Petrographic, geochemical, and geochronologic data for cenozoic volcanic rocks of the Tonopah, Divide, and Goldfield Mining Districts, Nevada
The purpose of this report is to summarize geochemical, petrographic, and geochronologic data for samples, principally those of unmineralized Tertiary…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: pubs.usgs.gov.
Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Tonopah, Divide, and Goldfield Mining Districts, Nevada Data Series 1099 U.S. Department of the Interior U.S. Geological Survey
Cover. View to the west from Preble Mountain, Goldfield district. Pittsburgh-Goldfield mine dump in the middle foreground; town of Goldfield and the productive part of the district are beneath the near-horizontal volcanic rocks that form a dark layer below the skyline. Photograph by Edward A. du Bray, U.S. Geological Survey, 2012.
Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Tonopah, Divide, and Goldfield Mining Districts, Nevada By Edward A. du Bray, David A. John, Peter G. Vikre, Joseph P. Colgan, Michael A. Cosca, Leah E. Morgan, Robert J. Fleck, Wayne R. Premo, and Christopher S. Holm-Denoma Data Series 1099 U.S. Department of the Interior U.S. Geological Survey
U.S. Department of the Interior DAVID BERNHARDT, Secretary U.S. Geological Survey James F. Reilly II, Director U.S. Geological Survey, Reston, Virginia: 2019 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit ://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit ://store.usgs.gov. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: du Bray, E.A., John, D.A., Vikre, P.G., Colgan, J.P., Cosca, M.A., Morgan, L.E., Fleck, R.J., Premo, W.R., and Holm-Denoma, C.S., 2019, Petrographic, geochemical, and geochronologic data for Cenozoic volcanic rocks of the Tonopah, Divide, and Goldfield mining districts, Nevada: U.S. Geological Survey Data Series 1099, 15 p., ://doi.org/10.3133/ds1099. ISSN 2327-638X (online)
Acknowledgments Supplemental geologic mapping and sample collection for this study were conducted as part of the Magmatic-Tectonic History and Component Sources of Major Precious Metal Deposits at Tonopah and Goldfield, Nevada Project funded by the U.S. Geological Survey Mineral Resources Program. We thank Lawrence J. Garside and Roger P. Ashley for providing access to samples collected during their pioneering work in the Tonopah, Divide, and Goldfield mining districts. Thanks to Matt Heizler (New Mexico Geochronological Research Laboratory) for the 40Ar/39Ar ages reported in appendix 6. Thanks also to Richard J. Moscati for help in various aspects of the U-Pb zircon geochronologic age determinations. Constructive reviews by Paul Denning and Bradley S. Van Gosen are much appreciated and helped clarify data presentation.
Contents Acknowledgments iii Introduction 1 Analytical Methods 5 Data Fields 7 References Cited 12 Appendixes can be accessed at ://doi.org/10.3133/ds1099 14
Appendix 1. Status and Treatment of Samples from the Tonopah, Divide, and Goldfield
Mining Districts.
Appendix 2. Petrographic Data for Samples from the Tonopah, Divide, and Goldfield
Mining Districts.
Appendix 3. Geochemical Data for Rock Samples from the Tonopah, Divide, and
Goldfield Mining Districts.
Appendix 4. 40Ar/39Ar Geochronologic Data for Samples from the Tonopah, Divide,
and Goldfield Mining Districts Obtained in the U.S. Geological Survey 40Ar/39Ar Laboratory in Denver, Colorado.
Appendix 5. Summary of New 40Ar/39Ar Age Determinations for Samples from the
Tonopah, Divide, and Goldfield Mining Districts Obtained in the U.S. Geological
Survey 40Ar/39Ar Laboratory in Denver, Colorado.
Appendix 6. 40Ar/39Ar Geochronologic Data for Samples from the Goldfield Mining
District Obtained in the New Mexico Geochronological Research Laboratory.
Appendix 7. 40Ar/39Ar Geochronologic Data for Samples from the Goldfield Mining
District Obtained in the U.S. Geological Survey 40Ar/39Ar Laboratory in Menlo
Park, California.
Appendix 8. Sensitive High Resolution Ion Microprobe (SHRIMP) Zircon U-Pb
Geochronologic Data for Rock Samples from the Tonopah, Divide, and Goldfield Mining Districts.
Appendix 9. Laser Ablation ICP-MS Zircon U-Pb Geochronologic Data for Rock
Samples from the Tonopah, Divide, and Goldfield Mining Districts.
Appendix 10. Results of Point Counts for Samples of the Fraction Tuff and Heller
Tuff from the Tonopah and Divide Mining Districts. ://doi.org/10.3133/ds1099
Figure
1. Maps showing location of the Tonopah, Divide, and Goldfield mining districts, Nevada. A, Index map of central Nevada showing the locations of the three mining districts relative to Tonopah and Goldfield. B, Map of northern California and western Nevada showing the inferred extent of ancestral and modern High Cascades magmatic arcs 2 Tables
1. Definition and characterization of data fields included in appendix 1 7
2. Definition and characterization of data fields included in appendix 2 8
3. Definition and characterization of data fields included in appendix 3 10
Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Tonopah, Divide, and Goldfield Mining Districts, Nevada By Edward A. du Bray, David A. John, Peter G. Vikre, Joseph P. Colgan, Michael A. Cosca, Leah E. Morgan, Robert J. Fleck, Wayne R. Premo, and Christopher S. Holm-Denoma Introduction The purpose of this report is to summarize geochemical, petrographic, and geochronologic data (du Bray and others, 2019) for samples, principally those of unmineralized Tertiary volcanic rocks, from the Tonopah, Divide, and Goldfield min ing districts of west-central Nevada (fig. 1). Much of the data presented here for the Tonopah and Divide mining districts are for samples collected by Bonham and Garside (1979) dur ing geologic mapping in and around those mining districts, whereas much of that for samples from the Goldfield mining district were obtained by Ashley (1974; 1979; 1990a). Addi tional data were derived from samples collected 2012–17, as part of the U.S. Geological Survey Mineral Resources Program funded project titled, “Magmatic-tectonic history and compo nent sources of major precious metal deposits in the southern Walker Lane.” A small amount of additional geochemical data for samples from each of the mining districts were compiled from other sources. Individual sample collectors are identified by appropriate entries in the “Collector” field (appendix 1) and published sources of geochemical data are defined by entries in the “Chem_Src” data field (appendix 1). The geologic setting of bonanza silver-gold quartzadularia veins in the Tonopah mining district is complex and incompletely understood. Basement rocks exposed about 10 kilometers (km) north and 15 km south of the mining district include Triassic (John and McKee, 1987) granitic rocks and the lower Paleozoic siliciclastic metasedimentary rocks of the “Nolan belt domain” (Crafford, 2007, 2008) that they intrude; these metasedimentary rocks were deposited on Precambrian rocks of the North American craton. These basement rocks are overlain by Miocene volcanic rocks that are manifestations of arc magmatism associated with the southern segment of the ancestral Cascades arc (du Bray and others, 2014). Arc mag matism in the Tonopah mining district was extinguished by northward migration of the Mendocino triple junction and the transition to a transform plate margin in this region at about 12 mega-annum (Ma). Lava flows and lava dome complexes are volumetrically dominant, although ash-flow tuffs, including the Fraction Tuff and the Heller Tuff of Bonham and Garside (1979), are also significant within the mining district. Miner alized veins are hosted primarily by andesite and dacite lava flows and breccias of the Mizpah Trachyte near the south end of a lava dome complex (Nolan, 1935; Bonham and Garside, 1979). New argon-argon (40Ar/39Ar) dates (this report and Cosca and Morgan, 2018) suggest that rocks of the Mizpah Trachyte were erupted about 21.4 Ma. The Fraction Tuff over lies the Mizpah Trachyte. In the Tonopah mining district, the Fraction Tuff was likely deposited in an intracaldera environ ment and was erupted from a caldera whose northern margin is about 10 km north of Tonopah (John and others, 2015). In the area around Tonopah, the overlying Siebert Formation of Bonham and Garside (1979) may constitute a voluminous, thick, in part ash-fall deposit that accumulated in the basin formed during collapse of the caldera that erupted the Fraction Tuff and in the surrounding lowlands. New 40Ar/39Ar dates of adularia on quartz-adularia veins in altered Mizpah Trachyte rocks range from about 20.5 to 19.9 Ma (this report and Cosca and Morgan, 2018). High-grade silver-gold deposits were mined from some of these veins. More than 174 million ounces (Moz) silver and 1.86 Moz gold were produced (mostly from 1910 to 1930). The principal ore minerals are argentite, polybasite, pyrar gyrite, and electrum; other vein minerals include sphalerite, galena, chalcopyrite, pyrite, pearcite, muscovite, and calciummanganese carbonates (Bonham and Garside, 1974; this report). Dates of the quartz-adularia veins suggest nearly simultaneous eruption of the Fraction Tuff, possible caldera formation, and vein mineralization (John and others, 2015). Compositions of Tonopah volcanic rocks vary essen tially continuously from about 60 to 78 weight percent silica (SiO2), although rocks with ≈67 to 72 weight percent SiO2 are somewhat under-represented. Tonopah rock compositions form a high-potassium calc-alkaline series with pronounced negative titanium-phosphorus-niobium-tantalum anomalies and high barium/niobium, barium/tantalum, and lanthanum/ niobium typical of subduction-related continental margin arcs (Gill, 1981). Most Tonopah mining district rocks are
2 Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada Manhattan Tonopah Goldfield Big Smoky Valley Ralston Valley San Antonio Mountains DIVIDE MINING DISTRICT TONOPAH MINING DISTRICT GOLDFIELD MINING DISTRICT NYE COUNTY ESMERALDA COUNTY A 117° 116°45' 117°15' 38°45' 117°30' 38°30' 38°15' 37°45' 37°30' 38° Base map from U.S. Geological Survey digital data The National Map, 1:2,000,000, 2018 Geographic projection North American Datum of 1983 20 KILOMETERS 20 MILES NEVADA Map area Location map Figure 1. Location of the Tonopah, Divide, and Goldfield mining districts, Nevada. A, Index map of central Nevada showing the locations of the three mining districts relative to Tonopah and Goldfield. B, Map of northern California and western Nevada (modified from Colgan and others, 2011; John and others, 2012) showing the inferred extent of ancestral (green polygons) and modern High Cascades (cross hatched polygons) magmatic arcs.
Introduction 3 TONOPAH MINING DISTRICT CALIFORNIA NEVADA JUAN DE FUCA (FARALLON) PLATE PACIFIC PLATE Cascadia Subduction zone OREGON IDAHO Southern Segment Ancestral Cascades Arc Terrane Sierra Nevada Batholith SA N
A Ndre A S
F A Ul T W A L K E R
L A N E PACIFIC OCEAN Mendocino Triple Junction DIVIDE MINING DISTRICT GOLDFIELD MINING DISTRICT B EXPLANATION Ancestral arc rocks Mesozoic plutons Modern arc rocks Major Quaternary
eruptive center Fault Thrust Fault Strike-slip fault 100 KILOMETERS 100 MILES 42º 40º 38º 120º 126º 124º 118º 116º 122º Base from U.S. Geological Survey digital data, 1:2,000,000, 2018 Lambert Conformal Conic projection Standard parallels 20º N. and 60º N. Central meridian 121º W., Latitude of origin 40º N. North American Datum of 1927 (NAD 27) Figure 1. Location of the Tonopah, Divide, and Goldfield mining districts, Nevada. A, Index map of central Nevada showing the locations of the three mining districts relative to Tonopah and Goldfield. B, Map of northern California and western Nevada (modified from Colgan and others, 2011; John and others, 2012) showing the inferred extent of ancestral (green polygons) and modern High Cascades (cross hatched polygons) magmatic arcs.—Continued porphyritic, commonly containing 10–35 volume percent phenocrysts principally composed of plagioclase, pyroxene, and hornblende ±biotite; quartz, alkali feldspar, or olivine are present in some samples. The geologic setting of the silver-gold dominated Divide mining district, centered about 8 km south of Tonopah, is similar to that of the Tonopah mining district; similarly, it is dominated by Miocene volcanic rocks. Like the Tonopah mining district, basement rocks, exposed about 10 km south of the mining district, are principally lower Paleozoic siliciclastic metasedimentary rocks of the “Nolan belt domain” (Crafford, 2007, 2008) but also include a distinctive Cretaceous mus covite granite (Bonham and Garside, 1979). The Miocene volcanic rocks, also associated with ancestral Cascades arc magmatism, overlie the Paleozoic and Mesozoic basement rocks and Fraction Tuff. Mineralized veins and breccias in the Divide mining district are also hosted in Miocene volcanic rocks, principally the Oddie Rhyolite, Heller Tuff, and tuffs
4 Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada of the Siebert Formation (Nolan, 1935; Bonham and Garside, 1979; Erdman and Barabas, 1996). The eastern part of the mining district and a large area fur ther east are dominated by additional Miocene volcanic rocks, including the Divide Andesite and the compositionally diverse volcanics of Donovan Peak. The Divide and Donovan rocks are associated with local eruptive or intrusive centers and consist of lava flows, lava dome complexes, and hypabyssal plugs. These rocks may represent resurgent magmatism associated with the southern of two hypothesized calderas in the Tonopah area. New 40Ar/39Ar dates (this report and Cosca and Morgan, 2018) indicate that shallowly emplaced Oddie Rhyolite domes were intruded between about 17.3 and 16.6 Ma. Potassiumargon (K-Ar) dates of air-fall tuffs of the Siebert Formation in the Tonopah area are poorly constrained between about 20 and 16 Ma (Bonham and Garside, 1979). New 40Ar/39Ar ages (this report and Cosca and Morgan, 2018) for these volcaniclastic rocks provide little clarity concerning the age of these deposits because feldspars and other minerals contained therein repre sent diverse, multiage sources. New 40Ar/39Ar dates (this report and Cosca and Morgan, 2018) indicate that ages for the Divide Andesite and volcanics of Donovan Peak are 17.6 to 17.4 and 17.3 to 16.5 Ma, respectively. Existing K-Ar dates for a variety of mineralized samples from the Divide mining district suggest that mineralization occurred between about 16.4 and 15.3 Ma (Bonham and Gar side, 1979), whereas new 40Ar/39Ar dates of adularia indicates ore formation between about 17.0 and 16.8 Ma. Quartz-adularia epithermal deposits in the Divide mining district consist of silver-dominated vein and breccia deposits from which about 3.7 Moz. silver and 0.04 Moz. gold were produced (Erdman and Barabas, 1996); the principal ore mineral in the mining district was cerargyrite although sphalerite, argentiferous galena, chalcopyrite, molybdenite, electrum, acanthite, pyrar gyrite, and possible tetrahedrite have been identified in dump samples (Bonham and Garside, 1974; Graney, 1987; Erdman and Barabas, 1996). Divide mining district volcanic rocks contain ≈61 to 77 weight percent SiO2. Rock compositions form a highpotassium calc-alkaline series with geochemical characteristics typical of subduction-related continental margin arcs (Gill, 1981). Many of the Divide mining district rocks are distinctly more alkaline, particularly sodic, than volcanic rocks in either the Tonopah or Goldfield mining districts. Most Divide mining district rocks are porphyritic, commonly containing 5–25 vol ume percent phenocrysts principally composed of plagioclase, biotite, and hornblende; quartz and alkali feldspar are present in samples of the more silicic units, especially the Oddie Rhyolite. The geology of the Goldfield mining district is domi nated by intensely quartz-alunite-altered Miocene volcanic and pre-Tertiary rocks (Vikre and Henry, 2011), including lower Paleozoic siliciclastic metasedimentary rocks, the “Nolan belt domain” of Crafford (2007, 2008), which were deposited on Precambrian rocks of the North American craton. These base ment rocks, exposed mostly in deeper mine workings, were intruded by Jurassic granitic rocks (this report). The volcanic rocks are principally lava flows but also include breccias and lava domes. Miocene and minor Oligocene volcanic rocks in the Goldfield mining district constitute the southernmost extent of magmatism associated with the southern segment of the ancestral Cascades arc (du Bray and others, 2014). Northward migration of the Mendocino triple junction terminated arc mag matism in the Goldfield mining district at about 12.9 Ma. These volcanic rocks at Goldfield are cut by a dense network of westnorthwest and north-northeast trending normal faults. Milltown Andesite lava flows are the volumetrically dominant volcanic rocks in the Goldfield mining district; a K-Ar date indicates that the andesite was erupted about 21.5 ± 0.5 Ma (Albers and Stewart, 1972), whereas several new 40Ar/39Ar dates (this report and Cosca and Morgan, 2018) indicate an age of about 22.3 to 21.9 Ma. Other important units in the Goldfield mining district include unnamed porphyritic andesite lava flows and domes, latite (Ransome, 1909), and small-volume rhyolite masses. Several new 40Ar/39Ar dates (this report and Cosca and Morgan, 2018) of the porphyritic andesite are 22.4 to 21.8 Ma. Ashley (1990a) suggests that silicic ash-flow tuffs (the Vindicator Rhyolite and the Morena Rhyolite of Ransome, 1909) represent eruptions from a 6-km diameter caldera delineated by a series of poorly defined, presumed ring fractures. However, geophysi cal data suggest that these fractures are not related to caldera formation but to pluton emplacement (Blakely and others, 2007). A new 40Ar/39Ar date of sanidine indicates eruption of the Morena Rhyolite of Ransome (1909) at 25.17 ± 0.03 Ma (this report and Cosca and Morgan, 2018). New 40Ar/39Ar dates of biotite and sanidine in rhyolite of Wildhorse Spring in the eastern part of the mining district indicate eruption between 22.2 and 21.5 Ma (this report and Cosca and Morgan, 2018). A series of younger, middle Miocene mafic lava flows overlie mineralized, lower Miocene rocks in the Goldfield mining district. Miocene and minor Oligocene volcanic rocks in the Goldfield mining district contain numerous, fault brecciahosted quartz-alunite epithermal deposits (Vikre and Henry, 2011) from which 4.19 Moz of gold and 1.45 Moz of silver were produced (Albers and Stewart, 1972). New 40Ar/39Ar dates (this report and Cosca and Morgan, 2018) of alunite in breccias and altered volcanic rocks range from 22.4 to 7.0 Ma though most dates cluster between 21.9 to 21.2 Ma. Abundant mineralized fault breccia masses are localized in a 40 (km2) area within which acidic hydrothermal fluids intensely altered Miocene, and minor Oligocene volcanic and pre-Tertiary rocks, to advanced argillic mineral assemblages (Ashley, 1990a; Vikre and Henry, 2011). Within this area, quartz-rich fault breccias form resistant zones or ledges enclosed within recessively weathered, quartz-poor, alunite- or pyrophyllite-rich rocks (Ransome, 1909; Ashley and Albers, 1975, Ashley, 1990a). Most Goldfield mining district volcanic rocks contain between ≈54 and 69 weight percent SiO2; andesitic and dacitic compositions are dominant. Like volcanic rocks in the Tonopah mining district, those in the Goldfield mining district form a high-potassium, calc-alkaline series with pronounced negative titanium-phosphorus-niobium-tantalum anomalies and high
Analytical Methods 5 barium/niobium typical of subduction-related continental margin arcs (Gill, 1981). These rocks are porphyritic and con tain 15–35 volume percent phenocrysts principally composed of plagioclase, pyroxene, hornblende, and biotite. Analytical Methods Standard petrographic microscope techniques were employed to identify phenocryst minerals and estimate their relative abundances in 468 volcanic rock samples from the Tonopah, Divide, and Goldfield mining districts (appendix 2; see Data Fields section). In addition, phenocryst size and crystallinity, rock textures, groundmass characteristics, and accessory mineral assemblages were recorded for each sample. New whole-rock chemical analyses of 190 samples, most collected between 2012 and 2017, were conducted in analytical laboratories of SGS Minerals, Toronto, Canada (appendix 3; see Data Fields section). Major oxide abun dances (recalculated to 100 percent, volatile free) were determined by wavelength dispersive X-ray fluorescence spectrometry. A 55-element method that uses a combination of inductively coupled plasma-atomic emission spectrom etry and inductively coupled plasma-mass spectrometry was used to determine trace element abundances. These chemical data are also archived in the National Geochemical Database (NGDB) of the U.S. Geological Survey. Pertinent analytical methods are described by Taggart (2002). Compositions of an additional 108 samples of Tonopah, Divide, and Gold field mining district rocks, from published and unpublished sources, are also included in this data compilation. These samples were analyzed by different laboratories employ ing diverse analytical techniques, which resulted in data of variable quality for a highly variable set of components. Laboratories, techniques, and the analyzed constituents are documented in the sources (identified in appendix 1; see Data Fields section) from which these data were compiled. Although efforts were made to collect only unaltered samples, a review of the available geochemical data indicated that some of the analyzed samples were affected by postmagmatic hydrothermal alteration. Samples with any of the following characteristics are considered to be altered: SiO2 abundances greater than 78 weight percent, volatile (loss on ignition) content greater than 4 weight percent (excluding hydrated vitrophyres), sodium oxide (Na2O) abundances less than 1 weight percent, or Na2O/K2O less than 0.5. Primary igneous rock compositions of samples with any of these char acteristics probably have not been preserved; these samples and the type of alteration they experienced are identified in appendix 3. New 40Ar/39Ar ages (appendixes 4–7) provide temporal constraints on volcanic and hydrothermal activity in the Tonopah, Divide, and Goldfield mining districts. Volcanic rocks were dated using either separates of one or more phenocryst minerals (plagioclase, sanidine, biotite, and amphi bole) or whole-rock aggregates. Ages of hydrothermal altera tion were determined using alunite or adularia separates. Samples collected for 40Ar/39Ar analysis were most com monly crushed and sieved to sizes appropriate for preparation of high-purity separates. Mineral separations were made using standard magnetic and heavy-liquid separation techniques. Whole-rock samples were prepared by crushing and isolating rock fragments of cubic millimeter (mm3) from fresh rock free of obvious alteration and xenocrysts. Analyzed samples were washed in deionized water. In many cases, final separates were prepared by hand picking individual crystals. The 40Ar/39Ar ages reported in appendixes 4 and 5 (Cosca and Morgan, 2018) were determined in the U.S. Geological Survey 40Ar/39Ar Laboratory in Denver, Colorado. Samples, together with standards, were irradiated in several separate experiments of either 5 or 7 megawatt hours in the central thimble position of the U.S. Geological Survey TRIGA® Reactor Facility in Denver, Colorado. Carbon dioxide (CO2) laser fusion of >10 individual Fish Canyon Tuff sanidine crystals (28.201 ± 0.09 Ma; Kuiper and others, 2008) at closely monitored positions within the irradiation package resulted in neutron flux ratios reproducible to ± 0.25% (2σ). Cadmium shielding during irradiation prevented any measur able nucleogenic (40Ar/39Ar) potassium (K). Isotopic produc tion ratios and interfering nucleogenic reactions were deter mined from irradiated calcium fluoride (CaF2) and zero age K-silicate glass, and for this study the following values were measured: (36Ar/37Ar)Ca (2.77 ± 0.03) × 10−4; (39Ar/37Ar)Ca (6.54 ± 0.33) × 10−4; and (38Ar/39Ar)K (1.29 ± 0.03) × 10−2. The irradiated samples and standards were loaded into known positions of a stainless steel planchette, placed into a chamber and sealed by an externally pumped zinc selenide window, and evacuated to ultrahigh vacuum conditions within a fully automated stainless steel extraction line designed and built at the USGS in Denver, Colorado. A 50 watt (W) CO2 laser equipped with a beam homogenizing lens was used to incre mentally heat and (or) fuse mineral grains and rock fragments. The liberated gas was expanded and purified by exposure to a cryogenic trap maintained at −135 ºC and to two SAES GP50® getters, one operated at 0 amps and one operated at 2.2 amps. Following purification, sample gas was expanded online into a Thermo Scientific ARGUS VI® mass spectrometer and Ar isotopes were measured simultaneously using faraday detectors (Ar masses 37–40) and ion counting (Ar mass 36). Blanks and sample data were acquired during 10 measurement cycles and time zero intercepts were determined by best-fit linear and (or) polynomial regressions to the data. The data were corrected for mass discrimination, blanks, radioactive decay, and interfering nucleogenic reactions and 40Ar/39Ar ages were calculated with the decay constants of Min and others (2000) and a 40Ar/36Ar ratio of trapped argon equal to the atmospheric value of 298.56 (Lee and others, 2006). Data collection and age calculations were conducted using the Masspec software program written by A. Deino of the Berkeley Geochronology Center.
6 Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada The 40Ar/39Ar ages reported in appendix 6 were deter mined in the New Mexico Geochronological Research Labora tory. Analytical methods are described by Heizler (2003, 2005). The 40Ar/39Ar ages reported in appendix 7 were deter mined in the U.S. Geological Survey 40Ar/39Ar laboratory in Menlo Park, California. Samples were crushed and sieved to sizes appropriate for preparation of high-purity alunite sepa rates. In many cases, final separates were prepared by hand picking individual crystals. Samples were irradiated in the U.S. Geological Survey TRIGA Reactor Facility in Denver, Colo rado; irradiation times were between 10 and 16 hours. Deter mined ages were obtained by laser-fusion analysis, whereby grains were fused with a CO2 laser in a single heating step (appendix 7). One or several grains were used in each analysis, depending on grain size. In all cases, a minimum number of grains were used to permit recognition and elimination of most xenocrystic or detrital contamination through identification of outliers. The reported age for laser-fusion analyses represents the weighted mean of the replicate analyses, with the inverse variance of propagated, within-run (internal) errors of each used as its weighting factor (Taylor, 1982). Sanidine from the Fish Canyon Tuff, with an age of 28.198 Ma, was used for calculation of neutron flux. Decay and abundance constants are those recommended by Steiger and Jäger (1977). Ages were calculated assuming a 40Ar/36Ar ratio of trapped argon equal to the atmospheric value of 295.5. Zircons were separated from crushed and ground samples using standard magnetic and heavy liquid techniques, hand picked under a binocular microscope, and mounted in epoxy discs. Zircons were analyzed by Sensitive High Resolution Ion Microprobe with Reverse-Geometry (SHRIMP-RG) at Stanford University and by laser ablation inductively coupled mass spectrometry (LA-ICPMS) in the U.S. Geological Survey Southwest Isotope Research Laboratory in Denver, Colorado (Colgan, 2018). For the SHRIMP analyses, zircon mounts were ground to expose grain interiors, polished, and imaged with cathodolu minescence (CL) on a JEOL 5600 SEM® to identify internal structure (rims, core, and so forth). The SHRIMP-RG was operated with an oxygen (O2 -)-primary ion beam that varied in intensity from 4.0 to 5.5 nA, with a typical spot diameter of 20–25 micrometers (µm). Zircon surfaces were rastered by the primary beam for 120–180 seconds before data was collected. For all samples, the following peaks were measured sequen tially: 89Y, 139La+, 140Ce+, 146Nd+, 147Sm+, 153Eu+, 155Gd+, 163Dy16O+, 166Er16O+, 172Yb16O+, 90Zr2 16O+, 180Hf16O+, 204Pb+, a background measured at 0.045 mass units above the 204Pb+ peak, 206Pb+, 207Pb+, 208Pb+, 232Th+, 238U+, 232Th16O+, 238U16O+, and 238U16O2 +. Mounts were analyzed with 4–5 scans (peak-hopping cycles in mass order) and measurements were made at mass resolutions of M/∆M 7,500–8,500 (10 percent peak height). Raw data were reduced using Squid 2 rev. 2.51 software (Ludwig, 2009), with corrections for background and collector dead time. Measured 206Pb/238U was corrected using a standard U+/Pb+ compared to U+/UO+ calibration for sputtering bias (Williams, 1997). Radiogenic U-Pb ratios were derived after correction for common Pb using a 207Pb correction scheme (Williams, 1997), or from measured 204Pb with model common Pb compositions from Stacey and Kramers (1975). 238U/235U was assumed to be 137.88. Concentration data for U, thorium (Th) and all of the measured trace elements were standardized against zircon standard Madagascar Green (MAD) (Barth and Wooden, 2010), which had standard deviations (2σ uncertainties) of about ±3 percent for hafnium Hf, ±5–10 percent for the yttrium (Y) and heavy rare earth elements (HREE), ±10–15 percent, and up to ±40 percent for lanthanum (La). U-Pb ages were calculated relative to the R33 zircon standard (420 Ma; Black and others, 2004; Mattinson, 2010). Data (appendix 8) were reduced using methods described by Williams (1997) and Ireland and Williams (2003), using Excel and the add-in programs Isoplot3 and Squid 2 rev. 2.51 (Ludwig 2003, 2009). Laser ablation-inductively coupled plasma analyses of igneous zircon grains were conducted using a Nu Instruments AttoM™ laser ablation, single collector, inductively coupled plasma mass spectrometer (LA-SC-ICPMS). Zircon was ablated with a Photon Machines Excite™ 193 nm ArF excimer laser in spot mode (150 total bursts for each spot analysis) with a repetition rate of 5 hertz (Hz), laser energy of mil liJoule, and an energy density of 4.11 joules/square centimeter. Pit depths are typically less than 20 µm. The rate of He carrier gas flow from the HelEx™ cell of the laser was ~0.6 L/min. Makeup Ar gas (~0.2 L/min) was added to the sample stream prior to its introduction into the plasma. Nitrogen with flow rate of 5.5 milliliter/minute was added to the sample stream to allow for significant reduction in ThO+/Th+ (<0.5 percent) and improved the ionization of refractory Th (Hu and others, 2008). Laser spot sizes on zircon were ~25 µm. With the magnet parked at a constant mass, the flat tops of the isotope peaks of 202Hg, 204(Hg+Pb), 206Pb, 207Pb, 208Pb, 232Th, 235U, and 238U were measured by rapidly deflecting the ion beam with a 30 second on peak background measured prior to each 30 s analysis. Raw data were reduced offline using the Iolite™ 2.5 program (Paton and others, 2011) to subtract on peak background signals, correct for U-Pb downhole fractionation, and normalize the instrumental mass bias using external mineral reference materials, the ages of which had previously been determined by isotope dilution thermal ionization mass spectrometry (ID-TIMS). Ages were corrected by standard sample bracketing with the primary zircon reference material Temora2 (417 Ma; Black and others, 2004) and secondary reference material Plešovice (337 Ma, Sláma and others, 2008) and an inhouse standard WRP-63-08 (1707 Ma; W. Premo, oral commun., 2016). Reduced data were compiled into Weth erill concordia diagrams using Isoplot 4.15 (Ludwig, 2012). 206Pb/238U ages are reported for igneous zircon samples less than ~1300 Ma and 207Pb/206Pb ages are used for older ages fol lowing the recommendations of Gehrels (2012). Standard petrographic microscope techniques and an automated point count stage were used to determine the rela tive proportions of various phenocryst minerals and matrix or groundmass in samples of the Fraction Tuff and Heller Tuff (appendix 10).
Data Fields 7 Data Fields Petrographic, geochemical, and geochronologic data for volcanic rocks exposed in the Tonopah, Divide, and Goldfield mining districts are presented in columns or sets of related col umns (appendixes 2–10) in Microsoft Excel 2010 workbooks (. format). The contents of appendix 1 (data fields defined in table 1) constitute basic sample characterization, including sample location, sample treatment, and lithologic characteriza tion. Appendix 2 contains petrographic observations for each sample (data fields defined in table 2). Appendix 3 contains geochemical data for analyzed samples (data fields defined in table 3). Geochemical data in some worksheet cells may Table 1. Definition and characterization of data fields included in appendix 1 (status and treatment of samples). Field name Field description Field_ID Field-assigned sample identifier; Field_ID entries link data for individual rows to the contents of particular rows in the other appendixes and, for U.S. Geological Survey samples, to the National Geochemical Database District Tonopah, Divide, or Goldfield Collector Sample collector initials, where EDB is E.A. du Bray, RPA is R.P. Ashley; PGV is P.G. Vikre; OTH is other (as identified in the Chem_Src field); HBLG is H.F. Bonham or L.J. Garside; DAJ is D.A. John; and MAC is M.A. Cosca Longitude In decimal degrees, relative to the North American Datum of 1927; locations (with four or five significant figures) are accurate within several to tens of meters, locations with three significant figures are accurate within hundreds of meters, locations with two significant figures are accurate within thousands of meters. Longitude is reported as a negative value (western hemisphere) Latitude In decimal degrees, relative to the North American Datum of 1927; locations with four or five significant figures are accurate within several to tens of meters, locations with three significant figures are accurate within hundreds of meters, locations with two significant figures are accurate within thousands of meters. Latitude is reported as a positive value (northern hemisphere) Chem X, chemical analysis for sample obtained (see appendix 3) TS X, thin section of sample prepared and examined using a petrographic microscope (see appendix 2) REF X, reference sample collected X, sample age determined by argon-argon (40Ar/39Ar) geochronology (this report and Cosca and Morgan, 2018) X, sample age determined by zircon uranium-lead (U-Pb) geochronology X, sample age determined by potassium-argon (K-Ar) geochronology Strat_Name Stratigraphic unit name (Bonham and Garside, 1979; Ashley, 1974; 1979; 1990a) Ign_Form Form (lava, ash-flow tuff, plug, stock, and so forth) of the igneous rock represented by each sample appear to be more precise than displayed values, but the implied precision is a misleading artifact of computational processes (for instance, recalculation to 100-percent volatile free) used to create data-cell contents. Blank cells in the worksheet appendixes indicate null values or that no data are available. In appendix 3 (geochemistry data), some blank cells reflect abundances that were reported as “less than the detection limit”; these values were replaced by blank cells to enable statistical analysis of the uncensored data. The results of 40Ar/39Ar age determination experiments are presented in appendixes 4–7, those for U-Pb analysis of zircon separates are presented in appendixes 8 and 9, and microscope-based point counts of Fraction Tuff and Heller Tuff samples in appendix 10.
8 Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada Table 2. Definition and characterization of data fields included in appendix 2 (petrographic data). Field name Field description Field_ID Field-assigned sample identifier; Field_ID entries link data for individual rows to the contents of particular rows in the other appendixes and, for U.S. Geological Survey samples, to the National Geochemical Database Unit Stratigraphic unit name (Bonham and Garside, 1979; Ashley, 1974; 1979; 1990a); repeated in this appendix to enable data sorting by unit name AbdQtz Microscope-based estimate of abundance of quartz phenocrysts relative to the whole rock, in volume percent. TR, trace (<0.5 volume percent) amounts AbdAlkFld Microscope-based estimate of abundance of alkali feldspar phenocrysts relative to the whole rock, in volume percent. TR, trace (<0.5 volume percent) amounts AbdPl Microscope-based estimate of abundance of plagioclase phenocrysts relative to the whole rock, in volume per cent. TR, trace (<0.5 volume percent) amounts AbdHbl Microscope-based estimate of abundance of hornblende phenocrysts relative to the whole rock, in volume per cent. TR, trace (<0.5 volume percent) amounts AbdBt Microscope-based estimate of abundance of biotite phenocrysts relative to the whole rock, in volume percent. TR, trace (<0.5 volume percent) amounts AbdPx Microscope-based estimate of abundance of pyroxene phenocrysts relative to the whole rock, in volume percent. TR, trace (<0.5 volume percent) amounts Cpx_Opx Presence of clinopyroxene (C) and orthopyroxene (O); if both are present, then letter designation for dominant pyroxene is uppercase, and letter designation for subordinate pyroxene follows in lower case; if both are capi talized the two pyroxenes are approximately equally abundant AbdOl Microscope-based estimate of abundance of olivine phenocrysts relative to the whole rock, in volume percent. TR, trace (<0.5 volume percent) amounts AbdOpq Microscope-based estimate of abundance of opaque iron-titanium oxide minerals relative to the whole rock, in volume percent. TR, trace (<0.5 volume percent) amounts TotXls Microscope-based estimate of total phenocryst content relative to the whole rock, in volume percent. TR, trace (<0.5 volume percent) amounts ClrIndx Microscope-based estimate of color index (sum of the abundances of hornblende, biotite, pyroxene, olivine, and opaque iron-titanium oxide minerals) in volume percent. TR, trace (<0.5 volume percent) amounts AgsQtz Microscope-based estimate of average grain size of quartz phenocrysts, in millimeters AgsAlkFld Microscope-based estimate of average grain size of alkali feldspar phenocrysts, in millimeters AgsPl Microscope-based estimate of average grain size of plagioclase phenocrysts, in millimeters AgsHbl Microscope-based estimate of average grain size of hornblende phenocrysts, in millimeters AgsBt Microscope-based estimate of average grain size of biotite phenocrysts, in millimeters AgsPx Microscope-based estimate of average grain size of pyroxene phenocrysts, in millimeters AgsOl Microscope-based estimate of average grain size of olivine phenocrysts, in millimeters AgsOpq Microscope-based estimate of average grain size of opaque iron-titanium oxide crystals, in millimeters
Data Fields 9 Table 2. Definition and characterization of data fields included in appendix 2 (petrographic data).—Continued Field name Field description MgsQtz Microscope-based estimate of maximum grain size (length) of largest quartz phenocryst, in millimeters MgsAlkFld Microscope-based estimate of maximum grain size (length) of largest alkali feldspar phenocryst, in millimeters MgsPl Microscope-based estimate of maximum grain size (length) of largest plagioclase phenocryst, in millimeters MgsHbl Microscope-based estimate of maximum grain size (length) of largest hornblende phenocryst, in millimeters MgsBt Microscope-based estimate of maximum grain size (length) of largest biotite phenocryst, in millimeters MgsPx Microscope-based estimate of maximum grain size (length) of largest pyroxene phenocryst, in millimeters MgsOl Microscope-based estimate of maximum grain size (length) of largest olivine phenocryst, in millimeters MgsOpq Microscope-based estimate of maximum grain size (length) of largest opaque iron-titanium oxide crystal, in millimeters Texture Characteristic petrographic textures as determined by microscopic observation—abbreviations: A, aphyric; F, fragmental; FL, flow laminated; H, hyalophitic; I, intersertal; IG, intergranular; P, porphyritic; PT, pilotaxitic; T, trachytic; V, vesicular AccessMnrls Accessory minerals identified by microscopic observation; listed in order of decreasing abundance—abbrevia tions: Aln, allanite; Ap, apatite; Ttn, titanite; Zrn, zircon XlQtz Microscope-based estimate of crystallinity of quartz phenocrysts—abbreviations: A, anhedral; S, subhedral; E, euhedral. If more than one crystallinity type is present, the dominant form is listed first XlAlkFld Microscope-based estimate of crystallinity of alkali feldspar phenocrysts—abbreviations: A, anhedral; S, subse dral; E, euhedral. If more than one crystallinity type is present, the dominant form is listed first XlPl Microscope-based estimate of crystallinity of plagioclase phenocrysts—abbreviations: A, anhedral; S, subhedral; E, euhedral. If more than one crystallinity type is present, the dominant form is listed first XlHbl Microscope-based estimate of crystallinity of hornblende phenocrysts—abbreviations: A, anhedral; S, subhedral; E, euhedral. If more than one crystallinity type is present, the dominant form is listed first XlBt Microscope-based estimate of crystallinity of biotite phenocrysts—abbreviations: A, anhedral; S, subhedral; E, euhedral. If more than one crystallinity type is present, the dominant form is listed first XlPx Microscope-based estimate of crystallinity of pyroxene phenocrysts—abbreviations: A, anhedral; S, subhedral; E, euhedral. If more than one crystallinity type is present, the dominant form is listed first XlOl Microscope-based estimate of crystallinity of olivine phenocrysts—abbreviations: A, anhedral; S, subhedral; E, euhedral. If more than one crystallinity type is present, the dominant form is listed first XlOpq Microscope-based estimate of crystallinity of opaque iron-titanium oxide phenocrysts—abbreviations: A, anhe dral; S, subhedral; E, euhedral. If more than one crystallinity type is present, the dominant form is listed first Petrog_Com Groundmass () characteristics and any other noteworthy features; the degree to which hornblende (Hbl) and biotite (Bt) are oxidized is also noted HblClr Pleochroic colors of hornblende phenocrysts, if present AltExtnt Microscope-based estimate of the extent of alteration where 1 indicates a completely fresh sample and 5 indi cates a completely altered sample in which primary textures and minerals are not identifiable; intermediate values of 2 through 4 identify progressively more altered samples
10 Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada Table 3. Definition and characterization of data fields included in appendix 3 (geochemical data). Field name Field description Field_ID Field-assigned sample identifier; Field_ID entries link data for individual rows to the contents of particular rows in the other appendixes and, for U.S. Geological Survey samples, to the National Geochemical Database Strat_Name Stratigraphic unit name (Bonham and Garside, 1979; Ashley, 1974; 1979; 1990a); repeated in this appendix to enable data sorting by unit name SiO2_pct Silicon, as silicon dioxide, in weight percent; recalculated to 100 percent on a volatile-free basis TiO2_pct Titanium, as titanium dioxide, in weight percent; recalculated to 100 percent on a volatile-free basis Al2O3_pct Aluminum, as aluminum trioxide, in weight percent; recalculated to 100 percent on a volatile-free basis FeO_pct Total iron, as ferrous oxide, in weight percent; recalculated to 100 percent on a volatile-free basis MnO_pct Manganese, as manganese oxide, in weight percent; recalculated to 100 percent on a volatile-free basis MgO_pct Magnesium, as magnesium oxide, in weight percent; recalculated to 100 percent on a volatile-free basis CaO_pct Calcium, as calcium oxide, in weight percent; recalculated to 100 percent on a volatile-free basis Na2O_pct Sodium, as sodium oxide, in weight percent; recalculated to 100 percent on a volatile-free basis K2O_pct Potassium, as potassium oxide, in weight percent; recalculated to 100 percent on a volatile-free basis P2O5_pct Phosphorus, as phosphorus pentoxide, in weight percent; recalculated to 100 percent on a volatile-free basis LOI_pct Volatile content lost on ignition, in weight percent H2O+(b)_pct Structurally bound or essential water, in weight percent H2O-(m)_pct Nonessential moisture, in weight percent CO2_pct Carbon dioxide, in weight percent Fluoride, in weight percent Initial, prerecalculation sum of oxide abundances, in weight percent Volatile_pct Total volatile content, in weight percent; calculated as the sum of bound water, moisture, carbon dioxide, and fluorine or as the content lost on ignition Barium, in parts per million Beryllium, in parts per million Cesium, in parts per million Rubidium, in parts per million Strontium, in parts per million Yttrium, in parts per million Zirconium, in parts per million Hafnium, in parts per million Niobium, in parts per million Thorium, in parts per million Uranium, in parts per million Gallium, in parts per million Lanthanum, in parts per million
Data Fields 11 Table 3. Definition and characterization of data fields included in appendix 3 (geochemical data).—Continued Field name Field description Cerium, in parts per million Praseodymium, in parts per million Neodymium, in parts per million Samarium, in parts per million Europium, in parts per million Gadolinium, in parts per million Terbium, in parts per million Dysprosium, in parts per million Holmium, in parts per million Erbium, in parts per million Thulium, in parts per million Ytterbium, in parts per million Lutetium, in parts per million Silver, in parts per million Gold, in parts per million Cobalt, in parts per million Chromium, in parts per million Nickel, in parts per million Scandium, in parts per million Vanadium, in parts per million Copper, in parts per million Molybdenum, in parts per million Lead, in parts per million Zinc, in parts per million Tin, in parts per million Tungsten, in parts per million Tantalum, in parts per million Arsenic, in parts per million Antimony, in parts per million Boron, in parts per million chem_src Source of geochemical data: 1, U.S. Geological Survey, National Geochemical Database, 2013; 2, samples collected by Ashley, R.P., U.S. Geological Survey, data presented in this report; 3, samples collected by du Bray, E.A., U.S. Geological Survey, data presented in this report; 4, Ransome (1909); 5, Knopf (1918); 6, Bonham and Garside (1979); 7, samples collected by Vikre, P.G., U.S. Geological Survey, data presented in this report. For a few samples, data were culled from two or more sources; for example, major oxide data may have been compiled from one source and trace element data from another
12 Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada References Cited Albers, J.P., and Stewart, J.H., 1972, Geology and mineral deposits of Esmeralda County, Nevada: Nevada Bureau of Mines and Geology Bulletin 78, 80 p. Ashley, R.P., 1974, Goldfield mining district: Nevada Bureau of Mines and Geology Report 19, p. 49–66. Ashley, R.P., 1979, Relation between volcanism and ore deposition at Goldfield, Nevada: Nevada Bureau of Mines and Geology Report 33, p. 77–86. Ashley, R.P., 1990a, The Goldfield gold district, Esmeralda and Nye Counties, Nevada, in Shawe, D.R., and Ashley, R.P., eds., Epithermal gold deposits—Part 1: U.S. Geological Survey Bulletin 1857–H, p. H1–H7. Ashley, R.P., 1990b, The Tonopah precious-metal district, Esmeralda and Nye Counties, Nevada, in Shawe, D.R., and Ashley, R.P., eds., Epithermal gold deposits—Part 1: U.S. Geological Survey Bulletin 1857–H, p. H8–H13. Ashley, R.P., and Albers, J.P., 1975, Distribution of gold and other ore-related elements near ore bodies in the oxidized zone at Goldfield, Nevada: U.S. Geological Survey Professional Paper 843–A, 48 p. Ashley, R.P., and Silberman, M.L., 1976, Direct dating of mineralization at Goldfield, Nevada by potassium-argon and fission-track methods: Economic Geology, v. 71, p. 904–924. Barth A.P., and Wooden J.L., 2010, Coupled elemental and isotopic analyses of polygenetic zircons from granitic rocks by ion microprobe, with implications for melt evolution and the sources of granitic magmas: Chemical Geology, v. 277, p. 149–159. Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley, J.W., Mudil, R., Campbell, I.H., Korsch, R.J., Williams, I.S., and Foudoulis, C., 2004, Improved 206Pb/238U microprobe geochronology by the monitoring of a trace-element-related matrix effect; SHRIMP, ID-TIMS, ELA-ICPMS and oxygen isotope documentation for a series of zircon standards: Chemical Geology, v. 205, p. 115–140. [Also available at ://doi.org/10.1016/j. chemgeo.2004.01.003.] Blakely, R.J., John, D.A., Box, S.E., Berger, B.R., Fleck, R.J., Ashley, R.P., and Heinemeyer, G.R., 2007, Crustal controls on magmatic-hydrothermal systems; a geophysical comparison of White River, Washington, with Goldfield, Nevada: Geosphere, v. 3, p. 91–107. Bonham, H.F., Jr., and Garside, L.J., 1974, Tonopah mining district and vicinity: Nevada Bureau of Mines and Geology Report 19, p. 42–48. Bonham, H.F., Jr., and Garside, L.J., 1979, Geology of the Tonopah, Lone Mountain, Klondike, and northern Mud Lake quadrangles, Nevada: Nevada Bureau of Mines and Geology Bulletin 92, 142 p. Colgan, J.P., Egger, A.E., John, D.A., Cousens, B., Fleck, R.J., and Henry, C.D., 2011, Oligocene and Miocene arc volcanism in northeastern California: Evidence for post-Eocene segmentation of the subducting Farallon plate: Geosphere, v. 7, p. 733–755. Colgan, J.P., 2018, Zircon U-Pb age and trace element data for Cenozoic igneous rocks in the Tonopah area, Nevada: U.S. Geological Survey data release, ://doi.org/10.5066/ P9FVS0UK. Cosca, M.A., and Morgan, L.E., 2018, 40Ar/39Ar geochronology of the Tonopah, Divide, and Goldfield districts, Nevada: U.S. Geological Survey data release, accessed June 2, 2018 at ://doi.org/10.5066/F7833R8Z. Crafford, A.E.J., 2007, Geologic Map of Nevada: U.S. Geological Survey Data Series 249, 1 CD-ROM, 46 p., 1 plate. [Also available online at ://pubs.usgs.gov/ds/2007/249/.] Crafford, A.E.J., 2008, Paleozoic tectonic domains of Nevada: An interpretive discussion to accompany the geologic map of Nevada: Geosphere, v. 4, p. 260–291. du Bray, E.A., John, D.A., Vikre, P.G., Colgan, J.P., Cosca, M.A., Morgan, L.E., Fleck, R.J., Premo, W.R., HolmDenoma, C.S., and Heizler, M.T., 2019, Data to accompany U.S. Geological Survey Data Series 1099: Petrographic, geochemical, and geochronologic data for Cenozoic volcanic rocks of the Tonopah, Divide, and Goldfield mining districts, Nevada: U.S. Geological Survey data release, :// doi.org/10.5066/P9HZCRGV. du Bray, E.A., John, D.A., and Cousens, B.L., 2014, Petrologic, tectonic, and metallogenic evolution of the southern segment of the ancestral Cascades magmatic arc, California and Nevada: Geosphere, v. 10, p. 1–39, accessed December 15, 2014 at ://doi.org/10.1130/GES00944.1. Erdman, C.P., and Barabas, A.H., 1996, Precious metal mineralization at Gold Mountain, Tonopah Divide district, Esmeralda County, Nevada, in Coyner, A.R, and Fahey, P.L., eds., Geology and Ore Deposits of the American Cordillera Symposium Proceedings: Reno, Geological Society of Nevada, p. 329–351.
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14 Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada 14 Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada Steiger, R.H., and Jäger, E., 1977, Subcommission on geochronology—Convention on the use of decay constants in geo- and cosmochronology: Earth and Planetary Science Letters, v. 36, p. 359–362. Taggart, J.E., Jr., 2002, Analytical methods for chemical analysis of geologic and other materials: U.S. Geological Survey Open-File Report 02–0223, available online at ://pubs. usgs.gov/of/2002/ofr-02-0223/OFR-02-0223.pdf. Taylor, J.R., 1982, An introduction to error analysis—The study of uncertainties in physical measurements: Mill Valley, California, University Science Books, 270 p. Vikre, P.G., and Henry, C.D., 2011, Quartz-alunite alteration cells in the ancestral southern Cascades magmatic arc, in Steininger, R., and Pennell, B., eds., Great Basin evolution and metallogeny: Proceedings, Geological Society of Nevada, 2010 Symposium Reno, Nevada, p. 701–745. Williams, I.S., 1997, U-Th-Pb geochronology by ion microprobe: not just ages but histories: Society of Economic Geologists Reviews in Economic Geology, v. 7, p. 1–35.
Appendixes 15 Appendixes 1 through 10 are tables and can be accessed at ://doi.org/10.3133/ds1099 Appendix 1. Status and Treatment of Samples from the Tonopah, Divide, and Goldfield Mining Districts. Appendix 2. Petrographic Data for Samples from the Tonopah, Divide, and Goldfield Mining Districts. Appendix 3. Geochemical Data for Rock Samples from the Tonopah, Divide, and Goldfield Mining Districts. Appendix 4. 40Ar/39Ar Geochronologic Data for Samples from the Tonopah, Divide, and Goldfield Mining Districts Obtained in the U.S. Geological Survey 40Ar/39Ar Laboratory in Denver, Colorado. Appendix 5. Summary of New 40Ar/39Ar Age Determinations for Samples from the Tonopah, Divide, and Goldfield Mining Districts Obtained in the U.S. Geological Survey 40Ar/39Ar Laboratory in Denver, Colorado. Appendix 6. 40Ar/39Ar Geochronologic Data for Samples from the Goldfield Mining District Obtained in the New Mexico Geochronological Research Laboratory. Appendix 7. 40Ar/39Ar Geochronologic Data for Samples from the Goldfield Mining District Obtained in the U.S. Geological Survey 40Ar/39Ar Laboratory in Menlo Park, California. Appendix 8. Sensitive High Resolution Ion Microprobe (SHRIMP) Zircon U-Pb Geochronologic Data for Rock Samples from the Tonopah, Divide, and Goldfield Mining Districts. Appendix 9. Laser Ablation ICP-MS Zircon U-Pb Geochronologic Data for Rock Samples from the Tonopah, Divide, and Goldfield Mining Districts. Appendix 10. Results of Point Counts for Samples of the Fraction Tuff and Heller Tuff from the Tonopah and Divide Mining Districts.
Geology, Geophysics, and Geochemistry Science Center Publishing support provided by the Science Publishing Network, Denver and West Trenton Publishing Service Centers For more information concerning the research in this report, contact the Center Director, USGS Geology, Geophysics, and Geochemistry Science Center Box 25046, Mail Stop 973 Denver, CO 80225 (303) 236-1800 Or visit Geology, Geophysics, and Geochemistry Science Center website at ://www.usgs.gov/centers/
du Bray and others—Petrographic, Geochemical, and Geochronologic Data for Cenozoic Volcanic Rocks of the Mining Districts, Nevada—Data Series 1099 ISSN 2327-638X (online) ://doi.org/10.3133/ds1099