Open-File Report 88-271 This report is preliminary and has not been reviewed for conformity with ... more Open-File Report 88-271 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Use of trade names in this report is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. DESCRIP'i ON OF SAMPLES Yata Deposit C-01A Mineralized pyrite-bearing, carbonaceous shale of the middle Triassic Xinyuan Formation, host rock of the Yata deposit. Sample is cut by veins of realgar, quartz, and calcite. Sample is from dump of the 940-m (elevation) tunnel. C-OIB Unmineralized carbonaceous shale of the middle Triassic Xinyuan Formation from same hand specimen as sample C-01A. C-01C Duplicate of sample C-OIB. C-02A Mineralized carbonaceous shale of the middle Triassic Xinyuan Formation, host rock of the Yata deposit. Sample is cut by veins of realgar and quartz. Sample is from the dump of the 997-m (elevation) tunnel. C-03A Black carbonaceous shale of the Xinyuan Formation intimately associated with the ore zone. Sample contains some realgar and pyrite. Sample is from the 997-m tunnel. C-04A Black carbonaceous shale of the Xinyuan Formation collected about 100 m away from the main ore zone in the 670-m tunnel. C-05A Carbonaceous shale and carbonate at the base of the Xinyuan Formation. Sample colleced near the village of Yata, 4 km from the mine. Getang Deposit C-06A Brecciated carbonaceous shale from 29.8 to 31.0 m depth in a core of the Upper Permian Longtan Formation, host rock of the Getang Deposit. Assay of shale from this interval is 11 g gold/ton. C-07A Low-grade coal from 19.8 to 20.0 m in same core of the Longtan Formation as sample C-06A. C-08A Jasperoid (silicified limestone) with leached pyrite from about 100 m above the orebody at the top of Two-Dragon Mouth Hill. C-08B Duplicate of sample C-08A. C-09A Silicified, brecciated carbonate(?) rock from the discovery trench of the Getang deposit. Sample is from the ore zone. C-10A Low-grade coal from bed about one-meter thick in the ore zone. C-11A Organic-rich shale from bed about 4 m above the ore zone. Coaly shale appears to be at the same stratigraphic horizon as that sampled by C-10A but from across the valley. C-12A Coal bed in the Longtan Formation that is actively being mined for coal. Coal bed is about 50m above ore zone at the mine. C-13A Coal from bed about 200 m above the mineralized zone and 2 km from the ore deposit. Sanchahe Deposit C-14A Limonite-stained, silicified limestone of the Lower Triassic Yelang Formation, the host rock of the Sanchahe deposit. Mine assay of sample from the same trench as this sample was 12.2 g gold/ton. C-15A Coal seam in the upper part of the Longtan Formation. Sample is from a depth of 108 m in a drill-hole core. C-16A Light gray calcareous shale. Core sample from ore zone. 85.0 to 95.7 m depth. Assay from the same horizon was 6.23 g gold/ton. C-17A Limestone cut by calcite veinlets at a depth of 22 m in a core. ANALYTICAL METHODS The samples were air-dried and ground to pass a 100-mesh (149 ym) sieve. Concentrations of 33 major, minor, and trace elements (Al,
Surficial deposits unconformably overlying Tertiary bedrock include middle and late Pleistocene g... more Surficial deposits unconformably overlying Tertiary bedrock include middle and late Pleistocene glacial deposits and latest Pleistocene and Holocene eruptive products of Mount St. Helens volcano. Debris from the volcano makes up much of the valley fill along the South Fork Toutle River, and (unmapped) tephra (chiefly the C and J sets of Mullineaux, 1986) erupted from Mount St. Helens during the last 50,000 years forms a thin but widespread cover in the northern and eastern parts of the Elk Mountain quadrangle. The area of the quadrangle was little impacted by the May 18,1980 eruption of Mount St. Helens. During the early stages of that event, a large lahar was generated from pyroclastic surges on the west flank of the volcano. This lahar flowed down the South Fork Toutle River, partially burying older laharic and glacial deposits (Scott, 1988). Glacial deposits Drift in the Elk Mountain quadrangle is correlated with similar deposits near Mount Rainier that represent the last two or three major advances of alpine glaciers in the Cascade Range (Crandell and Miller, 1974). The youngest glacial deposits occupy the floors of deep U-shaped valleys in the North Fork Kalama River and Trouble Creek drainages, the bench above the east canyon wall of Trouble Creek, and the area below a cirque occupied by Coweeman Lake on the north side of Elk Mountain. These deposits exhibit well-preserved glacial morphology and contain clasts with weathering rinds much less than 1 mm thick; they are correlated with the Evans Creek Drift deposited during the Fraser glaciation, the last major glacial advance in the Washington Cascade Range (Crandell, 1987). The pair of weakly weathered moraines in the upper Coweeman River provide evidence for two glacial advances during Evans Creek time, possibly corresponding to those recorded by terrace deposits in the Cowlitz River described by Dethier (1988). Glaciers in the Elk Creek quadrangle during Evans Creek time were mostly restricted to the larger valleys that headed on the steep northern slopes of peaks higher than about 4,000 ft. Earlier in the Pleistocene, however, ice cover in this area was much more extensive, as indicated by widespread older deposits that are correlated with the Hayden Creek Drift on the basis of similar weathering characteristics (Crandell and Miller, 1974). They veneer areas of low relief in the northern two-thirds of the quadrangle and are present sporadically along the lower valley walls of the South Fork Toutle River. Dissected but recognizable moraines of Hayden Creek age are found in several areas. The terminus of a Hayden Creek-age glacier in the South Fork Toutle River is marked by a moraine at the mouth of Whitten Creek (Crandell, 1987). Outwash deposits with similar weathering
Plot of gold grade versus copper grade for different time periods, United Verde mine D9 04. Plot ... more Plot of gold grade versus copper grade for different time periods, United Verde mine D9 04. Plot of Ag:Au ratio versus tonnage for different time periods, United Verde rome DlO 05. Plot of gold grade and Ag:Au ratio versus Cu:Zn ratio for ore, 1944-1953, United Verde mine Dll 06. Map showing generalized geology of the Jerome region D12 07. Chemical classification diagram for volcanic units in the Jerome and Prescott areas Dl3 08. Map showing geology of the Unjted Verde mine area D14 09. Element-element plots for the 2400 level of the United Verde massive sulfide deposit D 17 010. Element-element plots in ore of the United Verde massive sulfide deposit D20 Dll. Index map of southeastern Alaska showing location of Juneau D28 012. Generalized geologic map of Juneau area showing locations of mines in the A-J and Treadwell systems D29 013. Cross section through the North ore body of the Alaska-Juneau mine D31 014. Diagram showing paragenesis of minerals in the Alaska-Juneau South ore body D32 TABLES Dl. United Verde mine production records D4 02. Average grade of ore types, United Verde massive sulfide deposit D16 03. Correlation coefficients data for metals in ore types from the Unjted Verde mine
Field spectral measurements-Unaltered rocks Altered rocks Image processing Image interpretation C... more Field spectral measurements-Unaltered rocks Altered rocks Image processing Image interpretation Color-ratio composite derived from MSDS data Comparison with other imagery-«-Summary and conclusions Acknowledgments 17 References cited USE OF IMAGING IN THE 0.46-2.36 ym SPECTRAL REGION FOR ALTERATION MAPPING IN THE CUPRITE MINING DISTRICT, NEVADA
The main problem in geochemical exploration for gold ore bodies in the 40 km hydro thermally alte... more The main problem in geochemical exploration for gold ore bodies in the 40 km hydro thermally altered area at Goldfield is to decide which of the many silicified ledges exposed are most likely to yield deposits with additional subsurface exploration. We conclude that the most efficient way to search for exploration targets is to collect rock samples from the ledges and analyze for the following elements in decreasing order of priority: gold, lead and silver, bismuth, and mercury. These elements form relict hypogene aureoles restricted to the ledges and are not appreciably redistributed during supergene leaching.
As the Nation's principal conservation agency, the Department of the Interior has responsibility ... more As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural and cultural resources. This includes fostering sound use of our land and water resources; protecting our fish, wildlife, and biological diversity; preserving the environmental and cultural values of our national parks and historical places; and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to ensure that their development is in the best interests of all our people by encouraging stewardship and citizen participation in their care. The Department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration.
The heart of the Goldfield mining district occupies 0.5 square mile within a 15-square-mile area ... more The heart of the Goldfield mining district occupies 0.5 square mile within a 15-square-mile area of hydrothermally altered Tertiary volcanic rocks. Most of the ore shoots were irregular bodies of epithermal bonanza ore within a few contiguous silicified zones enclosed in claybearing altered rocks. In 1966, 278 samples of argillized and silicified dacite were collected from excavations at the Combination and January mines, which once yielded gold in commercial quantities. Semiquantitative analyses show that gold, silver, lead, bismuth, mercury, and arsenic are notably enriched in rocks of the cuts. All these elements except lead and mercury formed conspicuous ore minerals. Geochemical maps and one geochemical profile across strike show that relatively high concentrations of all these elements are restricted to silicified zones. This low-tenor metallization dispersed through silicified zones does not extend into adjacent clay-bearing rocks. During oxidation, arsenic, copper, molybdenum, and zinc were leached from the .silicified zones and the ore bodies within them, but these metals did not form distinct supergene halos in the surrounding argillized rocks. From the semiquantitative data available, the average amount of gold in silicified vein material is between 2 and 4 parts per million. Geochemical sampling to detect relict hypogene dispersion patterns in Goldfield altered area, using oxidized rock samples, should be restricted to the silicified zones. If only a few samples are collected from each silicified.zone, analysis for lead, of all the elements tested besides gold, is most likely to detect significant gold metallization, even though lead was only a minor constituent oft~e or~s. Abundance of iron oxides is not a reliable guide to anomalous amounts of gold.
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey e... more This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Deposit geology These deposits include quartz and quartz-carbonate veins mined primarily for gold... more Deposit geology These deposits include quartz and quartz-carbonate veins mined primarily for gold. They are found in accreted terranes dominated by greenstone and slate sequences that have been metamorphosed to greenschist, or less commonly to amphibolite or granulite facies (Berger, 1986a; Goldfarb and others, 1995). These veins generally contain no more than a few percent sulfide minerals. Wall rocks, which in some deposits include disseminated ore bodies, contain abundant carbonate minerals, quartz, sericite, and sulfides. Mineralization is commonly associated with regional shear zones, which may include melange zones with varied lithologies and tectonically-emplaced ultramafic rocks and serpentinite. Deposits spatially associated with plutonic rocks tend to have more varied suites of metals, and are more likely to contain more silver and to yield copper, lead, and zinc as byproducts. Arsenic is the minor element most commonly enriched in alteration haloes. These deposits are als...
Background: A realistic estimation of the health risk of human exposure to solid-phase arsenic (A... more Background: A realistic estimation of the health risk of human exposure to solid-phase arsenic (As) derived from historic mining operations is a major challenge to redevelopment of California’s famed “Mother Lode ” region. Arsenic, a known carcinogen, occurs in multiple solid forms that vary in bioaccessibility. X-ray absorption finestructure spectroscopy (XAFS) was used to identify and quantify the forms of As in mine wastes and biogenic solids at the Lava Cap Mine Superfund (LCMS) site, a historic “Mother Lode ” gold mine. Principal component analysis (PCA) was used to assess variance within water chemistry, solids chemistry, and XAFS spectral datasets. Linear combination, least-squares fits constrained in part by PCA results were then used to quantify arsenic speciation in XAFS spectra of tailings and biogenic solids. Results: The highest dissolved arsenic concentrations were found in Lost Lake porewater and in a groundwaterfed pond in the tailings deposition area. Iron, dissolve...
The U S. Geological Survey has released this report in open files. Copies are available for consu... more The U S. Geological Survey has released this report in open files. Copies are available for consultation in the Geological Survey Libraries, 1033 GSA Building, Washington, D.C. 20242; Building 25, Federal Center, Denver, Colorado 802255 345 Middlefield Road, Menlo Park, California 94025; and 601 E. Cedar Avenue, Flaostaff, Arizona 86001, Public Inquiries Office, 8102 Federal Building, 125 State St-reet, Salt Lake City, Utah 8411. Sincerely yours,
Page 1. Economic Geology Vol. 78, 19813, pp. 7137-749 Airborne Biogeophysical Mapping of Hidden M... more Page 1. Economic Geology Vol. 78, 19813, pp. 7137-749 Airborne Biogeophysical Mapping of Hidden Mineral Deposits WILLIAM COLLINS, SHENG-HUEI CHANG Aidridge Laboratory of Applied Geophysics, Columbia University, New York, New York 10027 ...
In natural settings that exhibit chemical and hydrologic complexity, As concentration and speciat... more In natural settings that exhibit chemical and hydrologic complexity, As concentration and speciation depend on system characteristics that respond to seasonal events and/or anthropogenic influences. As arsenic-bearing minerals decompose, As may be introduced to aqueous solutions with potential for human exposure or ecological impacts. This transformation may be attenuated by sorption, or precipitation of other phases. Two examples illustrate how
Bl Character and setting Bl Identified mineral resources Bl Mineral resource potential Bl Introdu... more Bl Character and setting Bl Identified mineral resources Bl Mineral resource potential Bl Introduction B2 Location and physiography B3 Procedures and sources of data B3 Appraisal of identified resources B3 Assessment of mineral resource potential B4 Geology B4 Paleozoic and Mesozoic rocks B5 Tertiary rocks B6 Quaternary surficial deposits B6 Geochemistry B6 Methods B6 Results and interpretations B6 Geophysics B7 Gravity data B7 Aeromagnetic data B8 Radiometric data B8 Mineral resource potential B8 References cited B9 Appendixes Definition of levels of mineral resource potential and certainty of assessment B12 Resource/reserve classification B13 Geologic time chart B14 FIGURES 1. Index map showing location of the Sheep Mountain Wilderness Study Area, Baker County, Oregon B2 2. Map showing mineral resource potential and generalized geology of the Sheep Mountain Wilderness Study Area, Baker County, Oregon
The author has identified the following significant results. The reflectance spectra of most hydr... more The author has identified the following significant results. The reflectance spectra of most hydrothermally altered rocks were characterized by broad ferric iron absorption bands short of 1.1 microns and a sharper hydroxyl band near 2.2 microns; maximum reflectance occurred near 1.6 microns. Their features became more prominent as albedo increased. The MSS color ratio composite images were the most effective and practical means for detecting and mapping limonitic rocks in areas having less than about 50 percent desert brush cover and less than 25-35 percent coniferous tree cover. Limonitic altered and unaltered rocks could not be distinguished in MSS color ratio composite images.
Mineralogical differences between altered rocks and most unaltered rocks in south‐central Nevada ... more Mineralogical differences between altered rocks and most unaltered rocks in south‐central Nevada cause visible and near‐infrared (0.45 to 2.4 μm) spectral‐reflectance differences which can be used to discriminate them broad categories of rocks in multispectral images. The most important mineralogical differences are the increased abundance of goethite, hematite, and jarosite, and the presence of alunite, montmorillonite, and kaolinite in the altered rocks. Analysis of reflectance spectra recorded in the field showed that the altered rock spectra are characterized by broad absorption bands in the 0.45–0.50 μm and 0.85–0.95 μm regions which are due to electronic processes in the iron ions, and a band near 2.2 μm which is due to vibrational processes in the OH ions. These features are absent or weak in most of the unaltered rock spectra. Therefore, the shapes of the 0.45–2.4 μm spectra for these altered and unaltered rocks are conspicuously different. However, because of the wavelength...
Open-File Report 88-271 This report is preliminary and has not been reviewed for conformity with ... more Open-File Report 88-271 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards. Use of trade names in this report is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. DESCRIP'i ON OF SAMPLES Yata Deposit C-01A Mineralized pyrite-bearing, carbonaceous shale of the middle Triassic Xinyuan Formation, host rock of the Yata deposit. Sample is cut by veins of realgar, quartz, and calcite. Sample is from dump of the 940-m (elevation) tunnel. C-OIB Unmineralized carbonaceous shale of the middle Triassic Xinyuan Formation from same hand specimen as sample C-01A. C-01C Duplicate of sample C-OIB. C-02A Mineralized carbonaceous shale of the middle Triassic Xinyuan Formation, host rock of the Yata deposit. Sample is cut by veins of realgar and quartz. Sample is from the dump of the 997-m (elevation) tunnel. C-03A Black carbonaceous shale of the Xinyuan Formation intimately associated with the ore zone. Sample contains some realgar and pyrite. Sample is from the 997-m tunnel. C-04A Black carbonaceous shale of the Xinyuan Formation collected about 100 m away from the main ore zone in the 670-m tunnel. C-05A Carbonaceous shale and carbonate at the base of the Xinyuan Formation. Sample colleced near the village of Yata, 4 km from the mine. Getang Deposit C-06A Brecciated carbonaceous shale from 29.8 to 31.0 m depth in a core of the Upper Permian Longtan Formation, host rock of the Getang Deposit. Assay of shale from this interval is 11 g gold/ton. C-07A Low-grade coal from 19.8 to 20.0 m in same core of the Longtan Formation as sample C-06A. C-08A Jasperoid (silicified limestone) with leached pyrite from about 100 m above the orebody at the top of Two-Dragon Mouth Hill. C-08B Duplicate of sample C-08A. C-09A Silicified, brecciated carbonate(?) rock from the discovery trench of the Getang deposit. Sample is from the ore zone. C-10A Low-grade coal from bed about one-meter thick in the ore zone. C-11A Organic-rich shale from bed about 4 m above the ore zone. Coaly shale appears to be at the same stratigraphic horizon as that sampled by C-10A but from across the valley. C-12A Coal bed in the Longtan Formation that is actively being mined for coal. Coal bed is about 50m above ore zone at the mine. C-13A Coal from bed about 200 m above the mineralized zone and 2 km from the ore deposit. Sanchahe Deposit C-14A Limonite-stained, silicified limestone of the Lower Triassic Yelang Formation, the host rock of the Sanchahe deposit. Mine assay of sample from the same trench as this sample was 12.2 g gold/ton. C-15A Coal seam in the upper part of the Longtan Formation. Sample is from a depth of 108 m in a drill-hole core. C-16A Light gray calcareous shale. Core sample from ore zone. 85.0 to 95.7 m depth. Assay from the same horizon was 6.23 g gold/ton. C-17A Limestone cut by calcite veinlets at a depth of 22 m in a core. ANALYTICAL METHODS The samples were air-dried and ground to pass a 100-mesh (149 ym) sieve. Concentrations of 33 major, minor, and trace elements (Al,
Surficial deposits unconformably overlying Tertiary bedrock include middle and late Pleistocene g... more Surficial deposits unconformably overlying Tertiary bedrock include middle and late Pleistocene glacial deposits and latest Pleistocene and Holocene eruptive products of Mount St. Helens volcano. Debris from the volcano makes up much of the valley fill along the South Fork Toutle River, and (unmapped) tephra (chiefly the C and J sets of Mullineaux, 1986) erupted from Mount St. Helens during the last 50,000 years forms a thin but widespread cover in the northern and eastern parts of the Elk Mountain quadrangle. The area of the quadrangle was little impacted by the May 18,1980 eruption of Mount St. Helens. During the early stages of that event, a large lahar was generated from pyroclastic surges on the west flank of the volcano. This lahar flowed down the South Fork Toutle River, partially burying older laharic and glacial deposits (Scott, 1988). Glacial deposits Drift in the Elk Mountain quadrangle is correlated with similar deposits near Mount Rainier that represent the last two or three major advances of alpine glaciers in the Cascade Range (Crandell and Miller, 1974). The youngest glacial deposits occupy the floors of deep U-shaped valleys in the North Fork Kalama River and Trouble Creek drainages, the bench above the east canyon wall of Trouble Creek, and the area below a cirque occupied by Coweeman Lake on the north side of Elk Mountain. These deposits exhibit well-preserved glacial morphology and contain clasts with weathering rinds much less than 1 mm thick; they are correlated with the Evans Creek Drift deposited during the Fraser glaciation, the last major glacial advance in the Washington Cascade Range (Crandell, 1987). The pair of weakly weathered moraines in the upper Coweeman River provide evidence for two glacial advances during Evans Creek time, possibly corresponding to those recorded by terrace deposits in the Cowlitz River described by Dethier (1988). Glaciers in the Elk Creek quadrangle during Evans Creek time were mostly restricted to the larger valleys that headed on the steep northern slopes of peaks higher than about 4,000 ft. Earlier in the Pleistocene, however, ice cover in this area was much more extensive, as indicated by widespread older deposits that are correlated with the Hayden Creek Drift on the basis of similar weathering characteristics (Crandell and Miller, 1974). They veneer areas of low relief in the northern two-thirds of the quadrangle and are present sporadically along the lower valley walls of the South Fork Toutle River. Dissected but recognizable moraines of Hayden Creek age are found in several areas. The terminus of a Hayden Creek-age glacier in the South Fork Toutle River is marked by a moraine at the mouth of Whitten Creek (Crandell, 1987). Outwash deposits with similar weathering
Plot of gold grade versus copper grade for different time periods, United Verde mine D9 04. Plot ... more Plot of gold grade versus copper grade for different time periods, United Verde mine D9 04. Plot of Ag:Au ratio versus tonnage for different time periods, United Verde rome DlO 05. Plot of gold grade and Ag:Au ratio versus Cu:Zn ratio for ore, 1944-1953, United Verde mine Dll 06. Map showing generalized geology of the Jerome region D12 07. Chemical classification diagram for volcanic units in the Jerome and Prescott areas Dl3 08. Map showing geology of the Unjted Verde mine area D14 09. Element-element plots for the 2400 level of the United Verde massive sulfide deposit D 17 010. Element-element plots in ore of the United Verde massive sulfide deposit D20 Dll. Index map of southeastern Alaska showing location of Juneau D28 012. Generalized geologic map of Juneau area showing locations of mines in the A-J and Treadwell systems D29 013. Cross section through the North ore body of the Alaska-Juneau mine D31 014. Diagram showing paragenesis of minerals in the Alaska-Juneau South ore body D32 TABLES Dl. United Verde mine production records D4 02. Average grade of ore types, United Verde massive sulfide deposit D16 03. Correlation coefficients data for metals in ore types from the Unjted Verde mine
Field spectral measurements-Unaltered rocks Altered rocks Image processing Image interpretation C... more Field spectral measurements-Unaltered rocks Altered rocks Image processing Image interpretation Color-ratio composite derived from MSDS data Comparison with other imagery-«-Summary and conclusions Acknowledgments 17 References cited USE OF IMAGING IN THE 0.46-2.36 ym SPECTRAL REGION FOR ALTERATION MAPPING IN THE CUPRITE MINING DISTRICT, NEVADA
The main problem in geochemical exploration for gold ore bodies in the 40 km hydro thermally alte... more The main problem in geochemical exploration for gold ore bodies in the 40 km hydro thermally altered area at Goldfield is to decide which of the many silicified ledges exposed are most likely to yield deposits with additional subsurface exploration. We conclude that the most efficient way to search for exploration targets is to collect rock samples from the ledges and analyze for the following elements in decreasing order of priority: gold, lead and silver, bismuth, and mercury. These elements form relict hypogene aureoles restricted to the ledges and are not appreciably redistributed during supergene leaching.
As the Nation's principal conservation agency, the Department of the Interior has responsibility ... more As the Nation's principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural and cultural resources. This includes fostering sound use of our land and water resources; protecting our fish, wildlife, and biological diversity; preserving the environmental and cultural values of our national parks and historical places; and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to ensure that their development is in the best interests of all our people by encouraging stewardship and citizen participation in their care. The Department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration.
The heart of the Goldfield mining district occupies 0.5 square mile within a 15-square-mile area ... more The heart of the Goldfield mining district occupies 0.5 square mile within a 15-square-mile area of hydrothermally altered Tertiary volcanic rocks. Most of the ore shoots were irregular bodies of epithermal bonanza ore within a few contiguous silicified zones enclosed in claybearing altered rocks. In 1966, 278 samples of argillized and silicified dacite were collected from excavations at the Combination and January mines, which once yielded gold in commercial quantities. Semiquantitative analyses show that gold, silver, lead, bismuth, mercury, and arsenic are notably enriched in rocks of the cuts. All these elements except lead and mercury formed conspicuous ore minerals. Geochemical maps and one geochemical profile across strike show that relatively high concentrations of all these elements are restricted to silicified zones. This low-tenor metallization dispersed through silicified zones does not extend into adjacent clay-bearing rocks. During oxidation, arsenic, copper, molybdenum, and zinc were leached from the .silicified zones and the ore bodies within them, but these metals did not form distinct supergene halos in the surrounding argillized rocks. From the semiquantitative data available, the average amount of gold in silicified vein material is between 2 and 4 parts per million. Geochemical sampling to detect relict hypogene dispersion patterns in Goldfield altered area, using oxidized rock samples, should be restricted to the silicified zones. If only a few samples are collected from each silicified.zone, analysis for lead, of all the elements tested besides gold, is most likely to detect significant gold metallization, even though lead was only a minor constituent oft~e or~s. Abundance of iron oxides is not a reliable guide to anomalous amounts of gold.
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey e... more This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Deposit geology These deposits include quartz and quartz-carbonate veins mined primarily for gold... more Deposit geology These deposits include quartz and quartz-carbonate veins mined primarily for gold. They are found in accreted terranes dominated by greenstone and slate sequences that have been metamorphosed to greenschist, or less commonly to amphibolite or granulite facies (Berger, 1986a; Goldfarb and others, 1995). These veins generally contain no more than a few percent sulfide minerals. Wall rocks, which in some deposits include disseminated ore bodies, contain abundant carbonate minerals, quartz, sericite, and sulfides. Mineralization is commonly associated with regional shear zones, which may include melange zones with varied lithologies and tectonically-emplaced ultramafic rocks and serpentinite. Deposits spatially associated with plutonic rocks tend to have more varied suites of metals, and are more likely to contain more silver and to yield copper, lead, and zinc as byproducts. Arsenic is the minor element most commonly enriched in alteration haloes. These deposits are als...
Background: A realistic estimation of the health risk of human exposure to solid-phase arsenic (A... more Background: A realistic estimation of the health risk of human exposure to solid-phase arsenic (As) derived from historic mining operations is a major challenge to redevelopment of California’s famed “Mother Lode ” region. Arsenic, a known carcinogen, occurs in multiple solid forms that vary in bioaccessibility. X-ray absorption finestructure spectroscopy (XAFS) was used to identify and quantify the forms of As in mine wastes and biogenic solids at the Lava Cap Mine Superfund (LCMS) site, a historic “Mother Lode ” gold mine. Principal component analysis (PCA) was used to assess variance within water chemistry, solids chemistry, and XAFS spectral datasets. Linear combination, least-squares fits constrained in part by PCA results were then used to quantify arsenic speciation in XAFS spectra of tailings and biogenic solids. Results: The highest dissolved arsenic concentrations were found in Lost Lake porewater and in a groundwaterfed pond in the tailings deposition area. Iron, dissolve...
The U S. Geological Survey has released this report in open files. Copies are available for consu... more The U S. Geological Survey has released this report in open files. Copies are available for consultation in the Geological Survey Libraries, 1033 GSA Building, Washington, D.C. 20242; Building 25, Federal Center, Denver, Colorado 802255 345 Middlefield Road, Menlo Park, California 94025; and 601 E. Cedar Avenue, Flaostaff, Arizona 86001, Public Inquiries Office, 8102 Federal Building, 125 State St-reet, Salt Lake City, Utah 8411. Sincerely yours,
Page 1. Economic Geology Vol. 78, 19813, pp. 7137-749 Airborne Biogeophysical Mapping of Hidden M... more Page 1. Economic Geology Vol. 78, 19813, pp. 7137-749 Airborne Biogeophysical Mapping of Hidden Mineral Deposits WILLIAM COLLINS, SHENG-HUEI CHANG Aidridge Laboratory of Applied Geophysics, Columbia University, New York, New York 10027 ...
In natural settings that exhibit chemical and hydrologic complexity, As concentration and speciat... more In natural settings that exhibit chemical and hydrologic complexity, As concentration and speciation depend on system characteristics that respond to seasonal events and/or anthropogenic influences. As arsenic-bearing minerals decompose, As may be introduced to aqueous solutions with potential for human exposure or ecological impacts. This transformation may be attenuated by sorption, or precipitation of other phases. Two examples illustrate how
Bl Character and setting Bl Identified mineral resources Bl Mineral resource potential Bl Introdu... more Bl Character and setting Bl Identified mineral resources Bl Mineral resource potential Bl Introduction B2 Location and physiography B3 Procedures and sources of data B3 Appraisal of identified resources B3 Assessment of mineral resource potential B4 Geology B4 Paleozoic and Mesozoic rocks B5 Tertiary rocks B6 Quaternary surficial deposits B6 Geochemistry B6 Methods B6 Results and interpretations B6 Geophysics B7 Gravity data B7 Aeromagnetic data B8 Radiometric data B8 Mineral resource potential B8 References cited B9 Appendixes Definition of levels of mineral resource potential and certainty of assessment B12 Resource/reserve classification B13 Geologic time chart B14 FIGURES 1. Index map showing location of the Sheep Mountain Wilderness Study Area, Baker County, Oregon B2 2. Map showing mineral resource potential and generalized geology of the Sheep Mountain Wilderness Study Area, Baker County, Oregon
The author has identified the following significant results. The reflectance spectra of most hydr... more The author has identified the following significant results. The reflectance spectra of most hydrothermally altered rocks were characterized by broad ferric iron absorption bands short of 1.1 microns and a sharper hydroxyl band near 2.2 microns; maximum reflectance occurred near 1.6 microns. Their features became more prominent as albedo increased. The MSS color ratio composite images were the most effective and practical means for detecting and mapping limonitic rocks in areas having less than about 50 percent desert brush cover and less than 25-35 percent coniferous tree cover. Limonitic altered and unaltered rocks could not be distinguished in MSS color ratio composite images.
Mineralogical differences between altered rocks and most unaltered rocks in south‐central Nevada ... more Mineralogical differences between altered rocks and most unaltered rocks in south‐central Nevada cause visible and near‐infrared (0.45 to 2.4 μm) spectral‐reflectance differences which can be used to discriminate them broad categories of rocks in multispectral images. The most important mineralogical differences are the increased abundance of goethite, hematite, and jarosite, and the presence of alunite, montmorillonite, and kaolinite in the altered rocks. Analysis of reflectance spectra recorded in the field showed that the altered rock spectra are characterized by broad absorption bands in the 0.45–0.50 μm and 0.85–0.95 μm regions which are due to electronic processes in the iron ions, and a band near 2.2 μm which is due to vibrational processes in the OH ions. These features are absent or weak in most of the unaltered rock spectra. Therefore, the shapes of the 0.45–2.4 μm spectra for these altered and unaltered rocks are conspicuously different. However, because of the wavelength...
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Papers by Roger Ashley