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At least 235 records · Page 13Linked to original sources
USGS1955

Geology of the Copper King uranium mine, Larimer County, Colorado

The Copper King mine in Larimer County, Colo., in the northern part of the Front Range of Colorado, was opened in World War I in an unsuccessful attempt to mine copper and zinc ore. In 1949, following the discovery of pitchblende on the dump, the mine was reopened, and it was worked until 1953 for uranium. A total of 652 tons of ore that contained an average of 0.28 percent U 3 O 8 was shipped. The bedrock consists predominantly of biotite granite, part of the Precamblian Log Cabin batholith, and minor metasedimentary rocks -- biotite-quartz-plagioclase gneiss, amphibole skarn, biotite schist, quartzite, amphibolite, and biotite sköls. The metasedimentary rocks occur as inclusions that trend northeast, essentially parallel to the prevailing foliation in the granite. In places the metasedimentary rocks are crosscut sharply by the granite and form angular, steep-walled blocks in the granite. Faults, confined to a narrow easterly-trending zone through the mine, cut all the Precambrian rocks. Mineral deposits of two types are present at the mines 1) sulfide-magnetite ore and 2) a uranium deposit in a filled fissure that cuts the skarn. The sulfide-magnetite deposits are small and consist of pyrite, sphalerite, chalcopyrite, pyrrhotite, and at places magnetite. Alpha-helium age determinations on ore magnetite by Hurley indicate that the mineral assemblage is late Precambrian in age. The deposits are pyrometasomatic in origin and possibly related to the granite. The uranium deposit consists of pitchblende and associated vein-forming minerals that occur in the Copper King fault and locally in pyrite boxwork adjacent to the fault. Three phases of black pitchblende have been identified -- uraninite, "coffinite", and UO 3 -rich pitchblend. Colored secondary minerals are absent. The pitchblende occurs in a steeply plunging, tabular shoot between 45 and 135 feet below the surface that has a horizontal length of about 50 feet. Within the shoot the pitchblende occurs in pods or layers generally only a few feet in height and length and as much as a foot thick that are separated by nearly barren vein. The grade of the ore within the pods ranges from 0.2 percent uranium to as much as 20 percent but averages about 1 to 2 percent. Age determinations by the Pb 206 /U 238 and Pb 207 /U 235 methods on two samples of hard pitchblende from the vein, not from the pyrite boxwork, gave ages by the two methods after suitable common lead corrections, ranging from 55 to 76 million years, corresponding to an early Tertiary age. Diamond core drilling and reconnaissance for radioactivity have not disclosed other uranium deposits the Prairie Divide region; nevertheless, it seems likely that other deposits are present.

Colorado↗
USGS2004

Geological and anthropogenic factors influencing mercury speciation in mine wastes: An EXAFS spectroscopy study

The speciation of Hg is a critical determinant of its mobility, reactivity, and potential bioavailability in mine-impacted regions. Furthermore, Hg speciation in these complex natural systems is influenced by a number of physical, geological, and anthropogenic variables. In order to investigate the degree to which several of these variables may affect Hg speciation, extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the Hg phases and relative proportions of these phases present in Hg-bearing wastes from selected mine-impacted regions in California and Nevada. The geological origin of Hg ore has a significant effect on Hg speciation in mine wastes. Specifically, samples collected from hot-spring Hg deposits were found to contain soluble Hg-chloride phases, while such phases were largely absent in samples from silica-carbonate Hg deposits; in both deposit types, however, Hg-sulfides in the form of cinnabar (HgS, hex.) and metacinnabar (HgS, cub.) dominate. Calcined wastes in which Hg ore was crushed and roasted in excess of 600??C, contain high proportions of metacinnabar while the main Hg-containing phase in unroasted waste rock samples from the same mines is cinnabar. The calcining process is thought to promote the reconstructive phase transformation of cinnabar to metacinnabar, which typically occurs at 345??C. The total Hg concentration in calcines is strongly correlated with particle size, with increases of nearly an order of magnitude in total Hg concentration between the 500-2000 ??m and <45 ??m size fractions (e.g., from 97-810 mg/kg Hg in calcines from the Sulphur Bank Mine, CA). The proportion of Hg-sulfides present also increased by 8-18% as particle size decreased over the same size range. This finding suggests that insoluble yet soft Hg-sulfides are subject to preferential mechanical weathering and become enriched in the fine-grained fraction, while soluble Hg phases are leached out more readily as particle size decreases. The speciation of Hg in mine wastes is similar to that in distributed sediments located downstream from the same waste piles, indicating that the transport of Hg from mine waste piles does not significantly impact Hg speciation. Hg LIII-EXAFS analysis of samples from Au mining regions, where elemental Hg(0) was introduced to aid in the Au recovery process, identified the presence of Hg-sulfides and schuetteite (Hg3O2SO4), which may have formed as a result of long-term Hg(0) burial in reducing high-sulfide sediments. ?? 2003 Elsevier Ltd. All rights reserved.

Applied Geochemistry↗
USGS2006

Idaho and Montana non-fuel exploration database 1980-1997

This report describes a relational database containing information about mineral exploration projects in the States of Idaho and Montana for the years 1980 through 1997 and a spatial (geographic) database constructed using data from the relational database. The focus of this project was to collect information on exploration for mineral commodities with the exception of sand, gravel, coal, geothermal, oil, and gas. The associate databases supplied with this report are prototypes that can be used or modified as needed. The following sources were used to create the databases-serial mining periodicals; annual mineral publications; mining company reports; U.S. Bureau of Mines (USBM) and U.S. Geological Survey (USGS) publications; an Idaho mineral property data base developed by Dave Boleneus, USGS, Spokane, Washington; Montana state publications; and discussions with representatives of Montana, principally the Montana Bureau of Mines and Geology and the Department of Environmental Quality. Fifty commodity groups were reported between the 596 exploration projects identified in this study. Precious metals (gold, silver, or platinum group elements) were the primary targets for about 67 percent of the exploration projects. Information on 17 of the projects did not include commodities. No location could be determined for 51 projects, all in Idaho. During the time period evaluated, some mineral properties were developed into large mining operations (for example Beal Mountain Mine, Stillwater Mine, Troy Mine, Montana Tunnels Mine) and six properties were reclaimed. Environmental Impact Statements were done on four properties. Some operating mines either closed or went through one or more shutdowns and re-openings. Other properties, where significant resources were delineated by recent exploration during this time frame, await the outcome of important factors for development such as defining additional reserves, higher metal prices, and the permitting process. Many of these projects examined relatively minor mineral occurrences. Approximately half of the exploration projects are located on Federal lands and about 40 percent were on lands managed by the U.S. Forest Service. More than 75 percent of the exploration occurred in areas with significant previous mineral activity.

Data Series↗
USGS2001

The Upper Pennsylvanian Pittsburgh coal bed: Resources and mine models

The U.S. Geological Survey recently completed a digital coal resource assessment model of the Upper Pennsylvanian Pittsburgh coal bed, which indicates that after subtracting mined-out coal, 16 billion short tons (14 billion tonnes) remain of the original 34 billion short tons (31 billion tonnes) of coal. When technical, environmental, and social restrictions are applied to the remaining Pittsburgh coal model, only 12 billion short tons (11 billion tonnes) are available for mining. Our assessment models estimate that up to 0.61 billion short tons (0.55 billion tonnes), 2.7 billion short tons (2.4 billion tonnes), and 8.5 billion short tons (7.7 billion tonnes) could be available for surface mining, continuous mining, and longwall mining, respectively. This analysis is an example of a second-generation regional coal availability study designed to model recoverability characteristics for all the major coal beds in the United States.

Maryland, Ohio, Pennsylvania, West Virginia↗
USGS1955

Geology of the northern Black Hills bentonite mining district

Extensive deposits of bentonite are present in the Cretaceous sedimentary rock strata cropping out on the northern flank of the Black Hills. These deposits have been the subject of a study by the U.S. Geological Survey as part of the program of the Department of the Interior for appraisal of natural resources of the Missouri River Basin. This report contains information concerning the geology of the bentonite deposits of the Northern Black Hills district. An attempt is made to explain some of the relations that exist between the physical properties and the mineralogical characteristics of the bentonite. Consideration is given to the occurrence of bentonite deposits and different types of sedimentary rocks and to depositional and post-depositional conditions which these rocks reveal. Evidence for sources of ancestral materials and conditions of alteration are discussed.

Black Hills↗
USGS2023

Responses of juvenile mussels to metals in sediment and water of the Tri-State Mining District

The U.S. Geological Survey and collaborators from EcoAnalysts, Inc., completed field and laboratory studies during 2016–19 to evaluate the toxicity of metals to freshwater mussels in streams draining the Tri-State Mining District. This project consisted of (1) sampling and analysis of metals in water and sediment, (2) surveys of mussel assemblages at sites with suitable mussel habitat, (3) toxicity tests with juvenile mussels exposed to zinc or to a mixture of metals (zinc, lead, and cadmium) in water, and (4) toxicity tests to evaluate the contributions of metals in sediment and metals in overlying water to toxic effects on mussels. Field sampling at sites in the Spring River and Neosho River and their tributaries demonstrated wide ranges of metal contamination in water and sediment. Zinc was the predominant toxic metal in water, and concentrations of lead and cadmium were much lower. Mussel areal density and species richness were greater at reference sites with low sediment metal concentrations (for example, zinc, 29–141 micrograms per gram) than at test sites that had higher concentrations of sediment zinc (416–3,420 micrograms per gram) as a result of effects of upstream mining activity. Juvenile mussels were highly sensitive to zinc in water in 12-week toxicity tests compared to previous water-only tests, and adding low levels of waterborne lead and cadmium typical of their occurrence in Tri-State Mining District streams produced greater toxicity. Thresholds for mussel toxicity were at or less than waterborne metal concentrations detected in Tri-State Mining District streams, and sites with waterborne metal concentrations exceeding thresholds had decreased mussel density and decreased mussel species richness. The 12-week toxicity tests with juvenile mussels in Tri-State Mining District sediments also demonstrated negative mussel responses with metal exposure. Thresholds for reductions in survival, growth, or biomass were at sediment metal concentrations less than thresholds reported for previous 4-week tests. We documented strong associations between reduced survival in laboratory tests and reduced species richness in community surveys. Attempts to estimate combined toxicity thresholds for metals in sediment and overlying water were not successful. These inconclusive results may be attributable to several factors, including (1) unexpected losses of waterborne metals from solution, (2) differences in sensitivity of different age/size classes of juvenile mussels, (3) disruption of sediment-water equilibria and changes in metal bioavailability, and (4) behavioral or physiological responses allowing juvenile mussels to temporarily reduce or avoid metal exposure. We also observed differences in metal toxicity thresholds between sediment toxicity tests started with different ages/sizes of test organisms. A followup study that combined exposure to Tri-State Mining District sediments with exposures to multiple levels of waterborne metals demonstrated toxic effects of sediments with low metal concentrations; however, some treatments also indicated unexpected reversals of concentration-response trends and reduced toxicity in treatments that had high metal concentrations in overlying water. These unusual responses may reflect development of physiological tolerance to metal toxicity by induction of metal-binding proteins (for example, metallothionein) in response to high metal levels in water. Results of laboratory and field studies indicated strong associations between metal exposure in Tri-State Mining District streams and toxic effects on juvenile freshwater mussels. Mussel community characteristics corresponded to differences in metal concentrations in sediment and water among Tri-State Mining District sampling sites. Responses of juvenile mussels in 12-week water and sediment exposures were strongly correlated with the status of mussel assemblages in Tri-State Mining District streams. The combined results support the hypothesis that exposure to metals from historical mining activities adversely affects freshwater mussel communities in the Spring River/Neosho River drainage.

Kansas, Missouri, Oklahoma↗
USGS2007

Hydrology and glacier-lake-outburst floods (1987-2004) and water quality (1998-2003) of the Taku River near Juneau, Alaska

The Taku River Basin originates in British Columbia, Canada, and drains an area of 6,600 square miles at the U.S. Geological Survey's Taku River gaging station. Several mines operated within the basin prior to 1957, and mineral exploration has resumed signaling potential for future mining developments. The U.S. Geological Survey in cooperation with the Douglas Indian Association, Alaska Department of Environmental Conservation, and the U.S. Environmental Protection Agency conducted a water-quality and flood-hydrology study of the Taku River. Water-quality sampling of the Taku River from 1998 through 2003 established a baseline for assessing potential effects of future mining operations on water quality. The annual mean discharge of the Taku River is 13,700 cubic feet per second. The monthly mean discharge ranges from a minimum of 1,940 cubic feet per second in February to a maximum of 34,400 cubic feet per second in June. Nearly 90 percent of the annual discharge is from May through November. The highest spring discharges are sourced primarily from snowmelt and moderate discharges are sustained throughout the summer by glacial meltwaters. An ice cover usually forms over the Taku River in December persisting through the winter into March and occasionally into April. Glacier-lake-outburst floods originating from two glacier-dammed lakes along the margin of the Tulsequah Glacier in British Columbia, Canada, are the source of the greatest peak discharges on the Taku River. The largest flood during the period of record was 128,000 cubic feet per second on June 25, 2004, resulting from an outburst of Lake No Lake. Lake No Lake is the larger of the two lakes. The outburst-flood contribution to peak discharge was 80,000 cubic feet per second. The volume discharged from Lake No Lake is relatively consistent indicating drainage may be triggered when the lake reaches a critical stage. This suggests prediction of the timing of these outburst floods might be possible if lake-stage data were available. Further increases in the volume of Lake No Lake are unlikely as all tributary glaciers have retreated out of the lake basin. Decreasing outburst-flood volumes from Tulsequah Lake suggests a continued decline in the volume of this lake. Physical and chemical parameters and concentrations of basic water-quality constituents indicate good water quality. Samples collected at the Taku River gaging station contained low concentrations of trace elements in the dissolved phase. Trace elements sampled were within acceptable limits when compared with the Alaska Department of Environmental Conservation aquatic-life criteria for fresh waters. The highest concentrations of total trace elements sampled were collected during glacial-outburst floods and likely are associated with suspended sediments. Total trace-element concentrations generally increase with increasing water discharge, although a high correlation for all constituents sampled does not always exist.

Alaska↗
USGS2008

Uranium in surface waters and sediments affected by historical mining in the Denver West 1:100,000 Quadrangle, Colorado

Geochemical sampling of 82 stream waters and 87 stream sediments within mountainous areas immediately west of Denver, Colorado, was conducted by the U.S. Geological Survey in October 1994. The primary purpose was to evaluate regionally the effects of geology and past mining on the concentration and distribution of uranium. The study area contains uranium- and thorium-rich bedrock, numerous noneconomic occurrences of uranium minerals, and several uranium deposits of variable size and production history. During the sampling period, local streams had low discharge and were more susceptible to uranium-bearing acid drainage originating from historical mines of base- and precious-metal sulfides. Results indicated that the spatial distribution of Precambrian granites and metamorphic rocks strongly influences the concentration of uranium in stream sediments. Within-stream transport increases the dispersion of uranium- and thorium rich mineral grains derived primarily from granitic source rocks. Dissolved uranium occurs predominantly as uranyl carbonate complexes, and concentrations ranged from less than 1 to 65 micrograms per liter. Most values were less than 5 micrograms per liter, which is less than the current drinking water standard of 30 micrograms per liter and much less than locally applied aquatic-life toxicity standards of several hundred micrograms per liter. In local streams that are affected by uranium-bearing acid mine drainage, dissolved uranium is moderated by dilution and sorptive uptake by stream sediments. Sorbents include mineral alteration products and chemical precipitates of iron- and aluminum-oxyhydroxides, which form where acid drainage enters streams and is neutralized. Suspended uranium is relatively abundant in some stream segments affected by nearby acid drainage, which likely represents mobilization of these chemical precipitates. The 234U/238U activity ratio of acid drainage (0.95-1.0) is distinct from that of local surface waters (more than 1.05), and this distinctive isotopic composition may be preserved in iron-oxyhydroxide precipitates of acid drainage origin. The study area includes a particularly large vein-type uranium deposit (Schwartzwalder mine) with past uranium production. Stream water and sediment collected downstream from the mine's surface operations have locally anomalous concentrations of uranium. Fine-grained sediments downstream from the mine contain rare minute particles (10-20 micrometers) of uraninite, which is unstable in a stream environment and thus probably of recent origin related to mining. Additional rare particles of very fine grained (less than 5 micrometer) barite likely entered the stream as discharge from settling ponds in which barite precipitation was formerly used to scavenge dissolved radium from mine effluent.

Colorado↗
USGS2023

The availability of primary rhenium as a by-product of copper and molybdenum mining

Rhenium is a valuable rare metal that is primarily captured as a by-product during the processing of copper and molybdenum. Its complex capture pathway and low annual production (< 100 tons per year) mean that there is limited information about how current capture compares with the amounts of rhenium geologically present in mined material. This study compiles deposit rhenium grades and mine production data to estimate the flow of rhenium in mined material, including through international trade. It is found that less than 12% of rhenium present in ore is captured; however, capture may be as high as 30 to 44% when accounting for technical recovery limits. This has substantial impacts on the future availability of rhenium as the current supply chain faces a geologically imposed limit of rhenium available in ores. Further increases in primary metal capture beyond technical recovery limits can only be achieved by increasing the mining of the copper and molybdenum host ores.

Mineral Economics↗
USGS1927

Geology and ore deposits of the Leadville mining district, Colorado

Adequate treatment of so large and so extensively developed a district as that of Leadville necessitates a voluminous report, in which the practical questions of prime interest to the commercial world can not be systematically answered until the data on which they depend are discussed. Many readers will no doubt wish to turn at once to the chapter on ore reserves, which will give them an appraisal of the district, without bothering with geologic detail. For those who wish a brief general account, a summary of the principal chapters of the report is presented below.

Colorado↗
USGS1979

Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Kenai and Tyonek quadrangles, Alaska

This summary of references is designed to aid in library research on metallic and nonmetallic (other than mineral fuels and construction materials) mineral deposits in the Kenai and Tyonek quadrangles, Alaska. References to most reports of the Geological Survey, U.S. Bureau of Mines, and State of Alaska Division of Geological and Geophysical Surveys and predecessor State and Territorial agencies released before September 1, 1979, are included. Certain, mainly statistical, reports such as the annual Minerals Yearbook of the U.S. Bureau of Mines and the biennial and annual reports of the Alaska Division of Geological and Geophysical Surveys and its predecessor agencies are not included. Also not included are data on geochemical anomalies and on many prospects and claims about which little more than their locations is known (for example, some of those in MacKevett and Holloway, 1977 (OF 77169A)). These omissions should not be interpreted as a judgement on my part that the prospects and claims are not valid mineral occurrences, but only that there are insufficient data to describe any mineral deposits that might be present. This report is divided into three parts: a section made up of summaries of references arranged alphabetically by occurrence name; a section that lists synonyms for names in the first section, claim names, and the names of operators and owners of mines and prospects; and a section that lists, by author, all references in the first section and in these introductory paragraphs.

Alaska↗
USGS1980

Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the Talkeetna Mountains Quadrangle, Alaska

These summaries of data on metallic and selected nonmetallic mineral occurrences and lists of selected references to them in Geological Survey, U.S. Bureau of Mines, and State of Alaska Division of Geological and Geophysical Surveys (and predecessor State agencies) reports and maps are designed to aid in library research on the mineral resources of the Talkeetna Mountains quadrangle, Alaska. The references listed are selected in the sense that mainly statistical reports such as the annual Minerals Yearbook of the U.S. Bureau of Mines and many annual and biennial reports of the Alaska Division of Geological and Geophysical Surveys and its predecessor agencies are not included. Also not included are data on many claims about which little more than their locations is known (for example, localities 3 and 6 in Csejtey and Miller, 1978 (OF 78- 558B)). These omissions should not be interpreted as a judgement that the claims are not on valid mineral occurrences, but only that there are insufficient data to describe any mineral deposit that might be present. Geochemical anomalies determined by analyses of rock and stream—sediment samples in which no metallic mineral was identified are also omitted. This report is divided into three parts: a section made up of summaries of data and reference lists arranged alphabetically by occurrence name; a second section that lists synonyms for names in the first section and the names of owners and operators of mines and prospects; and a final section that lists alphabetically by author all references mentioned in the first section and in these introductory paragraphs.

Alaska↗
USGS1999

Chemical data and lead isotopic compositions in stream-sediment samples from the Boulder River watershed, Jefferson County, Montana

Metal-mining related wastes in the Boulder River basin study area in northern Jefferson County, Montana, have been evaluated for their environmental effects as a part of the U.S. Geological Survey Abandoned Mine Lands Project. Many mine and prospect waste dumps, and mill wastes are located in the drainage basins of Basin Creek, Cataract Creek, and High Ore Creek, the three major tributaries to the Boulder River in the study area. Throughout the study area, mine-waste material has been transported into and down streams, where it mixes with and becomes incorporated into the bed sediments. In some locations, waste material was placed by mine operators directly in stream channels, and has been transported downstream forming fluvial tailings deposits along the stream banks. Water quality and aquatic habitat have been affected by acid generation and toxic-metal mobility during snowmelt and storm water runoff events. Colloids formed by the raising of pH downstream from these mine sites sorb metals contributing to the high concentrations observed in both bed and suspended sediments within the watershed. This report presents geochemical data for bed sediments from 67 sites and lead isotope data for 59 sites. Also included are geochemical data for seven suspended-sediment samples, and one smelter slag sample.

Montana↗
USGS1980

Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the McCarthy Quadrangle, Alaska

These summaries of data on metallic and selected nonmetallic mineral occurrences and lists of selected references to .them in Geological Survey, U.S. Bureau of Mines, and State of Alaska Division of Geological and Geophysical Surveys (and predecessor State and Territorial agencies) reports and maps and a very.few journal articles are designed to aid in library research on the mineral resources of the McCarthy quadrangle, Alaska. The references listed are selected in the sense that mainly statistical reports such as the annual Minerals Yearbook of the U.S. Bureau of Mines and many annual and biennial reports of the Alaska Division of Geological and Geophysical Surveys and its predecessor agencies are not included. Also not included are data on claims about which little more than their locations is known (for example, localities 126- 130 in MacKevett and Holloway, 1977 (OF 77-169A). These omissions should not be interpreted as a judgement that the claims are not on valid mineral occurrences, but only chat there are insufficient data to describe any mineral deposits that might be present. Geochemical anomalies determined by analyses of rock and stream-sediment samples in which no metallic mineral was indentified are also omitted.

Alaska↗
USGS1980

Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in fifteen quadrangles in southwestern and west-central Alaska

These summaries of data on metallic and selected nonmetallic mineral occurrences and lists of selected references to them in Geological Survey, U.S. Bureau of Mines, and State of Alaska Division of Geological and Geophysical Surveys (and predecessor State and Territorial agencies) reports and maps released before Jan. 1, 1980, and in one abstract of a report presented orally at a scientific meeting, are designed to aid in library research on the mineral resources of 14 quadrangles in southwestern Alaska and the Saint Lawrence quadrangle in west—central Alaska. The references are selected in the sense that mainly statistical reports such as the annual Minerals Yearbook of the U.S. Bureau of Mines and many annual and biennial reports of the Alaska Division of Geological and Geophysical Surveys and its predecessor agencies are not included. Also not included are data on many claims about which little more than their locations is known (for example, localities 11 to 14 in MacKevett and Holloway, 1977 (OF 77-169D), p. 28). These omissions should not be interpreted as a judgement that the claims are not on valid mineral occurrences, but only that there are insufficient data to describe any mineral deposit that might be present. Geochemical anomalies determined by analyses of rock and stream—sediment samples in which no metallic mineral was identified are also omitted. Work now in progress should add greatly to the knowledge of mineral resources in several quadrangles on the Alaska Peninsula.

Alaska↗
USGS2026

Coal beneath Federal lands in the United States—Mines, reserves, and resources

The U.S. Geological Survey (USGS) compiled a list of coal mines and tabulated the coal reserves and available coal resources beneath Federal lands in the conterminous United States. Coal resources beneath Federal lands in Alaska are also discussed in this report. In 2024, the 34 coal mines on Federal lands produced more than 261 million short tons of coal. Surface mining is used at 23 of the coal mines, and underground mining is used at 11. These 34 coal mines control more than 4.2 billion short tons of reported coal reserves. Most of the coal mines (31) and more than 98 percent of the reported coal reserves are on Federal lands west of the Mississippi River. Of all the States, Wyoming has the most coal mines on Federal lands (14) and produces the most coal from Federal lands. The Powder River Basin has the most coal mines per basin or coal field operating on Federal lands (12 in Wyoming, 2 in Montana). Most of the available coal resources in the conterminous United States are also west of the Mississippi River. There are five basins or coal fields in the West that each contain available coal resources of more than 25 billion short tons. The USGS estimates that more than 355 billion short tons of available coal resources remain beneath Federal lands in the conterminous United States. Alaska contains substantial quantities of coal resources. The USGS estimates that Alaska has at least 140 billion short tons of identified available coal resources but may ultimately have as much as 5.5 trillion short tons of coal resources.

Circular↗
USGS1977

Factors controlling localization of uranium deposits in the Dakota Sandstone, Gallup and Ambrosia Lake mining districts, McKinley County, New Mexico

Geologic studies were made at all of the uranium mines and prospects in the Dakota Sandstone of Early(?) and Late Cretaceous age in the Gallup mining district, McKinley County, New Mexico. Dakota mines in the adjacent Ambrosia Lake mining district were visited briefly for comparative purposes. Mines in the eastern part of the Gallup district, and in the Ambrosia Lake district, are on the Chaco slope of the southern San Juan Basin in strata which dip gently northward toward the central part of the basin. Mines in the western part of the Gallup district are along the Gallup hogback (Nutria monocline) in strata which dip steeply westward into the Gallup sag. Geologic factors which controlled formation of the uranium deposits in the Dakota Sandstone are: (1) a source of uranium, believed to be uranium deposits of the underlying Morrison Formation of Late Jurassic age; (2) the accessibility to the Dakota of uranium-bearing solutions from the Morrison; (3) the presence in the Dakota of permeable sandstone beds overlain by impermeable carbonaceous shale beds; and (4) the occurrence within the permeable Dakota sandstone beds of carbonaceous reducing material as bedding-plane laminae, or as pockets of carbonaceous trash. Most of the Dakota uranium deposits are found in the lower part of the formation in marginal-marine distributary-channel sandstones which were deposited in the backshore environment. However, the Hogback no. 4 (Hyde) Mine (Gallup district) occurs in sandy paludal shale of the backshore environment, and another deposit, the Silver Spur (Ambrosia Lake district), is found in what is interpreted to be a massive beach or barrier-bar sandstone of the foreshore environment in the upper part of the Dakota. The sedimentary depositional environment most favorable for the accumulation of uranium is that of backshore areas lateral to main distributary channels, where levee, splay, and some distributary-channel sandstones intertongue with gray carbonaceous shales and siltstones of the well-drained swamp environment. Deposits of black carbonaceous shale which were formed in the poorly drained swamp deposits of the interfluve area are not favorable host rocks for uranium. The depositional energy levels of the various environments in which the sandstone and shale beds of the Dakota were deposited govern the relative favorability of the strata as uranium host rocks. In the report area, uranium usually occurs in carbonaceous sandstone deposited under low- to medium-energy fluvial conditions within distributary channels. A prerequisite, however, is that such sandstone be overlain by impermeable carbonaceous shale beds. Low- to medium-energy fluvial conditions result in the deposition of sandstone beds having detrital carbonaceous material distributed in laminae or in trash pockets on bedding planes. The carbonaceous laminae and trash pockets provide the necessary reductant to cause precipitation of uranium from solution. High-energy fluvial conditions result in the deposition of sandstones having little or no carbonaceous material included to provide a reductant. Very low energy swampy conditions result in carbonaceous shale deposits, which are generally barren of uranium because of their relative impermeability to migrating uranium-bearing solutions.

Open-File Report↗
USGS2006

Structural fabrics, mineralization and Lamaride kinematics of the Idaho Springs-Ralston shear zone, Colorado mineral belt and central Front Range uplift

The Idaho Springs and Central City mining districts form the central portion of a structurally controlled hydrothermal precious- and base-metal vein system in the Front Range of the northeast-trending Colorado Mineral Belt. Three new 40Ar/39Ar plateau ages on hydrothermal sericite indicate the veins formed during the Laramide orogeny between 65.4??1.5 - 61.9??1.3 Ma. We compile structural geologic data from surface geological maps, subsurface mine maps, and theses for analysis using modern graphical methods and integration into models of formation of economic mineral deposits. Structural data sets, produced in the 1950s and 1960s by the U.S. Geological Survey, are compiled for fabric elements, including metamorphic foliations, fold axial trends, major brittle fault zones, quartz and precious- and base-metal veins and fault veins, Tertiary dikes, and joints. These fabric elements are plotted on equal-area projections and analyzed for mean fabric orientations. Strike-slip fault-vein sets are mostly parallel or sub-parallel, and not conjugate as interpreted by previous work; late-stage, normal-slip fault veins possibly show a pattern indicative of triaxial strain. Fault-slip kinematic analysis was used to model the trend of the Laramide maximum horizontal stress axis, or compression direction, and to determine compatibility of opening and shear motions within a single stress field. The combined-model maximum compression direction for all strike slip fault veins is ???068??, which is consistent with published Laramide compression directions of ???064?? (mean of 23 regional models) and ???072?? for the Front Range uplift. The orientations of fabric elements were analyzed for mechanical and kinematic compatibility with opening, and thus permeability enhancement, in the modeled regional east-northeast, Laramide compression direction. The fabric orientation analysis and paleostress modeling show that structural permeability during mineralization was enhanced along pre-existing metamorphic foliations and fold axial planes. Large orientation dispersion in most fabric elements likely caused myriad potential pathways for permeability. The dominant orientations of opening and shear mode structures are consistent with a sub-parallel network of structures that formed in the Laramide east-northeast compression direction. The results presented demonstrate the importance of using mechanical and kinematic theory integrated with contemporary ideas of permeability structure to better understand the coupled nature of fluid flow, mineral deposition, stress, and strain. Further, the results demonstrate that there is significant internal strain within this basement-cored uplift that was localized by optimally oriented pre-existing structures in a regional stress field.

Mountain Geologist↗