the highest structural levels in iron oxide-rich hydrothermal systems. Understanding the mineralogy, and geochemical conditions of formation in these sulfide-poor mineral assemblages have both genetic and environmental implications. New field observations and compilation of global occurrences of low-sulfur advanced argillic alteration demonstrates that in common with the sulfide-rich variants of advanced argillic alteration, sulfide-poor examples exhibit nearly complete removal of alkalis, leaving a residuum of aluminum-silicate + quartz. In contrast, the sulfur-poor variants lack the abundant pyrite ± other sulfides, hypogene alunite, Al-leached rocks (residual “vuggy” quartz) as well as the Au-Cu-Ag ± As-rich mineralization of some sulfur-rich occurrences. Associated mineralization is dominated by magnetite and/or hematite with accessory elements such as Cu, Au, REE, and P. These observations presented here indicate there must be distinct geologic processes that result in the formation of low-sulfur advanced argillic styles of alteration. Hydrolysis of magmatic SO2 to sulfuric acid is the most commonly recognized mechanism for generating hypogene advanced argillic alteration, but is not requisite for its formation. Low sulfur iron-oxide copper-gold systems are known to contain abundant acid-styles of alteration (e.g. sericitic, chloritic), which locally reaches advanced argillic assemblages. A compilation of mapping in four districts in northern Chile and reconnaissance observations elsewhere show systematic zoning from near surface low-sulfide advanced argillic alteration through chlorite-sericite-albite and locally potassic alteration. The latter is commonly associated with specular hematite-chalcopyrite mineralization. Present at deeper structural levels are higher-temperature styles of sodic-calcic (oligoclase/scapolite – actinolite) alteration associated with magnetite ± chalcopyrite mineralization. These patterns are in contrast to the more sulfur-rich examples which generally zone to higher pyrite and locally alunite-bearing alteration. Fluid inclusion evidence from the systems in northern Chile shows that many fluids contain 25 to >50 wt% NaCleq with appreciable Ca, Fe, and K contents with trapping temperatures >300 °C. These geological and geochemical observations are consistent with the origin of the low-sulfur advanced argillic assemblages from HCl generated by precipitation of iron oxides from iron chloride complexes from a high-salinity fluid by reactions such as 3FeCl2 + 4H2O = Fe3O4 + 6HCl + H2. Such HCl-rich (and relatively HSO4=-poor) fluids can then account for the intense acid, Al-silicate-rich styles of alteration observed at high levels in some iron-oxide-coppe-gold (IOCG) systems. The geochemical differences between the presence of sulfide-rich and sulfur-poor examples of advanced argillic alteration are important to distinguishing between system types and the acid-producing capacity of the system, including in the modern weathering environment. They have fundamental implications for effective mineral exploration in low-sulfur systems and provide yet another vector of exposed alteration in the enigmatic IOCG clan of mineral deposits. Furthermore, understanding the geochemistry and mineralogy of this distinct geologic environment has applications to understanding the acid generating capacity and deleterious heavy metals associated with advanced argillic alteration.
• Kreiner, D. C., & Barton, M. D. (2017). Sulfur-poor intense acid hydrothermal alteration: a distinctive hydrothermal environment. Ore Geology Reviews.
• Rathkopf, C., Mazdab, F. K., Barton, I. F., & Barton, M. D. (2017). Grain-scale and deposit-scale heterogeneity of Re distribution in molybdenite at the Bagdad porphyry Cu-Mo deposit, Arizona. Journal of Geochemical Exploration.
• Rathkopf, C., Mazdab, F., Barton, I., & Barton, M. D. (2017). Grain-scale and deposit-scale heterogeneity of Re distribution in molybdenite at the Bagdad porphyry Cu-Mo deposit, Arizona. Journal of Geochemical Exploration, 178. doi:10.1016/j.gexplo.2017.03.011
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  Electron microprobe analysis of Re concentration in molybdenite grains in 45 samples from 11 rock units at the Bagdad porphyry Cu-Mo deposit found high variability from the grain to the deposit scale. Measured Re concentrations range from < 15 to 4450 ppm and do not correlate with rock unit, age, alteration type, ore grade, proximity to ore, or other observed geological feature. Variability within samples and within grains is nearly as high as variability over the deposit. Within 23 grains of molybdenite from a single 2-cm-long sample, Re content varied from < 15 to 1215 ppm Re. Within single grains the Re content ranges just as widely (e.g. 20 analyses on one grain vary from 44 to 2061 ppm), with intra-grain relative standard deviation (RSD) typically > 0.5 and in some cases > 1. Although microprobe maps show that the Re variation in some crystals correlates with growth-related zoning to a limited extent, there was no pattern to the variation in most of the molybdenite grains and the few zoned examples had no clear sector or consistent oscillatory textures. Based on our current understanding of trace element incorporation during hydrothermal molybdenite growth, this evidently heterogeneous distribution of Re in molybdenite precludes the use of microprobe spot measurements of Re as a vector to mineralization, which was the original focus of this study. A follow-up analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) using spot diameters of 150 μm reduced the observed intra-grain variability from 1.67 to 1 order of magnitude, but still failed to yield data that correlated with any known geological features. This suggests that any further work toward using molybdenite Re content as a vector to mineralization should either focus on whole-grain methods of analysis or else should use detailed microprobe mapping of molybdenite growth zones to guide point analyses, and then correlate the growth zones in molybdenite samples taken over distance through the deposit. This approach could help shed light on how the development of heterogeneous Re concentrations on the micro-scale relates to the processes of molybdenite precipitation and alteration.
• Barton, I. F., Yang, H., & Barton, M. D. (2014). The mineralogy, geochemistry, and metallurgy of cobalt in the rhombohedral carbonates. Canadian Mineralogist, 52(4), (doi: 10.3749/canmin.1400006).
• Barton, M. D., Barton, I. F., & Yang, H. (2014). THE MINERALOGY, GEOCHEMISTRY, AND METALLURGY OF COBALT IN THE RHOMBOHEDRAL CARBONATES. Canadian Mineralogist, 52(4), 653-670. doi:10.3749/canmin.1400006
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  Abstract Carbonate ores of cobalt are a significant but under-recognized fraction of the global Co resource. Cobalt forms spherocobaltite (CoCO 3 , calcite group), whose complete solid solution with isostructural magnesite, MgCO 3 , is described here for the first time. Cobalt-rich dolomite, Ca(Mg,Co)(CO 3 ) 2 , and Co-rich calcite, (Ca,Co)CO 3 , can accommodate up to 20 mol.% Co and up to 2 mol.% Co, respectively. Cobalt has also been reported as a minor substituent of other calcite-group carbonates and as a major constituent of the non-rhombohedral carbonates comblainite, Ni 4 Co 3+ 2 (OH) 12 (CO 3 )·3H 2 O (hydrotalcite supergroup), and kolwezite, (Cu,Co) 2 (CO 3 )(OH) 2 (poorly understood, possibly rosasite group). Cobalt carbonates are most common in the supergene zones of Cu-Co sulfide ore deposits, especially the Central African Copperbelt. A study focused on the Tenke-Fungurume district (TFM) in the Copperbelt found Co-rich dolomite, Co-rich magnesite, spherocobaltite, and kolwezite. Cobalt-rich dolomite occurs as Co-rich bands in supergene dolomite and as individual Co-rich dolomite crystals filling void spaces. Members of the magnesite-spherocobaltite solid solution occur as crystals filling void spaces in rocks and as microscopic inclusions with kolwezite in supergene chalcocite (Cu 2 S) replacing primary carrollite (CuCo 2 S 4 ). The formation of Co-rich carbonates remains enigmatic. Evidence from Bou Azzer indicates that they can form under specific hypogene conditions, but in general Co-rich carbonates form from supergene processes. Dedolomitization has been proposed as a mechanism of formation for the analogous Zn carbonates, but there is no evidence of dedolomitization in the TFM cobalt carbonates. Most of them appear to have precipitated directly from pockets of Co-(Mg)-(Cu)-carbonate-enriched solution trapped within oxidizing hypogene sulfides. Cobalt carbonates pose a serious metallurgical problem. Most carbonate ores are processed by solvent extraction using acid. Solubility calculations indicate that the Co in carbonates is less soluble than Mg, Fe, and Ca by 3 to 4 orders of magnitude. Thus, acid leaching will liberate all other ions from carbonate ores before releasing appreciable Co. Furthermore, many of the Mg-rich spherocobaltites in this study were initially misidentified as Co-rich dolomite, which is far more soluble than spherocobaltite. This may cause Co recoveries to be lower than predicted at many Central African Copperbelt mines.
• Vikre, P. G., Graybeal, F. G., Fleck, R. J., Barton, M. D., & Seedorff, C. E. (2014). Succession of Laramide magmatic and magmatic-hydrothermal events in the Patagonia Mountains, Santa Cruz County, Arizona. Economic Geology, 109(6), 1667-1704.
• Vikre, P. G., Graybeal, F. T., Fleck, R. J., Barton, M. D., & Seedorff, E. (2014). Succession of laramide magmatic and magmatic-hydrothermal events in the Patagonia Mountains, Santa Cruz County, Arizona. Economic Geology, 109(Issue 6). doi:10.2113/econgeo.109.6.1667
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  This investigation of the space-time progression of magmatism and hydrothermal activity in the Patagonia Mountains of southern Arizona is based on field and paragenetic relationships, and on U-Pb and 40Ar/39Ar geochronology of igneous and hydrothermal minerals. The Patagonia Mountains consist of Precambrian, Paleozoic, and Mesozoic sedimentary, granitic, and volcanic rocks, Laramide volcanic rocks, and a core of Laramide intrusions that comprise the Patagonia Mountains batholith. Laramide igneous rocks and adjacent Paleozoic and Mesozoic rocks contain significant porphyry Cu-Mo deposits, Mo-Cu breccia pipes, Ag replacement deposits, and numerous other Cu-Pb-Zn-Ag replacement and vein deposits. Ages of igneous and hydrothermal minerals from 20 U-Pb and 52 40Ar/39Ar determinations define four magmatic and magmatic-hydrothermal events that formed the batholith and altered parts of it and adjacent rocks; cumulatively the events span at least 16 m.y., from ~74 to 58 Ma. The oldest event of this succession includes the 74 Ma Washington Camp stock and spatially associated Cu-Pb-Zn-Ag replacement deposits in Paleozoic carbonate rocks of the Washington Camp-Duquesne district. Eruption of 73 to 68 Ma volcanic rocks in the northern part of the range was the next youngest event, which coincides temporally with replacement and vein deposits in Paleozoic carbonate rocks at the Flux mine (~71 Ma). An event at 65 to 62 Ma is marked by emplacement of small-volume quartz monzonite, granodiorite, and diorite intrusions, formation of the Ventura breccia deposit in Jurassic granite at 65 to 64 Ma, and formation of other Pb-Zn-Ag-Cu replacement and vein deposits (~62 Ma; Blue Nose and Morning Glory). The Red Mountain porphyry Cu-Mo system is hosted by ~62 Ma granodiorite and Laramide volcanic rocks (73-68 Ma) at the northern end of the batholith. It includes a deep, chalcopyrite-bornite resource (~60 Ma) that is associated with potassic and sericitic alteration and a near-surface chalcocite-enargite resource (60 Ma) that is associated with advanced, supergene-enriched argillic alteration. The youngest event includes the Sunnyside porphyry Cu-Mo system and a Cu-Mo breccia deposit at Red Hill (Four Metals mine), both of which formed in large-volume quartz monzonite, granodiorite, quartz monzonite porphyry, and quartz feldspar porphyry (~61-59 Ma). Similar to the Red Mountain system, the Sunnyside system consists of a deep chalcopyrite resource that occurs in ~60 to 59 Ma quartz feldspar porphyry, and a near-surface, slightly younger (~59-58 Ma) enargite-chalcocite-tennantite resource that occurs in quartz feldspar porphyry, quartz monzonite porphyry, and Mesozoic rocks. The Red Hill Cu-Mo breccia deposit is hosted by large-volume quartz monzonite, granodiorite, and quartz monzonite porphyry (~61-59 Ma). Discrepancies between field and paragenetic relationships and some analytic ages at Sunnyside and Red Hill preclude precise dating of mineralization stages, and may reflect disturbance of isotope systems by multiple, co-spatial to juxtaposed intrusive and hydrothermal events, and/or by unrecognized intrusions. Numerous vein and replacement deposits at the northern end of the batholith, including the Hardshell Ag resource and the Three R supergene chalcocite resource, are distal deposits of the Sunnyside and Red Mountain systems. Small, ~61 to 59 Ma Cu-Mo deposits in large-volume intrusions in the southern part of the batholith consist of hydrothermal quartz, biotite, K-feldspar, muscovite, chalcopyrite, and molybdenite. The age span of magmatic and magmatic- hydrothermal events in the Patagonia Mountains, minimally 16 m.y., is comparable to that of certain other magmatic-hydrothermal successions that contain porphyry Cu-Mo systems. Magmatic-hydrothermal events of the Wasatch-Oquirrh igneous trend, Utah, and the Boulder batholith, Montana, both span ~17 m.y. and include the Bingham and Butte porphyry Cu-Mo, vein and replacement deposits, respectively. Plutons and mineral deposits in the Pima district, Arizona, which includes the porphyry Cu-Mo deposits at Sierrita-Esperanza, Mission-Pima-San Xavier North, and Twin Buttes, formed over an interval of ~14 m.y. The diversity of igneous and hydrothermal products likely reflects evolutionary processes occurring at multiple sites in the lithosphere and at different time scales from >10 m.y. to less than the geochronologic precision currently achievable. © 2014 Society of Economic Geologists, Inc.
• Barton, I. F., & Barton, M. D. (2012). Alteration and ore distribution in the Proterozoic Mines Series, Tenke-Fungurume Cu-Co district, Democratic Republic of Congo. Mineralium Deposita, 47(5), 501-519.
• Fay, I., & Barton, M. D. (2012). Alteration and ore distribution in the Proterozoic Mines Series, Tenke-Fungurume Cu-Co district, Democratic Republic of Congo. Mineralium Deposita, 47(5), 501-519.
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  Abstract: Two sediment-hosted stratiform Cu-Co deposits in the Tenke-Fungurume district of the Central African Copperbelt were examined to evaluate the alteration history of the ore-hosting Mines Series and its implications for ore distribution and processing. Core logging and petrography, focused on lithology and timing relationships, outlined a complex alteration sequence whose earliest features include formation of anhydrite nodules and laths, followed by precipitation of dolomite. Later alteration episodes include at least two silica introductions, accompanied by or alternating with two dolomite introductions into the existing gangue assemblages. One introduction of Cu-Co sulfides accompanied the last episode of dolomite alteration, overprinting an earlier generation of ore whose gangue association was unidentifiable. Sulfides and some carbonates were subsequently modified by supergene oxidation, transport, and reprecipitation to 100-200 m depth. Present-day ore distribution resulted from these successive processes. Ore is concentrated in two shale-dominated units on either side of a cavernous silicified dolomite, which is interpreted as the main conduit for the mineralizing fluids. Sulfide ores precipitated at the redox or sulfidation contacts between this dolomite and the shales. Later, supergene fluids dissolved and moved some of the metals, redepositing them as oxides and carbonates. Solubility differences between Cu and Co in supergene conditions caused them to precipitate separately. Thus, modern ore distribution at Tenke-Fungurume results both from original hypogene lithology- and contact-related precipitation and from supergene oxidation, transport, and Cu-Co decoupling. The supergene fluid flow also redistributed gangue minerals such as dolomite, which has an economically important influence on the processing costs of supergene ores. © 2011 Springer-Verlag.
• Fay, I., & Barton, M. D. (2012). Alteration and ore distribution in the Proterozoic Mines Series, Tenke-Fungurume Cu-Co district, Democratic Republic of Congo. Mineralium Deposita, 47(Issue 5). doi:10.1007/s00126-011-0391-2
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  Two sediment-hosted stratiform Cu-Co deposits in the Tenke-Fungurume district of the Central African Copperbelt were examined to evaluate the alteration history of the ore-hosting Mines Series and its implications for ore distribution and processing. Core logging and petrography, focused on lithology and timing relationships, outlined a complex alteration sequence whose earliest features include formation of anhydrite nodules and laths, followed by precipitation of dolomite. Later alteration episodes include at least two silica introductions, accompanied by or alternating with two dolomite introductions into the existing gangue assemblages. One introduction of Cu-Co sulfides accompanied the last episode of dolomite alteration, overprinting an earlier generation of ore whose gangue association was unidentifiable. Sulfides and some carbonates were subsequently modified by supergene oxidation, transport, and reprecipitation to 100-200 m depth. Present-day ore distribution resulted from these successive processes. Ore is concentrated in two shale-dominated units on either side of a cavernous silicified dolomite, which is interpreted as the main conduit for the mineralizing fluids. Sulfide ores precipitated at the redox or sulfidation contacts between this dolomite and the shales. Later, supergene fluids dissolved and moved some of the metals, redepositing them as oxides and carbonates. Solubility differences between Cu and Co in supergene conditions caused them to precipitate separately. Thus, modern ore distribution at Tenke-Fungurume results both from original hypogene lithology- and contact-related precipitation and from supergene oxidation, transport, and Cu-Co decoupling. The supergene fluid flow also redistributed gangue minerals such as dolomite, which has an economically important influence on the processing costs of supergene ores. © 2011 Springer-Verlag.
• Barton, M. D., Girardi, J. D., Kreiner, D. C., Seedorff, E., Zurcher, L., Dilles, J. H., Haxel, G. B., & Johnson, D. A. (2011). Jurassic igneous-related metallogeny of southwestern North America. Great Basin Evolution and Metallogeny, Geological Society of Nevada, Symposium Proceedings, 373-396.
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  Barton, M. D., Girardi, J. D., Kreiner, D. C., Seedorff, E., Zurcher, L., Dilles, J. H., Haxel, G. B., and Johnson, D. A., 2011, Jurassic igneous-related metallogeny of southwestern North America, in Steininger, R. C., and Pennell, W. M., eds., Great Basin evolution and metallogeny: Geological Society of Nevada, Symposium, Reno/Sparks, May 2010, Proceedings, v. 1, p. 373-396.
• John, D. A., Ayuso, R. A., Barton, M. D., & 10 others, –. (2010). Porphyry copper deposit model, Chap. B of Mineral deposit models for resource assessment. U.S. Geological Survey Scientific Investigations Report, 2010–5070–B, 169p.
• Nickerson, P. A., Barton, M. D., & Seedorff, E. (2010). Characterization and Reconstruction of the Multiple Copper-Bearing Hydrothermal Systems in the Tea Cup Porphyry System, Pinal County, Arizona. Society of Economic Geologists Special Publication, 15, 299-316.
• Nickerson, P. A., Barton, M. D., & Seedorff, E. (2010). Characterization and reconstruction of the multiple copper-bearing hydrothermal systems in the Tea Cup Porphyry system, Pinal County, Arizona. Society of Economic Geologists Special Publication 15, 299-316.
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  Nickerson, P. A., Barton, M. D., and Seedorff, E., 2010, Characterization and reconstruction of multiple copper-bearing hydrothermal systems in the Tea Cup porphyry system, Pinal County, Arizona, in Goldfarb, R. J., Marsh, E. E., and Monecke, T., eds., The challenge of finding new mineral resources: Global metallogeny, innovative exploration, and new discoveries: Society of Economic Geologists Special Publication 15, p. 299-316.
• Herrmann, W., Green, G. R., Barton, M. D., & Davidson, G. J. (2009). Lithogeochemical and stable isotopic insights into submarine genesis of pyrophyllite-altered facies at the Boco prospect, western Tasmania. Economic Geology, 104(6), 775-792.
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  Abstract: The Boco prospect is a large, fault dismembered, pipelike, hydrothermally altered zone in the Mount Read Volcanics of western Tasmania. It is a synvolcanic alteration zone hosted by felsic volcanic rocks formed in a subaqueous proximal intracaldera setting. Previous detailed geochemical and geophysical surveys and extensive drill testing have indicated it contains no economic metals. The strong to intense, pervasively quartz + phyllosilicate + pyrite-altered northern segment of the prospect is semiconcentrically zoned. Short wavelength infrared (SWIR) spectral analysis has revealed that phyllosilicate assemblages grade from phengitic white mica in the least altered peripheries, through normal potassic white mica, to central zones containing kaolinite, slightly sodic white mica, and pyrophyllite. Mass balance calculations indicate average net mass losses in the altered faciès were about 10 to 30 g/100 g, mainly owing to loss of SiO2, which implies very high hydrothermal water-rock ratios. Whole-rock oxygen isotope compositions of the enclosing least altered felsic rocks (δ18O values 8.2-11.7%c) are indistinguishable from those of altered faciès (9.6-11.8%o). We attribute the former to low-temperature diagenetic isotopic exchange with 0 per mil δ18O seawater in the peripheral least-altered zones, and the latter to exchange with 3 to 6 per mil δ18O hydrothermal fluids at high water/rock ratios and temperatures generally greater than 220°C, and locally greater than 270°C, in the intensely altered facies. Pyrite sulfur isotope compositions in the Boco altered faciès (δ34S values 1.2-7.2%o) are distinctly lower than most Tasmanian massive sulfide deposits (6-15%o), compatible with a dominantly magmatic source of sulfur. The alteration mineral assemblages, estimated mass changes, and isotopic data show that the Boco alteration system was formed by a large volume of focused acidic hydrothermal fluid which had an oxygen isotope composition of 3 to 6 per mil δ18O at and temperature greater than 270°C. The slightly 18O-enriched fluid isotope composition suggests derivation from either mixed magmatic fluid and seawater or isotopically evolved seawater. Its advanced argillic altered faciès place Boco among a newly recognized class of southeast Australian Cambrian volcanic-hosted prospects and deposits. These include Chester, Basin Lake, Western Tharsis, and North Lyell in Tasmania, and Rhyolite Creek, Hill 800, and Mike's Bluff in eastern Victoria. SWIR spectral analyses with field-portable spectrometers allow early discrimination of this type of hydrothermally altered system, and can potentially assist subsequent exploration in mapping facies zonation. © 2009 Society of Economic Geologists, Inc.
• Herrmann, W., Green, G. R., Barton, M. D., & Davidson, G. J. (2009). Lithogeochemical and stable isotopic insights into submarine genesis of pyrophyllite-altered facies at the Boco prospect, western Tasmania. Economic Geology, 104(Issue 6). doi:10.2113/gsecongeo.104.6.775
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  The Boco prospect is a large, fault dismembered, pipelike, hydrothermally altered zone in the Mount Read Volcanics of western Tasmania. It is a synvolcanic alteration zone hosted by felsic volcanic rocks formed in a subaqueous proximal intracaldera setting. Previous detailed geochemical and geophysical surveys and extensive drill testing have indicated it contains no economic metals. The strong to intense, pervasively quartz + phyllosilicate + pyrite-altered northern segment of the prospect is semiconcentrically zoned. Short wavelength infrared (SWIR) spectral analysis has revealed that phyllosilicate assemblages grade from phengitic white mica in the least altered peripheries, through normal potassic white mica, to central zones containing kaolinite, slightly sodic white mica, and pyrophyllite. Mass balance calculations indicate average net mass losses in the altered faciès were about 10 to 30 g/100 g, mainly owing to loss of SiO2, which implies very high hydrothermal water-rock ratios. Whole-rock oxygen isotope compositions of the enclosing least altered felsic rocks (δ18O values 8.2-11.7%c) are indistinguishable from those of altered faciès (9.6-11.8%o). We attribute the former to low-temperature diagenetic isotopic exchange with 0 per mil δ18O seawater in the peripheral least-altered zones, and the latter to exchange with 3 to 6 per mil δ18O hydrothermal fluids at high water/rock ratios and temperatures generally greater than 220°C, and locally greater than 270°C, in the intensely altered facies. Pyrite sulfur isotope compositions in the Boco altered faciès (δ34S values 1.2-7.2%o) are distinctly lower than most Tasmanian massive sulfide deposits (6-15%o), compatible with a dominantly magmatic source of sulfur. The alteration mineral assemblages, estimated mass changes, and isotopic data show that the Boco alteration system was formed by a large volume of focused acidic hydrothermal fluid which had an oxygen isotope composition of 3 to 6 per mil δ18O at and temperature greater than 270°C. The slightly 18O-enriched fluid isotope composition suggests derivation from either mixed magmatic fluid and seawater or isotopically evolved seawater. Its advanced argillic altered faciès place Boco among a newly recognized class of southeast Australian Cambrian volcanic-hosted prospects and deposits. These include Chester, Basin Lake, Western Tharsis, and North Lyell in Tasmania, and Rhyolite Creek, Hill 800, and Mike's Bluff in eastern Victoria. SWIR spectral analyses with field-portable spectrometers allow early discrimination of this type of hydrothermally altered system, and can potentially assist subsequent exploration in mapping facies zonation. © 2009 Society of Economic Geologists, Inc.
• Hitzman, M., Dilles, J., Barton, M., & Boland, M. (2009). Mineral resource geology in academia: An impendina crisis?. GSA Today, 19(8), 26-28.
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  Abstract: The costs of metals and other mineral products continues to rise as with the continues industrialization in the developing world but is also said to rebound by the time when the global economy recovers. The main reason for this price increase is with the slowdown of the addition of new supplies through discovery and the inability to expand the production from known deposits. The supply chain of minerals that is important for the industrial production and national security is now vulnerable due to the continues increase in demand. In addition, the number of mineral-resource geologists has decreased by a large amount whereby also affecting the supply chain of minerals. This decrease will negatively affect the economic geology education and research in the near future while also affecting a nation's competitiveness and its ability to make up a sound planning and land management.
• Hitzman, M., Dilles, J., Barton, M., & Boland, M. (2009). Mineral resource geology in academia: An impendina crisis?. GSA Today, 19(Issue 8). doi:10.1130/gsatg33gw.1
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  The costs of metals and other mineral products continues to rise as with the continues industrialization in the developing world but is also said to rebound by the time when the global economy recovers. The main reason for this price increase is with the slowdown of the addition of new supplies through discovery and the inability to expand the production from known deposits. The supply chain of minerals that is important for the industrial production and national security is now vulnerable due to the continues increase in demand. In addition, the number of mineral-resource geologists has decreased by a large amount whereby also affecting the supply chain of minerals. This decrease will negatively affect the economic geology education and research in the near future while also affecting a nation's competitiveness and its ability to make up a sound planning and land management.
• Pal, D. C., Barton, M. D., & Sarangi, A. K. (2009). Deciphering a multistage history affecting U-Cu(-Fe) mineralization in the Singhbhum Shear Zone, eastern India, using pyrite textures and compositions in the Turamdih U-Cu(-Fe) deposit. Mineralium Deposita, 44(1), 61-80.
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  Abstract: The ∼200-km-long intensely deformed Singhbhum Shear Zone (SSZ) in eastern India hosts India's largest U and Cu deposits and related Fe mineralization. The SSZ separates an Archaean cratonic nucleus to the south from a Mesoproterozoic fold belt in the North and has a complex geologic history that obscures the origin of the contained iron-oxide-rich mineral deposits. This study investigates aspects of the history of mineralization in the SSZ by utilizing new petrographic and electron microprobe observations of pyrite textures and zoning in the Turamdih U-Cu(-Fe) deposit. Mineralization at Turamdih is hosted in intensively deformed quartz-chlorite schist. Sulfides and oxides include, in inferred order of development: (a) magmatic Fe(-Ti-Cr) oxide and Fe-Cu(-Ni) sulfide minerals inferred to be magmatic (?) in origin; followed by (b) uranium, Fe-oxide, and Fe-Cu(-Co) sulfide minerals that predate most or all ductile deformation, and are inferred to be of hydrothermal origin; and (c) Fe-Cu sulfides that were generated during and postdating ductile deformation. These features are associated with the formation of three compositionally and texturally distinct pyrites. Pyrite (type-A), typically in globular-semiglobular composite inclusions of pyrite plus chalcopyrite in magnetite, is characterized by very high Ni content (up to 30,700 ppm) and low Co to Ni ratios (0.01-0.61). The textural and compositional characteristics of associated chalcopyrite and rare pyrrhotite suggest that this pyrite could be linked to the magmatic event via selective replacement of magmatic pyrrhotite. Alternatively, this pyrite and associated sulfide inclusions might be cogenetic with hydrothermal Fe-oxide. Type-B pyrite that forms elongate grains and irregular relics and cores of pyrite with high Co contents (up to 23,630 ppm) and high Co to Ni ratios (7.2-140.9) are interpreted to be related to hydrothermal mineralization predating ductile deformation. A third generation of pyrite (type C) with low Co, low Ni, and moderate Co to Ni ratios (0.19-13.93) formed during and postdating the ductile deformation stage overgrowing, replacing, and surrounding type-B pyrite. The textural evolution of pyrite parallels the tectonometamorphic evolution of the shear zone demonstrating grain elongation during progressive ductile deformation and prograde metamorphism, annealing at the peak metamorphic condition, porphyroblastic growth at the retrograde path and cataclasis following porphyroblastic growth. Compositional characteristics of hydrothermal pyrite and available geological information suggest that the U-Cu(-Fe) deposit at Turamdih might be a variant of the Fe oxide (-Cu-U-rare earth elements) family of deposits. © Springer-Verlag 2007.
• Pal, D. C., Barton, M. D., & Sarangi, A. K. (2009). Deciphering a multistage history affecting U-Cu(-Fe) mineralization in the Singhbhum Shear Zone, eastern India, using pyrite textures and compositions in the Turamdih U-Cu(-Fe) deposit. Mineralium Deposita, 44(Issue 1). doi:10.1007/s00126-007-0165-z
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  The ∼200-km-long intensely deformed Singhbhum Shear Zone (SSZ) in eastern India hosts India's largest U and Cu deposits and related Fe mineralization. The SSZ separates an Archaean cratonic nucleus to the south from a Mesoproterozoic fold belt in the North and has a complex geologic history that obscures the origin of the contained iron-oxide-rich mineral deposits. This study investigates aspects of the history of mineralization in the SSZ by utilizing new petrographic and electron microprobe observations of pyrite textures and zoning in the Turamdih U-Cu(-Fe) deposit. Mineralization at Turamdih is hosted in intensively deformed quartz-chlorite schist. Sulfides and oxides include, in inferred order of development: (a) magmatic Fe(-Ti-Cr) oxide and Fe-Cu(-Ni) sulfide minerals inferred to be magmatic (?) in origin; followed by (b) uranium, Fe-oxide, and Fe-Cu(-Co) sulfide minerals that predate most or all ductile deformation, and are inferred to be of hydrothermal origin; and (c) Fe-Cu sulfides that were generated during and postdating ductile deformation. These features are associated with the formation of three compositionally and texturally distinct pyrites. Pyrite (type-A), typically in globular-semiglobular composite inclusions of pyrite plus chalcopyrite in magnetite, is characterized by very high Ni content (up to 30,700 ppm) and low Co to Ni ratios (0.01-0.61). The textural and compositional characteristics of associated chalcopyrite and rare pyrrhotite suggest that this pyrite could be linked to the magmatic event via selective replacement of magmatic pyrrhotite. Alternatively, this pyrite and associated sulfide inclusions might be cogenetic with hydrothermal Fe-oxide. Type-B pyrite that forms elongate grains and irregular relics and cores of pyrite with high Co contents (up to 23,630 ppm) and high Co to Ni ratios (7.2-140.9) are interpreted to be related to hydrothermal mineralization predating ductile deformation. A third generation of pyrite (type C) with low Co, low Ni, and moderate Co to Ni ratios (0.19-13.93) formed during and postdating the ductile deformation stage overgrowing, replacing, and surrounding type-B pyrite. The textural evolution of pyrite parallels the tectonometamorphic evolution of the shear zone demonstrating grain elongation during progressive ductile deformation and prograde metamorphism, annealing at the peak metamorphic condition, porphyroblastic growth at the retrograde path and cataclasis following porphyroblastic growth. Compositional characteristics of hydrothermal pyrite and available geological information suggest that the U-Cu(-Fe) deposit at Turamdih might be a variant of the Fe oxide (-Cu-U-rare earth elements) family of deposits. © Springer-Verlag 2007.
• Barton, M. D., & Jensen, E. P. (2008). Geology, petrochemistry, and time-space evolution of the Cripple Creek district, Colorado. Field Guides, 10, 63-78. doi:10.1130/2007.fld010(04)
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  The Cripple Creek district is renowned for epithermal gold telluride veins which have produced over 22 million ounces of gold from an intensely altered diatreme complex (total production + economic resources of >1000 tons). The district is also renowned for its association with a rare class of alkaline igneous rocks. The volcanism at Cripple Creek was part of a regionally extensive episode of Oligocene magmatism, including large volumes of calc-alkaline rocks and smaller, but widely distributed alkaline centers. Amongst the mid-Tertiary alkaline intrusive complexes, only Cripple Creek is associated with a giant (>500 ton) gold deposit. Further study of the magmatic and hydrothermal evolution of these systems will be necessary to explain this apparent disparity in gold enrichment. Cripple Creek’s gold mineralization principally occurs as telluride minerals hosted by swarms of narrow veins. Most geological studies over the last century have focused on the high-grade veins and to a lesser degree, adjacent hydrothermal alteration, but metasomatism is now shown to be broadly developed and demonstrably accompanied many events throughout the evolution of the igneous complex. Alteration types ranged from minor early pyroxene-stable varieties through various biotitebearing assemblages into voluminous K-feldspar stable types. Hydrolytic (acid) styles of alteration are present but minor. Economic gold mineralization is intimately associated only with late, voluminous K-feldspar-pyrite alteration which affected >5 km3 of the explored portion (upper 1 km) of the complex. Although similar to other gold deposits related to alkaline magmatism, Cripple Creek differs markedly from other epithermal systems in terms of its large volume of K-feldspar added and paucity of quartz and acid alteration.
• Barton, M. D., Butler, R. F., Ferguson, C. A., Seedorff, E., & Stavast, W. J. (2008). TERTIARY TILTING AND DISMEMBERMENT OF THE LARAMIDE ARC AND RELATED HYDROTHERMAL SYSTEMS, SIERRITA MOUNTAINS, ARIZONA. Economic Geology, 103(3), 629-636. doi:10.2113/gsecongeo.103.3.629
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  Multiple lines of evidence, including new and published geologic mapping and paleomagnetic and geobarometric determinations, demonstrate that the rocks and large porphyry copper systems of the Sierrita Mountains in southern Arizona were dismembered and tilted 50° to 60° to the south by Tertiary normal faulting. Repetition of geologic features and geobarometry indicate that the area is segmented into at least three major structural blocks, and the present surface corresponds to oblique sections through the Laramide plutonic-hydrothermal complex, ranging in paleodepth from ~1 to ~12 km. These results add to an evolving view of a north-south extensional domain at high angles to much extension in the southern Basin and Range, contrast with earlier interpretations that the Laramide systems are largely upright and dismembered by thrust faults, highlight the necessity of restoring Tertiary rotations before interpreting Laramide structural and hydrothermal features, and add to the broader understanding of pluton emplacement and evolution of porphyry copper systems.
• Inverno, C. M., Solomon, M., Barton, M. D., & Foden, J. (2008). The Cu stockwork and massive sulfide ore of the Feitais volcanic-hosted massive sulfide deposit, Aljustrel, Iberian Pyrite Belt, Portugal: A mineralogical, fluid inclusion, and isotopic investigation. Economic Geology, 103(1), 241-267.
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  Abstract: The Variscan Feitais volcanic-hosted massive sulfide deposit in the Aljustrel district of the Iberian Pyrite Belt consists of 55 million metric tons of Zn-Pb-Cu massive sulfide overlying a Cu-rich stockwork. The massive ore is overlain by up to 30 m of feldspar-phyric, rhyolitic volcaniclastic rock and locally by a jasper and/or chert layer up to 15 m thick. The massive sulfide orebody consists dominantly of pyrite, sphalerite, galena, chalcopyrite, tetrahedrite-tennantite, arsenopyrite, and bournonite, together with minor quartz, chlorite, sericite, carbonate, and barite. The orebody is up to 100 m thick and is underlain by a tabular alteration zone of chlorite-dominated, locally silicified, felsic volcanic rock, the upper 30 to 60 m of which contains chalcopyrite-quartz-chlorite-sericite-carbonate-bearing stockwork vein(let)s that prior to deformation were at a shallow angle to the base of the massive orebody. Chloritized footwall rocks extend up to 20 in below the Cu stockwork zone and are underlain by up to 50 m of quartz-sericite-pyrite-altered rhyolitic rock. The stockwork veins also contain pyrite, tetrahedrite-tennantite, sphalerite, and arsenopyrite. Pyrite, both in stockwork and massive ore, locally displays partly recrystallized framboidal, reniform, and cellular textures. Two generations of quartz, Q1 and Q2, and carbonate in the stockwork veins contain primary (in growth zones) and pseudosecondary fluid inclusions, with homogenization temperatures of 270° to 315°C and salinities of 2.2 to 8.1 wt percent NaCl equiv. The δ34S(CDT) values of massive and stockwork ores range from -15.4 to +4.7 (mean, -2.8) and -11.2 to +11.9 (mean, -0.4) per mil, respectively, the lowest values from colloform-textured pyrite. With no evidence of oxidation of sulfide sulfur during mineralization, the most negative values indicate an origin by biogenic reduction of seawater sulfate. The 13C(PDB) values for carbonates, -7.5 to -13.7 and +9.3 to -14.3 per mil in massive and stockwork ore, respectively, indicate an origin mostly by oxidation of methane derived from organic matter in underlying sedimentary rocks and possibly a contribution of magmatic carbon. There are no significant lateral or vertical variations in S isotope values in sulfides or C-O isotope values in carbonates, either in massive or stockwork ore. The δ18O(smow) values for quartz in stockwork and massive sulfide are 11.6 to 13.9 and 16.7 to 17.9 per mil, respectively. Coexisting, and texturally contemporaneous, carbonate and quartz in stockwork veins are not in isotopic equilibrium, indicating that the C-O isotope values may have been reset. The δ18O values of fluid calculated to be in equilibrium with quartz at fluid inclusion homogenization temperatures are 4.2 to 5.2 per mil. Barite from the hanging wall and massive ore yields δ34S values (21.9-27.9‰) equal to or slightly higher than those of coeval seawater; 87Sr/86Sr ratios (0.708438-0.709063) are slightly more radiogenic than those of coeval seawater (0.7080-0.7085), and much more radiogenic than those of coeval volcanic rocks (0.703304-0.706642), probably representing mixtures between seawater Sr and radiogenic Sr in fluids sourced in the crustal pile. Deposition of the massive sulfide on the sea floor is suggested by its stratiform nature, the stronger alteration of footwall relative to hanging-wall rocks, the stockwork system terminating sharply at the base of the massive sulfide, the presence of sedimentary-like textures in the massive sulfide, the absence of replacement fronts, and the presence of framboidal and other sea-floor depositional textures indicative of fluid quenching. The sheetlike form, lack of rubble mounds and chimneys, scarcity of barite, reduced mineral assemblage, and metal zoning distinguish Feitais from Kuroko-type deposits. It shares most of the characteristics of those Iberian Pyrite Belt deposits for which a brine-pool origin has been proposed based on fluid inclusion data, suggesting a similar depositional origin, although the evidence from fluid inclusions in this study is equivocal. The sulfate that underwent biogenic reduction may have been derived from mixing with seawater during early filling of the brine pool; diffusion across the brine-seawater interface; and sulfate reduction in the footwall volcaniclastic rocks. Stable and radiogenic isotope compositions of sulfates, sulfides, and carbonates suggest involvement of modified seawater and crustal fluids convecting due to magmatic heating, but the calculated high fluid pressures in the stockwork may indicate the additional involvement of magmatic fluids. © 2008 Society of Economic Geologists, Inc.
• Seedorff, E., Barton, M. D., Stavast, W. J., & Maher, D. J. (2008). Root zones of porphyry systems: Extending the porphyry model to depth. Economic Geology, 103(Issue 5). doi:10.2113/gsecongeo.103.5.939
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  The root zone of a porphyry system is a specific region beneath a porphyry orebody that was a site of focused fluid flow, as evidenced by abundant quartz veins, widespread wall-rock alteration, or porphyry dikes merging downward into a porphyritic granite cupola. These zones constitute an important source region of ore fluids and other components, and in certain geologic terrains the characteristics of root zones may point to previously undiscovered deposits. The root zones of four Laramide porphyry copper systems in Arizona recently have been characterized at a reconnaissance level: the Miami Inspiration system associated with the Schultze Granite, the Sierrita-Esperanza system associated with the Ruby Star Granodiorite, the Ray system associated with the Granite Mountain pluton, and the Kelvin-Riverside system associated with the Tea Cup pluton. The two well-studied root zones related to the Jurassic Yerington batholith in Nevada, and associated with the Yerington mine and the AnnMason deposit, provide a basis of comparison. All six systems occur in areas with unusually large exposures in both lateral and vertical paleodirections, locally to paleodepths of > 10 km, because of postore extensional faulting and associated tilting, No two systems are alike, but many share the presence of the following hydrothermal characteristics: quartz veins and potassic alteration, sodic-calcic and sodic alteration, calcic alteration, and relatively coarse grained muscovite-quartz (greisen). Quartz veins and potassic alteration are focused centrally, directly above related cupolas; sodic-calcic and sodie alteration, calcic alteration, and evidence for leaching of silica are observed on the deep flanks of certain systems; and greisen occurs directly beneath ore within and beneath coeval cupolas in many systems. Certain systems exhibit evidence of multiple cycles of release of magmatic fluid followed by incursion of saline ground waters, which are analogous to the biological cycle of exhaleinhale, respectively. The characteristics of the root zones provide important constraints on the exsolution and transport of the magmatic aqueous phase that leads to ore formation, the variable incursion of external fluids into the hydrothermal system, and the degassing of magmatic volatiles that may not be related directly to porphyry ore formation. The most robust conclusions are drawn from the localities that offer the greatest quality of exposure and degree of continuity (including compelling structural reconstructions) between the roots and the ore deposit, from the studies that identify timelines linking processes in the roots with those in the mineral deposit, and from systems in which the deposit itself is well characterized. © 2008 Society of Economic Geologists, Inc.
• Seedorff, E., Seedorff, E., Barton, M. D., Barton, M. D., Stavast, W. J., Stavast, W. J., Maher, D. J., & Maher, D. J. (2008). Root zones of porphyry systems: Extending the porphyry model to depth. Economic Geology, 103(5), 939-956.
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  Abstract: The root zone of a porphyry system is a specific region beneath a porphyry orebody that was a site of focused fluid flow, as evidenced by abundant quartz veins, widespread wall-rock alteration, or porphyry dikes merging downward into a porphyritic granite cupola. These zones constitute an important source region of ore fluids and other components, and in certain geologic terrains the characteristics of root zones may point to previously undiscovered deposits. The root zones of four Laramide porphyry copper systems in Arizona recently have been characterized at a reconnaissance level: the Miami Inspiration system associated with the Schultze Granite, the Sierrita-Esperanza system associated with the Ruby Star Granodiorite, the Ray system associated with the Granite Mountain pluton, and the Kelvin-Riverside system associated with the Tea Cup pluton. The two well-studied root zones related to the Jurassic Yerington batholith in Nevada, and associated with the Yerington mine and the AnnMason deposit, provide a basis of comparison. All six systems occur in areas with unusually large exposures in both lateral and vertical paleodirections, locally to paleodepths of > 10 km, because of postore extensional faulting and associated tilting, No two systems are alike, but many share the presence of the following hydrothermal characteristics: quartz veins and potassic alteration, sodic-calcic and sodic alteration, calcic alteration, and relatively coarse grained muscovite-quartz (greisen). Quartz veins and potassic alteration are focused centrally, directly above related cupolas; sodic-calcic and sodie alteration, calcic alteration, and evidence for leaching of silica are observed on the deep flanks of certain systems; and greisen occurs directly beneath ore within and beneath coeval cupolas in many systems. Certain systems exhibit evidence of multiple cycles of release of magmatic fluid followed by incursion of saline ground waters, which are analogous to the biological cycle of exhaleinhale, respectively. The characteristics of the root zones provide important constraints on the exsolution and transport of the magmatic aqueous phase that leads to ore formation, the variable incursion of external fluids into the hydrothermal system, and the degassing of magmatic volatiles that may not be related directly to porphyry ore formation. The most robust conclusions are drawn from the localities that offer the greatest quality of exposure and degree of continuity (including compelling structural reconstructions) between the roots and the ore deposit, from the studies that identify timelines linking processes in the roots with those in the mineral deposit, and from systems in which the deposit itself is well characterized. © 2008 Society of Economic Geologists, Inc.
• Stavast, W. J., Butler, R. F., Seedorff, E., Barton, M. D., & Ferguson, C. A. (2008). Tertiary tilting and dismemberment of the Laramide arc and related hydrothermal systems, Sierrita Mountains, Arizona. Economic Geology, 103(3), 629-636.
• Stavast, W. J., Butler, R. F., Seedorff, E., Barton, M. D., & Ferguson, C. A. (2008). Tertiary tilting and dismemberment of the laramide arc and related hydrothermal systems, Sierrita Mountain, Arizona. Economic Geology, 103(3), 629-636.
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  Abstract: Multiple lines of evidence, including new and published geologic mapping and paleomagnetic and geobarometric determinations, demonstrate that the rocks and large porphyry copper systems of the Sierrita Mountains in southern Arizona were dismembered and tilted 50° to 60° to the south by Tertiary normal faulting. Repetition of geologic features and geobarometry indicate that the area is segmented into at least three major structural blocks, and the present surface corresponds to oblique sections through the Laramide plutonic-hydrothermal complex, ranging in paleodepth from ∼1 to ∼12 km. These results add to an evolving view of a north-south extensional domain at high angles to much extension in the southern Basin and Range, contrast with earlier interpretations that the Laramide systems are largely upright and dismembered by thrust faults, highlight the necessity of restoring Tertiary rotations before interpreting Laramide structural and hydrothermal features, and add to the broader understanding of pluton emplacement and evolution of porphyry copper systems. © 2008 Society of Economic Geologists, Inc.
• Ducea, M. N., & Barton, M. D. (2007). Igniting flare-up events in Cordilleran arcs. Geology, 35(11), 1047-1050.
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  Abstract: High-flux pulses of magmatism that make up most of the exposed North American Cordilleran arcs are derived primarily from upper plate lithospheric source materials, and not the mantle wedge as most models would predict, based on a compilation of thousands of previously published Sr, Nd, and O isotopic data. Mass balance calculations show that no more than 50% of that mass can be mantle-derived. Flare-ups must have fundamentally developed simultaneously with crustal/lithospheric thickening, thus implying a connection. Subduction erosion from the trench side, and retroarc shortening from the foreland side are the main tectonic shortening processes that operate in conjunction with high flux magmatism during subduction, and therefore are likely triggers for flare-up events in arc. These arcs represent the sites of crustal differentiation, and thus contribute to net continental growth, only if dense residual lower crust was returned to the convective mantle. Isotopic data shown here suggest that if convective removal of batholithic roots takes place, it must be a consequence and not a cause of episodic flare-ups. The Altiplano-Puna Volcanic Complex in South America may be the most recent continental arc segment in flare-up mode. © 2007 The Geological Society of America.
• Ducea, M. N., & Barton, M. D. (2007). Igniting flare-up events in Cordilleran arcs. Geology, 35(Issue 11). doi:10.1130/g23898a.1
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  High-flux pulses of magmatism that make up most of the exposed North American Cordilleran arcs are derived primarily from upper plate lithospheric source materials, and not the mantle wedge as most models would predict, based on a compilation of thousands of previously published Sr, Nd, and O isotopic data. Mass balance calculations show that no more than 50% of that mass can be mantle-derived. Flare-ups must have fundamentally developed simultaneously with crustal/lithospheric thickening, thus implying a connection. Subduction erosion from the trench side, and retroarc shortening from the foreland side are the main tectonic shortening processes that operate in conjunction with high flux magmatism during subduction, and therefore are likely triggers for flare-up events in arc. These arcs represent the sites of crustal differentiation, and thus contribute to net continental growth, only if dense residual lower crust was returned to the convective mantle. Isotopic data shown here suggest that if convective removal of batholithic roots takes place, it must be a consequence and not a cause of episodic flare-ups. The Altiplano-Puna Volcanic Complex in South America may be the most recent continental arc segment in flare-up mode. © 2007 The Geological Society of America.
• Ayers, J. C., Loflin, M., Miller, C. F., Barton, M. D., & Coath, C. D. (2006). In situ oxygen isotope analysis of monazite as a monitor of fluid infiltration during contact metamorphism: Birch Creek Pluton aureole, White Mountains, eastern California. Geology, 34(8), 653-656.
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  Abstract: Monazite from the hydrothermal aureole of the Cretaceous two-mica Birch Creek Pluton in the White Mountains of eastern California records the infiltration of magmatic fluids into the metasedimentary Early Cambrian Deep Spring Formation. Monazite in the Birch Creek Pluton displays concentric, euhedral magmatic zoning, δ18O = 8.7 ± 0.2‰, and Th-Pb magmatic ages of 78.0 ± 0.7 Ma. The middle Deep Spring Formation ∼0.5 km east of the contact underwent moderate- to low-temperature alteration by F-rich magmatic fluids; monazite displays patchy zoning but has similar δ18O values (8.7 ± 0.4‰) and Th-Pb ages (78.3 ± 1.6 Ma) to monazite in the Birch Creek Pluton. In contrast, monazite from the upper Deep Spring Formation ∼0.6 km west of the contact and outside the mapped hydrothermal zone shows concentric zoning, δ18O = 5.2 ± 0.3‰, and partially reset detrital ages from 583 to 1069 Ma. Deep Spring Formation monazite within the hydrothermal alteration zone dissolved and reprecipitated during magmatic fluid infiltration, whereas monazite outside the zone was unaffected. In contrast, Deep Spring zircon within the hydrothermal alteration zone preserved its magmatic zoning and Cambrian-Precambrian U-Pb ages. Zircon can reliably date events prior to hydrothermal activity, whereas monazite, being more susceptible to alteration by fluids, is useful for mapping the extent and timing of fluid infiltration events. © 2006 Geological Society of America.
• Ayers, J. C., Loflin, M., Miller, C. F., Barton, M. D., & Coath, C. D. (2006). In situ oxygen isotope analysis of monazite as a monitor of fluid infiltration during contact metamorphism: Birch Creek Pluton aureole, White Mountains, eastern California. Geology, 34(Issue 8). doi:10.1130/g22185.1
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  Monazite from the hydrothermal aureole of the Cretaceous two-mica Birch Creek Pluton in the White Mountains of eastern California records the infiltration of magmatic fluids into the metasedimentary Early Cambrian Deep Spring Formation. Monazite in the Birch Creek Pluton displays concentric, euhedral magmatic zoning, δ18O = 8.7 ± 0.2‰, and Th-Pb magmatic ages of 78.0 ± 0.7 Ma. The middle Deep Spring Formation ∼0.5 km east of the contact underwent moderate- to low-temperature alteration by F-rich magmatic fluids; monazite displays patchy zoning but has similar δ18O values (8.7 ± 0.4‰) and Th-Pb ages (78.3 ± 1.6 Ma) to monazite in the Birch Creek Pluton. In contrast, monazite from the upper Deep Spring Formation ∼0.6 km west of the contact and outside the mapped hydrothermal zone shows concentric zoning, δ18O = 5.2 ± 0.3‰, and partially reset detrital ages from 583 to 1069 Ma. Deep Spring Formation monazite within the hydrothermal alteration zone dissolved and reprecipitated during magmatic fluid infiltration, whereas monazite outside the zone was unaffected. In contrast, Deep Spring zircon within the hydrothermal alteration zone preserved its magmatic zoning and Cambrian-Precambrian U-Pb ages. Zircon can reliably date events prior to hydrothermal activity, whereas monazite, being more susceptible to alteration by fluids, is useful for mapping the extent and timing of fluid infiltration events. © 2006 Geological Society of America.
• Barton, M. D., Brown, J. M., Haxel, G., Hayes, T., Jensen, E. P., Johnson, D. R., Kamilli, R., Long, K. R., Maher, D. J., & Seedorff, E. (2005). Center for Mineral Resources: U.S. Geological Survey- University of Arizona, Department of Geosciences Porphyry Copper Deposit Life Cycles Field Conference, Southeastern Arizona, May 21-22, 2002. Scientific Investigations Report. doi:10.3133/sir20055020
• Seedorff, E., Dilles, J. H., Proffett, Jr., J. M., Einaudi, M. T., Zurcher, L., Stavast, W. J., Johnson, D. A., & Barton, M. D. (2005). Porphyry deposits: Characteristics and origin of hypogene features. Economic Geology 100th Anniversary Volume, 251-298.
• Zurcher, L., Kring, D. A., Barton, M. D., Dettman, D., & Rollog, M. (2005). Stable isotope record of post-impact fluid activity in the core of the Yaxcopoil-1 borehole, Chicxulub impact structure, Mexico. Special Paper of the Geological Society of America, 384, 223-238.
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  Abstract: Carbon, oxygen, and hydrogen isotope results from carbonate and silicate fractions of altered core samples from the Yaxcopoil-1 borehole drilled into the 65 Ma Chicxulub impact crater provide constraints on the physico-chemical parameters of the hydrothermal solutions, and their likely origin. Yaxcopoil-1 impactites were initially permeated with calcite and halite at ambient temperature. This was followed by thermal metamorphism (diopside after igneous augite) and widespread Na-K metasomatism (feldspar after igneous plagioclase), which were overprinted by abundant lower-temperature clay and calcite. Silicate fraction isotopic values have δ18OSMOW values between 10 and 23% indicating important isotopic exchange between impact melt (∼8%) and Cretaceous limestone (∼26%). Heavier δ18O values occur over depth intervals with intense feldspar alteration (813-833 m and 864-872 m). The δDSMOW values (-34 to -54%) are chiefl y infl uenced by smectite abundance and roughly mirror δ18O values. Carbonate fraction δ18OSMOW values (22-30%) are controlled by calcite contents, and several exceed the limestone signature. Most δ0.13CPDB (-1 to +2%) values also cluster around that of local limestone, but a number are signifi cantly lighter (down to -7%). Isotopic and fluid inclusion results indicate hydrothermal fluid temperatures between 270 and 100 °C, high salinities (∼20%), and minor kerogen contents. These data are compatible with mineralogical constraints, which further support an increase in oxidation state with decreasing temperature. Isotopic data point to a saline CO2-bearing fluid mixed with small amounts of reduced carbon, and decarbonation and infi ltration processes. Combined results are most consistent with a basinal oilfi eld saline brine that was driven by impact-induced heat. © 2005 Geological Society of America.
• Zurcher, L., Kring, D. A., Barton, M. D., Dettman, D., & Rollog, M. (2005). Stable isotope record of post-impact fluid activity in the core of the Yaxcopoil-1 borehole, Chicxulub impact structure, Mexico. Special Paper of the Geological Society of America. doi:10.1130/0-8137-2384-1.223
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  Carbon, oxygen, and hydrogen isotope results from carbonate and silicate fractions of altered core samples from the Yaxcopoil-1 borehole drilled into the 65 Ma Chicxulub impact crater provide constraints on the physico-chemical parameters of the hydrothermal solutions, and their likely origin. Yaxcopoil-1 impactites were initially permeated with calcite and halite at ambient temperature. This was followed by thermal metamorphism (diopside after igneous augite) and widespread Na-K metasomatism (feldspar after igneous plagioclase), which were overprinted by abundant lower-temperature clay and calcite. Silicate fraction isotopic values have δ 18O SMOW values between 10 and 23% indicating important isotopic exchange between impact melt (∼8%) and Cretaceous limestone (∼26%). Heavier δ 18 O values occur over depth intervals with intense feldspar alteration (813-833 m and 864-872 m). The δD SMOW values (-34 to -54%) are chiefl y infl uenced by smectite abundance and roughly mirror δ 18 O values. Carbonate fraction δ 18 O SMOW values (22-30%) are controlled by calcite contents, and several exceed the limestone signature. Most δ0.13C PDB (-1 to +2%) values also cluster around that of local limestone, but a number are signifi cantly lighter (down to -7%). Isotopic and fluid inclusion results indicate hydrothermal fluid temperatures between 270 and 100 °C, high salinities (∼20%), and minor kerogen contents. These data are compatible with mineralogical constraints, which further support an increase in oxidation state with decreasing temperature. Isotopic data point to a saline CO 2 -bearing fluid mixed with small amounts of reduced carbon, and decarbonation and infi ltration processes. Combined results are most consistent with a basinal oilfi eld saline brine that was driven by impact-induced heat. © 2005 Geological Society of America.
• Barton, M. D., & Young, S. (2002). Non-pegmatitic deposits of beryllium: Mineralogy, geology, phase equilibria and origin. Reviews in Mineralogy and Geochemistry, 50.
• Barton, M. D., & Young, S. (2002). Non-pegmatitic deposits of beryllium: Mineralogy, geology, phase equilibria and origin. Reviews in Mineralogy and Geochemistry.
• Bebout, G. E., & Barton, M. D. (2002). Tectonic and metasomatic mixing in a high-T, subduction-zone mélange - Insights into the geochemical evolution of the slab-mantle interface. Chemical Geology, 187(1-2), 79-106.
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  Abstract: The Catalina Schist (California) contains an amphibolite-grade (0.8- 1.1 GPa; 640-750 °C) mélange unit consisting of mafic and ultramafic blocks in high-Mg, schistose mélange matrix with varying modal proportions of talc, chlorite, anthophyllite, calcic-amphibole, enstatite, and minor phases including zircon, rutile, apatite, spinel, and Fe-Ni sulfides. This mélange unit is interpreted as a kilometer-scale zone of tectonic and metasomatic mixing formed within a juvenile subduction zone, the study of which may yield insight into chemical mixing processes at greater depths in subduction zones. Relationships among the major and trace element compositions of the mafic and ultramafic blocks in the mélange, the rinds developed at the margins of these blocks, and the surrounding mélange matrix are compatible with the evolution of the mélange matrix through a complex combination of infiltrative and diffusional metasomatism and a process resembling mechanical mixing. Simple, linear mixing models are compatible with the development of the mélange matrix primarily through simple mixture of the ultramafic and mafic rocks, with Cr/Al ratios serving as indicators of the approximate proportions of the two lithologies. This conclusion regarding mafic-ultramafic mixing is consistent with the field observations and chemical trends indicating strong resemblance of large parts of the mélange matrix with rinds developed at the margins of mafic and ultramafic blocks. The overall process involved development of metasomatic assemblages through complex fluid-mediated mixing of the blocks and matrix concurrent with deformation of these relatively weak rind materials, which are rich in layer silicates and amphibole. This deformation was sufficiently intense to transpose fabrics, progressively disaggregate more rigid, block-derived materials in weaker chorite- and talc-rich mélange, and in some particularly weak lithologies (e.g., chlorite-, talc, and amphibole-rich materials), intimately juxtapose adjacent lithologies at the (sub-)cm scale (approaching grain scale) sampled by the whole-rock geochemical analyses. Chemical systematics of various elements in the mélange matrix can be delineated based on the Cr/A1-based mixing model. Simple mixing relationships exhibited by A1, Cr, Mg, Ni, Fe, and Zr provide a geochemical reference frame for considerations of mass and volume loss and gain within the mélange matrix. The compositional patterns of many other elements are explained by either redistribution (local stripping or enrichment) at varying scales within the mélange (Ca, Na, K, Ba, and Sr) or massive addition from external sources (Si and H2O), the latter probably in infiltrating H2O-rich fluids that produced the dramatic O and H isotopic shifts in the mélange. Mélange formation, resulting in the production of high-variance ultramafic assemblages with high volatile contents, may aid retention of volatiles (in this case, H2O) to greater depths in subduction zones than in original subducted mafic and sedimentary materials. The presence of such assemblages (i.e., containing minerals such as talc, chlorite, and Mg-rich amphiboles) would impact the rheology of the slab-mantle interface and perhaps contribute to the low-velocity seismic structure observed at/near the slab-mantle interface in some subduction zones. If operative along the slab-mantle interface, complex mixing processes such as these, involving the interplay between fluid-mediated metasomatism and deformation, also could impact slab incompatible trace element and isotopic signatures ultimately observed in arc magmas, producing "fluids" with geochemical signatures inherited from interactions with hybridized rock compositions. © 2002 Elsevier Science B.V. All rights reserved.
• Bebout, G. E., & Barton, M. D. (2002). Tectonic and metasomatic mixing in a high-T, subduction-zone mélange - Insights into the geochemical evolution of the slab-mantle interface. Chemical Geology, 187(Issue 1-2). doi:10.1016/s0009-2541(02)00019-0
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  The Catalina Schist (California) contains an amphibolite-grade (0.8- 1.1 GPa; 640-750 °C) mélange unit consisting of mafic and ultramafic blocks in high-Mg, schistose mélange matrix with varying modal proportions of talc, chlorite, anthophyllite, calcic-amphibole, enstatite, and minor phases including zircon, rutile, apatite, spinel, and Fe-Ni sulfides. This mélange unit is interpreted as a kilometer-scale zone of tectonic and metasomatic mixing formed within a juvenile subduction zone, the study of which may yield insight into chemical mixing processes at greater depths in subduction zones. Relationships among the major and trace element compositions of the mafic and ultramafic blocks in the mélange, the rinds developed at the margins of these blocks, and the surrounding mélange matrix are compatible with the evolution of the mélange matrix through a complex combination of infiltrative and diffusional metasomatism and a process resembling mechanical mixing. Simple, linear mixing models are compatible with the development of the mélange matrix primarily through simple mixture of the ultramafic and mafic rocks, with Cr/Al ratios serving as indicators of the approximate proportions of the two lithologies. This conclusion regarding mafic-ultramafic mixing is consistent with the field observations and chemical trends indicating strong resemblance of large parts of the mélange matrix with rinds developed at the margins of mafic and ultramafic blocks. The overall process involved development of metasomatic assemblages through complex fluid-mediated mixing of the blocks and matrix concurrent with deformation of these relatively weak rind materials, which are rich in layer silicates and amphibole. This deformation was sufficiently intense to transpose fabrics, progressively disaggregate more rigid, block-derived materials in weaker chorite- and talc-rich mélange, and in some particularly weak lithologies (e.g., chlorite-, talc, and amphibole-rich materials), intimately juxtapose adjacent lithologies at the (sub-)cm scale (approaching grain scale) sampled by the whole-rock geochemical analyses. Chemical systematics of various elements in the mélange matrix can be delineated based on the Cr/A1-based mixing model. Simple mixing relationships exhibited by A1, Cr, Mg, Ni, Fe, and Zr provide a geochemical reference frame for considerations of mass and volume loss and gain within the mélange matrix. The compositional patterns of many other elements are explained by either redistribution (local stripping or enrichment) at varying scales within the mélange (Ca, Na, K, Ba, and Sr) or massive addition from external sources (Si and H2O), the latter probably in infiltrating H2O-rich fluids that produced the dramatic O and H isotopic shifts in the mélange. Mélange formation, resulting in the production of high-variance ultramafic assemblages with high volatile contents, may aid retention of volatiles (in this case, H2O) to greater depths in subduction zones than in original subducted mafic and sedimentary materials. The presence of such assemblages (i.e., containing minerals such as talc, chlorite, and Mg-rich amphiboles) would impact the rheology of the slab-mantle interface and perhaps contribute to the low-velocity seismic structure observed at/near the slab-mantle interface in some subduction zones. If operative along the slab-mantle interface, complex mixing processes such as these, involving the interplay between fluid-mediated metasomatism and deformation, also could impact slab incompatible trace element and isotopic signatures ultimately observed in arc magmas, producing "fluids" with geochemical signatures inherited from interactions with hybridized rock compositions. © 2002 Elsevier Science B.V. All rights reserved.
• Staude, J. -., & Barton, M. D. (2001). Jurassic to Holocene tectonics, magmatism, and metallogeny of Northwestern Mexico. Bulletin of the Geological Society of America, 113(10), 1357-1374.
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  Abstract: The present metallic distribution in northwestern Mexico is the culmination of superposed magmatism, tectonism, erosion, and burial over more than 150 m.y. Detailed palinspastic reconstructions of preextensional configurations - the first study of its kind for this region - clarify the interplay among these features on the present distribution and character of mineralized geologic systems. This new synthesis goes beyond previous metallogenic investigations of northwestern Mexico by separating events into specific timing and structural relationships, and by restoring the geology to its preextensional configuration. Metallogenic factors such as enrichment, preservation, and erosion play major roles in the present distributions and for the first time are related to the overall metallogenic framework of northwestern Mexico. The analysis concludes that modern metallogenic patterns are the result of the complex superposition and subsequent redistribution of geologic systems in a way that is related directly to the regional history, rather than simply metallic belts or interpreted angle of a subducting slab. Three main extensional events in the Oligocene- Holocene have been restored, and the palinspastic distribution have been analyzed. Reconstructions reveal the following: (1) Mineralization events, igneous centers, and sedimentary sequences are continuous across the Gulf of California and other areas with large amounts of extension. (2) Middle Tertiary gold-silver mineralization in Baja California may be the western part of the Sierra Madre Occidental metallogenic province, thus expanding the previously recognized extent of this province's mineralization. (3) Late Cretaceous-early Tertiary porphyry copper deposits and intrusive centers form a narrower belt than previously noted and are traceable for over 400 km, with parts of the belt buried beneath the younger Sierra Madre Occidental volcanic fields. (4) Interpreted alignments of older geologic features, including lineaments of ore deposits, are displaced in the reconstructions. (5) Sedimentary-rock-hosted gold deposits and low-angle-detachment gold systems are closely related and occur around core complexes. By using structurally restored time slices, it becomes clear that older deposit types tend to be those formed at greater depths and more proximal to intrusions, whereas younger deposits formed at shallower depths are less eroded and are more commonly volcanic-rock hosted. These characteristics express themselves in the regional distribution of deposit types. Second, mineralization of widely differing ages is spatially superposed, commonly associated with coeval magmatic and tectonic events. The structural and magmatic events together with paleodistribution of ore deposits define a new framework to interpret the metallogenic history of northwestern Mexico.
• Staude, J. M., & Barton, M. D. (2001). Jurassic to Holocene tectonics, magmatism, and metallogeny of Northwestern Mexico. Bulletin of the Geological Society of America, 113(Issue 10). doi:10.1130/0016-7606(2001)113<1357:jthtma>2.0.co;2
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  The present metallic distribution in northwestern Mexico is the culmination of superposed magmatism, tectonism, erosion, and burial over more than 150 m.y. Detailed palinspastic reconstructions of preextensional configurations - the first study of its kind for this region - clarify the interplay among these features on the present distribution and character of mineralized geologic systems. This new synthesis goes beyond previous metallogenic investigations of northwestern Mexico by separating events into specific timing and structural relationships, and by restoring the geology to its preextensional configuration. Metallogenic factors such as enrichment, preservation, and erosion play major roles in the present distributions and for the first time are related to the overall metallogenic framework of northwestern Mexico. The analysis concludes that modern metallogenic patterns are the result of the complex superposition and subsequent redistribution of geologic systems in a way that is related directly to the regional history, rather than simply metallic belts or interpreted angle of a subducting slab. Three main extensional events in the Oligocene- Holocene have been restored, and the palinspastic distribution have been analyzed. Reconstructions reveal the following: (1) Mineralization events, igneous centers, and sedimentary sequences are continuous across the Gulf of California and other areas with large amounts of extension. (2) Middle Tertiary gold-silver mineralization in Baja California may be the western part of the Sierra Madre Occidental metallogenic province, thus expanding the previously recognized extent of this province's mineralization. (3) Late Cretaceous-early Tertiary porphyry copper deposits and intrusive centers form a narrower belt than previously noted and are traceable for over 400 km, with parts of the belt buried beneath the younger Sierra Madre Occidental volcanic fields. (4) Interpreted alignments of older geologic features, including lineaments of ore deposits, are displaced in the reconstructions. (5) Sedimentary-rock-hosted gold deposits and low-angle-detachment gold systems are closely related and occur around core complexes. By using structurally restored time slices, it becomes clear that older deposit types tend to be those formed at greater depths and more proximal to intrusions, whereas younger deposits formed at shallower depths are less eroded and are more commonly volcanic-rock hosted. These characteristics express themselves in the regional distribution of deposit types. Second, mineralization of widely differing ages is spatially superposed, commonly associated with coeval magmatic and tectonic events. The structural and magmatic events together with paleodistribution of ore deposits define a new framework to interpret the metallogenic history of northwestern Mexico.
• Valencia-Moreno, M., Ruiz, J., Barton, M. D., Patchett, P. J., Zürher, L., Hodkinson, D. G., & Roldán-Quintana, J. (2001). A chemical and isotopic study of the Laramide granitic belt of northern Mexico: Idenfication of the southern edge of the North American Precambrian basement. Bulletin of the Geological Society of America, 113(11), 1409-1422.
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  Abstract: Along the Laramide belt of northwestern Mexico, granitic rocks of similar bulk composition show isotopic and trace element signatures that help to delineate the position of the southern edge of the North American Precambrian basement. In the northern part, the Laramide plutons (the "northern granites") intruded Proterozoic crystalline rocks and a thick Late Proterozoic through Paleozoic miogeoclinal cover of North American affinity. In the central part, the granitic bodies (the "central granites") were emplaced into a sequence of Paleozoic eugeoclinal rocks overlain by Late Triassic clastic units. The southern part of the belt (the "southern granites") intruded a less-known crust characterized by middle to late Mesozoic island-arc-related volcanic and sedimentary rocks of the Guerrero terrane. Data from a suite of metaluminous to slightly peraluminous calc-alkalic granitic rocks along the belt display north-to-south geochemical and isotopic variations, which could correlate with the type of intruded basement. The northern and central granites are characterized by strongly fractionated, light rare earth element (REE)-enriched patterns, which display generally pronounced negative europium anomalies, whereas the southern granites have lower total REE enrichments and much flatter chondrite-normalized slopes displaying almost no europium anomalies. Isotopic results also suggest regional variations, as shown by the following initial Sr and εNd ranges: 0.7070 to 0.7089 and-4.2 to-5.4, respectively, for the northern granites; 0.7060 to 0.7079 and-3.4 to-5.1 for the central granites; and 0.7026 to 0.7062 and-0.9 to +4.2 for the southern granites. On the basis of their isotopic similarities, the Proterozoic mafic to intermediate lower crust revealed by xenoliths from young volcanic flows in southern Arizona and northern Mexico is interpreted as a reasonable parental source for the northern and central granites; however, mantle-derived melts are not excluded. The more primitive southern granites are interpreted to come from a source that lacked Proterozoic basement. Instead, they were probably derived by mixing of juvenile mantle melts with partial melts of the lower parts of the Guerrero terrane. In general, the north-to-south compositional variations of the Laramide granitic rocks of northwestern Mexico reflect the crustal structure underneath the batholiths. The Sr and Nd data indicate that the edge of the North American Precambrian basement extends approximately southeastward from the coastal batholith of central Sonora; then, about 200 km south of Hermosillo in southern Sonora, the edge bends eastward and continues to the east beneath the Sierra Madre Occidental volcanic province.
• Valencia-Moreno, M., Ruiz, J., Barton, M. D., Patchett, P. J., Zürher, L., Hodkinson, D. G., & Roldán-Quintana, J. (2001). A chemical and isotopic study of the Laramide granitic belt of northern Mexico: Idenfication of the southern edge of the North American Precambrian basement. Bulletin of the Geological Society of America, 113(Issue 11). doi:10.1130/0016-7606(2001)113<1409:acaiso>2.0.co;2
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  Along the Laramide belt of northwestern Mexico, granitic rocks of similar bulk composition show isotopic and trace element signatures that help to delineate the position of the southern edge of the North American Precambrian basement. In the northern part, the Laramide plutons (the "northern granites") intruded Proterozoic crystalline rocks and a thick Late Proterozoic through Paleozoic miogeoclinal cover of North American affinity. In the central part, the granitic bodies (the "central granites") were emplaced into a sequence of Paleozoic eugeoclinal rocks overlain by Late Triassic clastic units. The southern part of the belt (the "southern granites") intruded a less-known crust characterized by middle to late Mesozoic island-arc-related volcanic and sedimentary rocks of the Guerrero terrane. Data from a suite of metaluminous to slightly peraluminous calc-alkalic granitic rocks along the belt display north-to-south geochemical and isotopic variations, which could correlate with the type of intruded basement. The northern and central granites are characterized by strongly fractionated, light rare earth element (REE)-enriched patterns, which display generally pronounced negative europium anomalies, whereas the southern granites have lower total REE enrichments and much flatter chondrite-normalized slopes displaying almost no europium anomalies. Isotopic results also suggest regional variations, as shown by the following initial Sr and εNd ranges: 0.7070 to 0.7089 and-4.2 to-5.4, respectively, for the northern granites; 0.7060 to 0.7079 and-3.4 to-5.1 for the central granites; and 0.7026 to 0.7062 and-0.9 to +4.2 for the southern granites. On the basis of their isotopic similarities, the Proterozoic mafic to intermediate lower crust revealed by xenoliths from young volcanic flows in southern Arizona and northern Mexico is interpreted as a reasonable parental source for the northern and central granites; however, mantle-derived melts are not excluded. The more primitive southern granites are interpreted to come from a source that lacked Proterozoic basement. Instead, they were probably derived by mixing of juvenile mantle melts with partial melts of the lower parts of the Guerrero terrane. In general, the north-to-south compositional variations of the Laramide granitic rocks of northwestern Mexico reflect the crustal structure underneath the batholiths. The Sr and Nd data indicate that the edge of the North American Precambrian basement extends approximately southeastward from the coastal batholith of central Sonora; then, about 200 km south of Hermosillo in southern Sonora, the edge bends eastward and continues to the east beneath the Sierra Madre Occidental volcanic province.
• Zürcher, L., Ruiz, J., & Barton, M. D. (2001). Paragenesis, elemental distribution, and stable isotopes at the Peña Colorada Iron Skarn, Colima, Mexico. Economic Geology, 96(3), 535-557.
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  Abstract: The Peña Colorada iron skarn is located in the southern part of the Guerrero terrane. It contains 150 million metric tons (Mt) with a grade of 36 percent magnetite. The deposit occurs at the contact of a 68 Ma equigranular diorite with mid-Cretaceous volcano-sedimentary rocks of the Tepalcatepec Formation. Volcanic units within this formation have tholeiitic affinity and REE patterns that are compatible with a primitive arc setting. The Peña Colorada diorite and associated voluminous aplitic phases are part of a Late Cretaceous calc-alkaline continental arc that subsequently intruded this basin. Northeast-vergent deformation affected the region in the Late Cretaceous. North-south and east-west reverse, and northwest and northeast strike-slip faults localize the mineralization. The alteration halo around the diorite intrusion is 500 m wide. Within an inner 200-m halo, the volcano-sedimentary section was affected by an early metamorphic event, with discontinuous bands of pyroxene (Di 68Hd 29Jo 3) hornfels and garnet (Gr 61Am 36Ad 3) disseminations. Metasomatic pyroxene, garnet, and plagioclase cut the early metamorphic event preferentially replacing carbonate and volcanic units up to and including a 35-m-thick marl located 200 m above the intrusion. Metasomatic pyroxene and garnet have average compositions of Di 77Hd 21Jo 2 and Ad 76Gr 20Am 2Sp 1Py 1, respectively. Pyroxene compositions reach Di 94Hd 5Jo 1, whereas garnet exhibits intragrain compositional zoning from Ad 49Gr 46 in the core to Ad 100Gr 0 in the rim. Albitization of preexisting protoliths modified igneous plagioclase compositions from Ab 67An 32Or 1 up to Ab 96An 3Or 1. Albitization is followed by abundant fracture-controlled Fe-epidote and Cl-bearing chlorite (Cha 84Cli 14Pen 2) that extend from the marl unit outward some 300 m. This association is cut by a later assemblage of epidote-chlorite-prehnite that affects the entire 500-m width of the alteration halo and part of the intrusion. Chlorite (Cha 54Cli 45Pen 1) from this later event is richer in Mg than that from the previous association. Igneous hornblende in the intrusion is altered to actinolite. A potassic alteration event related to a hydrothermal breccia and aplitic dikes overprints the pre-existing calc-silicate associations. Alteration minerals in the breccia and the 200-m potassic halo around it, evolve from early K feldspar-(biotite)-quartz, to late jasperoid-fluorapatite-calcite veins. Mg-rich biotite (Phl 77Ann 23) and REE-rich apatite contain F/Cl/OH ratios of 1/0/3 and 1/0/0, respectively. Massive magnetite (36%)-specular hematite (7%)-sulfide (
• Zürcher, L., Ruiz, J., & Barton, M. D. (2001). Paragenesis, elemental distribution, and stable isotopes at the Peña Colorada Iron Skarn, Colima, Mexico. Economic Geology, 96(Issue 3). doi:10.2113/gsecongeo.96.3.535
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  The Peña Colorada iron skarn is located in the southern part of the Guerrero terrane. It contains 150 million metric tons (Mt) with a grade of 36 percent magnetite. The deposit occurs at the contact of a 68 Ma equigranular diorite with mid-Cretaceous volcano-sedimentary rocks of the Tepalcatepec Formation. Volcanic units within this formation have tholeiitic affinity and REE patterns that are compatible with a primitive arc setting. The Peña Colorada diorite and associated voluminous aplitic phases are part of a Late Cretaceous calc-alkaline continental arc that subsequently intruded this basin. Northeast-vergent deformation affected the region in the Late Cretaceous. North-south and east-west reverse, and northwest and northeast strike-slip faults localize the mineralization. The alteration halo around the diorite intrusion is 500 m wide. Within an inner 200-m halo, the volcano-sedimentary section was affected by an early metamorphic event, with discontinuous bands of pyroxene (Di 68Hd 29Jo 3) hornfels and garnet (Gr 61Am 36Ad 3) disseminations. Metasomatic pyroxene, garnet, and plagioclase cut the early metamorphic event preferentially replacing carbonate and volcanic units up to and including a 35-m-thick marl located 200 m above the intrusion. Metasomatic pyroxene and garnet have average compositions of Di 77Hd 21Jo 2 and Ad 76Gr 20Am 2Sp 1Py 1, respectively. Pyroxene compositions reach Di 94Hd 5Jo 1, whereas garnet exhibits intragrain compositional zoning from Ad 49Gr 46 in the core to Ad 100Gr 0 in the rim. Albitization of preexisting protoliths modified igneous plagioclase compositions from Ab 67An 32Or 1 up to Ab 96An 3Or 1. Albitization is followed by abundant fracture-controlled Fe-epidote and Cl-bearing chlorite (Cha 84Cli 14Pen 2) that extend from the marl unit outward some 300 m. This association is cut by a later assemblage of epidote-chlorite-prehnite that affects the entire 500-m width of the alteration halo and part of the intrusion. Chlorite (Cha 54Cli 45Pen 1) from this later event is richer in Mg than that from the previous association. Igneous hornblende in the intrusion is altered to actinolite. A potassic alteration event related to a hydrothermal breccia and aplitic dikes overprints the pre-existing calc-silicate associations. Alteration minerals in the breccia and the 200-m potassic halo around it, evolve from early K feldspar-(biotite)-quartz, to late jasperoid-fluorapatite-calcite veins. Mg-rich biotite (Phl 77Ann 23) and REE-rich apatite contain F/Cl/OH ratios of 1/0/3 and 1/0/0, respectively. Massive magnetite (36%)-specular hematite (7%)-sulfide (
• Gleason, J. D., Marikos, M. A., Barton, M. D., & Johnson, D. A. (2000). Neodymium isotopic study of rare earth element sources and mobility in hydrothermal Fe oxide (Fe-P-REE) systems. Geochimica et Cosmochimica Acta, 64(6), 1059-1068.
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  Abstract: Rare earth element (REE)-enriched, igneous-related hydrothermal Fe-oxide hosted (Fe-P-REE) systems from four areas in North America have been analyzed for their neodymium isotopic composition to constrain REE sources and mobility in these systems. The Nd isotopic results evidence a common pattern of REE concentration from igneous sources despite large differences in age (Proterozoic to Tertiary), tectonic setting (subduction vs. intraplate), and magmatic style (mafic vs. felsic). In the Middle Proterozoic St. Francois Mountains terrane of southeastern Missouri, ε(Nd) for Fe-P-REE (apatite, monazite, xenotime) deposits ranges from +3.5 to +5.1, similar to associated felsic to intermediate igneous rocks of the same age (ε(Nd) = +2.6 to +6.2). At the mid-Jurassic Humboldt mafic complex in western Nevada, ε(Nd) for Fe-P-REE (apatite) mineralization varies between +1.1 and +2.4, similar to associated mafic igneous rocks (-1.0 to +3.5). In the nearby Cortez Mountains in central Nevada, mid-Jurassic felsic volcanic and plutonic rocks (ε(Nd) = -2.0 to -4.4) are associated with Fe-P-REE (apatite-monazite) mineralization having similar ε(Nd) (-1.7 to -2.4). At Cerro de Mercado, Durango, Mexico, all assemblages analyzed in this Tertiary rhyolite-hosted Fe oxide deposit have identical isotopic compositions with ε(Nd) = -2.5. These data are consistent with coeval igneous host rocks being the primary source of REE in all four regions, and are inconsistent with a significant contribution of REE from other sources. Interpretations of the origin of these hydrothermal systems and their concomitant REE mobility must account for nonspecialized igneous sources and varied tectonic settings. Copyright (C) 2000 Elsevier Science Ltd.
• Gleason, J. D., Marikos, M. A., Barton, M. D., & Johnson, D. A. (2000). Neodymium isotopic study of rare earth element sources and mobility in hydrothermal Fe oxide (Fe-P-REE) systems. Geochimica et Cosmochimica Acta, 64(Issue 6). doi:10.1016/s0016-7037(99)00325-7
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  Rare earth element (REE)-enriched, igneous-related hydrothermal Fe-oxide hosted (Fe-P-REE) systems from four areas in North America have been analyzed for their neodymium isotopic composition to constrain REE sources and mobility in these systems. The Nd isotopic results evidence a common pattern of REE concentration from igneous sources despite large differences in age (Proterozoic to Tertiary), tectonic setting (subduction vs. intraplate), and magmatic style (mafic vs. felsic). In the Middle Proterozoic St. Francois Mountains terrane of southeastern Missouri, ε(Nd) for Fe-P-REE (apatite, monazite, xenotime) deposits ranges from +3.5 to +5.1, similar to associated felsic to intermediate igneous rocks of the same age (ε(Nd) = +2.6 to +6.2). At the mid-Jurassic Humboldt mafic complex in western Nevada, ε(Nd) for Fe-P-REE (apatite) mineralization varies between +1.1 and +2.4, similar to associated mafic igneous rocks (-1.0 to +3.5). In the nearby Cortez Mountains in central Nevada, mid-Jurassic felsic volcanic and plutonic rocks (ε(Nd) = -2.0 to -4.4) are associated with Fe-P-REE (apatite-monazite) mineralization having similar ε(Nd) (-1.7 to -2.4). At Cerro de Mercado, Durango, Mexico, all assemblages analyzed in this Tertiary rhyolite-hosted Fe oxide deposit have identical isotopic compositions with ε(Nd) = -2.5. These data are consistent with coeval igneous host rocks being the primary source of REE in all four regions, and are inconsistent with a significant contribution of REE from other sources. Interpretations of the origin of these hydrothermal systems and their concomitant REE mobility must account for nonspecialized igneous sources and varied tectonic settings. Copyright (C) 2000 Elsevier Science Ltd.
• Barton, M. D., & Megaw, P. K. (1999). The Geology & Minerals of Cerro de Mercado, Durango, Mexico. Rocks & Minerals, 74(1), 20-28. doi:10.1080/00357529909602510
• Sorensen, S. S., Dunne, G. C., Hanson, R. B., Barton, M. D., Becker, J., Tobisch, O. T., & Fiske, R. S. (1998). From Jurassic shores to Cretaceous plutons: Geochemical evidence for paleoalteration environments of metavolcanic rocks, eastern California. Bulletin of the Geological Society of America, 110(3), 326-343.
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  Abstract: Volcanic and plutonic rocks exposed in east-central California record a long history of metasomatism and/or metamorphism within the Mesozoic Cordilleran continental arc. We use whole-rock and mineral elemental compositions, along with standard and cathodoluminescence petrography to characterize alteration histories of Late Triassic to Middle Jurassic metavolcanic rocks in the Ritter Range, White-Inyo Mountains, and Alabama Hills. Although alkali-metasomatism is wide-spread and pervasive, ratios and abundances of Ce, Th, Tb, and Ta suggest that mafic protoliths from the White-Inyo Mountains were shoshonitic, whereas those from the Ritter Range were calc-alkaline. Alkali exchange apparently modified the compositions of many metavolcanic rocks. Much of this metasomatism may have occurred at low-temperature (T) conditions, and attended or shortly post-dated deposition of the volcanic protoliths. High δ18O values for K-rich metatuffs from the Ritter Range suggest that the K-metaso-matizing fluid was low-T seawater. In contrast, low δ18O values for K-rich metatuffs from the Alabama Hills and Inyo Mountains seem to reflect rock interaction with meteoric water prior to contact metamorphism. Jurassic metatuffs deposited in marine (Ritter Range) and nonmarine (Alabama Hills, Inyo Mountains) settings display similar degrees of K for Na (or Ca) exchange that were affected by isotopically distinct fluids. Some alkali-metasomatism of Jurassic metavolcanic rocks is related to Cretaceous plutonism. In the Ritter Range and Alabama Hills, these effects are localized around pluton contacts, appear to be more vein related than pervasive, and overprint K-metasomatized assemblages.
• Sorensen, S. S., Dunne, G. C., Hanson, R. B., Barton, M. D., Becker, J., Tobisch, O. T., & Fiske, R. S. (1998). From Jurassic shores to Cretaceous plutons: Geochemical evidence for paleoalteration environments of metavolcanic rocks, eastern California. Bulletin of the Geological Society of America, 110(Issue 3). doi:10.1130/0016-7606(1998)110<0326:fjstcp>2.3.co;2
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  Volcanic and plutonic rocks exposed in east-central California record a long history of metasomatism and/or metamorphism within the Mesozoic Cordilleran continental arc. We use whole-rock and mineral elemental compositions, along with standard and cathodoluminescence petrography to characterize alteration histories of Late Triassic to Middle Jurassic metavolcanic rocks in the Ritter Range, White-Inyo Mountains, and Alabama Hills. Although alkali-metasomatism is wide-spread and pervasive, ratios and abundances of Ce, Th, Tb, and Ta suggest that mafic protoliths from the White-Inyo Mountains were shoshonitic, whereas those from the Ritter Range were calc-alkaline. Alkali exchange apparently modified the compositions of many metavolcanic rocks. Much of this metasomatism may have occurred at low-temperature (T) conditions, and attended or shortly post-dated deposition of the volcanic protoliths. High δ18O values for K-rich metatuffs from the Ritter Range suggest that the K-metaso-matizing fluid was low-T seawater. In contrast, low δ18O values for K-rich metatuffs from the Alabama Hills and Inyo Mountains seem to reflect rock interaction with meteoric water prior to contact metamorphism. Jurassic metatuffs deposited in marine (Ritter Range) and nonmarine (Alabama Hills, Inyo Mountains) settings display similar degrees of K for Na (or Ca) exchange that were affected by isotopically distinct fluids. Some alkali-metasomatism of Jurassic metavolcanic rocks is related to Cretaceous plutonism. In the Ritter Range and Alabama Hills, these effects are localized around pluton contacts, appear to be more vein related than pervasive, and overprint K-metasomatized assemblages.
• Ilchik, R. P., & Barton, M. D. (1997). An amagmatic origin of carlin-type gold deposits. Economic Geology, 92(3), 269-288.
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  Abstract: Carlin-type deposits are major sources of gold, yet their origins are enigmatic. Suggested genetic models make connections to magmatism, regional metamorphism, or regional extension. Depositional mechanisms are uncertain as well. We propose on the basis of geologic, physical, and chemical reasoning, a genetic model in which meteoric fluids were circulated by heat released during crustal extension. These fluids interacted at depth with the sedimentary rock pile and scavenged gold. Upon upwelling, these fluids interacted with various lithologies and/or other fluids and produced the characteristic alteration and metal suites of these deposits. To test the viability of this amagmatic model, we have investigated certain physical and chemical constraints implicit to the model. Heat balance calculations indicate that ample surface waters could be heated to appropriate temperatures and circulated during rapid crustal extension. Mass balance calculations indicate that solution transport efficiencies of
• Ilchik, R. P., & Barton, M. D. (1997). An amagmatic origin of carlin-type gold deposits. Economic Geology, 92(Issue 3). doi:10.2113/gsecongeo.92.3.269
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  Carlin-type deposits are major sources of gold, yet their origins are enigmatic. Suggested genetic models make connections to magmatism, regional metamorphism, or regional extension. Depositional mechanisms are uncertain as well. We propose on the basis of geologic, physical, and chemical reasoning, a genetic model in which meteoric fluids were circulated by heat released during crustal extension. These fluids interacted at depth with the sedimentary rock pile and scavenged gold. Upon upwelling, these fluids interacted with various lithologies and/or other fluids and produced the characteristic alteration and metal suites of these deposits. To test the viability of this amagmatic model, we have investigated certain physical and chemical constraints implicit to the model. Heat balance calculations indicate that ample surface waters could be heated to appropriate temperatures and circulated during rapid crustal extension. Mass balance calculations indicate that solution transport efficiencies of
• Barton, M. D. (1996). Granitic magmatism and metallogeny of southwestern North America. Special Paper of the Geological Society of America, 315, 261-280.
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  Abstract: In southwestern North America, late Palaeozoic through Cenozoic granitoids and their related mineral deposits show consistent patterns that can be interpreted in terms of combined provincial, exposure and process controls. Voluminous Cordilleran magmatism began in the Permian and continued with few major interruptions through the Mesozoic and Cenozoic, reaching maximum fluxes in the mid-Jurassic, Late Cretaceous and Oligocene. Two distinctive types of broad-scale igneous suites formed. The first type consists of calc-alkaline to alkaline suites that vary regularly with time from early intermediate-mafic centres to late felsic centres over intervals lasting 20-50 Ma. These suites formed during periods of stable convergence and compressional tectonics, most notably in the late Mesozoic and early-mid-Cenozoic. The second type is compositionally varied, but shows no obvious secular variation in composition. This type formed during neutral to extensional tectonics in the mid-Mesozoic and the mid- to late Cenozoic. Regional (west to east) and secular (old to young) changes from calcic to alkalic compositions do not correspond to basement types; they point to tectonic rather than crustal controls on magmatic evolution, although basement signatures are clearly transmitted in isotopic systematics. Contrasting types of intrusive centres formed in the same lithospheric columns, suggesting that variability reflects thermal and stress regimes, subcrustal magma flux and crustal thickness. Simple thermal and mechanical models of limits on assimilation and magma uprise are broadly consistent with these patterns. Igneous-related mineralisation is ubiquitous where epizonal environments are preserved, thus preservation (and exposure) form the first-order filter on metallogeny. Mineralisation includes porphyry, skarn, epithermal, replacement and syngenetic deposits of widely varying styles, metal contents and links to magmatic heat and materials. Metal contents and alteration styles correlate closely with igneous compositions and are broadly independent of setting, although systematic regional variations in metal ratios are documented. Ore element suites vary from Cu-Au-Fe associated with (quartz) dioritic to monzonitic intrusive centres through Cu-Zn-Mo-Pb-Ag-W-Au associated with broadly granodioritic centres, and finally to F-Mo-Zn-W-Ag-Be associated with metaluminous to strongly peraluminous granitic centres. A model that includes both composition and process controls rationalises this igneous correlation and the lack of strong regional control. Key features are (1) mineralogical controls on fluid compositions and (2) the efficacy of magmatic processes in producing voluminous ore-forming aqueous fluids. This interpretation is supported by field relationships, igneous petrographic and isotopic data, and theoretical considerations.
• Barton, M. D. (1996). Granitic magmatism and metallogeny of southwestern North America. Transactions of the Royal Society of Edinburgh, Earth Sciences, 87(1-2), 261-280.
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  Abstract: In southwestern North America, late Palaeozoic through Cenozoic granitoids and their related mineral deposits show consistent patterns that can be interpreted in terms of combined provincial, exposure and process controls. Voluminous Cordilleran magmatism began in the Permian and continued with few major interruptions through the Mesozoic and Cenozoic, reaching maximum fluxes in the mid-Jurassic, Late Cretaceous and Oligocene. Two distinctive types of broad-scale igneous suites formed. The first type consists of calc-alkaline to alkaline suites that vary regularly with time from early intermediate-mafic centres to late felsic centres over intervals lasting 20-50 Ma. These suites formed during periods of stable convergence and compressional tectonics, most notably in the late Mesozoic and early-mid-Cenozoic. The second type is compositionally varied, but shows no obvious secular variation in composition. This type formed during neutral to extensional tectonics in the mid-Mesozoic and the mid- to late Cenozoic. Regional (west to east) and secular (old to young) changes from calcic to alkalic compositions do not correspond to basement types; they point to tectonic rather than crustal controls on magmatic evolution, although basement signatures are clearly transmitted in isotopic systematics. Contrasting types of intrusive centres formed in the same lithospheric columns, suggesting that variability reflects thermal and stress regimes, subcrustal magma flux and crustal thickness. Simple thermal and mechanical models of limits on assimilation and magma uprise are broadly consistent with these patterns. Igneous-related mineralisation is ubiquitous where epizonal environments are preserved, thus preservation (and exposure) form the first-order filter on metallogeny. Mineralisation includes porphyry, skarn, epithermal, replacement and syngenetic deposits of widely varying styles, metal contents and links to magmatic heat and materials. Metal contents and alteration styles correlate closely with igneous compositions and are broadly independent of setting, although systematic regional variations in metal ratios are documented. Ore element suites vary from Cu-Au-Fe associated with (quartz) dioritic to monzonitic intrusive centres through Cu-Zn-Mo-Pb-Ag-W-Au associated with broadly granodioritic centres, and finally to F-Mo-Zn-W-Ag-Be associated with metaluminous to strongly peraluminous granitic centres. A model that includes both composition and process controls rationalises this igneous correlation and the lack of strong regional control. Key features are (1) mineralogical controls on fluid compositions and (2) the efficacy of magmatic processes in producing voluminous ore-forming aqueous fluids. This interpretation is supported by field relationships, igneous petrographic and isotopic data, and theoretical considerations.
• Barton, M. D. (1996). Granitic magmatism and metallogeny of southwestern North America. Transactions of the Royal Society of Edinburgh, Earth Sciences, 87(Issue 1-2). doi:10.1017/s0263593300006672
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  In southwestern North America, late Palaeozoic through Cenozoic granitoids and their related mineral deposits show consistent patterns that can be interpreted in terms of combined provincial, exposure and process controls. Voluminous Cordilleran magmatism began in the Permian and continued with few major interruptions through the Mesozoic and Cenozoic, reaching maximum fluxes in the mid-Jurassic, Late Cretaceous and Oligocene. Two distinctive types of broad-scale igneous suites formed. The first type consists of calc-alkaline to alkaline suites that vary regularly with time from early intermediate-mafic centres to late felsic centres over intervals lasting 20-50 Ma. These suites formed during periods of stable convergence and compressional tectonics, most notably in the late Mesozoic and early-mid-Cenozoic. The second type is compositionally varied, but shows no obvious secular variation in composition. This type formed during neutral to extensional tectonics in the mid-Mesozoic and the mid- to late Cenozoic. Regional (west to east) and secular (old to young) changes from calcic to alkalic compositions do not correspond to basement types; they point to tectonic rather than crustal controls on magmatic evolution, although basement signatures are clearly transmitted in isotopic systematics. Contrasting types of intrusive centres formed in the same lithospheric columns, suggesting that variability reflects thermal and stress regimes, subcrustal magma flux and crustal thickness. Simple thermal and mechanical models of limits on assimilation and magma uprise are broadly consistent with these patterns. Igneous-related mineralisation is ubiquitous where epizonal environments are preserved, thus preservation (and exposure) form the first-order filter on metallogeny. Mineralisation includes porphyry, skarn, epithermal, replacement and syngenetic deposits of widely varying styles, metal contents and links to magmatic heat and materials. Metal contents and alteration styles correlate closely with igneous compositions and are broadly independent of setting, although systematic regional variations in metal ratios are documented. Ore element suites vary from Cu-Au-Fe associated with (quartz) dioritic to monzonitic intrusive centres through Cu-Zn-Mo-Pb-Ag-W-Au associated with broadly granodioritic centres, and finally to F-Mo-Zn-W-Ag-Be associated with metaluminous to strongly peraluminous granitic centres. A model that includes both composition and process controls rationalises this igneous correlation and the lack of strong regional control. Key features are (1) mineralogical controls on fluid compositions and (2) the efficacy of magmatic processes in producing voluminous ore-forming aqueous fluids. This interpretation is supported by field relationships, igneous petrographic and isotopic data, and theoretical considerations.
• Barton, M. D., & Johnson, D. A. (1996). Evaporitic-source model for igneous-related Fe oxide-(REE-Cu-Au-U) mineralization. Geology, 24(3), 259-262.
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  Abstract: We propose that many igneous-related Fe oxide-rich (REE-Cu-Au-U-bearing) deposits form by hydrothermal processes involving evaporitic ligand sources, either coeval salars or older evaporites. These deposits are abundant in both Phanerozoic and Proterozoic extensional continental and continent-margin settings. They commonly form in global arid zones, but they also occur where magmatism is superimposed upon older evaporites. Magmatic compositions exert only second-order control, mainly on alteration mineralogy and on element abundances. Hot S-poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments (siderophile, lithophile) and hydrothermal alteration (sodic, locally alkaline) found in these systems. This model contrasts with immiscible oxide melt and magmatic-hydrothermal origins commonly proposed for these deposits, although all three mechanisms can occur.
• Barton, M. D., & Johnson, D. A. (1996). Evaporitic-source model for igneous-related Fe oxide-(REE-Cu-Au-U) mineralization. Geology, 24(Issue 3). doi:10.1130/0091-7613(1996)024<0259:esmfir>2.3.co;2
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  We propose that many igneous-related Fe oxide-rich (REE-Cu-Au-U-bearing) deposits form by hydrothermal processes involving evaporitic ligand sources, either coeval salars or older evaporites. These deposits are abundant in both Phanerozoic and Proterozoic extensional continental and continent-margin settings. They commonly form in global arid zones, but they also occur where magmatism is superimposed upon older evaporites. Magmatic compositions exert only second-order control, mainly on alteration mineralogy and on element abundances. Hot S-poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments (siderophile, lithophile) and hydrothermal alteration (sodic, locally alkaline) found in these systems. This model contrasts with immiscible oxide melt and magmatic-hydrothermal origins commonly proposed for these deposits, although all three mechanisms can occur.
• Battles, D. A., & Barton, M. D. (1995). Arc-related sodic hydrothermal alteration in the western US. Geology, 23(10), 913-916.
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  Abstract: Sodium-rich hydrothermal alteration is widely developed in Permian to Jurassic arc igneous rocks of the western US, but it is rare in younger rocks. Na-rich alteration reflects a paleogeographic control on development. Two varieties, NaCa and Na, can be defined by mineralogic and compositional changes. The transition away from widespread Na ± Ca-rich alteration in the late Mesozoic corresponds to and is consistent with the change from an early Mesozoic marine and/or arid rifted arc setting to a fully emergent, continental arc environment in the Cretaceous. -from Authors
• Battles, D. A., & Barton, M. D. (1995). Arc-related sodic hydrothermal alteration in the western US. Geology, 23(Issue 10). doi:10.1130/0091-7613(1995)023<0913:arshai>2.3.co;2
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  Sodium-rich hydrothermal alteration is widely developed in Permian to Jurassic arc igneous rocks of the western US, but it is rare in younger rocks. Na-rich alteration reflects a paleogeographic control on development. Two varieties, NaCa and Na, can be defined by mineralogic and compositional changes. The transition away from widespread Na ± Ca-rich alteration in the late Mesozoic corresponds to and is consistent with the change from an early Mesozoic marine and/or arid rifted arc setting to a fully emergent, continental arc environment in the Cretaceous. -from Authors
• Wallace, T. C., Barton, M., & Wilson, W. E. (1994). Silver & silver-bearing minerals featured mineral at the 1994 Tucson show. Rocks and Minerals, 69(Issue 1). doi:10.1080/00357529.1994.9925571
• Wallace, T. C., Barton, M., & Wilson, W. E. (1994). Silver & silver-bearing minerals. Rocks & Minerals, 69(1), 16-38.
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  Abstract: Today the annual worldwide production of silver is approximately 14 000 metric tons, more than at any time in history. Most of this silver is recovered as a byproduct of low-grade copper and lead mining. This fact, coupled with the historically low price of silver (~$5 US/troy once) and the continued mechanization of even high-grade mines, has greatly reduced the availability of "new' silver mineral specimens on the market. Only Mexico, Peru, and, to a lesser extent, Kazahkstan have produced a significant volume of specimen material in the last decade. Nevertheless, silver is an extremely important industrial metal, and the future is bright for more spectacular specimens. This article begins with a discussion of the history, mineralogy, and geology of the silver minerals, followed by a discussion of five classic localities. -from Authors
• Bebout, G. E., & Barton, M. D. (1993). Metasomatism during subduction: products and possible paths in the Catalina Schist, California. Chemical Geology, 108(1-4), 61-92.
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  Abstract: On Santa Catalina Island, southern California, lawsonite-albite to amphibolite facies metasedimentary, metamafic, and metaultramafic rocks show veining and chemical alteration that reflect fluid flow and mass transfer at 15 to 45 km depths in an Early Cretaceous subduction zone. In many exposures, multiple generations of cross-cutting syn- and post-kinematic veins record fluid transport and metasomatism during various stages of prograde metamorphism and uplift. Mineralogy and whole-rock compositions demonstrate chemical redistribution, especially of Si, Al, and alkali elements (Na, K), but also of many trace elements, particularly B and LILE (Rb, Cs, Sr, and Ba). Evidence exists for mass transfer, at both local and larger scales, via mechanical mixing, diffusional, and fluid-mediated transfer processes. Highest-grade, amphibolite facies rocks contain feldspar + quartz ± mica ± amphibole leucosomes and pegmatites attributed to migmatization; the leucosomes and pegmatites reflect high- P T mass transfer in felsic silicate liquids. Veining and replacement in blueschist grade rocks comprise three contrasting types of assemblages: (1) silica-saturated (quartz-rich), (2) potassic (white-mica ± quartz-rich), and (3) sodic and silica-undersaturated (albite/Na-amphibole-rich, quartz-absent). Evidence for silicification and alkali exchange also occurs in greenschist and amphibolite facies units. In all units, the evidence for metasomatism (e.g., veins; stable isotope homogenization; rinds on blocks) is particularly abundant in melange zones, in which melange matrix compositions resulting from mechanical mixtures of mafic, ultramafic, and sedimentary rocks were shifted by metasomatic additions and subtractions during melange formation. Geochemical evidence (particularly stable isotope data) indicates that the blueschist, greenschist, and amphibolite units exchanged with fluids of similar compositions. The diverse metasomatic features in the Catalina Schist provide evidence regarding fluid sources and paths. Based on the stable isotope data, the H2O-rich, low-salinity (∼ 1 to 2 equivalent wt. % NaCl), C/1bO/1bH/1bS/1bN fluids are believed to have been derived from low-grade, largely sedimentary parts of the subduction zone (analogs for fluid sources are the low-grade units). Metasomatic changes could be driven by flow across boundaries between contrasting lithologies and by variations in pressure and temperature along the fluid flow paths. Simple predictions of mass changes along different P-T paths suggest that both mechanisms could be effective at producing the range of observed features, even though the required equilibrium constants are only poorly estimated at the relevant P-T conditions. Decreasing T and P favors fixing of K, Si, C, and H in rocks, whereas increasing T (± moderately decreasing P) should fix Na but leach most other components. The Si-rich, K ± Si-rich, and Na-rich/Si-poor assemblages are thus consistent with differing fluid P-T flow paths. Regular differences are expected in silica precipitation/dissolution, alkali exchange, and hydrogen-alkali exchange reactions, among others. Silica ± carbonate addition, consistent with the majority of veins observed, is likely the consequence of cooling ± decompression whereas sodic (± silica-undersaturated) assemblages would be expected for rarer, but geologically plausible up-T fluid flow paths. A composite fluid flow path, first up-grade, then down P and T. is indicated for the silica addition to the largely ultramafic amphibolite-facies melange. Although mass balance and physical constraints appear to preclude pervasive major element metasomatism on large scales, focussing of fluids would likely produce pervasive changes in significant volumes (e.g., up to km-scale melange zones). Vein mineralogy would record the paths even at small fluxes. Study of the Catalina Schist demonstrates the significance of metasomatism at all scales, but indicates that large-scale changes in vein mineralogy and bulk composition are in some cases attributable to fluid flow over large distances. Comparison with other areas and elementary theoretical considerations suggest that these processes may be widely developed and that their petrographic and geochemical effects potentially give insight into the dynamics of subduction zones. © 1993.
• Bebout, G. E., & Barton, M. D. (1993). Metasomatism during subduction: products and possible paths in the Catalina Schist, California. Chemical Geology, 108(Issue 1-4). doi:10.1016/0009-2541(93)90318-d
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  On Santa Catalina Island, southern California, lawsonite-albite to amphibolite facies metasedimentary, metamafic, and metaultramafic rocks show veining and chemical alteration that reflect fluid flow and mass transfer at 15 to 45 km depths in an Early Cretaceous subduction zone. In many exposures, multiple generations of cross-cutting syn- and post-kinematic veins record fluid transport and metasomatism during various stages of prograde metamorphism and uplift. Mineralogy and whole-rock compositions demonstrate chemical redistribution, especially of Si, Al, and alkali elements (Na, K), but also of many trace elements, particularly B and LILE (Rb, Cs, Sr, and Ba). Evidence exists for mass transfer, at both local and larger scales, via mechanical mixing, diffusional, and fluid-mediated transfer processes. Highest-grade, amphibolite facies rocks contain feldspar + quartz ± mica ± amphibole leucosomes and pegmatites attributed to migmatization; the leucosomes and pegmatites reflect high- P T mass transfer in felsic silicate liquids. Veining and replacement in blueschist grade rocks comprise three contrasting types of assemblages: (1) silica-saturated (quartz-rich), (2) potassic (white-mica ± quartz-rich), and (3) sodic and silica-undersaturated (albite/Na-amphibole-rich, quartz-absent). Evidence for silicification and alkali exchange also occurs in greenschist and amphibolite facies units. In all units, the evidence for metasomatism (e.g., veins; stable isotope homogenization; rinds on blocks) is particularly abundant in melange zones, in which melange matrix compositions resulting from mechanical mixtures of mafic, ultramafic, and sedimentary rocks were shifted by metasomatic additions and subtractions during melange formation. Geochemical evidence (particularly stable isotope data) indicates that the blueschist, greenschist, and amphibolite units exchanged with fluids of similar compositions. The diverse metasomatic features in the Catalina Schist provide evidence regarding fluid sources and paths. Based on the stable isotope data, the H2O-rich, low-salinity (∼ 1 to 2 equivalent wt. % NaCl), C/1bO/1bH/1bS/1bN fluids are believed to have been derived from low-grade, largely sedimentary parts of the subduction zone (analogs for fluid sources are the low-grade units). Metasomatic changes could be driven by flow across boundaries between contrasting lithologies and by variations in pressure and temperature along the fluid flow paths. Simple predictions of mass changes along different P-T paths suggest that both mechanisms could be effective at producing the range of observed features, even though the required equilibrium constants are only poorly estimated at the relevant P-T conditions. Decreasing T and P favors fixing of K, Si, C, and H in rocks, whereas increasing T (± moderately decreasing P) should fix Na but leach most other components. The Si-rich, K ± Si-rich, and Na-rich/Si-poor assemblages are thus consistent with differing fluid P-T flow paths. Regular differences are expected in silica precipitation/dissolution, alkali exchange, and hydrogen-alkali exchange reactions, among others. Silica ± carbonate addition, consistent with the majority of veins observed, is likely the consequence of cooling ± decompression whereas sodic (± silica-undersaturated) assemblages would be expected for rarer, but geologically plausible up-T fluid flow paths. A composite fluid flow path, first up-grade, then down P and T. is indicated for the silica addition to the largely ultramafic amphibolite-facies melange. Although mass balance and physical constraints appear to preclude pervasive major element metasomatism on large scales, focussing of fluids would likely produce pervasive changes in significant volumes (e.g., up to km-scale melange zones). Vein mineralogy would record the paths even at small fluxes. Study of the Catalina Schist demonstrates the significance of metasomatism at all scales, but indicates that large-scale changes in vein mineralogy and bulk composition are in some cases attributable to fluid flow over large distances. Comparison with other areas and elementary theoretical considerations suggest that these processes may be widely developed and that their petrographic and geochemical effects potentially give insight into the dynamics of subduction zones. © 1993.
• Hanson, R. B., Sorensen, S. S., Barton, M. D., & Fiske, R. S. (1993). Long-term evolution of fluid-rock interactions in magmatic arcs: Evidence from the ritter range pendant, Sierra Nevada, California, and numerical modeling. Journal of Petrology, 34(1), 23-62.
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  Abstract: A record of > 100 million years of fluid flow, alteration, and metamorphism in the evolving Sierra Nevada magmatic are is preserved in metavolcanic rocks of the Ritter Range pendant and surrounding granitoids. The metavolcanic rocks consist of: (1) a lower section of mostly marine volcaniclastic rocks, lavas, and intercalated carbonate rocks that is Triassic to Jurassic in age, and (2) an upper section comprising a subaerial caldera-fill complex of mid-Cretaceous age. Late Cretaceous high-temperature contact metamorphism (∼2 kbar, >450-500°C) occurred after renewed normal faulting along the caldera-bounding fault system juxtaposed the two sections.The style and degree of alteration and δ18O values differ among the rocks of the upper and lower sections and the granitoids. Rocks of the lower section show pervasive lithologically controlled alkali alteration, local Mn and Mg enrichment, and oxidation. Some ash flow tuffs now contain up to 10% K2O by weight. The rocks of the upper section show lesser extents of alkali alteration. Granitoids that cut both sections are generally unaltered. Most metavolcanic rocks of the lower section have high δ18O values (+ 11 to + 16%; whole rock and quartz phenocrysts); however, lower-section rocks within the caldera-bounding fault system have low δ18O values of + 4 to +7‰. The metavolcanic rocks of the upper section also have low δ18O values of + 2 to + 7‰. Granitoids have δ18O values of + 7 to + 10‰, typical of unaltered Sierran granitoids. The lower section contains discontinuous veins of high-temperature (450-500°C) calc-silicate minerals. These veins are typically 10 m long, formed at temperatures of less than 450-500°C, and cross intrusive contacts. Veins have similar δ18O values to those of the local host rocks.The nature of the alteration and the high oxygen isotopic values of the rocks of the lower section indicate that these rocks interacted extensively with seawater at temperatures
• Hanson, R. B., Sorensen, S. S., Barton, M. D., & Fiske, R. S. (1993). Long-term evolution of fluid-rock interactions in magmatic arcs: Evidence from the ritter range pendant, Sierra Nevada, California, and numerical modeling. Journal of Petrology, 34(Issue 1). doi:10.1093/petrology/34.1.23
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  A record of > 100 million years of fluid flow, alteration, and metamorphism in the evolving Sierra Nevada magmatic are is preserved in metavolcanic rocks of the Ritter Range pendant and surrounding granitoids. The metavolcanic rocks consist of: (1) a lower section of mostly marine volcaniclastic rocks, lavas, and intercalated carbonate rocks that is Triassic to Jurassic in age, and (2) an upper section comprising a subaerial caldera-fill complex of mid-Cretaceous age. Late Cretaceous high-temperature contact metamorphism (∼2 kbar, >450-500°C) occurred after renewed normal faulting along the caldera-bounding fault system juxtaposed the two sections.The style and degree of alteration and δ18O values differ among the rocks of the upper and lower sections and the granitoids. Rocks of the lower section show pervasive lithologically controlled alkali alteration, local Mn and Mg enrichment, and oxidation. Some ash flow tuffs now contain up to 10% K2O by weight. The rocks of the upper section show lesser extents of alkali alteration. Granitoids that cut both sections are generally unaltered. Most metavolcanic rocks of the lower section have high δ18O values (+ 11 to + 16%; whole rock and quartz phenocrysts); however, lower-section rocks within the caldera-bounding fault system have low δ18O values of + 4 to +7‰. The metavolcanic rocks of the upper section also have low δ18O values of + 2 to + 7‰. Granitoids have δ18O values of + 7 to + 10‰, typical of unaltered Sierran granitoids. The lower section contains discontinuous veins of high-temperature (450-500°C) calc-silicate minerals. These veins are typically 10 m long, formed at temperatures of less than 450-500°C, and cross intrusive contacts. Veins have similar δ18O values to those of the local host rocks.The nature of the alteration and the high oxygen isotopic values of the rocks of the lower section indicate that these rocks interacted extensively with seawater at temperatures
• HACKER, B. R., ERNST, W. G., & BARTON, M. D. (1992). Metamorphism, geochemistry and origin of magnesian volcanic rocks, Klamath Mountains, California. Journal of Metamorphic Geology, 10(Issue 1). doi:10.1111/j.1525-1314.1992.tb00071.x
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  Metabasaltic rocks in the Klamath Mountains of California with ‘komatiitic’ major element concentrations were investigated in order to elucidate the origin of the magnesian signature. Trace‐element concentrations preserve relict igneous trends and suggest that the rocks are not komatitic basalts, but immature arc rocks and within‐plate alkalic lavas. Correlation of ‘excess’ MgO with the volume per cent hornblende (±clinopyroxene) suggests that the presence of cumulus phases contributes to the MgO‐rich compositions. Early submarine alteration produced regional δ18O values of +10±1.5%° and shifts in Al2O3, Na2O, and K2O concentrations. Regional metamorphic grade in the study area varies from biotite‐zone greenschist facies (350–550°C, c. 3 kbar) southward to prehnite–actinolite facies (200–400°C, ≤3 kbar), but little isotopic or elemental change occurred during the regional recrystallization. The greenschist facies assemblage is actinolitic hornblende + phengite + epidote + sodic plagioclase + microcline + chlorite + titanite + hematite + quartz in Ti‐poor metabasaltic rocks; in addition to these phases biotite is present in Ti‐rich analogues. Lower grade greenstones contain prehnite and more nearly stoichiometric actinolite. The moderate to low pressures of regional metamorphism are compatible with P–T conditions in a magmatic arc. Later contact metamorphism at 2–2.9±0.5 kbar and at peak temperatures approaching 600° C around the English Peak and Russian Peak granodiorites produced 3–4–km‐wide aureoles typified by gradual, systematic increases in the pargasite content of amphibole, muscovite content of potassic white mica, and anorthite content of plagioclase compositions. Metasomatism during contact metamorphism produced further increases in bulk‐rock δ18OSMOW of as much as +6%°. Thus, the unusually MgO‐rich nature of the Sawyers Bar rocks may be attributed at least partly to metasomatism and the presence of magnesian cumulus phases. Copyright © 1992, Wiley Blackwell. All rights reserved
• Hacker, B. R., Ernst, W. G., & Barton, M. D. (1992). Metamorphism, geochemistry and origin of magnesian volcanic rocks, Klamath Mountains, California. Journal of Metamorphic Geology, 10(1), 55-69.
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  Abstract: Metabasaltic rocks in the Klamath Mountains of California with "komatiitic' major element concentrations were investigated in order to elucidate the origin of the magnesian signature. Trace-element concentrations preserve relict igneous trends and suggest that the rocks are not komatiitic basalts, but immature arc rocks and within-plate alkalic lavas. Correlation of "excess' MgO with the volume per cent hornblende (±clinopyroxene) suggests that the presence of cumulus phases contributes to the MgO-rich compositions. The unusually MgO-rich nature of the Sawyers Bar rocks may be attributed at least partly to metasomatism and the presence of magnesian cumulus phases. -from Authors
• Ernst, W. G., Hacker, B. R., Barton, M. D., & Sen, G. (1991). Igneous petrogenesis of magnesian metavolcanic rocks from the central Klamath Mountains, northern California. Geological Society of America Bulletin, 103(1), 56-72.
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  Abstract: Mafic meta-igneous supracrustal rocks in the east-central part of the western Triassic and Paleozoic belt are interlayered with and appear to predominantly overlie fine-grained clastic and cherty metasedimentary strata. This complex constitutes a lithostratigraphic terrane exposed in the vicinity of Sawyers Bar, California. Element proportions suggest that the dark, Ti + Fe* + P-rich basaltic lavas may have been extruded in an oceanic intraplate setting. Interstratification with distal turbiditic strata indicates concurrent submarine volcanism and deep-sea sedimentary deposition. The main mass of the stratigraphically higher extrusive sequence is a light-colored, massive tholeiite series, poorer in Ti + Fe* + P + LREE's. Hypabyssal rocks belong exclusively to this second igneous suite. Compositions of the pale-colored, overlying basaltic/diabasic mass of the Yellow Dog greenstone section are consistent with eruption in an immature magmatic arc. Yellow Dog igneous activity was extinguished during mid-Jurassic suturing of the oceanward Sawyers Bar terrane against and beneath the pre-existing landward Stuart Fork blueschist complex of Late Triassic metamorphic age. -from Authors
• Ernst, W. G., Hacker, B. R., Barton, M. D., & Sen, G. (1991). Igneous petrogenesis of magnesian metavolcanic rocks from the central Klamath Mountains, northern California. Geological Society of America Bulletin, 103(Issue 1). doi:10.1130/0016-7606(1991)103<0056:ipommr>2.3.co;2
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  Mafic meta-igneous supracrustal rocks in the east-central part of the western Triassic and Paleozoic belt are interlayered with and appear to predominantly overlie fine-grained clastic and cherty metasedimentary strata. This complex constitutes a lithostratigraphic terrane exposed in the vicinity of Sawyers Bar, California. Element proportions suggest that the dark, Ti + Fe* + P-rich basaltic lavas may have been extruded in an oceanic intraplate setting. Interstratification with distal turbiditic strata indicates concurrent submarine volcanism and deep-sea sedimentary deposition. The main mass of the stratigraphically higher extrusive sequence is a light-colored, massive tholeiite series, poorer in Ti + Fe* + P + LREE's. Hypabyssal rocks belong exclusively to this second igneous suite. Compositions of the pale-colored, overlying basaltic/diabasic mass of the Yellow Dog greenstone section are consistent with eruption in an immature magmatic arc. Yellow Dog igneous activity was extinguished during mid-Jurassic suturing of the oceanward Sawyers Bar terrane against and beneath the pre-existing landward Stuart Fork blueschist complex of Late Triassic metamorphic age. -from Authors
• Tobisch, O. T., Barton, M. D., Vernon, R. H., & Paterson, S. R. (1991). Fluid-enhanced deformation: transformation of granitoids to banded mylonites, western Sierra Nevada, California, and southeastern Australia. Journal of Structural Geology, 13(10), 1137-1156.
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  Abstract: Deformation of tonalite and adamellite from the western Sierra Nevada, California, and southeastern Australia has produced mylonite zones that show a broad range of microstructural development, varying from strongly banded and/or foliated to locally non-foliated. Accompanying these fabrics are new mineral assemblages, commonly rich in quartz and epidote. Whereas the banded foliated varieties appear to develop from progressive deformation of the granitic host, they also occur in close proximity (cm-m) to domains of non-banded and/or weakly to non-foliated fabrics of similar mineralogy, suggesting a complex timing and partitioning of deformation, fluid flow and metamorphism in the mylonite zone. Whole-rock major and trace element analyses of the tonalites show large enrichments of SiO2, CaO, Fe2O3, total Fe and Sr, and strong depletions in Na2O, K2O, FeO, MgO, Ba and Rb with increasing stages of deformation, although substantial chemical change appears to occur under static conditions locally. Chemical changes in the adamellite are much less dramatic. All suites show systematic decrease in σ18O and convergence of oxygen isotopic compositions of whole-rock and quartz with increasing deformation. Minimum fluid/rock is estimated to lie between 0.1 and 10, increasing with intensity of deformation and depending on host composition. Isotopically exchanged seawater or connate water are the most plausible fluids. Chemical data from a number of mylonite zones in various orogenic belts show widely varying behavior (gain/loss) of major and minor elements. Eleven factors control which (and how much) elements are gained/lost during mylonitization of the granitoids, the most influential of which are primary composition, mineralogy and primary texture of the host, as well as several aspects of fluid interaction active during deformation. These influences may be a function of local rather than regional geological conditions. © 1991.
• Tobisch, O. T., Barton, M. D., Vernon, R. H., & Paterson, S. R. (1991). Fluid-enhanced deformation: transformation of granitoids to banded mylonites, western Sierra Nevada, California, and southeastern Australia. Journal of Structural Geology, 13(Issue 10). doi:10.1016/0191-8141(91)90074-s
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  Deformation of tonalite and adamellite from the western Sierra Nevada, California, and southeastern Australia has produced mylonite zones that show a broad range of microstructural development, varying from strongly banded and/or foliated to locally non-foliated. Accompanying these fabrics are new mineral assemblages, commonly rich in quartz and epidote. Whereas the banded foliated varieties appear to develop from progressive deformation of the granitic host, they also occur in close proximity (cm-m) to domains of non-banded and/or weakly to non-foliated fabrics of similar mineralogy, suggesting a complex timing and partitioning of deformation, fluid flow and metamorphism in the mylonite zone. Whole-rock major and trace element analyses of the tonalites show large enrichments of SiO2, CaO, Fe2O3, total Fe and Sr, and strong depletions in Na2O, K2O, FeO, MgO, Ba and Rb with increasing stages of deformation, although substantial chemical change appears to occur under static conditions locally. Chemical changes in the adamellite are much less dramatic. All suites show systematic decrease in σ18O and convergence of oxygen isotopic compositions of whole-rock and quartz with increasing deformation. Minimum fluid/rock is estimated to lie between 0.1 and 10, increasing with intensity of deformation and depending on host composition. Isotopically exchanged seawater or connate water are the most plausible fluids. Chemical data from a number of mylonite zones in various orogenic belts show widely varying behavior (gain/loss) of major and minor elements. Eleven factors control which (and how much) elements are gained/lost during mylonitization of the granitoids, the most influential of which are primary composition, mineralogy and primary texture of the host, as well as several aspects of fluid interaction active during deformation. These influences may be a function of local rather than regional geological conditions. © 1991.
• Barton, M. D. (1990). Chapter 16: Cretaceous magmatism, metamorphism, and metallogeny in the east-central Great Basin. Memoir of the Geological Society of America, 174(1), 283-302.
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  Abstract: Compilation of published and new data on the distribution, timing, and composition of igneous rocks, ore deposits, and metamorphic rocks in the east-central Great Basin reveals systematic relations among Cretaceous magmatism, mineralization, metamorphism, and deformation. Magmatic compositions change with time from Early Cretaceous (∼125 to 100 Ma) quartz diorite, monzonite, and quartz monzonite, to mid-Cretaceous metaluminous (± hornblende) granodiorite and granite, and ultimately to Late Cretaceous (∼90 to 70 Ma) strongly peraluminous (two-mica) granite and granodiorite. Sr, O, and Nd isotopic data indicate a concomitant increasing crustal component, with a significant (meta)sedimentary component in the later plutons. Style and type of mineralization closely correlate with intrusion compositions. Porphyry Cu and Cu skarn deposits associated with the early plutons give way to porphyry Mo-Cu, polymetallic W skarn, and base-metal replacement mineralization associated with the metaluminous granodiorites and granites. F-rich, lithophile-element skarns and greisen mineralization are characteristic of the Late Cretaceous two-mica granites. Ar-Ar and U-Pb studies in the Snake and Ruby ranges and clustering of metamorphic K-Ar dates elsewhere are compatible with a Late Cretaceous (90 to 70 Ma) metamorphic culmination. Major tectonic subsidence in the foreland basin in central Utah, reflecting Sevier thrusting, began at about the same time (∼90 Ma). These observations are interpreted in the following way: increased deep (conductive) heat input accompanied renewal of magmatism, leading to increasing incorporation of crustal components with time in subduction-related magmas. Metallogeny followed the systematic changes in magma compositions. The metamorphic (thermal) culmination occurred simultaneously with maximum incorporation of crustal components in the magmas. Progressive thermal weakening of the crust was enhanced by wholesale assimilation or anatexis at this stage; thus major thrusting and the metamorphic culmination were synchronous with emplacement of two-mica granites. Simple one-dimensional thermal models are consistent with this scenario. Alternative interpretations that depend on crustal thickening as the primary mechanism are inconsistent with thermal considerations and the geologic record, although thickening probably played some role. Similarities between the Cretaceous history in the east-central Great Basin and other areas in the western United States suggest analogous processes elsewhere, modified by local factors. Magmatic and metallogenic differences among the Cretaceous, Jurassic, and Tertiary periods in the eastern Great Basin, and between the Great Basin Cretaceous events and collisional orogens may reflect differences in the thermal evolution and magmatic fluxes.
• Barton, M. D. (1990). Chapter 16: Cretaceous magmatism, metamorphism, and metallogeny in the east-central Great Basin. Memoir of the Geological Society of America. doi:10.1130/mem174-p283
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  Compilation of published and new data on the distribution, timing, and composition of igneous rocks, ore deposits, and metamorphic rocks in the east-central Great Basin reveals systematic relations among Cretaceous magmatism, mineralization, metamorphism, and deformation. Magmatic compositions change with time from Early Cretaceous (∼125 to 100 Ma) quartz diorite, monzonite, and quartz monzonite, to mid-Cretaceous metaluminous (± hornblende) granodiorite and granite, and ultimately to Late Cretaceous (∼90 to 70 Ma) strongly peraluminous (two-mica) granite and granodiorite. Sr, O, and Nd isotopic data indicate a concomitant increasing crustal component, with a significant (meta)sedimentary component in the later plutons. Style and type of mineralization closely correlate with intrusion compositions. Porphyry Cu and Cu skarn deposits associated with the early plutons give way to porphyry Mo-Cu, polymetallic W skarn, and base-metal replacement mineralization associated with the metaluminous granodiorites and granites. F-rich, lithophile-element skarns and greisen mineralization are characteristic of the Late Cretaceous two-mica granites. Ar-Ar and U-Pb studies in the Snake and Ruby ranges and clustering of metamorphic K-Ar dates elsewhere are compatible with a Late Cretaceous (90 to 70 Ma) metamorphic culmination. Major tectonic subsidence in the foreland basin in central Utah, reflecting Sevier thrusting, began at about the same time (∼90 Ma). These observations are interpreted in the following way: increased deep (conductive) heat input accompanied renewal of magmatism, leading to increasing incorporation of crustal components with time in subduction-related magmas. Metallogeny followed the systematic changes in magma compositions. The metamorphic (thermal) culmination occurred simultaneously with maximum incorporation of crustal components in the magmas. Progressive thermal weakening of the crust was enhanced by wholesale assimilation or anatexis at this stage; thus major thrusting and the metamorphic culmination were synchronous with emplacement of two-mica granites. Simple one-dimensional thermal models are consistent with this scenario. Alternative interpretations that depend on crustal thickening as the primary mechanism are inconsistent with thermal considerations and the geologic record, although thickening probably played some role. Similarities between the Cretaceous history in the east-central Great Basin and other areas in the western United States suggest analogous processes elsewhere, modified by local factors. Magmatic and metallogenic differences among the Cretaceous, Jurassic, and Tertiary periods in the eastern Great Basin, and between the Great Basin Cretaceous events and collisional orogens may reflect differences in the thermal evolution and magmatic fluxes.
• Miller, C. F., & Barton, M. D. (1990). Phanerozoic plutonism in the Cordilleran Interior, USA. Special Paper of the Geological Society of America, 241, 213-231.
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  Abstract: Plutonism was widespread from mid-Mesozoic through Paleogene time in the Cordilleran Interior of the United States (CI, defined as the region underlain by broadly autochthonous ancient crust inland from the Sierra Nevada batholith). Intrusive activity here was broadly synchronous with intrusion of the coastal Sierra Nevada and Peninsular Ranges batholiths, but in detail, timing in the CI differed from that nearer the coast: Triassic plutons are absent in the CI, the Jurassic intrusive peak is less pronounced than in the Sierra Nevada, and the most intense plutonic activity occurred later than in the Sierra Nevada and Peninsular Ranges. Granitoid rocks of the CI, especially the younger ones, have clear isotopic signatures of ancient crustal source components and are commonly strongly peraluminous; both of these characteristics represent major contrasts with the coastal batholiths. The North American craton, which forms the basement of the CI and from which the plutons were to a considerable extent derived, underwent intense orogeny and high-grade metamorphism during the Early Proterozoic. For the next 1.5 b.y. the continent remained intact and free of orogenic modification. Compressional tectonics, manifested both by thin-skinned thrusting and ductile nappe formation, as well as plutonism, characterized Mesozoic reactivation. Emplacement of the dominant Cretaceous CI plutons was roughly synchronous with the major deformation. CI plutonism was distinctive in several respects: (1) although no continental collision and no apparent extensional tectonism were involved, it extended far inland (800 km at present; probably >400 km at the time of intrusion) in old, previously stable crust; (2) intermediate metaluminous (
• Barton, M. D., & Hanson, R. B. (1989). Magmatism and the development of low-pressure metamorphic belts: implications from the western United States and thermal modeling. Geological Society of America Bulletin, 101(8), 1051-1065.
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  Abstract: Two-dimensional numerical modeling and geological and geophysical constraints from ancient and modern magmatic arcs demonstrate that magmatic heat advection is sufficient to produce low-pressure metamorphic belts in many areas, and that it is apparently necessary in some areas. In the western United States and other areas, regionally extensive low-pressure facies-series metamorphism (LPM) occurs where intrusions form >~50% of the uppercrust. This effect does not depend strongly on the rate of emplacement: LPM results even with complete cooling between intrusions. Models with geologically reasonable emplacement rates show that in an active magmatic arc, temperatures are near metamorphic maxima for only a small fraction of the time. Arc magmatism cannot sustain widespread thermal gradients of the magnitude indicated by the final distribution of LPM, a result consistent with heat-flow data in active arcs. Low-pressure metamorphic belts can thus develop through numerous local, short-lived metamorphic events while most of the crust remains considerably cooler. Metamorphic maxima largely depend on the biggest nearby intrusion; emplacement rates and other heat sources affect mainly the magnitude, not the distribution of metamorphism. -from Authors
• Barton, M. D., & Hanson, R. B. (1989). Magmatism and the development of low-pressure metamorphic belts: implications from the western United States and thermal modeling. Geological Society of America Bulletin, 101(Issue 8). doi:10.1130/0016-7606(1989)101<1051:matdol>2.3.co;2
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  Two-dimensional numerical modeling and geological and geophysical constraints from ancient and modern magmatic arcs demonstrate that magmatic heat advection is sufficient to produce low-pressure metamorphic belts in many areas, and that it is apparently necessary in some areas. In the western United States and other areas, regionally extensive low-pressure facies-series metamorphism (LPM) occurs where intrusions form >~50% of the uppercrust. This effect does not depend strongly on the rate of emplacement: LPM results even with complete cooling between intrusions. Models with geologically reasonable emplacement rates show that in an active magmatic arc, temperatures are near metamorphic maxima for only a small fraction of the time. Arc magmatism cannot sustain widespread thermal gradients of the magnitude indicated by the final distribution of LPM, a result consistent with heat-flow data in active arcs. Low-pressure metamorphic belts can thus develop through numerous local, short-lived metamorphic events while most of the crust remains considerably cooler. Metamorphic maxima largely depend on the biggest nearby intrusion; emplacement rates and other heat sources affect mainly the magnitude, not the distribution of metamorphism. -from Authors
• Bebout, G. E., & Barton, M. D. (1989). Fluid flow and metasomatism in a subduction zone hydrothermal system: Catalina Schist terrane, California. Geology, 17(11), 976-980.
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  Abstract: On Santa Catalina Island, southern California, blueschist to amphibolite facies metasedimentary, metamafic, and meta-ultramafic rocks show veining and alteration that reflect fluid flow and mass transfer at 25-45 km depths in an Early Cretaceous subduction zone. Synkinematic and postkinematic veins record fluid transport and metasomatism during prograde metamorphism and uplift. Vein and host-rock mineralogy and whole-rock compositions demonstrate large-scale chemical redistribution, especially of Si and alkali elements. -from Authors
• Bebout, G. E., & Barton, M. D. (1989). Fluid flow and metasomatism in a subduction zone hydrothermal system: Catalina Schist terrane, California. Geology, 17(Issue 11). doi:10.1130/0091-7613(1989)017<0976:ffamia>2.3.co;2
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  On Santa Catalina Island, southern California, blueschist to amphibolite facies metasedimentary, metamafic, and meta-ultramafic rocks show veining and alteration that reflect fluid flow and mass transfer at 25-45 km depths in an Early Cretaceous subduction zone. Synkinematic and postkinematic veins record fluid transport and metasomatism during prograde metamorphism and uplift. Vein and host-rock mineralogy and whole-rock compositions demonstrate large-scale chemical redistribution, especially of Si and alkali elements. -from Authors
• Hanson, R. B., & Barton, M. D. (1989). Thermal development of low-pressure metamorphic belts: results from two-dimensional numerical models. Journal of Geophysical Research, 94(B8), 10,363-10,377.
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  Abstract: We have used two-dimensional numerical models and analytical solutions to heat flow equations to investigate the mechanisms and the spatial and temporal development of regionally extensive low-pressure facies-series metamorphism (LPM). Two-dimensional models are necessary for describing the evolution of isotherms in the crust where lateral heat flow and local time-dependent heat sources are important. The models demonstrate that felsic intrusions can produce regionally extensive LPM where their abundance through time in the upper crust exceeds approximately 50%. Evenly spaced intrusions elevate vertical metamorphic gradients in regions between intrusions by ~5° to 10°C km-1 over background values at ~40% abundance and by ~15° to >30°C km-1 at ~70% abundance. Other mechanisms, such as intrusion of mafic magmas in the lower crust, crustal extension, or aqueous fluid advection, cannot independently produce maximum temperatures in such regions. If coeval with intrusion, these other processes will contribute to maximum temperatures; however, the distribution of isotherms and the timing of metamorphism in the upper crust are governed by the shallow intrusions. -from Authors
• Hanson, R. B., & Barton, M. D. (1989). Thermal development of low-pressure metamorphic belts: results from two-dimensional numerical models. Journal of Geophysical Research, 94(Issue 8). doi:10.1029/jb094ib08p10363
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  We have used two-dimensional numerical models and analytical solutions to heat flow equations to investigate the mechanisms and the spatial and temporal development of regionally extensive low-pressure facies-series metamorphism (LPM). Two-dimensional models are necessary for describing the evolution of isotherms in the crust where lateral heat flow and local time-dependent heat sources are important. The models demonstrate that felsic intrusions can produce regionally extensive LPM where their abundance through time in the upper crust exceeds approximately 50%. Evenly spaced intrusions elevate vertical metamorphic gradients in regions between intrusions by ~5° to 10°C km-1 over background values at ~40% abundance and by ~15° to >30°C km-1 at ~70% abundance. Other mechanisms, such as intrusion of mafic magmas in the lower crust, crustal extension, or aqueous fluid advection, cannot independently produce maximum temperatures in such regions. If coeval with intrusion, these other processes will contribute to maximum temperatures; however, the distribution of isotherms and the timing of metamorphism in the upper crust are governed by the shallow intrusions. -from Authors
• Bin, Z., & Barton, M. D. (1988). Compositional characteristics of garnets and pyroxenes in contact-metasomatic skarn deposits and their relationship with metallization. Chinese Journal of Geochemistry, 7(4), 329-335.
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  Abstract: The compositions of more than 300 granets and pyroxenes from 14 contact-metasomatic calcic skarn deposits and calcic-magnesia skarn skarn deposits in China have been examined using electron microprobe technique. The compositions of garnets and pyroxenes from a wide variety of ore types represent ten major classes of calcic skarn deposits (Fe, Fe-Cu, Pb-Zn,W, Sn, Sn-Mo-Bi-W, W-Bi-Cu-Mo, Cu-Zn and W-Zn-Cu) and three major classes of calcic-magnesia skarn deposits (Fe-Cu, Mo, Pb-Zn). Garnets and pyroxenes show a wide range of variation in composition, but the majority of garnets are grossular-andradite solid solutions containing less than 15 mol% (spessartine + almandine + pyrope), whereas most pyroxenes are diopside-hedenbergite solid solutions containing less than 5 mol% johannesenile. Some pyroxenes from a Pb-Zn calcic-magnesia skarn deposit display an increase in Mn content. Only Sn-W calcic skarn deposits and Pb-Zn calcic-magnesia skarn deposits contain garnets with more than 15 mol% (spessartine + almandine + pyrope). Some relationships have been established between the compositions of garnets and pyroxenes and the metallization types of economically important metals in skarn deposits. © 1988 Institute of Geochemistry, Chinese Academy of Sciences.
• Bin, Z., & Barton, M. D. (1988). Compositional characteristics of garnets and pyroxenes in contact-metasomatic skarn deposits and their relationship with metallization. Chinese Journal of Geochemistry, 7(Issue 4). doi:10.1007/bf02842337
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  The compositions of more than 300 granets and pyroxenes from 14 contact-metasomatic calcic skarn deposits and calcic-magnesia skarn skarn deposits in China have been examined using electron microprobe technique. The compositions of garnets and pyroxenes from a wide variety of ore types represent ten major classes of calcic skarn deposits (Fe, Fe-Cu, Pb-Zn,W, Sn, Sn-Mo-Bi-W, W-Bi-Cu-Mo, Cu-Zn and W-Zn-Cu) and three major classes of calcic-magnesia skarn deposits (Fe-Cu, Mo, Pb-Zn). Garnets and pyroxenes show a wide range of variation in composition, but the majority of garnets are grossular-andradite solid solutions containing less than 15 mol% (spessartine + almandine + pyrope), whereas most pyroxenes are diopside-hedenbergite solid solutions containing less than 5 mol% johannesenile. Some pyroxenes from a Pb-Zn calcic-magnesia skarn deposit display an increase in Mn content. Only Sn-W calcic skarn deposits and Pb-Zn calcic-magnesia skarn deposits contain garnets with more than 15 mol% (spessartine + almandine + pyrope). Some relationships have been established between the compositions of garnets and pyroxenes and the metallization types of economically important metals in skarn deposits. © 1988 Institute of Geochemistry, Chinese Academy of Sciences.
• Barton, M. D. (1987). Lithophile-element mineralization associated with Late Cretaceous two- mica granites in the Great Basin ( USA).. Geology, 15(4), 337-340.
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  Abstract: Late Cretaceous two-mica granitoids in the Great Basin are closely associated with a characteristic style of lithophile- element (Be, F, W, Mo, Sn, and Zn) mineralization. This kind of deposit is characterized by greisenlike zones in the intrusions, distinctive F- and Al-rich skarns in carbonate rocks, F-deficient quartz veins in clastic rocks, and distal metal-bearing, quartz-carbonate veins. Mineralization can be extensive, locally reaching economic grades. These occurrences resemble greisen-type ore deposits found in other parts of the world; collectively, they constitute a new metallogenic province in the western US.-Author
• Barton, M. D. (1987). Lithophile-element mineralization associated with Late Cretaceous two- mica granites in the Great Basin ( USA).. Geology, 15(Issue 4). doi:10.1130/0091-7613(1987)15<337:lmawlc>2.0.co;2
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  Late Cretaceous two-mica granitoids in the Great Basin are closely associated with a characteristic style of lithophile- element (Be, F, W, Mo, Sn, and Zn) mineralization. This kind of deposit is characterized by greisenlike zones in the intrusions, distinctive F- and Al-rich skarns in carbonate rocks, F-deficient quartz veins in clastic rocks, and distal metal-bearing, quartz-carbonate veins. Mineralization can be extensive, locally reaching economic grades. These occurrences resemble greisen-type ore deposits found in other parts of the world; collectively, they constitute a new metallogenic province in the western US.-Author
• Barton, M. D. (1987). Lithophile-element mineralization associated with late Cretaceous two-mica granites in the Great Basin.. Geology, 15(4), 337-340.
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  Abstract: Distinctive lithophile-element (Be, F, W, Mo, Sn and Zn) mineralization is closely associated with at least 7 to perhaps 20 or more late Cretaceous two-mica granitic rocks in the Great Basin. These occurrences are distributed approximately along the axis of the Cordilleran miogeosyncline ranging from east-central California to NW Nevada. This kind of deposit is characterized by greisen- like zones in the intrusions, distinctive F- and Al-rich skarns in the carbonate rocks, F-deficient quartz veins in clastic rocks, and distal metal-bearing, quartz-carbonate veins. Mineralization can be extensive, locally reaching economic grades. Despite lack of B minerals, topaz, and significant Sn, these occurrences resemble greisen-type ore deposits found in other parts of the world; collectively, they constitute a new metallogenic province in the western United States.-L.C.H.
• Robie, R. A., Bin, Z., Hemingway, B. S., & Barton, M. D. (1987). Heat capacity and thermodynamic properties of andradite garnet, Ca3Fe2Si3O12, between 10 and 1000 K and revised values for ΔfGom (298.15 K) of hedenbergite and wollastonite. Geochimica et Cosmochimica Acta, 51(Issue 8). doi:10.1016/0016-7037(87)90271-7
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  The heat capacity of synthetic andradite garnet (Ca3Fe2Si3O12) was measured between 9.6 and 365.5 K by cryogenic adiabatic calorimetry and from 340 to 990 K by differential scanning calorimetry. At 298.15 K Cop,m and Som are 351.9 ± 0.7 and 316.4 ± 2.0 J/(mol·K), respectively. Andradite has a λ-peak in Cop,m with a maximum at 11.7 ± 0.2 K which is presumably associated with the antiferromagnetic ordering of the magnetic moments of the Fe3+ ions. The Gibbs free energy of formation, ΔfGom (298.15 K) of andradite is -5414.8 ± 5.5 kJ/mol and was obtained by combining our entropy and heat capacity data with the known breakdown of andradite to pseudowollastonite and hematite at ≈ 1410 to 1438 K. From a reexamination of the calcite + quartz = wollastonite equilibrium data we obtained ΔfHom (298.15 K) = - 1634.5 ± 1.8 kJ/mol for wollastonite. Between 300 and 1000 K the molar heat capacity of andradite can be represented by the equation Cop,m = 809.24 - 7.025 × 10-2T- 7.403 × 103T-0.5 - 6.789 × 105T-2. We have also used our thermochemical data for andradite to estimate the Gibbs free energy of formation of hedenbergite (CaFeSi2O6) for which we obtained ΔfGom (298.15 K) = -2674.3 ± 5.8 kJ/mol. © 1987.
• Robie, R. A., Bin, Z., Hemingway, B. S., & Barton, M. D. (1987). Heat capacity and thermodynamic properties of andradite garnet, Ca₃Fe₂Si₃O₁₂, between 10 and 1000 K and revised values for Δ_fG^o_m (298.15 K) of hedenbergite and wollastonite. Geochimica et Cosmochimica Acta, 51(8), 2219-2224.
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  Abstract: The heat capacity of synthetic andradite garnet (Ca3Fe2Si3O12) was measured between 9.6 and 365.5 K by cryogenic adiabatic calorimetry and from 340 to 990 K by differential scanning calorimetry. At 298.15 K Cop,m and Som are 351.9 ± 0.7 and 316.4 ± 2.0 J/(mol·K), respectively. Andradite has a λ-peak in Cop,m with a maximum at 11.7 ± 0.2 K which is presumably associated with the antiferromagnetic ordering of the magnetic moments of the Fe3+ ions. The Gibbs free energy of formation, ΔfGom (298.15 K) of andradite is -5414.8 ± 5.5 kJ/mol and was obtained by combining our entropy and heat capacity data with the known breakdown of andradite to pseudowollastonite and hematite at ≈ 1410 to 1438 K. From a reexamination of the calcite + quartz = wollastonite equilibrium data we obtained ΔfHom (298.15 K) = - 1634.5 ± 1.8 kJ/mol for wollastonite. Between 300 and 1000 K the molar heat capacity of andradite can be represented by the equation Cop,m = 809.24 - 7.025 × 10-2T- 7.403 × 103T-0.5 - 6.789 × 105T-2. We have also used our thermochemical data for andradite to estimate the Gibbs free energy of formation of hedenbergite (CaFeSi2O6) for which we obtained ΔfGom (298.15 K) = -2674.3 ± 5.8 kJ/mol. © 1987.
• Sorensen, S. S., & Barton, M. D. (1987). Metasomatism and partial melting in a subduction complex: Catalina schist, southern California.. Geology, 15(2), 115-118.
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  Abstract: Migmatitic blocks containing leucocratic zones, veins and pods with albitic plagioclase + quartz + muscovite are found in the amphibolite unit of the Catalina schist, a subduction-zone metamorphic terrain. Field relations, mineral and bulk chemistry, phase-equilibrium along with element partitioning and fluid inclusion data, suggest that the migmatites and dykes are partial melts of variably metasomatized amphibolites at P approx 8-11 kbar and T approx 640-750oC, in the presence of low-salinity aqueous fluid. The Catalina metamorphism occurred at much shallower levels than those inferred for subduction-related magmatism and is one of multi-stage, slab-derived metasomatic contamination of the mantle in the 'hanging wall' of a subduction zone. -L.C.H.Dept. of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington DC 20560, USA.
• Sorensen, S. S., & Barton, M. D. (1987). Metasomatism and partial melting in a subduction complex: Catalina schist, southern California.. Geology, 15(Issue 2). doi:10.1130/0091-7613(1987)15<115:mapmia>2.0.co;2
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  Migmatitic blocks containing leucocratic zones, veins and pods with albitic plagioclase + quartz + muscovite are found in the amphibolite unit of the Catalina schist, a subduction-zone metamorphic terrain. Field relations, mineral and bulk chemistry, phase-equilibrium along with element partitioning and fluid inclusion data, suggest that the migmatites and dykes are partial melts of variably metasomatized amphibolites at P approx 8-11 kbar and T approx 640-750oC, in the presence of low-salinity aqueous fluid. The Catalina metamorphism occurred at much shallower levels than those inferred for subduction-related magmatism and is one of multi-stage, slab-derived metasomatic contamination of the mantle in the 'hanging wall' of a subduction zone. -L.C.H.Dept. of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington DC 20560, USA.
• Barton, M. D. (1986). Phase equilibria and thermodynamic properties of minerals in the BeO-Al2O3-SiO2-H2O (BASH) system, with petrologic applications.. American Mineralogist, 71(Issue 3-4).
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  The phase relations and thermodynamic properties of behoite, bertrandite, beryl, bromellite, chrysoberyl, euclase and phenakite have been quantitatively evaluated from a combination of new phase-equilibrium, solubility, calorimetric and volumetric measurements, and with data from the literature. The resulting thermodynamic model is consistent with natural low-variance assemblages and can be used to interpret many beryllium-mineral occurrences.-J.A.Z.
• Barton, M. D. (1986). Phase equilibria and thermodynamic properties of minerals in the BeO-Al₂O₃-SiO₂-H₂O (BASH) system, with petrologic applications.. American Mineralogist, 71(3-4), 277-300.
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  Abstract: The phase relations and thermodynamic properties of behoite, bertrandite, beryl, bromellite, chrysoberyl, euclase and phenakite have been quantitatively evaluated from a combination of new phase-equilibrium, solubility, calorimetric and volumetric measurements, and with data from the literature. The resulting thermodynamic model is consistent with natural low-variance assemblages and can be used to interpret many beryllium-mineral occurrences.-J.A.Z.
• Hemingway, B. S., Barton, M. D., Robie, R. A., & Haselton Jr, H. T. (1986). Heat capacities and thermodynamic functions for beryl, Be₃Al₂Si₆O₁₈, phenakite, Be₂SiO₄, euclase, BeAlSiO₄(OH), bertrandite, Be₄Si₂O₇(OH)₂, and chrysoberyl, BeAl₂O₄.. American Mineralogist, 71(3-4), 557-568.
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  Abstract: The heat capacities of beryl, phenakite, euclase and bertrandite have been measured between approx 5 and 800 K by combined quasi-adiabatic cryogenic calorimetry and differential scanning calorimetry. The heat capacities of chrysoberyl have been measured from 340 to 800 K. The resulting data have been combined with solution and phase-equilibrium experimental data and simultaneously adjusted using the programme PHAS20 to provide an internally consistent set of thermodynamic properties for several important beryllium phases. The experimental heat capacities and tables of derived thermodynamic properties are presented.-J.A.Z.
• Hemingway, B. S., Barton, M. D., Robie, R. A., & Haselton, H. T. (1986). Heat capacities and thermodynamic functions for beryl, Be3Al2Si6O18, phenakite, Be2SiO4, euclase, BeAlSiO4(OH), bertrandite, Be4Si2O7(OH)2, and chrysoberyl, BeAl2O4.. American Mineralogist, 71(Issue 3-4).
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  The heat capacities of beryl, phenakite, euclase and bertrandite have been measured between approx 5 and 800 K by combined quasi-adiabatic cryogenic calorimetry and differential scanning calorimetry. The heat capacities of chrysoberyl have been measured from 340 to 800 K. The resulting data have been combined with solution and phase-equilibrium experimental data and simultaneously adjusted using the programme PHAS20 to provide an internally consistent set of thermodynamic properties for several important beryllium phases. The experimental heat capacities and tables of derived thermodynamic properties are presented.-J.A.Z.
• Ruiz, J., & Barton, M. D. (1985). GEOLOGY AND GEOCHEMISTRY OF NAICA, CHIHUAHUA, MEXICO.. Preprint - Society of Mining Engineers of AIME.
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  Abstract: Naica consists of at least 10 mantos and 40 chimneys that have produced over 15 million tons of ore with 10% Zn, 13% Pb and 13 oz/ton Ag. The ore occurs in thick-bedded, folded Cretaceous limestone. Fractures and 26 Ma old felsite dikes with an initial strontium isotopic ratio of 0. 708 localize the mineralization. The mantos follow the dikes and have abundant early skarn with manganohedenbergite, calcic garnet, idocrase, quartz, calcite, wollastonite, schellite and later sulfides. The chimneys arise from the mantos and change from silicate-rich to silicate-free sulfide limestone replacements. Carbon, oxygen and sulfur isotope data on carbonates, silicates, sulfides and sulfates are compatible with a single evolving (magmatic? ) fluid.
• Barton, M. D. (1983). Calculation of C-O-H-S equilibria at constant bulk composition: some petrologic implications.. Carnegie Institution of Washington Year Book, 82(1905), 381-386.
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  Abstract: Geologically reasonable amounts of fluids in the C-O-H-S system can control oxidation and sulphidation states of mineral assemblages in both closed and open systems. Examples of fluid buffering are given for graphitic metamorphic rocks, crystallizing volatile-rich felsic magmas, and skarns. The effect is likely to be most important for the last example where sequences of retrograde assemblages are compatible with the cooling of a single fluid. -K.F.
• Barton, M. D. (1983). Calculation of C-O-H-S equilibria at constant bulk composition: some petrologic implications.. Carnegie Institution of Washington Year Book, 82(Issue 1905).
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  Geologically reasonable amounts of fluids in the C-O-H-S system can control oxidation and sulphidation states of mineral assemblages in both closed and open systems. Examples of fluid buffering are given for graphitic metamorphic rocks, crystallizing volatile-rich felsic magmas, and skarns. The effect is likely to be most important for the last example where sequences of retrograde assemblages are compatible with the cooling of a single fluid. -K.F.
• Barton, M. D., & Frantz, J. D. (1983). Exchange equilibria of alkali feldspars with fluoride-bearing fluids.. Carnegie Institution of Washington Year Book, 82(1905), 377-38.
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  Abstract: Ordered, low-structural-state alkali feldspars were equilibrated with K-Na fluoride solutions (total fluoride concentration 0.8 molal) at 450, 500, 600oC at 2000 bar in run times varying from 11 to 40 days. The results are very similar to those of previous workers with alkali chloride solutions. A free-energy difference between Na(aq) and KF(aq) is reported as 8720 + or - 500 calories. -K.F.
• Barton, M. D., & Frantz, J. D. (1983). Exchange equilibria of alkali feldspars with fluoride-bearing fluids.. Carnegie Institution of Washington Year Book, 82(Issue 1905).
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  Ordered, low-structural-state alkali feldspars were equilibrated with K-Na fluoride solutions (total fluoride concentration 0.8 molal) at 450, 500, 600oC at 2000 bar in run times varying from 11 to 40 days. The results are very similar to those of previous workers with alkali chloride solutions. A free-energy difference between Na(aq) and KF(aq) is reported as 8720 + or - 500 calories. -K.F.
• Hazen, R. M., Finger, L. W., & Barton, M. (1983). High-pressure crystal structures and compressibilities of bertrandite, beryl, and euclase.. Carnegie Institution of Washington Year Book, 82(1905), 357-359.
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  Abstract: Unit-cell parameters are reported for these minerals at various P up to 54 kbar. Bertrandite compression is highly anisotropic because of tetrahedral-bond bending along b, but not a and c. Beryl is less anisotropic, regardless of whether molecules of the pressurizing medium were too large to enter the structural channels. Euclase is least compressible in the direction of the chain of 3-member tetrahedral rings and most compressible along b. Be-O bonds are more compressible than Al-O or Si-O; bending of tetrahedral-bond angles contributes significantly to compressibility.-K.F.
• Hazen, R. M., Finger, L. W., & Barton, M. (1983). High-pressure crystal structures and compressibilities of bertrandite, beryl, and euclase.. Carnegie Institution of Washington Year Book, 82(Issue 1905).
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  Unit-cell parameters are reported for these minerals at various P up to 54 kbar. Bertrandite compression is highly anisotropic because of tetrahedral-bond bending along b, but not a and c. Beryl is less anisotropic, regardless of whether molecules of the pressurizing medium were too large to enter the structural channels. Euclase is least compressible in the direction of the chain of 3-member tetrahedral rings and most compressible along b. Be-O bonds are more compressible than Al-O or Si-O; bending of tetrahedral-bond angles contributes significantly to compressibility.-K.F.
• Barton, M. D. (1982). Some aspects of the geology and mineralogy of the fluorine-rich skarn at McCullough Butte, Eureka County, Nevada.. Carnegie Institution of Washington Year Book, 81(Issue).
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  A stockwork of veins and their alteration envelopes in Palaeozoic miogeosynclinal sedimentary rocks is exposed on two sides of some Cretaceous two-mica granite porphyry intrusions. The mineralization contains appreciable F, Zn and Be, and minor Mo, W and Sn. From the intrusions, the distal limit of garnet veins comes first, followed sequentially by those of plagioclase, muscovite and quartz veins. Early garnets and pyroxenes are Fe-poor; later garnets are Fe- and Mn-enriched. The skarn is attributed to F-rich fluids from the intrusions reacting with the carbonate host-rock under moderate T, and low P, fO2, fS2 and fCO2 conditions. Total Fe, Cu and Pb contents are low, but acid, F-bearing species and LIL elements are significant.-K.F.
• Barton, M. D. (1982). Some aspects of the geology and mineralogy of the fluorine-rich skarn at McCullough Butte, Eureka County, Nevada.. Carnegie Institution of Washington Year Book, 81, 324-328.
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  Abstract: A stockwork of veins and their alteration envelopes in Palaeozoic miogeosynclinal sedimentary rocks is exposed on two sides of some Cretaceous two-mica granite porphyry intrusions. The mineralization contains appreciable F, Zn and Be, and minor Mo, W and Sn. From the intrusions, the distal limit of garnet veins comes first, followed sequentially by those of plagioclase, muscovite and quartz veins. Early garnets and pyroxenes are Fe-poor; later garnets are Fe- and Mn-enriched. The skarn is attributed to F-rich fluids from the intrusions reacting with the carbonate host-rock under moderate T, and low P, fO2, fS2 and fCO2 conditions. Total Fe, Cu and Pb contents are low, but acid, F-bearing species and LIL elements are significant.-K.F.
• Barton, M. D. (1982). The thermodynamic properties of topaz solid solutions and some petrologic applications.. American Mineralogist, 67(9-10), 956-974.
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  Abstract: Reversed experiments on andalusite + water = hydroxyl topaz were run between 600o-900oC and 650-2000 kbar. The thermodynamic calculations based on this data agree well with observations on natural assemblages. -K.A.R.
• Barton, M. D. (1982). The thermodynamic properties of topaz solid solutions and some petrologic applications.. American Mineralogist, 67(Issue 9-10).
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  Reversed experiments on andalusite + water = hydroxyl topaz were run between 600o-900oC and 650-2000 kbar. The thermodynamic calculations based on this data agree well with observations on natural assemblages. -K.A.R.
• Barton, M. D., Haselton Jr, H. T., Hemingway, B. S., Kleppa, O. J., & Robie, R. A. (1982). The thermodynamic properties of fluor-topaz.. American Mineralogist, 67(3-4), 350-355.
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  Abstract: The standard thermodynamic properties were calculated from low- and high-T heat capacities and from high-T oxide melt calorimetry. Topaz (F 20.3%) from Topaz Mountain, Thomas Range, Utah, was used in all experiments. The data are tabulated and discussed. -K.A.R.
• Barton, M. D., Haselton, H. T., Hemingway, B. S., Kleppa, O. J., & Robie, R. A. (1982). The thermodynamic properties of fluor-topaz.. American Mineralogist, 67(Issue 3-4).
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  The standard thermodynamic properties were calculated from low- and high-T heat capacities and from high-T oxide melt calorimetry. Topaz (F 20.3%) from Topaz Mountain, Thomas Range, Utah, was used in all experiments. The data are tabulated and discussed. -K.A.R.
• Barton, M. D., Ruiz, J., Ito, E., & Jones, L. (1982). Tracer studies of the fluorine-rich skarn at McCullough Butte, Eureka County, Nevada.. Carnegie Institution of Washington Year Book, 81(Issue).
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  Calcite and dolomite from skarn veins (12) and altered host-rock (18) have delta 18O and delta 13C values (relative to PDB) between those of the unaltered host rock and magmatic water, indicating that it played a large part in skarn formation. Carbonates from veins lacking fluorite (5) show depletion in delta 18O only, indicating fluid dominated by meteoric water. Values for fluorite 87Sr/86Sr intermediate between host-rock and granite require at least two sources. Fluorite REE values resemble those of the host suggesting limited REE mobility.K.F.
• Barton, M. D., Ruiz, J., Ito, E., & Jones, L. (1982). Tracer studies of the fluorine-rich skarn at McCullough Butte, Eureka County, Nevada.. Carnegie Institution of Washington Year Book, 81, 328-331.
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  Abstract: Calcite and dolomite from skarn veins (12) and altered host-rock (18) have delta 18O and delta 13C values (relative to PDB) between those of the unaltered host rock and magmatic water, indicating that it played a large part in skarn formation. Carbonates from veins lacking fluorite (5) show depletion in delta 18O only, indicating fluid dominated by meteoric water. Values for fluorite 87Sr/86Sr intermediate between host-rock and granite require at least two sources. Fluorite REE values resemble those of the host suggesting limited REE mobility.K.F.
• Barton, M. D. (1980). Ag-Au-S SYSTEM.. Economic geology Lancaster, Pa., 75(2), 303-316.
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  Abstract: Study of the Ag-Au-S system shows that all ternary sulfides lie on or close to the Ag//2S-Au//2S join. At temperatures below 310 degree C a eutectoid exists between the compounds Ag//2S and Ag//3AuS//2; another may exist between Ag//3AuS//2 and AgAuS. Several natural assemblages in the Ag-Au-S system can be interpreted in terms of disequilibrium cooling. Due to rapid inversion rates only the low-temperature phases in the system are likely to be found in nature, and the ternary phases only in environments with unusually high sulfur concentrations and high gold to silver ratios.
• Barton, M. D. (1980). The Ag-Au-S system. Economic Geology, 75(2), 303-316. doi:10.2113/gsecongeo.75.2.303
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  Determination of phase relations in the Ag-Au-S system between 100 degrees and 850 degrees C by silica tube, differential thermal analysis, and high-temperature X-ray experiments reveals that the condensed system consists of three basic parts: the Ag-Au complete solid solution, the Ag 2 S-Au 2 S partial solid solution, and sulfur. At low temperatures, two ordered silver-gold sulfides exist, Ag 3 AuS 2 and AgAuS; they invert at 185 degrees and 310 degrees C, respectively, to a simple, cubic solid solution. Above 310 degrees C a complete solid solution exists from Ag 2 S to approximately Ag (sub 0.9) Au (sub 1.1) S. This solid solution has a body-centered cubic structure for silver-rich compositions, which changes via a second-order transition to a simple, cubic structure between Ag 2 S and Ag (sub 1.5) Au (sub 0.5) S. The silver-rich end of the solid solution inverts to a face-centered modification at high temperatures. The sulfides melt in the interval 680 degrees to 838 degrees C with a minimum in the liquidus at Ag (sub 1.3) Au (sub 0.7) S.Enthalpies of transition for the Ag 2 S III-II, Ag 3 AuS 2 low-high, and AgAuS low-high transitions were measured by differential scanning calorimetry and found to be, respectively: 950; 2,270(min)-2,760(max); and 1,570(min)-1,920(max) calories/mole. Within experimental error, the sulfide solid can be modeled as a regular solution with components AgS (sub 0.5) and AuS (sub 0.5) and with W G [asymp] - 1,000 calories. Estimated temperature-dependent standard free energies of formation are (T = K and units of calories): -43,880 + 20.8T (acanthite, Ag 2 S III), -40,410 + 20.8T (uytenbogaardtite, low Ag 3 AuS 2 ), -37,910 + 15.3T (high Ag 3 AuS 2 ), -36,740 + 23.4T (low AgAuS), -33,340 + 17.6T (high AgAuS), and -22,700+ 29.6T (Au 2 S).
• Barton, M. D., Burke, E. A., Kieft, C., & Oen, I. S. (1978). Uytenbogaardtite, a new silver-gold sulfide. Canadian Mineralogist, 16(4), 651-657.

Proceedings Publications

• Robinson, B. G., & Barton, M. D. (2020, May). An evaluation of thermal metamorphism and its relationship to mineralization in the Maggie Creek District, Carlin Trend, Nevada. In Geological Society of Nevada, Vision for Discovery: Geology and Ore Deposits of the Great Basin, 30 p.
• Barton, I. F., Gabriel, M. J., & Barton, M. D. (2019, summer). Hyperspectral remote sensing characterization of mine materials for process control. In Copper 2019, 9.
• Barton, M. D., Barton, I. F., & Thorson, J. P. (2019). ROLE OF POST-DIAGENETIC REDUCTION (BY HYDROCARBONS?) IN THE FORMATION OF PARADOX BASIN (COLORADO PLATEAU) U-V DEPOSITS. In Geological Society of America Abstracts with Programs.
• Barton, M. D., Barton, I. F., Davis, G. H., Hughes, A. N., Kirk, J. M., Krantz, R. W., Mcintosh, J. C., Person, M., Reiners, P. W., & Thorson, J. P. (2019). EVOLUTION OF THE PARADOX BASIN SUBSURFACE FLUID-FLOW SYSTEM AND PALEOFLUID-ROCK REACTION PRODUCTS. In Geological Society of America Abstracts with Programs.
• Barton, M. D., Ferguson, G., Hughes, A. N., Krantz, R. W., Lingrey, S., Lucero, D., Mcintosh, J. C., Person, M., Reiners, P. W., Tech, N. M., & Thorson, J. P. (2019). HYDROLOGIC CONSTRAINTS ON LISBON VALLEY COPPER MINERALIZATION WITHIN THE PARADOX BASIN, UTAH. In Geological Society of America Abstracts with Programs.
• Barton, M. D., Gabriel, M. J., & Barton, I. F. (2019, August). Hyperspectral remote sensing characterization of mine materials for process control. In Copper 2019.
• Barton, M. D., Hughes, A. N., Lucero, D., Person, M., Reiners, P. W., & Tech, N. M. (2019). INFLUENCE OF INTERNAL FLUID GENERATION MECHANISMS ON COPPER MINERALIZATION IN THE LISBON VALLEY, PARADOX BASIN, UTAH. In Geological Society of America.
• Barton, M. D., King, C. A., Pape, J. R., Richardson, C. A., & Seedorff, E. (2019). CENOZOIC NORMAL FAULTING IN NORTHERN GREAT BASIN: TIME-SPACE PATTERNS, INSIGHTS INTO THE PRE-EXTENSIONAL ARCHITECTURE, AND IMPLICATIONS FOR ORE DEPOSITS. In Geological Society of America.
• Barton, M. D., Reiners, P. W., Hughes, A. N., Person, M., & Lucero, D. (2019). Influence of Internal Fluid Generation Mechanisms on Copper Mineralization In the Lisbon Valley, Paradox Basin, Utah. In Geological Society of America Abstracts with Programs.
• Lecumberri-sanchez, P., Mazdab, F. K., Barton, M. D., Runyon, S. E., Seedorff, E., & Steele-macinnis, M. (2019). COARSE MUSCOVITE ALTERATION IN PORPHYRY COPPER SYSTEMS OF ARIZONA: CHARACTERISTICS AND IMPLICATIONS. In Geological Society of America Abstracts with Programs.
• Barton, M. D. (2015, October). Arc-scale hydrothermal alteration, and the distribution and origin of Cordilleran Fe-oxide(-Cu-Au-P-REE) systems. In XIV Congreso Geologico Chileno, 2, 444-447.
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  Barton, Mark D., 2015, Arc-scale hydrothermal alteration, and the distribution and origin of Cordilleran Fe-oxide(-Cu-Au-P-REE) systems: XIV Congreso Geologico Chileno, v. 2, La Serana, Colegio de Geólogos de Chile, p. 444-447.
• Hoge, A. K., Seedorff, C. E., Barton, M. D., Richardson, C. A., & Favorito, D. A. (2015, May). The Jackson-Lawton-Bowman normal fault system and its relationship to Carlin-type gold mineralization, Eureka district, Nevada. In Proceedings of the Geological Society of Nevada Symposium, New Concepts and Discoveries: Geological Society of Nevada 2015 Symposium, 967-1000.
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  oge, A.K., Seedorff, E., Barton, M.D., Richardson, C.A., and Favorito, D.A., 2015, The Jackson-Lawton-Bowman normal fault system and its relationship to Carlin-type gold mineralization, Eureka district, Nevada. In New Concepts and Discoveries: Geological Society of Nevada 2015 Symposium. Reno, Nevada: Geological Society of Nevada, p. 967-1000.
• Mizer, J. D., Barton, M. D., & Stegen, R. (2015, May). U-Pb geochronology of Laramide magmatism related to Cu-, Zn-, and Fe- mineralized systems, Central Mining District, New Mexico. In Geological Society of Nevada Symposium, New Concepts and Discoveries: Geological Society of Nevada 2015 Symposium, 1109-1129.
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  Mizer, J.D., Barton, M.D., and Stegen, R., 2015, U-Pb geochronology of Laramide magmatism related to Cu-, Zn-, and Fe- Mineralized Systems, Central Mining District, New Mexico. In New Concepts and Discoveries: Geological Society of Nevada 2015 Symposium. Reno, Nevada: Geological Society of Nevada, p. 1109-1129.
• Runyon, S. E., Barton, M. D., Dilles, J. H., Ohlin, H., Seedorff, C. E., Johnson, D. A., & Carpenter, K. (2015, May). Iron Oxide-rich Mineralization and Related Alteration in the Yerington District, Lyon County, Nevada. In Proceedings of the Geological Society of Nevada Symposium, New Concepts and Discoveries: Geological Society of Nevada 2015 Symposium, 251-283.
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  Runyon, S.E., Barton, M.D., Dilles, J.H., Seedorff, E., and Ohlin, H., 2015 Iron oxide-rich mineralization and related alteration in the Yerington District, Lyon County, Nevada. In New Concepts and Discoveries: Geological Society of Nevada 2015 Symposium. Reno, Nevada: Geological Society of Nevada, p 251-283.
• Runyon, S. E., Barton, M. D., Seedorff, E., Dilles, J. H., Ohlin, H. N., Carpenter, K., & Johnson, D. A. (2015, May). Iron oxide-rich mineralization and related alteration in the Yerington district, Lyon County, Nevada. In New concepts and discoveries: Geological Society of Nevada Symposium Proceedings, Reno/Sparks, May 2015, 1, 251-283.
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  Runyon, S. E., Barton, M. D., Seedorff, E., Dilles, J. H., Ohlin, H. N., Carpenter, K., and Johnson, D. A., 2015, Iron oxide-rich mineralization and related alteration in the Yerington district, Lyon County, Nevada, in Pennell, W. M., and Garside, L. J., eds., New concepts and discoveries: Geological Society of Nevada, Symposium, Reno/Sparks, May 2015, Proceedings, v. 1, p. 251-283.
• Barton, M. D., Johnson, D. A., Kreiner, D. C., & Jensen, E. P. (2013, August). Vertical zoning and continuity in Fe oxide(-Cu-Au-Ag-Co-U-P-REE) (or 'IOCG') systems: Cordilleran insights. In Proceedings of the 12th Biennial Meeting, Society for Geology Applied to Ore Deposits, 12, 1348-1351.
• Barton, M. D., Kreiner, D. C., Jensen, E. P., & Girardi, J. P. (2011, August). Superimposed hydrothermal systems and related IOCG and porphyry mineralization near Copiapó, Chile. In 11th Biennial Meeting, Society for Geology Applied to Ore Deposits, 11th Biennial Meeting, 521-523.
• Daroch, G., & Barton, M. D. (2011, August). Hydrothermal Alteration and Mineralization in Santo Domingo Sur Iron Oxide (-Cu-Au) Deposit, Atacama Region, Chile. In 11th Biennial Meeting, Society for Geology Applied to Ore Deposits, 11th Biennial Meeting, 488-490.
• Kreiner, D. C., & Barton, M. D. (2011, August). District-scale view of the upper levels of iron-oxide(-Cu-Au) (‘IOCG’) vein systems, Copiapó, Chile. In 11th Biennial Meeting, Society for Geology Applied to Ore Deposits, 11th Biennial Meeting, 497-499.
• Inverno, C. M., Solomon, M., Barton, M. D., & Foden, J. (2008). The Cu stockwork and massive sulfide ore of the Feitais volcanic-hosted massive sulfide deposit, Aljustrel, Iberian Pyrite Belt, Portugal: A mineralogical, fluid inclusion, and isotopic investigation. In (this is a journal publication), 103.
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  The Variscan Feitais volcanic-hosted massive sulfide deposit in the Aljustrel district of the Iberian Pyrite Belt consists of 55 million metric tons of Zn-Pb-Cu massive sulfide overlying a Cu-rich stockwork. The massive ore is overlain by up to 30 m of feldspar-phyric, rhyolitic volcaniclastic rock and locally by a jasper and/or chert layer up to 15 m thick. The massive sulfide orebody consists dominantly of pyrite, sphalerite, galena, chalcopyrite, tetrahedrite-tennantite, arsenopyrite, and bournonite, together with minor quartz, chlorite, sericite, carbonate, and barite. The orebody is up to 100 m thick and is underlain by a tabular alteration zone of chlorite-dominated, locally silicified, felsic volcanic rock, the upper 30 to 60 m of which contains chalcopyrite-quartz-chlorite-sericite-carbonate-bearing stockwork vein(let)s that prior to deformation were at a shallow angle to the base of the massive orebody. Chloritized footwall rocks extend up to 20 in below the Cu stockwork zone and are underlain by up to 50 m of quartz-sericite-pyrite-altered rhyolitic rock. The stockwork veins also contain pyrite, tetrahedrite-tennantite, sphalerite, and arsenopyrite. Pyrite, both in stockwork and massive ore, locally displays partly recrystallized framboidal, reniform, and cellular textures. Two generations of quartz, Q1 and Q2, and carbonate in the stockwork veins contain primary (in growth zones) and pseudosecondary fluid inclusions, with homogenization temperatures of 270° to 315°C and salinities of 2.2 to 8.1 wt percent NaCl equiv. The δ34S(CDT) values of massive and stockwork ores range from -15.4 to +4.7 (mean, -2.8) and -11.2 to +11.9 (mean, -0.4) per mil, respectively, the lowest values from colloform-textured pyrite. With no evidence of oxidation of sulfide sulfur during mineralization, the most negative values indicate an origin by biogenic reduction of seawater sulfate. The 13C(PDB) values for carbonates, -7.5 to -13.7 and +9.3 to -14.3 per mil in massive and stockwork ore, respectively, indicate an origin mostly by oxidation of methane derived from organic matter in underlying sedimentary rocks and possibly a contribution of magmatic carbon. There are no significant lateral or vertical variations in S isotope values in sulfides or C-O isotope values in carbonates, either in massive or stockwork ore. The δ18O(smow) values for quartz in stockwork and massive sulfide are 11.6 to 13.9 and 16.7 to 17.9 per mil, respectively. Coexisting, and texturally contemporaneous, carbonate and quartz in stockwork veins are not in isotopic equilibrium, indicating that the C-O isotope values may have been reset. The δ18O values of fluid calculated to be in equilibrium with quartz at fluid inclusion homogenization temperatures are 4.2 to 5.2 per mil. Barite from the hanging wall and massive ore yields δ34S values (21.9-27.9‰) equal to or slightly higher than those of coeval seawater; 87Sr/86Sr ratios (0.708438-0.709063) are slightly more radiogenic than those of coeval seawater (0.7080-0.7085), and much more radiogenic than those of coeval volcanic rocks (0.703304-0.706642), probably representing mixtures between seawater Sr and radiogenic Sr in fluids sourced in the crustal pile. Deposition of the massive sulfide on the sea floor is suggested by its stratiform nature, the stronger alteration of footwall relative to hanging-wall rocks, the stockwork system terminating sharply at the base of the massive sulfide, the presence of sedimentary-like textures in the massive sulfide, the absence of replacement fronts, and the presence of framboidal and other sea-floor depositional textures indicative of fluid quenching. The sheetlike form, lack of rubble mounds and chimneys, scarcity of barite, reduced mineral assemblage, and metal zoning distinguish Feitais from Kuroko-type deposits. It shares most of the characteristics of those Iberian Pyrite Belt deposits for which a brine-pool origin has been proposed based on fluid inclusion data, suggesting a similar depositional origin, although the evidence from fluid inclusions in this study is equivocal. The sulfate that underwent biogenic reduction may have been derived from mixing with seawater during early filling of the brine pool; diffusion across the brine-seawater interface; and sulfate reduction in the footwall volcaniclastic rocks. Stable and radiogenic isotope compositions of sulfates, sulfides, and carbonates suggest involvement of modified seawater and crustal fluids convecting due to magmatic heating, but the calculated high fluid pressures in the stockwork may indicate the additional involvement of magmatic fluids. © 2008 Society of Economic Geologists, Inc.
• Ruiz, J., & Barton, M. D. (1985). GEOLOGY AND GEOCHEMISTRY OF NAICA, CHIHUAHUA, MEXICO.. In SME-AIME Annual Meeting..
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  Naica consists of at least 10 mantos and 40 chimneys that have produced over 15 million tons of ore with 10% Zn, 13% Pb and 13 oz/ton Ag. The ore occurs in thick-bedded, folded Cretaceous limestone. Fractures and 26 Ma old felsite dikes with an initial strontium isotopic ratio of 0. 708 localize the mineralization. The mantos follow the dikes and have abundant early skarn with manganohedenbergite, calcic garnet, idocrase, quartz, calcite, wollastonite, schellite and later sulfides. The chimneys arise from the mantos and change from silicate-rich to silicate-free sulfide limestone replacements. Carbon, oxygen and sulfur isotope data on carbonates, silicates, sulfides and sulfates are compatible with a single evolving (magmatic? ) fluid.

Presentations

• Radwany, M. R., Barton, I. F., Barton, M. D., & Bos Orent, E. (2021, October). Characterization of U(-V) deposits in the La Sal district, UT and CO and their relationship to Paradox Basin fluid flow. Annual Meeting of the Geological Society of America. Portland, OR: Geological Society of America.
• Reiners, P. W., Person, M., Ballentine, C., Barton, M. D., Barton, I. F., Ferguson, G., Tyne, R., Lucero, D., Bailey, L., Marza, M., Kim, J., & Mcintosh, J. C. (2021, October). Emergent behavior of subsurface microbe-rock-fluid systems related to Cu, U, V, and Li mineralization. Annual Meeting of the Geological Society of America. Portland, OR: Geological Society of America.
• Barton, M. D., Shumway, L., & Barton, I. F. (2020, February). Process mineralogy of Colorado Plateau uranium and vanadium ores. Annual Meeting of the Society for Mining, Metallurgy, and Exploration (SME). Phoenix, AZ: Society for Mining, Metallurgy, and Exploration (SME).
• Cornoyer, J., Barton, M. D., Barton, I. F., & He, J. (2020, February). Identifying zones of geotechnical weakness at the Ray mine by hyperspectral remote sensing. Annual Meeting of the Society for Mining, Metallurgy, and Exploration (SME). Phoenix, AZ: Society for Mining, Metallurgy, and Exploration (SME).
• Getz, C., Whiteheaad, A., Thorson, J. P., Barton, I. F., & Barton, M. D. (2020, February). Contrasting copper mineralized systems of the Paradox Basin, Colorado Plateau. Annual Meeting of the Society for Mining, Metallurgy, and Exploration (SME). Phoenix, AZ: Society for Mining, Metallurgy, and Exploration (SME).
• He, J., Cornoyer, J., Barton, M. D., DuPlessis, L., Lyons-Baral, J., & Barton, I. F. (2020, February). Application of UAV-based imaging spectrometry to mining and metallurgy. Annual Meeting of the Society for Mining, Metallurgy, and Exploration (SME). Phoenix, AZ: Society for Mining, Metallurgy, and Exploration (SME).
• Barton, M. D., Gabriel, M. J., & Barton, I. F. (2019, August). Hyperspectral remote sensing characterization of mine materials for process control. Copper 2019. Vancouver, BC.
• Thorson, J. P., Barton, M. D., & Barton, I. F. (2019, September). Role of post-diagenetic reduction (by hydrocarbons?) in the formation of Paradox Basin (Colorado Plateau) U-V deposits. Geological Society of America Annual Conference.
• Barton, M. D., & Barton, I. F. (2018, September). Iron deficiency and cobalt concentration in sediment-hosted copper deposits. Society of Economic Geologists Annual Conference. Keystone, CO: Society of Economic Geologists.
• Barton, I. F., Stegen, R. J., & Barton, M. D. (2017, February). Zircon trace-element composition as an indicator of porphyry mineralization. Society for Mining, Metallurgy, and Exploration, National Meeting. Denver, Colorado: Society for Mining, Metallurgy, and Exploration.
• Barton, I. F., Yang, H., & Barton, M. D. (2016, February). Petrography saves money: a case study from the Central African Copperbelt. Annual Conference and Expo of the Society for Mining, Metallurgy, and Exploration. Phoenix, AZ.
• Barton, I. F., Yang, H., & Barton, M. D. (2016, March). Petrography saves money: A case study from the Central African Copper Belt:. SME Annual National Meeting. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration.
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  Barton, Isabel F., Yang, H., and Barton, Mark D., 2016, Petrography saves money: A case study from the Central African Copper Belt: Society for Mining, Metallurgy, and Exploration, National Meeting, p. 68.
• Barton, M. D. (2016, March). Cordilleran Fe oxide(-copper-gold) "IOCG" mineralization: Synthesis and opportunities. SME Annual National Meeting. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration.
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  Barton, Mark D., 2016, Cordilleran Fe oxide(-copper-gold) "IOCG" mineralization: Synthesis and opportunities: Society for Mining, Metallurgy, and Exploration, National Meeting, p. 184.
• Barton, M. D., & King, C. (2016, March). Eocene magmatism, Na-Ca hydrothermal alteration, and gold mineralization in NE Nevada. SME Annual National Meeting. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration.
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  King, Caleb, and Barton, Mark D., 2016, Eocene magmatism, Na-Ca hydrothermal alteration, and gold mineralization in NE Nevada: Society for Mining, Metallurgy, and Exploration, National Meeting, p. 61.
• Mizer, J. D., Barton, M. D., Seedorff, E., & Metz, R. (2016, March). Vein-hosted Ag in the Cerro Colorado District, Pima County, Arizona. SME Annual National Meeting. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration.
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  Mizer, Jason D., Barton, Mark D., Seedorff, Eric, and Metz, Robert A., 2016, Vein-hosted Ag in the Cerro Colorado District, Pima County, Arizona: Society for Mining, Metallurgy, and Exploration, National Meeting, p. 185.
• Mizer, J. D., Barton, M. D., Seedorff, E., & Metz, R. A. (2016, February). Vein-hosted Ag in the Cerro Colorado district, Pima County, Arizona [abs.]. The Future for Mining in a Data-Driven World, Technical Program, p. 259. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration, 2016 Annual Conference and Expo, 21-24 February 2016.
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  Mizer, J.D., Barton, M.D., Seedorff, E., and Metz, R. A., 2016, Vein-hosted Ag in the Cerro Colorado district, Pima County, Arizona [abs.]: The Future for Mining in a Data-Driven World: Society for Mining, Metallurgy, and Exploration, 2016 Annual Conference and Expo, Phoenix, Arizona, 21-24 February 2016, Technical Program, p. 259.
• Rathkopf, C. A., Barton, M. D., & Barton, I. F. (2016, February). Rhenium in molybdenite as an indicator of metal grade. Annual Conference and Expo of the Society for Mining, Metallurgy, and Exploration. Phoenix, AZ: Society for Mining, Metallurgy, and Exploration.
• Rathkopf, C., Barton, I. F., & Barton, M. D. (2016, March). Rhenium in molybdenite as an indicator of ore grade. SME Annual National Meeting. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration.
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  Rathkopf, Christian, Barton, Isabel F., and Barton, Mark D., 2016, Rhenium in molybdenite as an indicator of ore grade: Society for Mining, Metallurgy, and Exploration, National Meeting, 60-61.
• Runyon, S. E., Barton, M. D., & Seedorff, E. (2016, February). Yerington district, western Nevada: Brownfields activity in the midst of diverse Jurassic hydrothermal systems and subsequent normal faulting and associated tilting [abs.]. The Future for Mining in a Data-Driven World, Technical Program, p. 148-149. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration, 2016 Annual Conference and Expo, 21-24 February 2016.
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  Runyon, S. E., Barton, M. D., and Seedorff, E., 2016, Yerington district, western Nevada: Brownfields activity in the midst of diverse Jurassic hydrothermal systems and subsequent normal faulting and associated tilting [abs.]: The Future for Mining in a Data-Driven World: Society for Mining, Metallurgy, and Exploration, 2016 Annual Conference and Expo, Phoenix, Arizona, 21-24 February 2016, Technical Program, p. 148-149.
• Runyon, S. E., Barton, M. D., Ohlin, H., & Seedoff, E. (2016, March). Yerington district, western Nevada: Brownfields activity in the midst of diverse Jurassic hydrothermal systems. SME Annual National Meeting. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration.
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  Runyon, Simone E., Barton, Mark D., Ohlin, Henry, and Seedorff, Eric, 2016, Yerington district, western Nevada: Brownfields activity in the midst of diverse Jurassic hydrothermal systems: Society for Mining, Metallurgy, and Exploration, National Meeting, p. 102.
• Stegen, R. J., Mizer, J. D., Barton, M. D., & Seedorff, E. (2016, February). The U-Pb dating of and implications for Laramide porphyry copper systems [abs.]. The Future for Mining in a Data-Driven World, Technical Program, p. 259. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration, 2016 Annual Conference and Expo, 21-24 February 2016.
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  Favorito, D. A., and Seedorff, E., 2016, Contractional deformation, magmatism, and hydrothermal systems in the southern Tortilla Mountains, Laramide porphyry copper province, Arizona [abs.]: The Future for Mining in a Data-Driven World: Society for Mining, Metallurgy, and Exploration, 2016 Annual Conference and Expo, Phoenix, Arizona, 21-24 February 2016, Technical Program, p. 239.
• Stegen, R., Mizer, J. D., Barton, M. D., & Seedorff, E. (2016, March). U-Pb dating of and implications for Laramide porphyry copper system. SME Annual National Meeting. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration.
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  Stegen, Ralph, Mizer, Jason, D., Barton, Mark D., and Seedorff, Eric, 2016, U-Pb dating of and implications for Laramide porphyry copper systems: Society for Mining, Metallurgy, and Exploration, National Meeting, p. 184.
• Wetzel, M., Canby, V., & Barton, M. D. (2016, March). Hydrothermal alteration and mineralization at the Chukaru Peki project, Timok Cu-Au district, Serbia. SME Annual National Meeting. Phoenix, Arizona: Society for Mining, Metallurgy, and Exploration.
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  Wetzel, Matthew, Canby, Vertrees, and Barton, Mark D., 2016, Hydrothermal alteration and mineralization at the Chukaru Peki project, Timok Cu-Au district, Serbia: Society for Mining, Metallurgy, and Exploration, National Meeting, p. 186.
• Barton, M. D., Seedorff, E., & Ghidotti, G. A. (2015, May). Contrasting, variably superimposed hydrothermal systems, Eureka Mining District, northern Fish Creek Range, Nevada. Geological Society of Nevada Symposium. Reno, Nevada: Geological Society of Nevada.
• Barton, M. D., Seedorff, E., & Ghidotti, G. A. (2015, May). Contrasting, variably superimposed hydrothermal systems, Eureka mining district, northern Fish Creek Range, Nevada [abs.]. Geological Society of Nevada Symposium, Program with Abstracts, p. 35.. Reno, Nevada: Geological Society of Nevada.
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  Barton, M.D., Seedorff, E., and Ghidotti, G.A., 2015, Contrasting, variably superimposed hydrothermal systems, Eureka mining district, northern Fish Creek Range, Nevada [abs.], in New concepts and discoveries: Geological Society of Nevada, Symposium, Reno/Sparks, May 2015, Program with Abstracts, p. 35.
• King, C. A., & Barton, M. D. (2015, May). Eocene hydrothermal systems and contrasting hydrothermal alteration in the Battle Mountain district, Nevada. Geological Society of Nevada Symposium. Reno, Nevada: Geological Society of Nevada.
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  King, Caleb, and Barton, Mark D., 2015, Eocene hydrothermal systems and contrasting hydrothermal alteration in the Battle Mountain district, Nevada: Geological Society of Nevada Abstracts with Programs.
• Runyon, S. E., Barton, M. D., Dilles, J. H., Ohlin, H. N., Seedorff, E., Carpenter, K., & Johnson, D. A. (2015, May). Iron oxide-rich mineralization and related alteration in the Yerington district, Lyon County, Nevada. New concepts and discoveries: Geological Society of Nevada Symposium, Reno/Sparks, May 2015, Program with Abstracts, p. 98-99.. Reno, Nevada: Geological Society of Nevada.
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  Runyon, S. E., Barton, M. D., Dilles, J. H., Ohlin, H. N., Seedorff, E., Carpenter, K., and Johnson, D. A., 2015, Iron oxide-rich mineralization and related alteration in the Yerington district, Lyon County, Nevada [abs.], in New concepts and discoveries: Geological Society of Nevada, Symposium, Reno/Sparks, May 2015, Program with Abstracts, p. 98-99.
• Seedorff, E., Barton, M. D., & Takaichi, M. L. (2015, May). East-west swath of mid-Cretaceous intrusions in east-central Nevada: U-Pb geochronology and metallogeny [abs.]. Geological Society of Nevada Symposium, Program with Abstracts, p. 101-102. Reno, Nevada: Geological Society of Nevada.
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  Seedorff, E., Barton, M. D., and Takaichi, M. L., East-west swath of mid-Cretaceous intrusions in east-central Nevada: U-Pb geochronology and metallogeny [abs.], in New concepts and discoveries: Geological Society of Nevada, Symposium, Reno/Sparks, May 2015, Program with Abstracts, p. 101-102.
• Seedorff, E., Barton, M. D., & Takaichi, M. L. (2015, May). East-west swath of mid-Cretaceous intrusions in east-central Nevada: U-Pb geochronology and metallogeny. Geological Society of Nevada Symposium. Reno, Nevada: Geological Society of Nevada.
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  Seedorff, E., Barton, M. D., and Takaichi, M. L., East-west swath of mid-Cretaceous intrusions in east-central Nevada: U-Pb geochronology and metallogeny: Geological Society of Nevada, Symposium, Reno/Sparks, May 2015
• Barton, M. D., Kreiner, D. C., Girardi, J. D., & Jensen, E. P. (2014, September). Contrasting footprints and characteristics of IOCG-type and porphryry-type hydrothermal systems related to episodic Mesozoic arc magmatism in coastal northern Chile. SEG 2014. Keystone, Colorado: Society of Economic Geologists.
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  Invited presentation
• King, C. A., & Barton, M. D. (2014, September). Observations of Na-Ca, Ca, and K-Ca alteration at Battle Mountain and other districts in northern Nevada. SEG 2014. Keystone, Colorado: Society of Economic Geologists.
• Barton, M. D. (2013, October). Integrated view of Jurassic iron-oxide-rich hydrothermal systems, southeastern California and western Arizona. Geological Society of America Annual Meeting. Denver, Colorado: Geological Society of America.
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  GIRARDI, James D. and BARTON, Mark D., 2013, AN INTEGRATED VIEW OF JURASSIC IRON-OXIDE-RICH HYDROTHERMAL SYSTEMS, SOUTHEASTERN CALIFORNIA AND WESTERN ARIZONA: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 500
• Barton, M. D., Girardi, J. D., & Kreiner, D. C. (2013, October). Contrasting hydrothermal systems related to episodic Mesozoic arc magmatism in coastal northern Chile. Geological Society of America Annual Meeting. Denver, Colorado: Geological Society of America.
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  Barton, Mark D., Girardi, James D., and Kreiner, Douglas C., 2013, CONTRASTING HYDROTHERMAL SYSTEMS RELATED TO EPISODIC MESOZOIC ARC MAGMATISM IN COASTAL NORTHERN CHILE: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 275
• Girardi, J. D., & Barton, M. D. (2013, October). Mesozoic magmatic fluxes, northern Chile. Geological Society of America Annual Meeting. Denver, Colorado: Geological Society of America.
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  GIRARDI, James D. and BARTON, Mark D., 2013, MESOZOIC MAGMATIC FLUXES, NORTHERN CHILE: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 292
• Mizer, J. D., & Barton, M. D. (2013, October). Geochronology of Laramide magmatism related to Cu-, Zn-, and Fe-mineralized systems, Central Mining District, New Mexico. Geological Society of America Annual Meeting. Denver, Colorado: Geological Society of America.
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  MIZER, Jason D., BARTON, Mark D., 2013, U-Pb GEOCHRONOLOGY OF LARAMIDE MAGMATISM RELATED TO CU-, ZN-, AND FE- MINERALIZED SYSTEMS, CENTRAL MINING DISTRICT, NEW MEXICO: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 555
• Rougvie, J. R., Sorensen, S. S., Barton, M. D., & Skoza, R. A. (2013, October). Low-T alteration of volcanoplutonic arc rocks; processing fluids in the uppermost subduction factory. Geological Society of America Annual Meeting. Denver, Colorado: Geological Society of America.
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  Rougvie, James R., Sorensen, Sorena S., Barton, Mark D., and Skoza, Rachel A., 2013, Low-T alteration of volcanoplutonic arc rocks; processing fluids in the uppermost subduction factory: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 276
• Runyon, S. E., & Barton, M. D. (2013, October). Fe oxide-Cu mineralization at the Minnesota and Pumpkin Hollow deposits, Yerington district, Nevada. Geological Society of America Annual Meeting. Denver, Colorado: Geological Society of America.
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  Runyon, Simone E., and Barton, Mark D., 2013, Fe oxide-Cu mineralization at the Minnesota and Pumpkin Hollow deposits, Yerington district, Nevada: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 537
• Sorensen, S. S., Rougvie, J. R., & Barton, M. D. (2013, October). Veins, geochemistry and the evolution of the upper arc crust. Geological Society of America Annual Meeting. Denver, Colorado: Geological Society of America.
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  Sorensen, Sorena S., Rougvie, James R., and Barton, Mark D., 2013, Veins, geochemistry and the evolution of the upper arc crust: Geological Society of America Abstracts with Programs. Vol. 45, No. 7, p. 275
• Barton, M. D. (2012, August). System-scale similarity vs deposit-scale diversity in the Fe oxide(-P-Cu-Au-REE-U-Co) ~ IOCG clan. 34th International Geological Congress. Brisbane, Australia: International Union of Geological Sciences.
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  Barton, M. D., 2012, System-scale similarity vs deposit-scale diversity in the Fe oxide(-P-Cu-Au-REE-U-Co) ~ IOCG clan: 34th International Geological Congress, Brisbane, Australia. p. 2861.
• Barton, M. D., Kreiner, D. C., & Girardi, J. D. (2012, August). Multiple hydrothermal systems in coastal northern Chile and the footprints of IOCG systems. 34th International Geological Congress. Brisbane, Australia: International Union of Geological Sciences.
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  Barton, M. D., Kreiner, D.C., and Girardi, J. D., 2012, Multiple hydrothermal systems in coastal northern Chile and the footprints of IOCG systems: 34th International Geological Congress, Brisbane, Australia. p. 611.
• Seedorff, E., Barton, M. D., & Zurcher, L. (2011, January). Porphyry deposits of southwestern North America: Regional scale space-time relationships [abs.]. Association for Mineral Exploration British Columbia (AME BC), Mineral Exploration Roundup, Abstract Volume, p. 23-24.. Vancouver, British Columbia, Canada: Association for Mineral Exploration British Columbia (AME BC).
• Seedorff, E., Barton, M. D., & Zurcher, L. (2010, Oct). Porphyry deposits of southwestern North America: Space-time relationships at the regional scale and comparison with young arcs and magmatic centers [abs.]. Society of Economic Geologists 2010 Conference: The challenge of finding new mineral resources: Global metallogeny, innovative exploration, and new discoveries, Keystone, Colorado, 2-5 October 2010, 1 p.. Keystone, Colorado: Society of Economic Geologists.
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  Seedorff, E., Barton, M. D., and Zurcher, L., 2010, Porphyry deposits of southwestern North America: Space-time relationships at the regional scale and comparison with young arcs and magmatic centers [abs.]: Society of Economic Geologists 2010 Conference: The challenge of finding new mineral resources: Global metallogeny, innovative exploration, and new discoveries, Keystone, Colorado, 2-5 October 2010, 1 p.

Poster Presentations

• Barton, I. F., & Barton, M. D. (2016, June). Metal ratios in sediment-hosted copper deposits: the role of iron. Gordon Research Conference in Geochemistry of Ore Deposits. Les Diablerets, Switzerland: Gordon Research Conferences.
• Hoge, A. K., Seedorff, E., Barton, M. D., Richardson, C. A., & Favorito, D. A. (2015, May). The Jackson-Lawton-Bowman normal fault system and its relationship to Carlin-type gold mineralization, Eureka district, Nevada [abs.]. Geological Society of Nevada Symposium, Program with Abstracts, p. 62. Reno, Nevada: Geological Society of Nevada.
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  Hoge, A. K., Seedorff, E., Barton, M. D., Richardson, C. A., and Favorito, D. A., 2015, The Jackson-Lawton-Bowman normal fault system and its relationship to Carlin-type gold mineralization, Eureka district, Nevada [abs.], in New concepts and discoveries: Geological Society of Nevada, Symposium, Reno/Sparks, May 2015, Program with Abstracts, p. 62.

Others

• Greig, R. E., & Barton, M. D. (2019, September). Regional-scale evolution of the Laramide arc and porphyry copper province, southwestern North America. in Pearthree, P.A., ed., Geologic Excursions in Southwestern North America: Geological Society of America Field Guide 55, p. 401–406..
• Richardson, C. A., Favorito, D. A., Runyon, S. E., Seedorff, C. E., Maher, D. J., Barton, M. D., & Greig, R. E. (2019, September). Superimposed Laramide contraction, porphyry copper systems, and Cenozoic extension, east-central Arizona: A road log. in Pearthree, P.A., ed., Geologic Excursions in Southwestern North America: Geological Society of America Field Guide 55, p. 337-367..
• Seedorff, C. E., Barton, M. D., Gehrels, G. E., Valencia, V. A., Johnson, D. A., Maher, D. J., Stavast, W. J., & Marsh, T. M. (2019, September). Temporal evolution of the Laramide arc: U-Pb geochronology of plutons associated with porphyry copper mineralization in east-central Arizona. in Pearthree, P.A., ed., Geologic Excursions in Southwestern North America: Geological Society of America Field Guide 55, p. 369-400..
• Seedorff, C. E., Richardson, C. A., Favorito, D. A., Barton, M. D., & Greig, R. E. (2019, September). Crustal shortening and porphyry copper mineralization in the Laramide arc and superimposed extension: Introduction and themes. in Pearthree, P.A., ed., Geologic Excursions in Southwestern North America: Geological Society of America Field Guide 55, p. 319-335..