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At least 1,603 records · Page 89Linked to original sources

USGS1982

Geologic report and recommendations for the cobalt mission to Morocco sponsored by The Trade and Development Program of the International Development Cooperation Agency

A mission sponsored by the Trade and Development Program (TDP) of the International Development Cooperation Agency (IDCA) went to Morocco to evaluate the possibility of finding additional sources of cobalt in that country, as well as other types of mineralization. Information obtained during this trip shows Morocco to be a country for which much geologic information is available and in which there are many favorable target areas for future exploration. Work in the Bou Azzer district (Morocco's principal cobalt district) shows that much excellent geologic work has been done in searching for additional deposits. However, a number of useful approaches to locate cobalt have not been tried, and their use might be successful. The potential for undiscovered deposits in the Bou Azzer region seems very high. The cobalt mineralization in the Siroua uplift is different from that in the Bou Azzer district. However, geologic similarities between the two areas suggest that a genetic link may exist between the two types of mineralization. This further indicates that cobalt deposits of the Bou Azzer types might be present in the Siroua region. Examination of the Bleida copper mine shows it to be a well-exposed volcanic hosted stratabound copper deposit. Large unexplored areas containing similar rocks occur near this deposit and may contain as yet undiscovered copper mineralization.

Open-File Report↗

USGS2012

Analyzing legacy U.S. Geological Survey geochemical databases using GIS: applications for a national mineral resource assessment

This report emphasizes geographic information system analysis and the display of data stored in the legacy U.S. Geological Survey National Geochemical Database for use in mineral resource investigations. Geochemical analyses of soils, stream sediments, and rocks that are archived in the National Geochemical Database provide an extensive data source for investigating geochemical anomalies. A study area in the Egan Range of east-central Nevada was used to develop a geographic information system analysis methodology for two different geochemical datasets involving detailed (Bureau of Land Management Wilderness) and reconnaissance-scale (National Uranium Resource Evaluation) investigations. ArcGIS was used to analyze and thematically map geochemical information at point locations. Watershed-boundary datasets served as a geographic reference to relate potentially anomalous sample sites with hydrologic unit codes at varying scales. The National Hydrography Dataset was analyzed with Hydrography Event Management and ArcGIS Utility Network Analyst tools to delineate potential sediment-sample provenance along a stream network. These tools can be used to track potential upstream-sediment-contributing areas to a sample site. This methodology identifies geochemically anomalous sample sites, watersheds, and streams that could help focus mineral resource investigations in the field.

Egan Range↗

USGS1990

Metamorphism in the Adirondacks: II. The role of fluids

Quantitative estimates of metamorphic fluid speciation, stable isotopic analyses, and studies of fluid inclusions all document the local complexity of fluids in the deep crustal rocks exposed in the Adirondack Mountains, NY. Estimates of the activity of H 2 O in the granulite facies are substantially lower than in the amphibolite facies gneisses. The onset of low water activities in semi-pelitic gneisses generally correlates with migmatitic textures in the uppermost amphibolite facies, suggesting that partial melts absorbed H 2 O at the peak of metamorphism. In granulite facies marbles and calc-silicates, conditions varied from extremely undersaturated in H 2 O-CO 2 fluid to fluid saturated, and α H2O and α CO2 show sharp gradients within single outcrops. Low values of f O2 and f H2O , or of f CO2 , and f H2O indicate fluid-absent conditions for some orthogneisses and marbles, which are inferred to have been ‘dry’ rocks before and during granulite facies recrystallization. Wollastonite is preserved from early contact metamorphism and serves as an index mineral for fluid-absent conditions in granulites where α H2O is low. Values of f O2 range from near the hematite + magnetite buffer in metamorphosed iron formation to substantially below the quartz + magnetite + fayalite buffer in some orthogneisses. The anorthosite suite is more oxidized than some associated granitic gneisses. Halogens (F and Cl) substitute extensively for OH in micas and amphiboles, extending their stability, although F 2 , Cl 2 , HCl, and HF are minor components in any fluid. Oxybiotite-type exchanges involving O for OH are also important, extending the stability of biotite. Stable isotopic ratios of O and C demonstrate that premetamorphic whole-rock compositions are commonly preserved whereas mineral compositions generally reflect equilibration at the peak of metamorphism. The Marcy Anorthosite Massif was intruded as a high δ 18 O magma. The combination of mineral equilibria, stable isotope data, and fluid inclusions is used to identify and to distinguish among pre-orogenic contact metamorphic/hydrothermal events, peak metamorphic events, and retrograde/postmetamorphic events. Polymetamorphism is documented at skarn zones adjacent to anorthosite, where large volumes of hydrothermal fluid were channeled during early, shallow contact metamorphism and where conditions were fluid poor during subsequent regional metamorphism. Peak metamorphic events are inferred to have been caused primarily by magmatic processes of intrusion and anatexis. Partial melting has caused low values of α H2O in many rocks, but in other cases low values of α H2O are recorded in orthogneisses derived from H 2 O-poor magmas. Isotopic studies show that maximum fluid/rock ratios were <0·l and possibly 0·0 for infiltrating fluids at the peak of metamorphism in many localities. No evidence of pervasive, regional infiltration by a fluid at the peak of metamorphism has been substantiated in the Adirondacks. Fluid inclusions containing high-density CO 2 or CO 2 + H 2 O represent conditions from after the peak of metamorphism and document isobaric cooling, in agreement with estimates from garnet zoning. Fine-scale retrograde veins are common and are associated with high-density CO 2 -rich fluid inclusions.

New York↗

USGS1987

Mineral Resources of the Antelope Wilderness Study Area, Nye County, Nevada

At the request of the U.S. Bureau of land Management, 83,100 acres of the Antelope Wilderness Study Area (NV-4)60-231/241) was studied. In this report the studied area is called the 'wilderness study area', or simply the 'study area.' No identified mineral or energy resources occur within the study area. The southern part of the area has moderate mineral resource potential for undiscovered gold and silver, and the Woodruff Formation in the southern part of the area has high resource potential for undiscovered vanadium, zinc, selenium, molybdenum, and silver (fig. 1). This assessment is based on field geochemical studies in 1984 and 1985 by the U.S. Bureau of Mines and field geochemical studies and geologic mapping by the U.S. Geological Survey in 1984 and 1985. The remainder of the study area has low resource potential for undiscovered gold, silver, lead, zinc, manganese, tin, and molybdenum. The study area also has low resource potential for undiscovered oil and gas resources. The Antelope Wilderness Study Area is about midway between Tonopah and Eureka, Nev., in the northern Hot Creek Range and southern Antelope Range of central Nevada. It is accessible by unimproved dirt roads extending 20 mi (miles) north from U.S. Highway 6 and 40 mi south from U.S. Highway 50 (fig. 2). Most of the study area consists of rugged mountainous terrain having approximately 2,600 ft (feet) of relief. The mountain range is a block tilted gently to the east and bounded on both sides by normal faults that dip steeply to moderately west and have major displacements. Most of the study area is underlain by a thick sequence of Tertiary volcanic rocks that predominantly consist of silicic ash-flow tuff, the Windous Butte Formation. Paleozoic and lower Mesozoic (see geologic time chart in appendix) marine sediments occur along the southern margin of the study area, and lower Paleozoic rocks are exposed in the northeast corner. The areas of exposed Paleozoic-Mesozoic rocks along the southern margin of the study area have moderate mineral resource potential for gold and silver in sediment-hosted, disseminated, epithermal (low-temperature) gold-silver deposits (fig. 1). These rocks consist of folded and thrust-faulted, fine-grained clastic sediments and limestone and dolomite that locally have been brecciated and hydrothermally altered. The alteration (locally, strong silicification) and geochemical associations of these rocks indicate a favorable environment for such deposits. Exploration for disseminated gold deposits in the same geologic environment is currently being conducted just south of the study area. The remainder of the study area has low resource potential for epithermal gold and silver vein deposits in the Tertiary volcanic rocks. The Cenozoic sedimentary basins adjacent to the fault-bounded mountain block have moderate potential for petroleum resources; the study area itself has low potential for petroleum resources.

Bulletin↗

USGS1982

A topology of mineralization and its meaning for prospecting

Epigenetic mineral deposits are universal members of an orderly spatial and temporal arrangement of igneous rocks, endomorphic rocks, and hydrothermally altered rocks. The association and sequence of these rocks is invariant whereas the metric relations and configurations of the properties of these rocks are unlimited in variety. This characterization satisfies the doctrines of topology. Metric relations are statistical, and their modes are among the better guides to optimal areas for exploration. Metric configurations are graphically irregular and unpredictable mathematical surfaces like mountain topography. Each mineral edifice must be mapped to locate its mineral deposits. All measurements and observations are only positive or neutral for the occurrence of a mineral deposit. Effective prospecting is based on an increasing density of positive data with proximity to the mineral deposit. This means sampling for maximal numbers of positive data, pragmatically the highest ore-element assays at each site, by selecting rock showing maximal development of lode attributes.

Book chapter↗

USGS1980

A topology of mineralization and its meaning for prospecting

Epigenetic mineral deposits are universal members of an orderly spatial-temporal arrangement of igneous rocks, endomorphic rocks, and hydrothermally altered rocks. The association and sequence of these rocks is invariant whereas the metric relations and configurations of the properties of these rocks are unlimited in variety. This characterization satisfies the doctrines of topology. Metric relations are statistical, and their modes are among the better guides to optimal areas for exploration. Metric configurations are graphically irregular and unpredictable mathematical surfaces like mountain topography. Each mineral edifice must be mapped to locate its mineral deposits. All measurements and observations are only positive or neutral for the occurrence of a mineral deposit. Effective prospecting is based on an increasing density of positive data with proximity to the mineral deposit. This means sampling for maximal numbers of positive data, pragmatically the highest ore-element assays at each site, by selecting rock showing maximal development of lode attributes.

Open-File Report↗

USGS1998

Exploring caves: teaching packet for grades K-3

"Exploring Caves" is an interdisciplinary set of materials on caves for grades K-3. Caves entail at least five scientific disciplines: earth science, hydrology, mapping, biology, and anthropology. Each of these disciplines involves a unique content area as well as the development of particular intellectual skills. This unit aims at helping teachers to sort and organize the most important ideas in this rich scientific area. Detailed lesson plans serve as ways to pass these ideas on to very young students. Most American caves are big holes that form in limestone rock. The holes begin as cracks in limestone. The cracks get bigger and bigger. They grow into underground streams, rivers, and even lakes. When water drains away, the waterways turn into open cave tunnels, passages, and caverns. It takes 10,000 to 100,000 years to form a cave big enough for people to move around inside. Water drips constantly in caves. The drips dissolve limestone minerals in one part of the cave. As water dries out, the minerals build up in other places. In this way, beautiful cave rock formations and crystals grow over thousands of years. These rock formations change dark limestone caves into hidden fantasy lands.

General Information Product↗

USGS1992

Bedrock geology and mineral resources of the Knoxville 1° x 2° quadrangle, Tennessee, North Carolina, and South Carolina

The Knoxville 1° x 2° quadrangle spans the Southern Blue Ridge physiographic province at its widest point from eastern Tennessee across western North Carolina to the northwest corner of South Carolina. The quadrangle also contains small parts of the Valley and Ridge province in Tennessee and the Piedmont province in North and South Carolina. Bedrock in the Valley and Ridge consists of unmetamorphosed, folded and thrust-faulted Paleozoic miogeoclinal sedimentary rocks ranging in age from Cambrian to Mississippian. The Blue Ridge is a complex of stacked thrust sheets divided into three parts: (1) a west flank underlain by rocks of the Late Proterozoic and Early Cambrian Chilhowee Group and slightly metamorphosed Late Proterozoic Ocoee Supergroup west of the Greenbrier fault; (2) a central part containing crystalline basement of Middle Proterozoic age (Grenville), Ocoee Supergroup rocks east of the Greenbrier fault, and rocks of the Murphy belt; and (3) an east flank containing the Helen, Tallulah Falls, and Richard Russell thrust sheets and the amphibolitic basement complex. All of the east flank thrust sheets contain polydeformed and metamorphosed sedimentary and igneous rocks of mostly Proterozoic age. The Blue Ridge is separated by the Brevard fault zone from a large area of rocks of the Inner Piedmont to the east, which contains the Six Mile thrust sheet and the ChaugaWalhalla thrust complex. All of these rocks are also polydeformed and metamorphosed sedimentary and igneous rocks. The Inner Piedmont rocks in this area occupy both the Piedmont and part of the Blue Ridge physiographic provinces. The intensity of deformation and metamorphism increases from west to east in the Blue Ridge. The west flank is mostly chlorite grade or relatively unmetamorphosed, and the central part of the Blue Ridge is mostly staurolite, garnet, or biotite grade, although sillimanite grade rocks occur along the eastern part of the central Blue Ridge in the vicinity of the leading edge of the Hayesville fault. The east flank of the Blue Ridge and much of the Inner Piedmont are at kyanite or sillimanite grade of regional metamorphism except for a zone of retrograde rocks in the Brevard fault zone and a small area of biotite-grade rocks in the extreme southwest part of the Grandfather Mountain window in the northeast corner of the quadrangle. The major mineral resources in the Knoxville 1° x 2° quadrangle are construction materials and a variety of industrial minerals mostly related to either granite and pegmatite or ultramafic rocks. Past production in the quadrangle of metals, which are of secondary importance relative to construction materials and industrial minerals, include copper in massive sulfides of the Besshi type, gold-bearing quartz veins, and residual iron and manganese deposits. Resources are discussed in relation to the Valley and Ridge, Blue Ridge, and Piedmont provinces. The following resources are the most important: A. Construction materials: Dimension stone of the Tennessee marble district in the Valley and Ridge. Limestone and dolomite of the Valley and Ridge. Sand and gravel and crushed stone, widespread throughout the quadrangle. B. Industrial minerals: Feldspar, flake mica, and quartz produced by flotation methods from the Spruce Pine Alaskite (muscovite granodiorite) in the east flank of the Blue Ridge. The district produces about half of the U.S. feldspar and significant amounts of the U.S. flake mica. Olivine produced from alpine-type dunite bodies in the east flank of the Blue Ridge. Talc and marble from the Murphy belt in the central part of the Blue Ridge. Vermiculite produced from a large deposit near Tigerville, S.C., in the Inner Piedmont. Deposit worked out and mine backfilled. Smaller deposits associated with ultramafic rocks in the east flank of the Blue Ridge are now uneconomic and have not been worked in the past 20 years. C. Metals: Copper in three deposits, the Fontana and Hazel Creek mines in the Great Smoky Mountains National Park in the Central Blue Ridge, and the Cullowhee mine in the east flank of the Blue Ridge. D. Organic fuels: The rocks of the quadrangle contain no coal and probably lie outside the maximum range in thermal maturity permitting the survival of oil. The rocks in the Valley and Ridge and for a short distance eastward below the west flank of the Blue Ridge probably lie within a zone of thermal maturity permitting the survival of natural gas. Consequently the western part of the quadrangle is an area of high risk for hydrocarbon exploration. No exploration drilling has been done in this belt.

North Carolina, South Carolina, Tennessee↗

USGS2004

Bedrock geology and mineral resources of the Knoxville 1° x 2° quadrangle, Tennessee, North Carolina, and South Carolina

The Knoxville 1°x 2° quadrangle spans the Southern Blue Ridge physiographic province at its widest point from eastern Tennessee across western North Carolina to the northwest corner of South Carolina. The quadrangle also contains small parts of the Valley and Ridge province in Tennessee and the Piedmont province in North and South Carolina. Bedrock in the Valley and Ridge consists of unmetamorphosed, folded and thrust-faulted Paleozoic miogeoclinal sedimentary rocks ranging in age from Cambrian to Mississippian. The Blue Ridge is a complex of stacked thrust sheets divided into three parts: (1) a west flank underlain by rocks of the Late Proterozoic and Early Cambrian Chilhowee Group and slightly metamorphosed Late Proterozoic Ocoee Supergroup west of the Greenbrier fault; (2) a central part containing crystalline basement of Middle Proterozoic age (Grenville), Ocoee Supergroup rocks east of the Greenbrier fault, and rocks of the Murphy belt; and (3) an east flank containing the Helen, Tallulah Falls, and Richard Russell thrust sheets and the amphibolitic basement complex. All of the east flank thrust sheets contain polydeformed and metamorphosed sedimentary and igneous rocks of mostly Proterozoic age. The Blue Ridge is separated by the Brevard fault zone from a large area of rocks of the Inner Piedmont to the east, which contains the Six Mile thrust sheet and the ChaugaWalhalla thrust complex. All of these rocks are also polydeformed and metamorphosed sedimentary and igneous rocks. The Inner Piedmont rocks in this area occupy both the Piedmont and part of the Blue Ridge physiographic provinces. The intensity of deformation and metamorphism increases from west to east in the Blue Ridge. The west flank is mostly chlorite grade or relatively unmetamorphosed, and the central part of the Blue Ridge is mostly staurolite, garnet, or biotite grade, although sillimanite grade rocks occur along the eastern part of the central Blue Ridge in the vicinity of the leading edge of the Hayesvil Ie fault. The east flank of the Blue Ridge and much of the Inner Piedmont are at kyanite or silli manite grade of Manuscript approved for publication February 22, 1991. regional metamorphism except for a zone of retrograde rocks in the Brevard fault zone and a small area of biotite-grade rocks in the extreme southwest part of the Grandfather Mountain window in the northeast corner of the quadrangle. The major mineral resources in the Knoxville 1°x2° quadrangle are construction materials and a variety of industrial minerals mostly related to either granite and pegmatite or ultramafic rocks. Past production in the quadrangle of metals, which are of secondary importance relative to construction materials and industrial minerals, include copper in massive sulfides of the Besshi type, gold-bearing quartz veins, and residual iron and manganese deposits. Resources are discussed in relation to the Valley and Ridge, Blue Ridge, and Piedmont provinces. The following resources are the most important: A. Construction materials: Dimension stone of the Tennessee marble district in the Valley and Ridge. Limestone and dolomite of the Valley and Ridge. Sand and gravel and crushed stone, widespread throughout the quadrangle. B. Industrial minerals: Feldspar, flake mica, and quartz produced by flotation methods from the Spruce Pine Alaskite (muscovite granodiorite) in the east flank of the Blue Ridge. The district produces about half of the U.S. feldspar and significant amounts of the U.S. flake mica. Olivine produced from alpine-type dunite bodies in the east flank of the Blue Ridge. Talc and marble from the Murphy belt in the central part of the Blue Ridge, Vermiculite produced from a large deposit near Tigerville, S.C-, in the Inner Piedmont. Deposit worked out and mine backfilled. Smaller deposits associated with ultramafic rocks in the east flank of the Blue Ridge are now uneconomic and have not been worked in the past 20 years. C. Metals: Copper in three deposits, the Fontana and Hazel Creek mines in the Great Smoky Mountains Abstract Figure 1. Location of the Knoxville 1ºx2º quadrangle, with state and county boundaries National Park in the Central Blue Ridge, and the Cullowhee mine in the east flank of the Blue Ridge. D. Organic fuels: The rocks of the quadrangle contain no coal and probably lie outside the maximum range in thermal maturity permitting the survival of oil. The rocks in the Valley and Ridge and for a short distance eastward below the west flank of the Blue Ridge probably lie within a zone of thermal maturity permitting the survival of natural gas. Consequently the western part of the quadrangle is an area of high risk for hydrocarbon exploration. No exploration drilling has been done in this belt.

North Carolina, South Carolina, Tennessee↗

USGS2014

Database for the geologic map of upper Eocene to Holocene volcanic and related rocks in the Cascade Range, Washington

This geospatial database for a geologic map of the Cascades Range in Washington state is one of a series of maps that shows Cascade Range geology by fitting published and unpublished mapping into a province-wide scheme of lithostratigraphic units. Geologic maps of the Eocene to Holocene Cascade Range in California and Oregon complete the series, providing a comprehensive geologic map of the entire Cascade Range that incorporates modern field studies and that has a unified and internally consistent explanantion. The complete series will be useful for regional studies of volcanic hazards, volcanology, and tectonics. Originally a project supported by the Geothermal Research Program of the U.S. Geological Survey, the maps emphasize Quaternary volcanic rocks, because large igneous-related hydrothermal systems that have high temperatures are associated with Quaternary volcanic fields. Rocks older than a few million years are also included on the maps as they help to unravel geologic puzzles of the present-day Cascade Range. The deeply eroded older volcanoes found in the Western Cascades physiographic subprovince are analogues of today's snow-covered shield volcanoes and stratovolcanoes. The fossil hydrothermal systems of the Eocene to Pliocene vents now exposed provide clues to processes active today beneath the Pleistocene and Holocene volcanic peaks along the present-day crest of the Cascade Range. Study of these older rocks can aid in developing models of geothermal systems. These rocks also give insight into the origins of volcanic-hosted mineral deposits and even to future volcanic hazards. This digital database contains information used to produce the geologic map published as Sheet 1 in U.S. Geological Survey Miscellaneous Investigations Series Map I-2005. (Sheet 2 of Map I-2005 shows sources of geologic data used in the compilation and is available separately). Sheet 1 of Map I-2005 shows the distribution and relations of volcanic and related rock units in the Cascade Range of Washington at a scale of 1:500,000. This digital release is produced from stable materials originally compiled at 1:250,000 scale that were used to publish Sheet 1. The database therefore contains more detailed geologic information than is portrayed on Sheet 1. This is most noticeable in the database as expanded polygons of surficial units and the presence of additional strands of concealed faults. No stable compilation materials exist for Sheet 1 at 1:500,000 scale. The main component of this digital release is a spatial database prepared using geographic information systems (GIS) applications. This release also contains links to files to view or print the map sheet, main report text, and accompanying mapping reference sheet from Map I-2005. For more information on volcanoes in the Cascade Range in Washington, Oregon, or California, please refer to the U.S. Geological Survey Volcano Hazards Program website.

Washington↗

USGS1976

Mineral deposits and occurrences in the McCarthy Quadrangle, Alaska

The McCarthy quadrangle contains numerous and diverse mineral deposits in various geologic settings. Copper is the dominant mineral commodity, both historically and in terms of potential future production. Gold and silver are the only other metals that have been produced. The metalliferous deposits are concentrated in a northwest-trending belt along the southern flank of the Wrangell Mountains, and, to a lesser extent, in a similar belt along the northeast flank of the range. Both belts have upper Paleozoic (Skolai Group) basements, abundant Mesozoic rocks, and some Tertiary intrusive rocks. They are marked by numerous faults, mainly northwest-striking. Mineral deposits are uncommon elsewhere in the quadrangle, especially in large tracks underlain by Wrangell Lava and in smaller areas underlain by the Kaskawulsh Group of Kindle (1953). Both the Wrangell Lava and the Kaskawulsh underlie rugged mountainous regions with extensive snow and ice cover, and could conceivably contain undetected concealed deposits. The metallic, nonmetallic, and energy resources of the quadrangle are described sequentially. Copper, gold, and silver, because of their importance, are described early in the section on metal commodities; descriptions of the other metals follows in alphabetic sequence. Locations of the deposits and relative supplementary data for individual deposits are given in the accompanying map and table.

Alaska↗

USGS2000

Ore-fluid evolution at the Getchell Carlin-type gold deposit, Nevada, USA

Minerals and fluid-inclusion populations were examined using petrography, microthermometry, quadrupole mass-spectrometer gas analyses and stable-isotope studies to characterize fluids responsible for gold mineralization at the Getchell Carlin-type gold deposit. The gold-ore assemblage at Getchell is superimposed on quartz-pyrite vein mineralization associated with a Late-Cretaceous granodiorite stock that intruded Lower-Paleozoic sedimentary rocks. The ore assemblage, of mid-Tertiary age, consists of disseminated arsenian pyrite that contains submicrometer gold, jasperoid quartz, and later fluorite and orpiment that fill fractures and vugs. Late ore-stage realgar and calcite enclose ore-stage minerals. Pre-ore quartz trapped fluids with a wide range of salinities (1 to 21 wt.% NaCl equivalent), gas compositions (H 2 O, CO 2 , and CH 4 ), and temperatures (120 to > 360°C). Oxygen- and hydrogen-isotope ratios indicate that pre-ore fluids likely had a magmatic source, and were associated with intrusion of the granodiorite stock and related dikes. Ore-stage jasperoid contains moderate salinity, aqueous fluid inclusions trapped at 180 to 220°C. Ore fluids contain minor CO 2 and trace H 2 S that allowed the fluid to react with limestone host rocks and transport gold, respectively. Aqueous inclusions in fluorite indicate that fluid temperatures declined to ∼ 175°C by the end of ore-stage mineralization. As the hydrothermal system collapsed, fluid temperatures declined to 155 to 115°C and realgar and calcite precipitated. Inclusion fluids in ore-stage minerals have high δD H2O and δ 18 O H2O values that indicate that the fluid had a deep source, and had a metamorphic or magmatic origin, or both. Late ore-stage fluids extend to lower δ H2O values, and have a wider range of δ 18 O H2O values suggesting dilution by variably exchanged meteoric waters. Results show that deeply sourced ore fluids rose along the Getchell fault system, where they dissolved carbonate wall rocks and deposited gold-enriched pyrite and jasperoid quartz. Gold and pyrite precipitated together as H 2 S in the ore fluids reacted with iron in the host rocks. As ore fluids mixed with local aquifer fluids, ore fluids became cooler and more dilute. Cooling caused precipitation of ore-stage fluorite and orpiment, and late ore-stage realgar. Phase separation and/or neutralization of the ore fluid during the waning stages of the hydrothermal ore system led to deposition of late ore-stage calcite.

Nevada↗

USGS1978

Tin and related elements in sediments and beach sands from Afghanistan, Iran, and Turkey

Sixty samples of sediments from stream beds, outwash plains, and beaches were collected in Afghanistan, Iran, and Turkey by Fred L. Klinger, U.S. Bureau of Mines, as part of the field work undertaken by the National Geographic-Smithsonian Pyrotechnological Expedition of 1968. Facilities for the analysis of the samples for tin and other metals were not immediately available, but in 1973 arrangements were made for analyses to be made on a time-permitting basis in the U.S. Geological Survey. The original purpose in collecting the samples was to determine whether tin was present in amounts indicative of sources for tin ores used in antiquity for the manufacture of bronze. The results of the analyses not only permitted an evaluation of the potential for tin in the localities sampled, but also afforded chemical and mineralogical data that were interpretable in the context of regional potential for other elements of current industrial use. These include gold, base metals, ferro-alloy metals, beryllium, rare earths, and barium. The original 60 samples of sand were sieved to make three size fraction (>0.707 mm, <O.707->O.177 mm, and <0.177 mm) for spectrographic and chemical analysis. Splits of these fractions were used for replicate analyses to permit evaluation of the precision of the analytical procedures. Further splitting of the <0.707->0.177 mm sand gave fractions from each sample that were separated in bromoform. Concentrates from the heavy-liquid separations were divided magnetically into six parts from most magnetic to least magnetic. These concentrates were analyzed spectrographically. The precision of the spectrographic analyses is well within the limits of precision expected from semiquantitative procedures. Such precision allows semiquantitative spectrographic procedures to be used with confidence as a valuable tool for reconnaissance investigations in which multi-element analyses are necessary. The analyses of the various fractions of sediments and sediment concentrates indicate the sample media in which an element was most likely to occur. Tin exhibited no preferential concentration into any particular medium. However, many elements with which tin is associated, and other elements of industrial use, do concentrate into one or more of the sample media. This indication of a preferred medium permits interpretation of the analyses as to the best sample medium for a particular element in the environment of western Asia. Cassiterite and/or tin were detected in many samples from Afghanistan, Iran, and Turkey, but in most of the samples the tin was present in normal crustal abundance. Sixteen samples, including seven from Afghanistan, eight from Iran, and one from Turkey contain unusually large amounts of tin. The most notable areas of anomalous tin are near Mirzaka, Qala-i-Asad, and Shah Agha in Afghanistan; near Meshed, Shir Kuh, Natanz, Nodus, and Talmesi in Iran; and on the shore of the Balck Sea just west of Trabzon in Turkey. Even in these localities the tin appears to be a minor element associated with other ores. The most common association of tin is with copper at known mineralized areas. This relation may have historical significance in the context of the development of bronze. The results of the analyses provided geochemical data on the distribution of other elements of industrial use and clearly identified nine of the ten known mineral deposits represented by the samples. The known metallization at the reported deposits may be only a part of more complex groups of metals. In Afghanistan an array of anomalous elements at the known gold placers around Mirzaka and along the Anguri River signals the presence of complex ore deposits. These elements are silver, arsenic, gold, bismuth, cadmium, copper, mercury, indium, molybdenum, lead, antimony, tin, thallium, tungsten, and zinc. They may indicate a Carlin-type gold deposit in which the wall-rocks are enriched in micron-sized particles of gold. Other localities in Afghanistan signalled by the results of the analyses to be anomalous and to merit further geochemical exploration are: (1) a reach of the Panjshir River for beryllium, lead, zinc, chromium and nickel; (2) the area near Bamian for beryllium; (3) the Siakhak village area for gold and copper; (4) around Qala-i-Asad and Shah Agha for lead, zinc, gold, and tungsten. Some attention to the distribution of monazite around Siakhak, Shahjui, Qala-i-Asad, and Shah Agha is justified to determine if this ore mineral for the rare earths and thorium is enriched over its normally expectable trace as an accessory mineral in granitic rocks, pelitic schists, and gneisses. In Iran, the pluton of granodiorite porphyry near Sar Cheshmeh, an area where a huge porphyry copper deposit was being investigated by the Geological Survey of Iran when the present samples were collected in 1968, shows as a strong geochemical anomaly for copper and molybdenum. The granitic area near Meshed is geochemically enriched persistently in beryllium, tin, and barium, and locally in gold, lanthanum, niobium, yttrium, and other elements. This area deserves a thorough regional geochemical survey for beryl and nonberyl sources of beryllium, for fluorite, and for the ores of niobium, tin, barium, the rare earths, and thorium. Other localities in Iran that merit geochemical exploration on the basis of these data are: ;1) the areas between Tabas and Deyhuk, east of Naiband, and south of Naiband for barium and zinc; (2) a locality about midway between Kerman and Sirdjan for barium, lanthanum, strontium, and zinc; (4) the Meskani copper mine area for mercury, lead, and nickel as well as copper; (5) the Talmesi copper mine area for such other elements as barium, cobalt, mercury, strontium, and zinc; (6) a small pluton of granodiorite north of Natanz for tungsten and base metals; (7) the vicinity of Zendjan for auriferous polymetallic sufide deposits; (8) gold in the gorge 15 km east of Miyaneh; and (9) the area near Nodus for gold, base metals, molybdenum, and niobium, and possibly uranium. The Harsit River basin in Turkey appears to be a suitable target for geochemical exploration for gold and low-temperature hydrothermal deposits of base metals, barium, and mercury.

Open-File Report↗

USGS1983

Map showing outcrops of basaltic rocks of early Quaternary and Tertiary age, Basin and Range province, Southern California

This map report is one of a series of geologic and hydrologic maps covering all or parts of States within the Basin and Range province of the western United States. The map reports contain detailed information on subjects that characterize the geohydrology of the province, including the ground-water hydrology/ ground-water quality, surface distribution of selected rock types, tectonic conditions, areal geophysics, Pleistocene lakes and marshes, and mineral and energy resources. This is a part of the U.S. Geological Survey's program for geologic and hydrologic evaluation of the province to identify prospective regions for further study relative to isolation of high-level nuclear waste (Bedinger, Sargent, and Reed, 1984). This map was prepared from published geologic maps and reports utilizing the project guidelines defined in Sargent and Bedinger (1984). As used in this study, basaltic rocks include basaltic andesite and basalt. The map shows the known occurrences of basaltic rocks largely of Tertiary age. Locally, however, where basalts of Quaternary age were not differentiated from those of Tertiary age, the younger basalts have been included on the map. The Description of Map Units includes the geologic and, if available, radiometric age; lithology; thickness where available; and sources of data for the basaltic units in outlined and numbered areas within the counties of the study area. No information was available on the rock outcrops that are unnumbered. The listed radiometric ages do not necessarily represent the entire age range of a unit.

California↗

USGS1982

Mineral resource potential map of the James River Face Wilderness, Bedford and Rockbridge counties, Virginia

The rocks in the James River Face Wilderness are shales and quartzites that overlie a meta-igneous basement. They are folded into a large southwestward-plunging anticline that is cut off on the east and south by an extensive thrust fault that brings old basement rocks over the younger sedimentary rocks. Geochemical studies of stream sediments, soils, and rocks do not reveal any unusually high metal concentrations, but a large resource of metallurgical-grade quartzite and shale suitable for structural clay products and lightweight aggregate is in the wilderness. Antietam (Erwin) Quartzite has been quarried at three sites in the wilderness as raw material for silicon used in the manufacture of ferrosilicon. Other uses included crushed rock for concrete aggregate, road metal, and railroad ballast, and sand for cement and mortar. Potential uses include ganister for silica brick and specialty sands such as filter and furnace sand. Firing tests on samples of shale from the Harpers (Hampton) Formation show that it could be used for the manufacture of brick and as lightweight aggregate. Of marginal economic interest are heavy-mineral layers in the basal Unicoi (Weverton) Formation.

Virginia↗

USGS1978

Origin of a South Texas roll-type deposit; II, Sulfide petrology and sulfur isotope studies

Petrologic and sulfur isotopic studies have been carried out on drill core samples from a roll-type uranium deposit in the mid-Tertiary Catahoula Tuff, Webb County, south Texas. Epigenetic iron disulfide minerals formed in two distinct stages. The first stage involved sulfidization of the host rock by sulfide (H 2 S, HS-)-bearing solutions that emanated from a fault about 1.5 km downdip from and subparallel to the orebody. Pyrite was the dominant iron disulfide mineral formed from this fault sulfide. The isotopic composition (delta 34 S) of first-stage iron disulfide is quite heavy (>0 per mil), in part because the fault-derived H 2 S was isotopically heavy. The development of the second-stage sulfides was related to processes that formed the uranium roll. Iron disulfide minerals produced during this second stage commonly occur as rims around the first-stage sulfides. The rims are exclusively marcasite in and adjacent to ore, but the pyrite content in these rims increases with increasing distance from ore. The sulfur of the second-stage sulfides in the vicinity of the roll front is isotopically light (--25 to --40 per mil). The virtual absence of organic carbon in the host sand precludes a bacterial origin for the ore-stage iron disulfide minerals and, therefore, eliminates bacterial metabolism as the mechanism for isotopic fractionation. Instead, the sulfur source for ore-stage sulfides was preore (first stage) sulfides, remobilized via partial oxidation to soluble metastable sulfur oxyanions.

Texas↗

USGS1959

Some aspects of the origin of the Ironwood iron-formation of Michigan and Wisconsin

The Ironwood iron-formation of the Gogebic Range of Michigan and Wisconsin is made up of several rock types, each of which is characterized by a different iron-rich mineral: hematite, magnetite, pyrite, iron carbonate, or iron silicate (minnesotaite, stilpnomelane). Where the Ironwood iron-formation is relatively unaltered the Plymouth, Norrie, and Anvil members consist of wavy-bedded magnetite and silicate-rich rocks, whereas the Yale and Pence members consist of even-bedded carbonate, silicate, magnetite, and pyrite-rich rocks. These rock types represent primary facies of the iron-formation that were deposited under differing physical and chemical conditions during a period of continuous iron-rich sedimentation. Animikie sedimentation in the Gogebic district began with the deposition of sandstone and dolomitic limestone in a shallow sea advancing over a low-lying land mass of lower Precambrian granite and green-stone. Continued advance of the sea, with effective separation of clastic material near shore, permitted the dominantly chemical sedimentation of the iron- formation in somewhat deeper water. The development of an off-shore basin with partially restricted circulation would have facilitated such deposition. Minor fluctuations in the physical and chemical conditions within the depositional environment are reflected in the differing facies of the iron-formation. Deposition of the iron and silica-rich chemical sediments was terminated by increased tectonism and the deposition of the thick sequence of slates and graywackes of the Tyler formation.

Michigan, Wisconsin↗

USGS1996

Fluid inclusions and biomarkers in the Upper Mississippi Valley zinc-lead district; implications for the fluid-flow and thermal history of the Illinois Basin

The Upper Mississippi Valley zinc-lead district is hosted by Ordovician carbonate rocks at the northern margin of the Illinois Basin. Fluid inclusion temperature measurements on Early Permian sphalerite ore from the district are predominantly between 90?C and I50?C. These temperatures are greater than can be explained by their reconstructed burial depth, which was a maximum of approximately 1 km at the time of mineralization. In contrast to the temperatures of mineral formation derived from fluid inclusions, biomarker maturities in the Upper Mississippi Valley district give an estimate of total thermal exposure integrated over time. Temperatures from fluid inclusions trapped during ore genesis with biomarker maturities were combined to construct an estimate of the district's overall thermal history and, by inference, the late Paleozoic thermal and hydrologic history of the Illinois Basin. Circulation of groundwater through regional aquifers, given sufficient flow rates, can redistribute heat from deep in a sedimentary basin to its shallower margins. Evidence for regional-scale circulation of fluids is provided by paleomagnetic studies, regionally correlated zoned dolomite, fluid inclusions, and thermal maturity of organic matter. Evidence for igneous acti vity contemporaneous with mineralization in the vicinity of the Upper Mississippi Valley district is absent. Regional fluid and heat circulation is the most likely explanation for the elevated fluid inclusion temperatures (relative to maximum estimated burial depth) in the Upper Mississippi Valley district. One plausible driving mechanism and flow path for the ore-forming fluids is groundwater recharge in the late Paleozoic Appalachian-Ouachita mountain belt and northward flow through the Reelfoot rift and the proto- Illinois Basin to the Upper Mississippi Valley district. Warm fluid flowing laterally through Cambrian and Ordovician aquifers would then move vertically upward through the fractures that control sphalerite mineralization in the Upper Mississippi Valley district. Biomarker reactant-product measurements on rock extracts from the Upper Mississippi Valley district define a relatively low level ofthermal maturity for the district, 0.353 for sterane and 0.577 for hopane. Recently published kinetic constants permit a time-temperature relationship to be determined from these biomarker maturities. Numerical calculations were made to simulate fluid heat flow through the fracture-controlled ore zones of the Thompson-Temperly mine and heat transfer to the adjacent rocks where biomarker samples were collected. Calculations that combine the fluid inclusion temperatures and the biomarker constraints on thermal maturity indicate that the time interval during which mineralizing fluids circulated through the Upper Mississippi Valley district is on the order of 200,000 years. Fluid inclusion measurements and thermal maturities from biomarkers in the district reflect the duration of peak temperatures resulting from regional fluid circulation. On the basis of thermal considerations, the timing of fluorite mineralization in southern Illinois, and the northward-decreasing pattern of fluorine enrichment in sediments, we hypothesize that the principal flow direction was northward through the Cambrian and Ordovician aquifers of the Illinois Basin. A basin-scale flow system would result in mass transport (hydrocarbon migration, transport of metals in solution) and energy (heat) transport, which would in turn drive chemical reactions (for example, maturation of organic matter, mineralization, diagenetic reactions) within the Illinois Basin and at its margins.

Bulletin↗