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At least 109 records · Page 6Linked to original sources
USGS2023

Long-term mercury loading and trapping dynamics in a Western North America reservoir

Study Region The Carson River including Lahontan Reservoir in Northwestern Nevada, USA Study Focus The discovery, mining, and processing of silver and gold from the Comstock Lode in northwestern Nevada heavily contaminated the Carson River system with mercury (Hg). The river now contains some of the highest recorded water column and bed sediment Hg concentrations reported in peer-reviewed literature. Acute Hg contamination in river and reservoir bed sediment has led to elevated methylmercury (MeHg) concentrations across all trophic levels of Lahontan Reservoir, culminating in significant health risks to humans. Lahontan Reservoir, located downstream from the mills that processed Comstock ore, has served as a Hg trap since the completion of the dam in 1915. Starting in 1997 and extending through 2021, the U.S. Geological Survey has collected and analyzed hundreds of discrete water samples entering and exiting Lahontan Reservoir for unfiltered total Hg (uf.THg), thereby providing a first-of-its-kind opportunity for studying long-term Hg trapping efficiencies within a western North American reservoir. Continuous time series of uf.THg concentration and flux above and below the reservoir were estimated using the weighted regressions on time, discharge, and season with the Kalman filtering (WRTDS-K) method employed with newly developed methods to account for non-natural (i.e., managed) hydrographs below a reservoir. New hydrological insights for the region An estimated 31,650 kg (34.89 US tons) of uf.THg entered Lahontan Reservoir during the 25 year period of analysis, accounting for approximately 0.5% of the total uf.THg estimated to have been released to the Carson River system [6.8 million kg (7500 US tons)] over a multi-decade mining boom. Moreover, approximately 92% of the estimated uf.THg entering Lahontan Reservoir was trapped. On an annual basis, however, trapping efficiencies range between 34% and 98%, and are closely related to the total annual discharge. Results also indicate that flow-normalized uf.THg concentrations and loads above and below the reservoir are trending down.

Nevada↗
USGS2001

Geochemical constraints on the origin of the Sterling Hill and Franklin zinc deposits, and the furnace magnetite bed, northwestern New Jersey

T he p urpose of this chapter is to review two aspects of the geochemistry of the Sterling Hill and Franklin zinc-ironmanganese deposits and the Furnace magnetite bed that underlies the Franklin deposit. These are (1) oxidation and sulfidation states determined from heterogeneous phase equilibria, and (2) stable isotopic compositions determined from analyses of carbonate, silicate, oxide, and sulfide minerals. The data place constraints on the genesis of the ores, which is the topic of the final section of the chapter. This review draws heavily from the results of my own dissertation research on Sterling Hill (Johnson, 1990; Johnson et al., 1990a) and from recent and continuing projects (Johnson et al., 1990b, Johnson, 1994, 1996, 1997; Volkert et al., 2000); it also includes the sulfur isotope results obtained by Ault (1957). For a complete review of the geology of the deposits, the reader is referred to the chapter by Metsger (2001), and to Metsger et al. (1958) and Frondel and Baum (1974). A complete catalog of the extensive literature on the deposits is given by Dunn (1995).

New Jersey↗
USGS2015

The fate of cyanide in leach wastes at gold mines: an environmental perspective

This paper reviews the basic chemistry of cyanide, methods by which cyanide can be analyzed, and aspects of cyanide behavior that are most relevant to environmental considerations at mineral processing operations associated with gold mines. The emphasis is on research results reported since 1999 and on data gathered for a series of U.S. Geological Survey studies that began in the late 1990s. Cyanide is added to process solutions as the CN − anion, but ore leaching produces numerous other cyanide-containing and cyanide-related species in addition to the desired cyanocomplex of gold. These can include hydrogen cyanide (HCN); cyanometallic complexes of iron, copper, zinc, nickel, and many other metals; cyanate (CNO − ); and thiocyanate (SCN − ). The fate of these species in solid wastes and residual process solutions that remain once gold recovery activities are terminated and in any water that moves beyond the ore processing facility dictates the degree to which cyanide poses a risk to aquatic organisms and aquatic-dependent organisms in the local environment. Cyanide-containing and cyanide-related species are subject to attenuation mechanisms that lead to dispersal to the atmosphere, chemical transformation to other carbon and nitrogen species, or sequestration as cyanometallic precipitates or adsorbed species on mineral surfaces. Dispersal to the atmosphere and chemical transformation amount to permanent elimination of cyanide, whereas sequestration amounts to storage of cyanide in locations from which it can potentially be remobilized by infiltrating waters if conditions change. From an environmental perspective, the most significant cyanide releases from gold leach operations involve catastrophic spills of process solutions or leakage of effluent to the unsaturated or saturated zones. These release pathways are unfavorable for two important cyanide attenuation mechanisms that tend to occur naturally: dispersal of free cyanide to the atmosphere and sunlight-catalyzed dissociation of strong cyanometallic complexes, which produces free cyanide that can then disperse to the atmosphere. The widest margins of environmental safety will be achieved where mineral processing operations are designed so that time for offgassing, aeration, and sunlight exposure are maximized in the event that cyanide-bearing solutions are released inadvertently.

Applied Geochemistry↗
USGS1995

Porphyry copper and other intrusion-related mineralization in Mexico

Intrusion-related copper-bearing ore deposits in Mexico span a wide-range of deposit types and geological settings and formed from the mid-Mesozoic through the Holocene. These deposits include world-class copper porphyry and skarn deposits as well as a continuum of similar skarn, porphyry, vein, and replacement deposits that contain variable quantities of molybdenum, zinc, silver, lead, iron, gold, tungsten, tin, fluorine, and beryllium. Based on a new compilation, this paper reviews data on the full spectrum of intrusion-related deposits, concentrating on copper-rich systems, and attempts to place them in a generalized geological and petrological context. In Mexico, intrusion-related mineral deposits are primarily Mesozoic to middle Tertiary in age. Three broad periods are prominent in the mineralization record: the late Mesozoic, the Laramide, and the middle Tertiary. Jurassic to Late Cretaceous calc-alkalic batholiths with sparse volcanic rocks occur along the Pacific margin mainly on eugeoclinal crust, although locally on continental crust (for example, in Sonora). Latest Cretaceous to Early Tertiary ('Laramide') calc-alkalic batholithic, subvolcanic, and volcanic centers occur in an overlapping but somewhat more easterly band that extends with diminished intensity and somewhat younger ages into the Sierra Madre Oriental. Mid-Tertiary volcanism and local intrusive centers are widely developed, with the greatest abundance of calcalkalic felsic volcanics in the Sierra Madre Occidental and more mafic middle to late Tertiary arc volcanics in the Sierra Madre del Sur in southern Mexico and as a fringe of alkalic volcanic' and sub volcanic centers in northeastern Mexico. Over 600 copper-rich intrusion-related systems can be inferred from the literature; about 100 can be documented with some confidence. Copper-rich deposits occur with both intermediate (dioritic) and felsic (granodioritic) intrusive centers and show a corresponding variety of associated metals and alteration types. Styles include porphyry-type disseminated or stockwork mineralization, skarn, breccia pipes, and pegmatites. Multiple styles commonly occur in the same district. Porphyry copper deposits are best developed in association with the Laramide intrusive centers of northern Mexico and the mid-Tertiary intrusions in southern Mexico. Other intrusion-related deposit types occur within the same magmatic framework, but they have different temporal and spatial correlations related to their igneous composition and exposure level. The continuum of intrusion-related mineralization in Mexico can be divided by geological associations, metal contents, and styles of alteration. Although more than 1,500 intrusion-associated mineral deposits are known, the scarcity of data requires a simplified approach focusing on major districts. We distinguish the following overlapping groups of deposits based on their metal contents and igneous compositions: (1) porphyry or skarn Cu(-Mo-Zn) associated with intermediate to felsic granitoids, (2) porphyry or skarn Cu (-Au-Fe) associated with intermediate intrusions, (3) greisen, skarn, or pegmatite W(-Mo) associated with intermediate to felsic granitoids, (4) replacement or skarn Zn-Pb-Ag(-Cu-F) deposits associated with felsic intrusions, (5) volcanic-hosted vein Ag-Au(-Zn-F-Sn) deposits associated with hypabyssal felsic intrusions, (6) vein ± replacement Ag-Au(-Cu-Zn-Pb) deposits associated with intermediate stocks, (7) volcanichosted Au-Ag(-Cu) systems, (8) rhyolite-related F(-Sn-Be) deposits, (9) diorite-related Fe(-Au-Cu) skarns, and (9) rhyolite-related Fe deposits. Some inferences can be drawn from examination of these patterns: • Igneous compositions vary in time and space in Mexico, but multiple compositions commonly were emplaced at different times in the same region. Temporal variations (as in Sonora) are as important as differences in province (as between Sonora and southern Mexico). • Alteration and metal differences between alkaline and sub alkaline, felsic and mafic magma suites can be partly rationalized from equilibria among igneous minerals (for example, in terms of a Al 2 O 3 vs a CaO [vs a SiO 2 ]), fluid chloride and sulfur contents, and magmatic metal contents which reflect province and process. • Exposure and preservation filter observed Mexican metallogeny. Erosion of the Mesozoic arc superstructure in the west leaves mainly tungsten-skarns, burial of the Laramide arc in central Mexico interrupts porphyry copper patterns, and minimal exhumation of mid-Tertiary intrusive centers preserves distal vein or replacement systems. • The superimposed metallogenic patterns in Mexico have parallels with metallogenic patterns in the western United States in terms of the effects of preservation, process, and province. Future work should focus on increasing the basic geological data on mineral deposits and igneous rocks. Geochronology, petrology, and geochemistry would help better define the temporal, spatial, and compositional interrelationships between tectonism, magmatism, and mineralization.

Book chapter↗
USGS2010

The Myszkow porphyry copper-molybdenum deposit, Poland

The porphyry copper-molybdenum deposit at Myszkow, south-central Poland, lies in the Cracow-Silesian orogenic belt, in the vicinity of a Paleozoic boundary between two tectonic plates. The deposit is hosted in a complex that includes early Paleozoic metasedimentary rocks intruded in the late Paleozoic by a predominantly granodioritic pluton. This deposit exhibits many features that are typical of porphyry copper deposits associated with calc-alkaline intrusive rocks, including ore- and alteration-mineral suites, zoning of ore and alteration minerals, fluid-inclusion chemistry, tectonic setting, and structural style of veining. Unusual features of the Myszkow deposit include high concentrations of tungsten and the late Paleozoic (Variscan) age.

International Geology Review↗
USGS2012

Geologic and environmental characteristics of porphyry copper deposits with emphasis on potential future development in the Bristol Bay Watershed, Alaska (Appendix H)

This report is prepared in cooperation with the Bristol Bay Watershed Assessment being conducted by the U.S. Environmental Protection Agency. The goal of the assessment is to help understand how future large-scale development in this watershed may affect water quality and the salmon fishery. Mining has been identified as a potential source of future large scale development in the region, especially because of the advanced stage of activity at the Pebble prospect. The goal of this report is to summarize the geologic and environmental characteristics of porphyry copper deposits in general, largely on the basis of literature review. Data reported in the Pebble Project Environmental Baseline Document, released by the Pebble Limited Partnership in 2011, are used to enhance the relevance of this report to the Bristol Bay watershed. The geologic characteristics of mineral deposits are paramount to determining their geochemical signatures in the environment. The geologic characteristics of mineral deposits are reflected in the mineralogy of the mineralization and alteration assemblages; geochemical associations of elements, including the commodities being sought; the grade and tonnage of the deposit; the likely mining and ore-processing methods used; the environmental attributes of the deposit, such as acid-generating and acid-neutralizing potentials of geologic materials; and the susceptibility of the surrounding ecosystem to various stressors related to the deposit and its mining, among other features (Seal and Hammarstrom, 2003). Within the Bristol Bay watershed, or more specifically the Nushagak and Kvichak watersheds, the geologic setting is permissive for the occurrence of several mineral deposit types that are amenable for large-scale development. Of these deposit types, porphyry copper deposits (e.g., Pebble) and intrusion-related gold deposits (e.g., Shotgun) are the most important on the basis of the current maturity of exploration activities by the mining industry. The Pebble deposit sits astride the drainage divide between the Nushagak and Kvichak watersheds, whereas the Humble, Big Chunk, and Shotgun deposits are within the Nushagak watershed. The Humble and Big Chunk prospects are geophysical anomalies that exhibit some characteristics similar to those found at Pebble. Humble was drilled previously in 1958 and 1959 as an iron prospect on the basis of an airborne magnetic anomaly. Humble is approximately 85 miles (137 km) west of Pebble; Big Chunk is approximately 30 miles (48 km) north-northwest of Pebble; and Shotgun is approximately 110 miles (177 km) northwest of Pebble. The H and D Block prospects, west of Pebble, represent additional porphyry copper exploration targets in the watershed.

Alaska↗
USGS2026

Production of mineral commodities and geospatial map of the mineral industries and related infrastructure of China

As part of the U.S. Geological Survey’s (USGS) mission to distribute global mineral information and analyze supply chains, this study provides a comprehensive review of the global significance of China’s mineral production and capacity in 2023. Of 77 mineral commodities in the USGS dataset, China produced 74 and was the world’s first-ranked producer for 39 of the 74. Compared to the high share of global mineral production, including up to 98 percent of global gallium production, the country’s share of global mineral reserves was relatively small, ranging from 20 percent (zinc ore) to 52 percent (tungsten ore). China’s imports of metal ores, slag, and ash accounted for 64 percent of global imports of such commodities by value. The country’s exports of base metals and articles of base metal accounted for 17 percent of the global exports. To help nongeographic information system users assess the spatial distribution of mineral mines, processing facilities, and ports for trades in China, this study created a geospatial (also called “georeferenced”) portable document format (GeoPDF) map. In addition, the GeoPDF contains mineral resource tracts (such as antimony, copper, potash, coal, and oil and gas), exploration sites, and energy infrastructure based on the preexisting USGS data.

Open-File Report↗
USGS2022

Marine minerals in Alaska — A review of coastal and deep-ocean regions

Minerals occurring in marine environments span the globe and encompass a broad range of mineral categories, forming within varied geologic and oceanographic settings. They occur in coastal regions, either from the continuation or mechanical reworking of terrestrial mineralization, as well as in the deep ocean, from diagenetic, hydrogenetic, and hydrothermal processes. The oceans cover most of the Earth’s surface and as a result, any inventory of global resources is incomplete without the inclusion of marine minerals. This study by the U.S. Geological Survey reviews current knowledge regarding deep-ocean and coastal marine minerals within the marine areas surrounding Alaska, including the Alaska Outer Continental Shelf (OCS). For the purposes of this study, we have divided these areas in to eight regions: (1) Gulf of Alaska seamounts, (2) Chukchi Borderland, (3) Canada Basin, (4) Aleutian Arc, (5) Seward Peninsula, (6) Goodnews Bay, (7) Bristol Bay and Alaska Peninsula, and (8) southern and southeastern Alaska. The Alaska OCS encompasses several areas broadly conducive to marine mineral formation, including extensional basins resulting from an active subduction zone where massive sulfide deposits may form, deep abyssal plains with conditions that may lead to manganese nodule formation, seamounts that can provide substrate for the growth of ferromanganese crusts, and erosional settings and submerged continental crust where placer deposits are found. For deep-ocean hydrothermal minerals and manganese nodules, the Alaska OCS contains prospective regions, including the Canada Basin and the Aleutian Arc; however, no such minerals have yet been identified. We explore the probability that these minerals occur based on reviews of existing geologic and oceanographic data within the relevant sections. In regions far from shore data are limited. Deep-ocean ferromanganese crusts are known to occur in two regions: (1) the Gulf of Alaska seamounts and (2) the Chukchi Borderland in the Arctic Ocean. Limited sampling has occurred in both regions, and along the Chukchi Borderland the sampling was outside of the OCS and the U.S. Exclusive Economic Zone. Data relevant to coastal minerals is more extensive, and in some places fairly systematic sampling was conducted. Several nearshore placer deposits have been exploited for decades; however, the potential for nearshore extension of terrestrial ore deposits is less well considered. This contribution considers the state of knowledge regarding marine mineral occurrences within the Alaska regions and identifies the data gaps in order to help inform future marine mineral related research efforts around Alaska.

Alaska↗
USGS1968

Feasibility study for an airborne geophysical survey of the Republic of Liberia

A feasibility study for an airborne geophysical survey of the Republic of Liberia indicates that airborne magnetometer and airborne scintillation detector surveys would be useful 1) in providing support for the current geologic mapping program, 2) as a guide in locating concentrations of economic minerals, and 3) delimiting the extent of known mineral deposits. Preliminary study of earlier airborne magnetometer surveys covering several iron ore localities shows that future geophysical surveys should be flown at a slightly closer flight-line spacing, and that the iron ore localities are characterized by anomalies interpreted as being produced by rocks having a strong anomalous remanent magnetization. In areas of the United States and Canada underlain by crystalline rock types similar to those found in Liberia, airborne geophysical surveys have been successful in locating additional buried economic mineral deposits, in extending known economic mineral deposits, and in contributing useful information to geologic mapping programs, especially in areas overlain by thick glacial deposits or by weathered rock. Some problems regarding the availability of accurate base maps for Liberia, combined with the inherent complex relationships that exist between a rock's geological properties and its magnetization, are briefly reviewed. The importance of obtaining a meaningful geologic interpretation of the geophysical data and coordinating the geophysical survey with the geological mapping program is stressed. Specifications and tolerances for the proposed airborne magnetometer and scintillometer survey of the Republic of Liberia are outlined.

Open-File Report↗
USGS1986

METEORIC-HYDROTHERMAL SYSTEMS.

This paper summarizes the salient characteristics of meteoric-hydrothermal systems, emphasing the isotopic systematics. Discussions of permeable-medium fluid dynamics and the geology and geochemistry of modern geothermal systems are also provided, because they are essential to any understanding of hydrothermal circulation. The main focus of the paper is on regions of ancient meteoric-hydrothermal activity, which give us information about the presently inaccessible, deep-level parts of modern geothermal systems. It is shown oxygen and hydrogen isotopes provide a powerful method to discover and map fossil hydrothermal systems and to investigate diverse associated aspects of rock alteration and ore deposition.

Reviews in Mineralogy↗
USGS2016

Book Review: Potassic igneous rocks and associated gold-copper mineralization, Fourth edition (D. Muller and D.I. Groves)

The fourth edition of this comprehensive textbook, which succeeds those published in 1995, 1997, and 2000, very nicely summarizes the geochemical and petrological characteristics of potassic igneous rock complexes and the different tectonic settings in which they occur. The authors provide an overview and a classification of these rocks and they outline the geochemical differences between barren and mineralized potassic igneous complexes. Owing to the common association of potassic igneous rocks with many gold- and copper-rich ore deposits, this book will be of interest not only to research scientists but also to those exploring for major deposits in young and ancient terranes. In fact, there was a clear attempt by the authors to provide a good mix of theoretical discussions based on experimental work, with case studies that illustrate field and applied research. Review info: Potassic Igneous Rocks and Associated Gold-Copper Mineralization , Fourth Edition. By Daniel Müller, David I. Groves. 2016. ISBN 978-3-319-23051-1. 311 p.

Economic Geology↗
USGS1929

Geology of the De Queen and Caddo Gap quadrangles, Arkansas

The field study of the geology of the De Queen and Caddo Gap quadrangles extended over a period of many years, and although the scientific and economic results from the study are here set forth fully for the first time in a single report, a number of publications have been issued that have presented some of the more important results. The field work was begun in 1907 and continued intermittently until 1925. The work in 1907 was done under a cooperative agreement between the United States Geological Survey and the Arkansas Geological Survey and involved primarily an investigation of the slate deposits of west-central Arkansas but also the mapping of the rocks in the mountainous part of the Caddo Gap quadrangle. In that year A. H. Purdue, State geologist of Arkansas, had charge of the work and was assisted by R. D. Mesler and H. D. Miser. All the subsequent work in the Caddo Gap quadrangle, as well as all in the De Queen quadrangle, was done by the United States Geological Survey. The work since 1907 is briefly outlined below. In 1908 Mr. Purdue, assisted by Mr. Miser, completed the mapping of the rocks of the Caddo Gap quadrangle with the aid of valuable suggestions from C. W. Hayes, chief geologist, J. A. Taff, and E. O. Ulrich, who visited the field for several days. In 1910 Mr. Purdue, assisted by Mr. Miser, reviewed a part of the previous work in the Caddo Gap quadrangle and mapped the rocks in most of the mountainous portion of the De Queen quadrangle. In 1911 these geologists did additional work in both the De Queen and Caddo Gap quadrangles, and in 1912 Mr. Miser, assisted by Mr. Mesler, completed the mapping of the rocks in the De Queen quadrangle and then reviewed some of the earlier work in the Caddo Gap quadrangle. In 1913 Arthur Keith, and Messrs. Purdue and Miser spent several days in a field conference in the Caddo Gap quadrangle. During the conference the first identifiable fossils in the Blaylock sandstone, of Silurian age, were discovered. In 1914 Mr. Miser obtained a small collection of fossil plants from the Stanley shale near Gillham, Ark., also the first fossils from the Arkansas novaculite. In 1916 he made a special study of some of the mineral deposits of the quadrangles, including the deposits of diamonds, manganese ore, gravel, and asphalt, and in 1917 he revisited the diamond mines. An investigation of the volcanic ash and tuff in the "Bingen formation," of Upper Cretaceous age, in the Caddo Gap quadrangle and adjoining areas to the south and southwest was made in 1923 by Clarence S. Ross and Mr. Miser. Also in that year other fossil plants were collected from the Stanley shale at the earlier discovered locality near Gillham by Mr. Miser. (See pl. 9, A .) The aggregate time spent in collecting fossils at this locality was eight days, so scare are the fossils and so difficult are the conditions for collecting them. Besides the above work the authors made frequent reconnaissance studies of adjoining areas, and Mr. Miser was joined in 1923 by C. W. Honess for a field conference of a few days in the De Queen and Caddo Gap quadrangles. In 1925 Mr. Miser joined in the field Messrs. L. W. Stephenson and C. H. Dane for a few days in a study of the " Bingen " (Woodbine and Tokio) and other formations of Upper Cretaceous age in and near the Caddo Gap quadrangle. Mr. Dane was making at that time a special study of the deposits of Upper Cretaceous age in southwestern Arkansas under a cooperative agreement between the United States Geological Survey and the Arkansas Geological Survey. For some of the information on the Tokio formation the present writers are indebted to Mr. Dane.

Arkansas, Oklahoma↗
USGS1966

Dawsonite in the green river formation of Colorado

Dawsonite NaAl(OH)2C03 is a rare mineral that occurs in relative abundance over hundreds of square miles in the Piceance Creek Basin of northwestern Colorado, as a rock-forming constituent of the oil shales in the green River Formation. In some specimens it makes up 25 percent by weight of the shale. Containing 35 percent of acid-soluble A1203, it has been viewed as a potential ore of aluminum. The dawsonite extends through 700 feet of continuous section of high-grade oil shale (averaging 25 gallons per ton), which may be as much as 1,500 feet in thickness. Its distribution, areally and stratigraphically, is reviewed; methods for its identification, and for its quantitative determination in the oil shale, with special reference to X-ray diffraction procedures are described; and the geochemistry of dawsonite, as it relates to the origin of the mineral, is considered. The scattered literature on dawsonite is briefly summarized. © 1966 Society of Economic Geologists, Inc..

Colorado↗
USGS2011

Review and interpretation of previous work and new data on the hydrogeology of the Schwartzwalder Uranium Mine and vicinity, Jefferson County, Colorado

The Schwartzwalder deposit is the largest known vein type uranium deposit in the United States. Located about eight miles northwest of Golden, Colorado it occurs in Proterozoic metamorphic rocks and was formed by hydrothermal fluid flow, mineralization, and deformation during the Laramide Orogeny. A complex brittle fault zone hosts the deposit comprising locally brecciated carbonate, oxide, and sulfide minerals. Mining of pitchblende, the primary ore mineral, began in 1953 and an extensive network of underground workings was developed. Mine dewatering, treatment of the effluent and its discharge into the adjacent Ralston Creek was done under State permit from about 1990 through about 2008. Mining and dewatering ceased in 2000 and natural groundwater rebound has filled the mine workings to a current elevation that is above Ralston Creek but that is still below the lowest ground level adit. Water in the 'mine pool' has concentrations of dissolved uranium in excess of 1,000 times the U.S. Environmental Protection Agency drinking-water standard of 30 milligrams per liter. Other dissolved constituents such as molybdenum, radium, and sulfate are also present in anomalously high concentrations. Ralston Creek flows in a narrow valley containing Quaternary alluvium predominantly derived from weathering of crystalline bedrock including local mineralized rock. Just upstream of the mine site, two capped and unsaturated waste rock piles with high radioactivity sit on an alluvial terrace. As Ralston Creek flows past the mine site, a host of dissolved metal concentrations increase. Ralston Creek eventually discharges into Ralston Reservoir about 2.5 miles downstream. Because of highly elevated uranium concentrations, the State of Colorado issued an enforcement action against the mine permit holder requiring renewed collection and treatment of alluvial groundwater. As part of planned mine reclamation, abundant data were collected and compiled into a report by Wyman and Effner (2007), which was to be used as a basis for eventual mine site closure. In 2010 the U.S. Geological Survey was asked by the State of Colorado to provide an objective and independent review of the Wyman and Effner (2007) report and to identify gaps in knowledge regarding the hydrogeology of the mine site. Key findings from the U.S. Geological Survey assessment include geological structural analysis indicating that although the primary uranium-hosting fault likely does not cross under Ralston Creek, many complex subsidiary faults do cross under Ralston Creek. It is unknown if any of these faults act as conduits for mine pool water to enter Ralston Creek. Reported bedrock permeabilities are low, but local hydraulic gradients are sufficient to potentially drive groundwater flow from the mine pool to the creek. Estimated average linear velocities for the full range of reported hydraulic conductivities indicate groundwater transit times from the mine pool to the creek on the order of a few months to about 3,800 years or 11 to 65 years using mean reported input values. These estimates do not account for geochemical reactions along any given flow path that may differentially enhance or retard movement of individual dissolved constituents. New reconnaissance data including 34S isotope and 234U/238U isotopic activity ratios show potentially distinctive signatures for the mine pool compared to local groundwater and Ralston Creek water above the mine site. Although the mine pool may be near an equilibrium elevation, evidence for groundwater recharge transients indicates inflow to the workings that are greater than outflow. There is not enough hydraulic head data adjacent to the mine workings to adequately constrain a final equilibrium elevation or to predict how several wet years in succession might affect variations in mine pool elevation. Although ground level adits are sealed with bulkheads, if the mine pool elevation were to rise slightly to the elevation of or abo

Open-File Report↗
USGS1958

The next decade in geochemistry

The purpose, associations, functions; and activities of the Geochmical Society are reviewed briefly. Work on the Colorado Plateau uranium deposits is described as an example of what geochemical research, in conjunction with detailed field work, mineralogical studies, and related techniques can contribute to the understanding of a type of deposit. It is pointed out that not only have these studies given a great deal of information about the origin of the ores, but they have brought about directly a manifold increase in production and reserves of uranium in the United States. Indirectly, they aided the discovery of the tremendous deposits of the Blind River area in Ontario. It is suggested that similar broad cooperative attacks could not only yield comparable results with other types of mineral deposits, such as laterites and Mississippi Valley type lead-zinc deposits, but could also advance our knowledge and understanding of such diverse problems of geology and cosmology as the origin of granites, origin and geologic implications of meteorites (including tektites), origin and search for petroleum, and geochemical relations and interpretations of natural waters. For each of these problems methods of approach are outlined and for some of them, specific projects and correlative problems are mentioned. It is further suggested that the broad cooperative attack needed for most of these problems might be fostered most effectively by a programme comparable to that of the I.G.Y., even though for most types of geochemical research synoptic sampling and observations are not as important as they are for many projects in geophysics.

Geochimica et Cosmochimica Acta↗
USGS1974

Relation of mineralization to calderas in the San Juan volcanic field, southwestern Colorado

A review of the calderas in the San Juan volcanic field, southwestern Colorado, indicates that lead, zinc, copper, gold, and silver mineralization took place in and near calderas which had complex histories of postsubsidence intrusive and extrusive igneous activity. Most known ore occurs in veins that follow fractures formed during the different caldera cycles, but some intrusive bodies were extensively mineralized and possibly may host disseminated, porphyry-type deposits. The mineral deposits seem to be related most commonly to the youngest and most highly differentiated late intrusives of a caldera cycle.

Colorado↗
USGS1968

Environments of generation of some base-metal ore deposits

The origin of the ore fluids, their dissolved constituents, the force that drives them, and the causes for deposition of their constituents are reviewed for five districts: Providencia, Mexico; Mississippi Valley (Pb-Zn); Salton Sea geothermal system; Red Sea geothermal system; Nonesuch Shale, Michigan. The compositions (chemical and isotopic) and temperatures, determined directly for brines and from fluid inclusions for ancient deposits, reveal significant differences between the Providencia deposit (close magmatic affiliations) and the others, in which connate water and constituents dissolved from country rock appear to be important. Deposits formed by complex processes, with multiple sources for materials, may well be more common than simple 'end-member' deposits.

Economic Geology↗
USGS2010

Paleomagnetism of the Siberian flood basalts of the Noril'sk area: A constraint on eruption duration

The volcanic sequence of the Noril'sk area, northern Siberia, provides the most complete section of early Siberian flood-basalt volcanism. Paleomagnetic measurements for more than 4000 samples of lava and tuff indicate that nearly all of this >3500-m-thick sequence was laid down during one interval of normal magnetic polarity. Lavas of the lower third of this sequence are cut by the ore-bearing Noril'sk-I intrusion, which has an age of 251 Ma, identical to that of the Permian-Triassic boundary. Thus, the normal-polarity interval represented by this sequence is inferred to be the first of the Triassic Period. Eruption of this enormous volume of material in a relatively brief period coincident with the earth's greatest mass extinction requires that all aspects of Siberian flood-basalt volcanism be evaluated carefully as possibly contributing to that catastrophe.

Noril'sk Area, Siberia↗