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At least 523 records · Page 29Linked to original sources
USGS1994

Analysis of nitrogen saturation potential in Rocky Mountain tundra and forest: implications for aquatic systems

We employed grass and forest versions of the CENTURY model under a range of N deposition values (0.02–1.60 g N m −2 y −1 ) to explore the possibility that high observed lake and stream N was due to terrestrial N saturation of alpine tundra and subalpine forest in Loch Vale Watershed, Rocky Mountain National Park, Colorado. Model results suggest that N is limiting to subalpine forest productivity, but that excess leachate from alpine tundra is sufficient to account for the current observed stream N. Tundra leachate, combined with N leached from exposed rock surfaces, produce high N loads in aquatic ecosystems above treeline in the Colorado Front Range. A combination of terrestrial leaching, large N inputs from snowmelt, high watershed gradients, rapid hydrologic flushing and lake turnover times, and possibly other nutrient limitations of aquatic organisms constrain high elevation lakes and streams from assimilating even small increases in atmospheric N. CENTURY model simulations further suggest that, while increased N deposition will worsen the situation, nitrogen saturation is an ongoing phenomenon.

Biogeochemistry↗
USGS2009

Continental-scale patterns in soil geochemistry and mineralogy: results from two transects across the United States and Canada

In 2004, the US Geological Survey (USGS) and the Geological Survey of Canada (GSC) initiated a pilot study that involved collection of more than 1500 soil samples from 221 sites along two continental transects across Canada and the United States. The pilot study was designed to test and refine protocols for a soil geochemical survey of North America. The two transects crossed a wide array of soil parent materials, soil ages, climatic conditions, landforms, land covers and land uses. Sample sites were selected randomly at approximately 40-km intervals from a population defined as all soils of the continent. At each site, soils representing 0 to 5 cm depth, and the O, A, and C horizons, if present, were collected and analyzed for their near-total content of over 40 major and trace elements. Soils from 0–5 cm depth were also collected for analysis of organic compounds. Results from the transects confirm that soil samples collected at a 40-km spacing reveal coherent, continental- to subcontinental-scale geochemical and mineralogical patterns that can be correlated to aspects of underlying soil parent material, soil age and climate influence. The geochemical data also demonstrate that at the continental-scale the dominance of any of these major factors that control soil geochemistry can change across the landscape. Along both transects, soil mineralogy and geochemistry change abruptly with changes in soil parent materials. However, the chemical influence of a soil’s parent material can be obscured by changing climatic conditions. For the transects, increasing precipitation from west to east and increasing temperature from north to south affect both soil mineralogy and geochemistry because of climate effects on soil weathering and leaching, and plant productivity. Regional anomalous metal concentrations can be linked to natural variations in soil parent materials, such as high Ni and Cr in soils developed on ultramafic rocks in California or high P in soils formed on weathered Ordovician limestones in central Kentucky. On local scales, anomalous metal concentrations recognized in soil profiles, such as high P in soils from animal confinement sites, are consistent with local anthropogenic disturbances. At a larger scale, the distribution of Hg across the west to east transect demonstrates that it can be difficult to distinguish between natural or anthropogenic contributions and that many factors can contribute to an element’s spatial distribution. Only three samples in a subset of seventy-three 0–5 cm depth soil samples from the north to south transect had organochlorine pesticides values above the method detection limit, apparently related to historic usage of the pesticides DDT and dieldrin.

Applied Geochemistry↗
USGS2026

The petrogenesis of Þingmúli volcano, East Fjords, Iceland

In this work we revisit Þingmúli volcano (Þ = Th), a classic locality known as an example of a complete tholeiitic differentiation. Þingmúli is a ~ 9.5 Ma extinct central volcano located in the East Fjords of Iceland, in which the whole compositional spectrum from basalt to rhyolites have erupted. These volcanic products have been previously considered as petrogenetically related by an ideal fractionation trend, regardless any temporal relationship or volumetric considerations. Here we report new whole-rock geochemistry, mineral chemistry, isotope analyses, estimation of residence times of the different eruptive deposits, and an update of the original petrogenetic model. Our results highlight that an enriched source, likely spinel lherzolites, generated transitional-alkaline basaltic melts after 15–20% of partial melting at depths of 40–45 km. Many of these basaltic melts erupted at various stages of the volcano's history, while others remained longer in the volcanic plumbing system. These evolved by fractional crystallisation into basaltic andesite magmas with a residence time of ~5 years based on the crystal size distribution of the plagioclase population. Isotopic differences between the basalts/basaltic andesites ( 87 Sr/ 86 Sr ~ 0.7034; 143 Nd/ 144 Nd ~ 0.51315) and the erupted rhyolites ( 87 Sr/ 86 Sr ~ 0.7037; 143 Nd/ 144 Nd ~ 0.51304) indicate that the latter are not petrogenetically related to the former. Therefore, instead of a fractional crystallisation mechanism to generate the rhyolites, we propose the partial melting of ignimbrite layers located beneath the volcano. The broad range of trace element concentrations in andesites and dacites and their different isotopic values compared to the basalts strongly suggest that these magmas have been generated by magma mixing between basaltic and rhyolitic melts, similar to modern day Icelandic volcanoes such as Hekla. These results highlight the need to revisit previously studied Icelandic classic localities and reassess their traditionally proposed petrogenetic models.

Þingmúli volcano, East Fjords↗
USGS2019

Overview of spirit microscopic imager results

This paper provides an overview of Mars Exploration Rover Spirit Microscopic Imager (MI) operations and the calibration, processing, and analysis of MI data. The focus of this overview is on the last five Earth years (2005–2010) of Spirit 's mission in Gusev crater, supplementing the previous overview of the first 450 sols of the Spirit MI investigation. Updates to radiometric calibration using in‐flight data and improvements in high‐level processing are summarized. Released data products are described, and a table of MI observations, including target/feature names and associated data sets, is appended. The MI observed natural and disturbed exposures of rocks and soils as well as magnets and other rover hardware. These hand‐lens‐scale observations have provided key constraints on interpretations of the formation and geologic history of features, rocks, and soils examined by Spirit . MI images complement observations by other Spirit instruments, and together show that impact and volcanic processes have dominated the origin and evolution of the rocks in Gusev crater, with aqueous activity indicated by the presence of silica‐rich rocks and sulfate‐rich soils. The textures of some of the silica‐rich rocks are similar to terrestrial hot spring deposits, and observations of subsurface cemented layers indicate recent aqueous mobilization of sulfates in places. Wind action has recently modified soils and abraded many of the rocks imaged by the MI, as observed at other Mars landing sites.

Journal of Geophysical Research E: Planets↗
USGS2021

Molecular and isotopic gas composition of the Devonian Berea Sandstone and implications for gas evolution, eastern Kentucky

Since 2011, the Devonian Berea Sandstone in northeastern Kentucky has produced oil where thermal maturity studies indicate that likely source rocks, namely, the Devonian Ohio Shale and Mississippian Sunbury Shale, are thermally immature. Downdip, where source rocks are mature for oil, the Berea Sandstone and Ohio Shale primarily produce gas. To investigate this thermal maturity discordancy, the molecular and isotopic composition of gases from the Berea Sandstone (oil associated) and Ohio Shale (nonassociated) were analyzed to understand the gas generation and migration history. Collected along a northwest-southeast transect in eastern Kentucky, samples range from 1079 to 4602 ft, respectively. All are wet gases with a thermogenic origin (δ 13 C-CH 4 = −53.5‰ to −46.1‰). This is mostly consistent with a reevaluation of thermal maturity in a companion study that expands the area mature for oil. Gas migration is required, however, in updip parts of the Berea play where vitrinite reflectance ( VR o ) values are less than 0.6%. Southeast regional dip exerts a first-order influence on thermal maturity as gases become drier and isotopically heavier downdip. Correlation of δ 13 C values for heavier hydrocarbon gases in a natural gas plot with VR o contour spacing demonstrates the influence of nearby source rock thermal maturity on gas composition. Downdip, migration of oil and the attendant increase in permeability relative to gas may account for the dominance of gas production in the Ohio Shale. Migration along with basin uplift after the Alleghany orogeny may have contributed to development of a gas phase that exsolved from oil.

Kentucky↗
USGS2007

Petroleum systems and assessment of undiscovered oil and gas in the Raton Basin – Sierra Grande Uplift Province, Colorado and New Mexico — USGS Province 41

Introduction The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geologically based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States. The USGS recently completed an assessment of undiscovered oil and gas resources of the Raton Basin-Sierra Grande Uplift Province of southeastern Colorado and northeastern New Mexico (USGS Province 41). The Cretaceous Vermejo Formation and Cretaceous-Tertiary Raton Formation have production and undiscovered resources of coalbed methane. Other formations in the province exhibit potential for gas resources and limited production. This assessment is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and hydrocarbon traps (trap formation and timing). The USGS used this geologic framework to define two total petroleum systems and five assessment units. All five assessment units were quantitatively assessed for undiscovered gas resources. Oil resources were not assessed because of the limited potential due to levels of thermal maturity of petroleum source rocks.

Colorado, New Mexico↗
USGS2016

Revisions to the original extent of the Devonian Shale-Middle and Upper Paleozoic Total Petroleum System

Technically recoverable undiscovered hydrocarbon resources in continuous accumulations are present in Upper Devonian and Lower Mississippian strata in the Appalachian Basin Petroleum Province. The province includes parts of New York, Pennsylvania, Ohio, Maryland, West Virginia, Virginia, Kentucky, Tennessee, Georgia, and Alabama. The Upper Devonian and Lower Mississippian strata are part of the previously defined Devonian Shale-Middle and Upper Paleozoic Total Petroleum System (TPS) that extends from New York to Tennessee. This publication presents a revision to the extent of the Devonian Shale-Middle and Upper Paleozoic TPS. The most significant modification to the maximum extent of the Devonian Shale-Middle and Upper Paleozoic TPS is to the south and southwest, adding areas in Tennessee, Georgia, Alabama, and Mississippi where Devonian strata, including potential petroleum source rocks, are present in the subsurface up to the outcrop. The Middle to Upper Devonian Chattanooga Shale extends from southeastern Kentucky to Alabama and eastern Mississippi. Production from Devonian shale has been established in the Appalachian fold and thrust belt of northeastern Alabama. Exploratory drilling has encountered Middle to Upper Devonian strata containing organic-rich shale in west-central Alabama. The areas added to the TPS are located in the Valley and Ridge, Interior Low Plateaus, and Appalachian Plateaus physiographic provinces, including the portion of the Appalachian fold and thrust belt buried beneath Cretaceous and younger sediments that were deposited on the U.S. Gulf Coastal Plain.

Open-File Report↗
USGS1979

Ground-water availability in carbonate rocks of the Dandridge area, Jefferson County, Tennessee

Groundwater in Jefferson County, Tenn., occurs in solution openings that follow bedding planes and strike joints in the dense limestone and dolomite. Recharge beginning at topographic highs in the northwest moves across strike to lows in the southeast; it is intercepted and collected by high permeability beds in the middle of the Knox Group and is routed along strike to discharge at large springs. Exploratory wells were drilled at two sites to test this concept of the flow system. Three wells at Moore Spring site in the recharge area penetrated only mud and solid rock. Four wells at Riley Spring site in the discharge area each penetrated at least five water-bearing openings that gave these wells an average production of 93 gallons per minute and a maximum of 180 gallons per minute. (USGS)

Open-File Report↗
USGS2017

Tin

Tin (Sn) is one of the first metals to be used by humans. Almost without exception, tin is used as an alloy. Because of its hardening effect on copper, tin was used in bronze implements as early as 3500 B.C. The major uses of tin today are for cans and containers, construction materials, transportation materials, and solder. The predominant ore mineral of tin, by far, is cassiterite (SnO 2 ). In 2015, the world’s total estimated mine production of tin was 289,000 metric tons of contained tin. Total world reserves at the end of 2016 were estimated to be 4,700,000 metric tons. China held about 24 percent of the world’s tin reserves and accounted for 38 percent of the world’s 2015 production of tin. The proportion of scrap used in tin production is between 10 and 25 percent. Unlike many metals, tin recycling is relatively efficient, and the fraction of tin in discarded products that get recycled is greater than 50 percent. Only about 20 percent of the world’s identified tin resources occur as primary hydrothermal hard-rock veins, or lodes. These lodes contain predominantly high-temperature minerals and almost invariably occur in close association with silicic, peraluminous granites. About 80 percent of the world’s identified tin resources occur as unconsolidated secondary or placer deposits in riverbeds and valleys or on the sea floor. The largest concentration of both onshore and offshore placers is in the extensive tin belt of Southeast Asia, which stretches from China in the north, through Thailand, Burma (also referred to as Myanmar), and Malaysia, to the islands of Indonesia in the south. Furthermore, tin placers are almost always found closely allied to the granites from which they originate. Other countries with significant tin resources are Australia, Bolivia, and Brazil. Most hydrothermal tin deposits belong to what can be thought of as a superclass of porphyry-greisen deposits. The hydrothermal tin deposits are all characterized by a close spatial, temporal, and genetic association with highly differentiated, peraluminous porphyritic granite intrusions. The intrusions form pegmatites; disseminated ore; parallel or subparallel, greisen-bordered sheeted veins that either cross-cut the intrusion or are peripheral to it; skarns; and (or) limestone replacements that contain different amounts of cassiterite, molybdenite, and wolframite. The tectonic settings of tin-bearing granites are relatively well understood and of limited variety. Tin and tungsten deposits and their associated igneous rocks are found mainly in continental settings. Historically, prospecting for tin has been carried out by the time-honored methods of panning, drilling, trenching, and assaying. Geophysical and geochemical surveys have been employed to cover large areas more rapidly, isolating areas of possible tin deposits so that drilling can be more effective and less costly. Elemental concentrations and relationships of the lithophile elements, especially barium, lithium, niobium, potassium, rubidium, and zirconium, are the most reliable chemical indicators of ore-forming processes and tin-bearing potential. The average human diet includes an intake of about 10 milligrams per day of tin. Ingestion of tin in significantly greater amounts than 10 milligrams per day may lead to a stomach ache, anemia, and liver and kidney problems. Exposure to some organo-tin compounds can interfere with brain and nervous system function and, in severe cases, can cause death. Extended inhalation of tin oxide—an issue mainly for those people who work in the tin industry—results in a higher potential to develop stannosis, which is a mild disease of the lungs caused by the inhalation of tin-bearing dust. Inorganic tin is poorly absorbed by the body, and no evidence exists for the carcinogenicity of metallic tin and tin compounds in humans. Most placer tin deposits are mined by open pit and (or) dredging methods. Mining of alluvial placers in modern streambeds and riverbeds is likely to increase the amount of sediment delivered downstream. This, combined with potential diversion of rivers and streams, may negatively affect downstream ecosystems. Many of the placer deposits located in Burma, Indonesia, Malaysia, and Thailand are located offshore. Most offshore placer tin deposits are mined by dredging methods, which have the potential to negatively affect benthic, midwater, and pelagic ecosystems. In a congressionally mandated U.S. Department of Defense study of strategic minerals published in 2013, tin has the greatest shortfall amount (insufficient supply to meet demand) at \$416 million; this amount is more than twice that of antimony ($182 million), which is the strategic mineral with the next largest shortfall amount (U.S. Department of Defense, 2013). The United States imported 75 percent of its tin supply in 2015. During the period 2012–15, these imports were from, in descending order of amount imported, Peru, Indonesia, Malaysia, and Bolivia. A promising advancement concerning research into the origin of tin deposits is the recent development of a reliable method of analyzing tin isotopes in cassiterite. Although the mechanism of transport and deposition of tin is fairly well understood, the means by which tin is incorporated into the parent magma at the points of magma generation and ascent needs further investigation. Tin metallogenic provinces worldwide are well known. Consequently, any undiscovered tin deposits will likely be spatially close to known deposits or extensions of the same.

Professional Paper↗
USGS2005

Stratabound copper-silver deposits of the Mesoproterozoic Revett Formation, Montana and Idaho, with a section on databases and spatial-data files for the geology and mineral deposits of the Revett Formation

The western Montana copper belt in western Montana and northern Idaho contains several large stratabound copper-silver deposits in fine- to medium-grained quartzite beds of the Revett Formation of the Mesoproterozoic (1,470-1,401 Ma) Belt Supergroup. Production from the deposits at the Troy Mine and lesser production from the Snowstorm Mine has yielded 222,237 tons Cu and 1,657.4 tons Ag. Estimates of undeveloped resources, mostly from the world-class Rock Creek-Montanore deposits, as well as lesser amounts at the Troy Mine, total more than 2.9 million tons Cu and 2,600 tons Ag in 406 million tons of ore.The Rock Creek-Montanore and Troy deposits, which are currently the most significant undeveloped resources identified in the copper belt, are also among the largest stratabound copper-silver deposits in North America and contain about 15 percent of the copper in such deposits in North America. Worldwide, stratabound copper-silver deposits contain 23 percent of all copper resources and are the second-most important global source of the metal after porphyry copper deposits.The Revett Formation, which consists of subequal amounts of argillite, siltite, and quartzite, is informally divided into lower, middle, and upper members on the basis of the proportions of the dominant rock types. The unit thickness increases from north to south, from 1,700 ft near the Troy Mine, 55 mi north of Wallace, Idaho, to more than 5,300 ft at Wallace, Idaho, in the Coeur d'Alene Trough south of the Osburn Fault, a major right-lateral strike-slip fault.Mineral deposits in the Revett Formation occur mostly in the A-D beds of the lower member and in the middle quartzite of the upper member. The deposits are concentrated along a preore pyrite/hematite interface in relatively coarse grained, thick quartzite beds that acted as paleoaquifers for ore fluids. The deposits are characterized by mineral zones (alteration-mineral assemblages) that are a useful guide to the locations of mineral deposits. In particular, the gradational zone between the chalcopyrite-ankerite and pyrite-calcite zones is the site of most mineral deposits. Detailed information on the geology and mineral deposits of the Revett Formation is presented in the accompanying files that include (1) a tab-delimited text file providing details of the geologic and mineral-resource data for 57 Revett-subtype stratabound copper-silver deposits, occurrences, and prospects; (2) the stratigraphic records of 40 diamond-drill cores and 86 measured sections, totaling 150,752 ft of true thickness, which are provided in Excel spreadsheet and Adobe Portable Document Format files; and (3) spatial geologic data consisting of geologic maps of the Revett Formation, the subsurface locations of resources in Revett-subtype stratabound copper-silver deposits based on diamond-drill-core data, and the locations of diamond-drill holes and measured sections. The spatial data are contained in Arc/Info interchange files. Spatial information derived from these data includes the locations of mineral zones, a digital database showing untested exploration areas, and a digital database of permissive tracts for undiscovered mineral deposits.

Idaho, Montana↗
USGS1954

Uranium deposits in Fall River County, South Dakota

In 1951 uranium deposits contained carnotite were discovered in the southern Black Hills near Edgemont, Fall River County, S. Dak. Numerous carnotite deposits have since been found in sandstones in the Inyan Kara group of early Cretaceous age, and uranium-bearing material has been discovered in the Pennsylvania Minnelusa sandstone of Pennsylvanian age and the Deadwood formation of Cambrian age in the southern Black Hills. Ore has been produced only from the Inyan Kara group, mostly within an area of about 30 square miles along the southwest flank of the Black Hills uplift between Dewey and Hot Springs in Custer and Fall River Counties. In addition, occurrences of uranium in other parts of the Black Hills and the surrounding area are known or reported from sedimentary, igneous, and metamorphic rocks of pre-Cambrian to Tertiary age. The upper and lowermost formations of the Inyan Kara group - the Fall River and Lakota sandstones - contain the productive uranium deposits. These terrestrial formations are composed predominantly of massive sandstone lenses within units of thinly bedded sandstone and mudstone, but locally these formations contain abundant mudstone and thinly bedded sandstone. Massive sandstone lenses in the Lakota sandstone commonly overlap and truncate underlying lenses. The lenses are separated by thin units of thinly bedded sandstone and mudstone. Iron stain, carbonaceous material, thin seams of gypsum, ripple marks, concretions, and fossil roots are common in the mudstone and thinly bedded portions of these formations. Some high angle normal faults of small displacement are found in the area containing the largest number of uranium occurrences in the Inyan Kara group. Although no ore deposits seen were cut by faults, high-angle fractures parallel and at right angles to the faults contain carnotite for short distances. The productive uranium deposits are most common where the Fall River and Lakota sandstones locally contain a large proportion of mudstone and thinly bedded sandstone. Other deposits are in the massive sandstone lenses of the Lakota sandstone and in the thin units between the lenses. Although carnotite is the most conspicuous and important mineral in most deposits, corvusite is an important constituent of some deposits. Other uranium minerals in the deposits are tyuyamunite, rauvite, and autunite. Ore produced in 1952 from the Fall River and Lakota sandstones contained about 0.2 percent U 3 O 8 and 0.6 percent V 2 O 5 . In general, deposits in the Fall River and Lakota sandstones contain about the same percentage of U 3 O 8 , but the deposits in the Fall River sandstone appear to have a higher percentage of vanadium. The grade of individual deposits, however, is highly variable. Most deposits are small, but a few have yielded as much as a thousand tons of ore.

South Dakota↗
USGS2020

Conceptual framework and approach for conducting a geoenvironmental assessment of undiscovered uranium resources

This report presents a novel conceptual framework and approach for conducting a geologically based environmental assessment, or geoenvironmental assessment, of undiscovered uranium resources within an area likely to contain uranium deposits. The framework is based on a source-to-receptor model that prioritizes the most likely contaminant sources, contaminant pathways, and affected environmental media for three common uranium extraction methods—open pit or underground mining with milling and in situ recovery (ISR). Data on regional geology, hydrology, and climate, as well as historical uranium mining and milling records are used to estimate the probable amounts of waste rock, tailings, wastewater, surface land disturbance, and subsurface aquifer disturbance for likely mining methods. Constituents of concern that might take the form of leachates, dust, radon, and sediments formed by chemical and physical weathering are also identified in the geoenvironmental assessment. Finally, areas where constituents of concern are likely to occur and persist in air, land, surface water, and groundwater are indicated by the potential for dispersion of dust by wind, accumulation of radon because of air stagnation, dispersion of sediments and wastewater by runoff, and infiltration of wastewater or leachates with consideration of the likely mobility of contaminants in surface water and groundwater. The geoenvironmental assessment output can be summarized in the following primary products: (1) a descriptive geoenvironmental model; (2) maps and statistics of variables that indicate the potential for constituents of concern to occur and persist in air, land, surface water, and groundwater within a tract that is geologically permissive for the occurrence of uranium; and (3) tables providing estimated or indicated quantities of waste rock, tailings, wastewater, dust, and radon emissions that could be associated with undiscovered uranium resources, if extracted, for each permissive tract. The uranium geoenvironmental assessment could help natural resource managers to prioritize and (or) identify (1) important potential contaminant pathways, (2) management practices required depending on the types of constituents that could be of concern, (3) areas for response in the event of accidental release, and (4) future directions for study. Furthermore, indicators of rock and water volumes potentially associated with an undiscovered uranium deposit may be evaluated to make quantitative comparisons of water required for uranium production or potential waste products generated during uranium extraction from areas permissive for uranium resource occurrence throughout the United States.

Scientific Investigations Report↗
USGS1956

Geology and ore deposits of the Whitepine area, Tomichi mining district, Gunnison County, Colorado

The Tomichi mining district is on the western slope of the Continental Divide near the southern end of the Sawatch Range in southeastern Gunnison County, Colorado. The most productive part of the Tomichi district was the Whitepine area. It is estimated that since the discovery of ore in 1879 the area has produced approximately $7,000,000, principally in lead and zinc, with lesser amounts of silver, copper, and gold. Geologically, the Whitepine area is a faulted syncline of Paleozoic rocks that was intruded by Tertiary igneous rocks. The oldest rock of the area is the Silver Plume granite of pre-Cambrian age. Deposited upon this successively were the Sawatch quartzite (Late Cambrian), Manitou dolomite (Early Ordovician), Harding quartzite (Middle Ordovician), Fremont dolomite (Lade Ordovician), Chaffee formation (Late Devonian), Leadville limestone (Late Mississippian), and Beldon shale (Late Pennsylvanian); a total thickness of about 1,450 feet. During the Laramide Revolution, the sedimentary rocks were folded into a broad northward-plunging syncline, faulted, and intruded by a series of igneous rocks. The igneous rocks, in order of relative age from oldest to youngest, are: a rhyolite stock, the Princeton quartz monzonite batholith, quartz monzonite or quartz latite porphyry dikes, and rhyolite or pitchstone porphyry dikes. The ore deposits of the Whitepine area may be classified into replacement deposits, vein deposits, and contact metamorphic deposits. The replacement deposits may be further subdivided into deposits along faults and bedded deposits. Of the types of deposits, the most productive have been the replacement deposits along faults. The major replacement deposits along faults are those of the Akron, Morning Star, and Victor mines. The ore deposits of these mines are in the foot wall of the Star faults in the Akron mine in the Manitou dolomite and in the Morning Star and Victor mines in the Leadville limestone. The chief bedded replacement deposits are those of the Erie, North Star, and Tenderfoot mines. In the Erie mine the ore deposits are in the Leadville limestone at, or just below, its contact with the Belden shale. In the North Star and Tenderfoot mines the ore bodies are in the Manitou dolomite along the crest of an anticline and the trough of a syncline, respectively. The vein deposits occur in the Silver Plume granite, Princeton quartz monzonite, and Paleozoic sedimentary rocks. The only vein of commercial importance was that of the Spar Copper mine, which is in the Silver Plume granite. Contact metamorphic minerals are found chiefly in the top of the Leadville limestone in the vicinity of the Erie mine, and in the limestone of the Belden shale. Magnetite is the only ore mineral and it was produced only from the Iron King mine. The replacement deposits consist, in general, of sphalerite, galena, pyrite, and chalcopyrite in a gangue of siliclfied limestone or dolomite, quartz, and calcite. The veins, for the most part, consist of pyrite and quartz with only minor amounts of galena, sphalerite, and chalcopyrite. In both types of deposits gold is believed to be associated with the pyrite and sphalerite and silver with the galena. Oxidized ore was the chief product of the early mining. This ore consists of calamine, cerussite, smithsonite, or anglesite, or a combination of these minerals, in a gangue of siliceous limestone or silicified limestone or dolomite. Oxidation did not extend, in most cases, for more than 150 feetbelow the surface. The ore deposits are believed to be genetically related to the Princeton quartz monzonite batholith. Ore-bearing solutions derived from the cooling of magma are believed to have migrated upwards along the pre-existing faults replacing favorable zones in the sedimentary rocks, or depositing quartz and ore minerals in open fissures in the igneous rocks.

Open-File Report↗
USGS2014

Coal and petroleum resources in the Appalachian basin: index maps of included studies

This chapter B.1 of U.S. Geological Survey (USGS) Professional Paper 1708 provides index maps for many of the studies described in other chapters of the report. Scientists of the USGS and State geological surveys studied coal and petroleum resources in the central and southern Appalachian structural basins. In the southern Appalachian basin, studies focused on the coal-bearing parts of the Black Warrior basin in Alabama. The scientists used new and existing geologic data sets to create a common spatial geologic framework for the fossil-fuel-bearing strata of the central Appalachian basin and the Black Warrior basin in Alabama. Digital data have been compiled into a geographic information system (GIS) that is included in chapter I.1 (Trippi and others, this volume). Shape files and related metadata for features shown in the index maps of this chapter can be downloaded from chapter I.1. The study area for the Appalachian basin resource framework study includes the fossil-fuel-bearing strata of the following States (listed alphabetically): Alabama, Kentucky, Maryland, New York, Ohio, Pennsylvania, Tennessee, Virginia, and West Virginia. The outline of the study area is shown in figure 1; it differs from the boundary of the Appalachian Basin Province (Province 67) defined for the 1995 National Oil and Gas Assessment (NOGA) by the U.S. Geological Survey (1996a). The difference is that the study area includes regions where the Pennsylvanian coal-bearing strata crop out but does not include all of the oil- and gas-bearing strata of the Black Warrior basin, Alabama. The reasons for providing the index maps in this chapter are to show the locations of different studies, to give an overview of topics covered, and to help the user choose which chapter to read. Figures 1 and 2 show the study area outline and county names. Figure 3 shows oil and gas production in 1995 and 2005. Figure 4 shows locations of Upper Devonian sandstone oil and gas fields. Figure 5 shows major coal regions and coal fields. Figure 6 shows coal production by county. Figure 7 shows the locations of 10 cross sections of regional extent through the subsurface of the Appalachian basin. Figure 8 shows conodont alteration index sample locations and interpreted isograds for Ordovician rocks. Figure 9 shows vitrinite-reflectance data for Pennsylvanian coal in the Appalachian basin. Figure 10 shows the locations of coalbed-methane (CBM) assessment units in the study area, and figure 12 shows counties producing CBM. Figure 12 shows sulfur content of coal delivered to powerplants from coal-producing counties in the Appalachian basin and Black Warrior basin. Figure 13 shows locations of wells in Ohio and Pennsylvania where oil and gas were sampled in Lower Silurian reservoirs. Figure 14 shows the Conasauga-Rome/Conasauga Total Petroleum System and selected wells in the Rome trough in Kentucky and West Virginia having oil and gas production and shows. Figure 15 shows the locations of samples from Silurian reservoirs in Kentucky, New York, Ohio, Pennsylvania, and West Virginia; the samples yielded total organic carbon data. Figure 16 shows the locations of the Ben Hur and Rose Hill oil fields, Virginia, and the Swan Creek oil field, Tennessee. The one index map that is not shown is the areal extent of the shale gas plays in the basin. The extents of the plays can be found in Coleman and others (this volume, chap. G.13).

Appalachian basin↗
USGS2011

Secular trends in the geologic record and the supercontinent cycle

Geologic secular trends are used to refine the timetable of supercontinent assembly, tenure, and breakup. The analysis rests on what is meant by the term supercontinent, which here is defined broadly as a grouping of formerly dispersed continents. To avoid the artificial pitfall of an all-or-nothing definition, quantitative measures of “supercontinentality” are presented: the number of continents, and the area of the largest continent, which both can be gleaned from global paleogeographic maps for the Phanerozoic. For the secular trends approach to be viable in the deep past when the very existence of supercontinents is debatable and reconstructions are fraught with problems, it must first be calibrated in the Phanerozoic against the well-constrained Pangea supercontinent cycle. The most informative geologic variables covering both the Phanerozoic and Precambrian are the abundances of passive margins and of detrital zircons. Both fluctuated with size of the largest continent during the Pangea supercontinent cycle and can be quantified back to the Neoarchean. The tenure of Pangea was a time represented in the rock record by few zircons and few passive margins. Thus, previously documented minima in the abundance of detrital zircons (and orogenic granites) during the Precambrian (Condie et al., 2009a, Gondwana Research 15, 228–242) now can be more confidently interpreted as marking the tenures of supercontinents. The occurrences of carbonatites, granulites, eclogites, and greenstone-belt deformation events also appear to bear the imprint of Precambrian supercontinent cyclicity. Together, these secular records are consistent with the following scenario. The Neoarchean continental assemblies of Superia and Sclavia broke up at ca. 2300 and ca. 2090 Ma, respectively. Some of their fragments collided to form Nuna by about 1750 Ma; Nuna then grew by lateral accretion of juvenile arcs during the Mesoproterozoic, and was involved in a series of collisions at ca. 1000 Ma to form Rodinia. Rodinia broke up in stages from ca. 1000 to ca. 520 Ma. Before Rodinia had completely come apart, some of its pieces had already been reassembled in a new configuration, Gondwana, which was completed by 530 Ma. Gondwana later collided with Laurentia, Baltica, and Siberia to form Pangea by about 300 Ma. Breakup of Pangea began at about 180 Ma (Early Jurassic) and continues today. In the suggested scenario, no supercontinent cycle in Earth history corresponded to the ideal, in which all the continents were gathered together, then broke apart, then reassembled in a new configuration. Nuna and Gondwana ended their tenures not by breakup but by collision and name change; Rodinia's assembly overlapped in time with its disassembly; and Pangea spalled Tethyan microcontinents throughout much of its tenure. Many other secular trends show a weak or uneven imprint of the supercontinent cycle, no imprint at all. Instead, these secular trends together reveal aspects of the shifting background against which the supercontinents came and went, making each cycle unique. Global heat production declined; plate tectonics sped up through the Proterozoic and slowed down through the Phanerozoic; the atmosphere and oceans became oxidized; life emerged as a major geochemical agent; some rock types went extinct or nearly so (BIF, massif-type anorthosite, komatiite); and other rock types came into existence or became common (blueschists, bioclastic limestone, coal).

Earth-Science Reviews↗
USGS2007

'Snake River (SR)-type' volcanism at the Yellowstone hotspot track: Distinctive products from unusual, high-temperature silicic super-eruptions

A new category of large-scale volcanism, here termed Snake River (SR)-type volcanism, is defined with reference to a distinctive volcanic facies association displayed by Miocene rocks in the central Snake River Plain area of southern Idaho and northern Nevada, USA. The facies association contrasts with those typical of silicic volcanism elsewhere and records unusual, voluminous and particularly environmentally devastating styles of eruption that remain poorly understood. It includes: (1) large-volume, lithic-poor rhyolitic ignimbrites with scarce pumice lapilli; (2) extensive, parallel-laminated, medium to coarse-grained ashfall deposits with large cuspate shards, crystals and a paucity of pumice lapilli; many are fused to black vitrophyre; (3) unusually extensive, large-volume rhyolite lavas; (4) unusually intense welding, rheomorphism, and widespread development of lava-like facies in the ignimbrites; (5) extensive, fines-rich ash deposits with abundant ash aggregates (pellets and accretionary lapilli); (6) the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre; (7) a bimodal association between the rhyolitic rocks and numerous, coalescing low-profile basalt lava shields; and (8) widespread evidence of emplacement in lacustrine-alluvial environments, as revealed by intercalated lake sediments, ignimbrite peperites, rhyolitic and basaltic hyaloclastites, basalt pillow-lava deltas, rhyolitic and basaltic phreatomagmatic tuffs, alluvial sands and palaeosols. Many rhyolitic eruptions were high mass-flux, large volume and explosive (VEI 6-8), and involved H2O-poor, low-??18O, metaluminous rhyolite magmas with unusually low viscosities, partly due to high magmatic temperatures (900-1,050??C). SR-type volcanism contrasts with silicic volcanism at many other volcanic fields, where the fall deposits are typically Plinian with pumice lapilli, the ignimbrites are low to medium grade (non-welded to eutaxitic) with abundant pumice lapilli or fiamme, and the rhyolite extrusions are small volume silicic domes and coule??es. SR-type volcanism seems to have occurred at numerous times in Earth history, because elements of the facies association occur within some other volcanic fields, including Trans-Pecos Texas, Etendeka-Paran, Lebombo, the English Lake District, the Proterozoic Keewanawan volcanics of Minnesota and the Yardea Dacite of Australia. ?? Springer-Verlag 2007.

Bulletin of Volcanology↗
USGS2012

Advances in carbonate exploration and reservoir analysis

The development of innovative techniques and concepts, and the emergence of new plays in carbonate rocks are creating a resurgence of oil and gas discoveries worldwide. The maturity of a basin and the application of exploration concepts have a fundamental influence on exploration strategies. Exploration success often occurs in underexplored basins by applying existing established geological concepts. This approach is commonly undertaken when new basins ‘open up’ owing to previous political upheavals. The strategy of using new techniques in a proven mature area is particularly appropriate when dealing with unconventional resources (heavy oil, bitumen, stranded gas), while the application of new play concepts (such as lacustrine carbonates) to new areas (i.e. ultra-deep South Atlantic basins) epitomizes frontier exploration. Many low-matrix-porosity hydrocarbon reservoirs are productive because permeability is controlled by fractures and faults. Understanding basic fracture properties is critical in reducing geological risk and therefore reducing well costs and increasing well recovery. The advent of resource plays in carbonate rocks, and the long-standing recognition of naturally fractured carbonate reservoirs means that new fracture and fault analysis and prediction techniques and concepts are essential.

Geological Society Special Publication↗
USGS2003

Ophiolite and volcanic arc assemblages on the Vizcaino Peninsula and Cedros Island region, Baja California Sur, Mexico: Mesozoic forearc lithosphere of the Cordilleran magmatic arc

Mesozoic ophiolites in the Vizcaíno Peninsula and Cedros Island region of Baja California Sur are suprasubduction zone Cordilleran-type ophiolites structurally juxtaposed with underlying high pressure-temperature subduction complex assemblages. The region is divided into three separate tectonostratigraphic terranes, but here we recognize stratigraphic, intrusive, and petrologie links between these terranes and interpret the evolution of the entire region within the same Late Triassic to Early Cretaceous tectonic framework. Several phases of extension are recognized, including two major phases that resulted in development of distinct ophiolite assemblages. The Late Triassic Vizcaine Peninsula Ophiolite (221 ± 2 Ma) represents the earliest stage of this history and comprises a complete spreading center sequence with depleted upper mantle and mafie crustal rocks, including sheeted dike complex, Jurassic are magmatic rocks with low-Ti are tholelite and boninite geochemical affinities were intruded through and constructed on the Triassic ophiolite basement. Ultra-depleted are-ankaramites on Cedros Island may represent an initial phase of are rifting that was followed by major Middle Jurassic extension and production of the Cedros Island Ophiolite (173 ± 2 Ma). The Late Jurassic-Early Cretaceous Coloradito and Eugenia Formations contain mudflows and olistostrome blocks intercalated with are volcanogenic sediment and rift-related pillow lavas; these units record extension and/or transtension and provide the earliest definite evidence of are-continent interaction in the region. Middle Jurassic to Early Cretaceous are plutonic rocks (ca. 165-135 Ma) were shallowly intruded into low greenschist-facies ophiolite and are volcanic basement. Plutonic rocks range in composition from gabbro to granodiorite, but tonalite dominates. These intrusions are typical I-type Cordilleran batholithic rocks with relatively primitive are geochemical affinities (initial Sr 87 / 86 Sr range from ~0.704 to 0.706), but they are distinctly calcic in nature, a feature common to the adjacent Cretaceous Peninsular Ranges batholith. The Vizca í no-Cedros region correlates to ophiolitic terranes of the western Sierra Klamath belt and Coast Ranges of California and Oregon that were constructed in part across the North American margin. Age, stratigraphic, and petrochemical data from the Vizca í no-Cedros region support previously proposed forearc rifting models developed for the U.S. sector of the Cordilleran orogen that interpret the ophiolite assemblages as autochthonous or parautochthonous forearc lithosphere constructed outboard of the Mesozoic continental margin arc.

GSA Special Papers↗