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At least 721 records · Page 40Linked to original sources

USGS2013

Chemical controls on fault behavior: weakening of serpentinite sheared against quartz-bearing rocks and its significance for fault creep in the San Andreas system

The serpentinized ultramafic rocks found in many plate-tectonic settings commonly are juxtaposed against crustal rocks along faults, and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults. To investigate this possibility, we conducted triaxial experiments under hydrothermal conditions (200-350°C), shearing serpentinite gouge between forcing blocks of granite or quartzite. In an ultramafic chemical environment, the coefficient of friction, µ, of lizardite and antigorite serpentinite is 0.5-0.6, and µ increases with increasing temperature over the tested range. However, when either lizardite or antigorite serpentinite is sheared against granite or quartzite, strength is reduced to µ ~ 0.3, with the greatest strength reductions at the highest temperatures (temperature weakening) and slowest shearing rates (velocity strengthening). The weakening is attributed to a solution-transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks. The operation of this process will promote aseismic slip (creep) along serpentinite-bearing crustal faults at otherwise seismogenic depths. During short-term experiments serpentine minerals reprecipitate in low-stress areas, whereas in longer experiments new Mg-rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite-crustal rock contact. Long-term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages, which may include extremely weak minerals such as saponite or talc, to play an increasingly important role in the mechanical behavior of the fault. Our results may explain the distribution of creep on faults in the San Andreas system.

California↗

USGS1978

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

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

Open-File Report↗

USGS2017

Selenium

Selenium (Se) was discovered in 1817 in pyrite from copper mines in Sweden. It is a trace element in Earth’s crust, with an abundance of three to seven orders of magnitude less than the major rock-forming elements. Commercial use of selenium began in the United States in 1910, when it was used as a pigment for paints, ceramic glazes, and red glass. Since that time, it has had many other economic uses—notably, in the 1930s and 1940s, when it was used in rectifiers (which change alternating current to direct current), and in the 1960s, when it began to be used in the liner of photocopier drums. In the 21st century, other compounds have replaced selenium in these older products; modern uses for selenium include energy-efficient windows that limit heat transfer and thin-film photovoltaic cells that convert solar energy into electricity. In Earth’s crust, selenium is found as selenide minerals, selenate and selenite salts, and as substitution for sulfur in sulfide minerals. It is the sulfide minerals, most commonly those in porphyry copper deposits, that provide the bulk of the selenium produced for the international commodity market. Selenium is obtained as a byproduct of copper refining and recovered from the anode slimes generated in electrolytic production of copper. Because of this, the countries that have the largest resources and (or) reserves of copper also have the largest resources and (or) reserves of selenium. Because selenium occurs naturally in Earth’s crust, its presence in air, water, and soil results from both geologic reactions and human activity. Selenium is found concentrated naturally in soils that overlie bedrock with high selenium concentrations. Selenium mining, processing, use in industrial and agricultural applications, and disposal may all contribute selenium to the environment. A well-known case of selenium contamination from agricultural practices was discovered in 1983 in the Kesterson National Wildlife Refuge in California. There, waters draining from agricultural fields created wetlands with high concentrations of dissolved selenium in the water. The selenium was taken up by aquatic wildlife and caused massive numbers of embryonic deformities and deaths. Regulatory agencies have since worked to safeguard ecological and human health by creating environmental exposure guidelines based upon selenium concentrations in water and in fish tissue. Any attempt to regulate selenium concentrations requires a delicate balance because selenium occurs naturally and is also a vital nutrient for the health of wildlife, domestic stock, and humans. Selenium is commonly added as a vitamin to animal feed, and in some regions of the United States and the world, it is added as an amendment to soils for uptake by agricultural crops. The important role of selenium in economic products, energy supply, agriculture, and health will continue for well into the future. The challenge to society is to balance the benefits of selenium use with the environmental consequences of its extraction. Increased understanding of the elemental cycle of selenium in the earth may lead to new (or unconventional) sources of selenium, the discovery of new methods of extraction, and new technologies for minimizing the transfer of selenium from rock to biota, so to protect environmental and human health.

Professional Paper↗

USGS1976

Water resources of the Rainy Lake watershed, northeastern Minnesota

The watershed includes 1,481 lakes that are 10 acres (4 square hectometers) or larger (Minnesota Division of Waters, Soils, and Minerals, 1968). The area of these lakes total about 435,000 acres (176,000 hm 2 ) or 15 percent of the watershed. Most of the lakes are smaller than 250 acres (101 hm 2 ) (graph); data pertaining to selected large lakes are given in the table below. More than 60 percent of the lakes larger than 10 acres (4 hm 2 ) are in the BWCA. The primitive character of the BWCA is maintained in accordance with the Wilderness Act of September 3, 1964. Most lakes not in the BWCA were assigned a Public Waters Classification by the Minnesota Department of Natural Resources, based upon the suitability of the lake for future shoreland development (unpublished data from the Minnesota Department of Natural Resources). “Natural environment” is most restrictive and “general development” least restrictive with respect to development standards. About 80 percent of lakes classified in the watershed have been designated “natural environment.”

Minnesota↗

USGS2017

Cobalt—Styles of deposits and the search for primary deposits

Cobalt (Co) is a potentially critical mineral. The vast majority of cobalt is a byproduct of copper and (or) nickel production. Cobalt is increasingly used in magnets and rechargeable batteries. More than 50 percent of primary cobalt production is from the Central African Copperbelt. The Central African Copperbelt is the only sedimentary rock-hosted stratiform copper district that contains significant cobalt. Its presence may indicate significant mafic-ultramafic rocks in the local basement. The balance of primary cobalt production is from magmatic nickel-copper and nickel laterite deposits. Cobalt is present in several carbonate-hosted lead-zinc and copper districts. It is also variably present in Besshi-type volcanogenic massive sulfide and siliciclastic sedimentary rock-hosted deposits in back arc and rift environments associated with mafic-ultramafic rocks. Metasedimentary cobalt-copper-gold deposits (such as Blackbird, Idaho), iron oxide-copper-gold deposits, and the five-element vein deposits (such as Cobalt, Ontario) contain different amounts of cobalt. None of these deposit types show direct links to mafic-ultramafic rocks; the deposits may result from crustal-scale hydrothermal systems capable of leaching and transporting cobalt from great depths. Hydrothermal deposits associated with ultramafic rocks, typified by the Bou Azzer district of Morocco, represent another type of primary cobalt deposit. In the United States, exploration for cobalt deposits may focus on magmatic nickel-copper deposits in the Archean and Proterozoic rocks of the Midwest and the east coast (Pennsylvania) and younger mafic rocks in southeastern and southern Alaska; also, possibly basement rocks in southeastern Missouri. Other potential exploration targets include— The Belt-Purcell basin of British Columbia (Canada), Idaho, Montana, and Washington for different styles of sedimentary rock-hosted cobalt deposits; Besshi-type VMS deposits, such as the Greens Creek (Alaska) deposit and the Ducktown (Tennessee) waste and tailings; and Known five-element vein districts in Arizona and New Mexico, as well as in the Yukon-Tanana terrane of Alaska; and hydrothermal deposits associated with ultramafic rocks along the west coast, in Alaska, and in the Appalachian Mountains.

Open-File Report↗

USGS1994

An interactive code (NETPATH) for modeling NET geochemical reactions along a flow PATH, version 2.0

NETPATH is an interactive Fortran 77 computer program used to interpret net geochemical mass-balance reactions between an initial and final water along a hydrologic flow path. Alternatively, NETPATH computes the mixing proportions of two to five initial waters and net geochemical reactions that can account for the observed composition of a final water. The program utilizes previously defined chemical and isotopic data for waters from a hydrochemical system. For a set of mineral and (or) gas phases hypothesized to be the reactive phases in the system, NETPATH calculates the mass transfers in every possible combination of the selected phases that accounts for the observed changes in the selected chemical and (or) isotopic compositions observed along the flow path. The calculations are of use in interpreting geochemical reactions, mixing proportions, evaporation and (or) dilution of waters, and mineral mass transfer in the chemical and isotopic evolution of natural and environmental waters. Rayleigh distillation calculations are applied to each mass-balance model that satisfies the constraints to predict carbon, sulfur, nitrogen, and strontium isotopic compositions at the end point, including radiocarbon dating. DB is an interactive Fortran 77 computer program used to enter analytical data into NETPATH, and calculate the distribution of species in aqueous solution. This report describes the types of problems that can be solved, the methods used to solve problems, and the features available in the program to facilitate these solutions. Examples are presented to demonstrate most of the applications and features of NETPATH. The codes DB and NETPATH can be executed in the UNIX or DOS1 environment. This report replaces U.S. Geological Survey Water-Resources Investigations Report 91-4078, by Plummer and others, which described the original release of NETPATH, version 1.0 (dated December, 1991), and documents revisions and enhancements that are included in version 2.0. 1 The use of trade, brand or product names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

Water-Resources Investigations Report↗

USGS1983

Lithologic mapping using Landsat thematic mapper data

The Landsat-4 Thematic Mapper (TM), with its new near infrared bands centered at 1.65 μm and 2.20 μm and spatial resolution of 30 m has been used to distinguish rocks containing minerals having ferric-iron absorption bands in the visible and near-infrared and Al-O- and CO 3 absorption bands in the 2.1-2.4 μm regions. On the basis of characteristic absorption bands, digitally processed TM data were used to differentiate vegetated from non-vegetated areas, limonitic from nonlimonitic rocks, rocks containing minerals having absorption bands in the near-infrared region from rocks lacking infrared absorption bands. Specific minerals were detected in both the humid eastern and semi-arid western United States. The absorption bands in the near-infrared region were used to detect kaolinite in open-pit exposures of a kaolin mining district near Macon, Georgia; calcium carbonate in the back sands along the east coast of Floridia; and kaolinite, alunite, jarosite, sericite and gypsum in natural exposures near Boulder City, Nevada. These results show that the additional spectral bands in the near-infrared region and increased spatial resolution of the Thematic Mapper provide a valuable tool for distinguishing several significant geologic materials not distinguishable from space using previous imaging systems. They also show that TM data can be successfully used in a variety of geologic environments.

Pecora VIII Symposium↗

USGS1970

Distribution of silver and copper in placer gold derived from the northeastern part of the Colorado Mineral Belt

Placer gold grains from the modern streams originating in the Colorado Mineral Belt were examined for silver and copper content on a quantitative basis utilizing the electron microprobe. The variation among grains from a particular locality is large, but the mean silver content of the interior of the placer gold grains from each locality and (or) the variation in copper content may be of value in distinguishing lode sources and gold mining districts. Microprobe analysis of the interior of gold grains is independent of chemical actions that affect the border of placer gold grains during their transport history, and it is shown that distinct compositional groups of different lode sources may be identified even in a single sample--information that may aid in recognizing the existence of concealed lodes that once contributed to a placer environment.

Colorado↗

USGS1979

Modern marine sediments as a natural analog to the chemically stressed environment of a landfill

Chemical reactions that occur in landfills are analogous to those reactions that occur in marine sediments. Lateral zonation of C, N, S, O, H, Fe and Mn species in landfills is similar to the vertical zonation of these species in marine sediments and results from the following reaction sequence: (1) oxidation of C, N and S species in the presence of dissolved free oxygen to HCO 3 - , NO 3 - and SO 4 2 ; (2) after consumption of molecular oxygen, then NO 3 - is reduced, and Fe and Mn are solubilized; (3) SO 4 2- is reduced to sulfide; and (4) organic compounds become the source of oxygen, and CH 4 and NH 4 + are formed as fermentation products. In a landfill in Delaware the oxidation potential increases down-gradient and the redox zones in the reducing plume are characterized by: CH 4 , NH 4 + ,Fe 2+ . Mn 2+ , HCO 3 - and NO 3 - . Lack of SO 4 2- at that landfill eliminates the sulfide zone. Although it has not been observed at landfills, mineral alteration should result in precipitation of pyrite and/or siderite downgradient. Controls on the pH of leachate are the relative rates of production of HCO 3 - , NH 4 + and CH 4 . Production of methane by fermentation at landfills results in 13 C isotope fractionation and the accumulation of isotopically heavy σ CO 2 (+10 to +18 0 / 00 PDB). Isotope measurements may be useful to determine the extent of CO 2 reduction in landfills and extent of dilution downgradient. The boundaries of reaction zones in stressed aquifers are determined by head distribution and flow velocity. Thus, if the groundwater flow is rapid relative to reaction rates, redox zones will develop downgradient. Where groundwater flow velocities are low the zones will overlap to the extent that they may be indeterminate.

Journal of Hydrology↗

USGS1968

The geologic classification of the meteorites

The meteorite classes of Prior and Mason are assigned to three proposed genetic groups on the basis of a combination of compositional, mineralogical, and elemental characteristics: l) the calcium-poor, volatile-rich carbonaceous chondrites and achondrites; 2) the calcium-poor, volatile-poor chondrites (enstatite, bronzite, hypersthene, and pigeonite), achondrites (enstatite, hypersthene, and pigeonite), stonyirons (pallasites, siderophyre), and irons; and, 3) the calcium-rich (basaltic) achondrites. Chondrites are correlated with calcium-poor achondrites and the silicate phase of the pallasitic meteorites on Fe contents of olivine and pyroxene; and with metal of the stony-irons and irons on the basis of trace elements (Ga and Ge). Transitions in structure and texture between the chondrites and achondrites are recognized. The Van Schmus-Wood chemical-petrologic classification of the chondrites has been modified and expanded to a mineralogic-petrologic classification of the chondrites and calcium-poor achondrites. Chondrites apparently are the first rocks of the solar system. Paragenetic and textural relations in the Murray carbonaceous chondrite shed new light on the manner of accretion, and on the character of dispersed solid materials ('dust', and chondrules and metal) that existed in the solar system before accretion. Two pre-accretionary mineral assemblages (components) are recognized in the carbonaceous chondrites and in the unequilibrated volatile-poor chondrites. They are: 1) a 'low temperature' water-, rare gas-, and carbon-bearing component; and, 2) a high temperature anhydrous silicate and metal component. Paragenetic relations indicate that component 2 materials predate chondrite formation. An accretionary assemblage (component 3) also is recognized in the carbonaceous chondrites and in the unequilibrated volatile-poor chondrites. Component 3 consists of very fine grains of olivine and pyroxene, which occur as pervasive disseminations, as small irregular aggregates of grains, and as large subround to round, finely granular accretional chondrules. Evidence in Murray indicates that component 3 silicates precipitated abruptly and at low pressures, possibly from a high temperature gas, in an environment that contained dispersed component 1 and 2 materials. All component 3 aggregates in Murray contain component 1 material, most commonly as flakes, and locally as tiny granules and larger spherules, some of which are hollow and some of which were broken prior to their mechanical incorporation in accretionary chondrules. Accretion may have occurred as ices associated with dispersed water-bearing component 1 materials temporarily melted during the precipitation of component 3 silicates, and then abruptly refroze to form an icy cementing material. Group 1 materials may be cometary, and group 2 materials may be asteroidal. Schematic models are proposed. Evidence is reviewed for the lunar origin of the pyroxeneplagioclase achondrites. On the basis of natural remanent magnetism, it is suggested that the very scarce diopside-olivine achondrites may be samples from Mars. A classification of the meteorite breccias, including the calcium-poor and calcium-rich mesosiderites, and irons that contain silicate fragments, is proposed. A fragmentation history of the meteorites is outlined on the basis of evidence in the polymict breccias, and from gas retention ages in stones and exposure ages in irons. Cometal impacts appear to have caused the initial fragmentation, stud possibly the perturbation of orbits, of two inferred asteroidal bodies (enstatite and bronzite), one and possibly both events occurring before 2000 m.y. ago. Several impacts apparently occurred on the inferred hypersthene body in the interval 1000 to 2000 m.y. ago. Major breakups of the three bodies apparently occurred as the result of interasteroidal collisions at about 900 m.y. ago, and 600 to 700 m.y. ago. The breakups were followed by a number of fr

Open-File Report↗

USGS1996

Petrography and geochemistry of the San Miguel lignite, Jackson Group (Eocene), south Texas

The San Miguel lignite deposit (late Eocene, lower Jackson Group) of south Texas consists of four or more thin (generally < 1 m thick) lignite benches that are separated by claystone and mudstone partings. The partings are composed of altered volcanic air-fall ash that has been reworked by tidal or channel processes associated with a back-barrier depositional environment. The purpose of this study is to examine the relationship between the ash yield and the petrographic and geochemical characteristics of the San Miguel lignite as mined. Particular attention is given to 12 of the environmentally sensitive trace elements (As, Be, Cd, Cr, Co, Hg, Mn, Ni, Pb, Sb, Se, and U) that have been identified as possible hazardous air pollutants (HAPs) by the United States Clean Air Act Amendments of 1990. A total of 29 rock and lignite samples were collected and characterized by geochemical and petrographic methods. The major conclusions of the study are as follows: (1) The distribution of Mn is inversely related to the ash yield of the lignite samples. This indicates an organic affinity, or an association with finely disseminated minerals in the lignite that contain this element. (2) On a whole-coal basis, the concentration of the HAPs' element Pb is positively related to ash yield in lignite samples. This indicates an inorganic affinity for Pb. (3) Average whole-coal concentrations of As, Be, Sb, and U in the San Miguel samples are greater than published averages for these elements in other U.S. lignites. (4) The upper and lower lignite benches of the San Miguel deposit are both ash- and algal-rich, indicating that these intervals were probably deposited in wetter conditions than those in which the middle intervals formed. (5) The dominance of the eugelinite maceral subgroup over the huminite subgroup indicates that the San Miguel lignites were subjected to peat-forming conditions (either biogenic or chemical) that enabled degradation of wood cellular material into matrix gels, or that the plants that formed these lignite benches were less woody and more prone to formation of matrix gels. (6) An inertinite-rich layer (top of the B bed) might have formed from widespread oxidation of the San Miguel peat as a result of a volcanic ash fall which was subsequently reworked.

Organic Geochemistry↗

USGS2021

Emergent biogeochemical risks from Arctic permafrost degradation

The Arctic cryosphere is collapsing, posing overlapping environmental risks. In particular, thawing permafrost threatens to release biological, chemical and radioactive materials that have been sequestered for tens to hundreds of thousands of years. As these constituents re-enter the environment, they have the potential to disrupt ecosystem function, reduce the populations of unique Arctic wildlife and endanger human health. Here, we review the current state of the science to identify potential hazards currently frozen in Arctic permafrost. We also consider the cascading natural and anthropogenic processes that may compound the impacts of these risks, as it is unclear whether the highly adapted Arctic ecosystems have the resilience to withstand new stresses. We conclude by recommending research priorities to address these underappreciated risks.

Nature Climate Change↗

USGS2013

Silicate melt inclusion evidence for extreme pre-eruptive enrichment and post-eruptive depletion of lithium in silicic volcanic rocks of the western United States: implications for the origin of lithium-rich brines

To evaluate whether anatectic and/or highly fractionated lithophile element-enriched rhyolite tuffs deposited in arid lacustrine basins lose enough lithium during eruption, lithification, and weathering to generate significant Li brine resources, pre-eruptive melt compositions, preserved in inclusions, and the magnitude of post-eruptive Li depletions, evident in host rhyolites, were documented at six sites in the western United States. Each rhyolite is a member of the bimodal basalt-rhyolite assemblage associated with extensional tectonics that produced the Basin and Range province and Rio Grande rift, an evolving pattern of closed drainage basins, and geothermal energy or mineral resources. Results from the 0.8 Ma Bishop tuff (geothermal) in California, 1.3 to 1.6 Ma Cerro Toledo and Upper Bandelier tephra (geothermal) and 27.9 Ma Taylor Creek rhyolite (Sn) in New Mexico, 21.7 Ma Spor Mountain tuff (Be, U, F) and 24.6 Ma Pine Grove tuff (Mo) in Utah, and 27.6 Ma Hideaway Park tuff (Mo) in Colorado support the following conclusions. Melt inclusions in quartz phenocrysts from rhyolite tuffs associated with hydrothermal deposits of Sn, Mo, and Be are extremely enriched in Li (1,000s of ppm); those from Spor Mountain have the highest Li abundance yet recorded (max 5,200 ppm, median 3,750 ppm). Forty-five to 98% of the Li present in pre-eruptive magma was lost to the environment from these rhyolite tuffs. The amount of Li lost from the small volumes (1–10 km3) of Li-enriched rhyolite deposited in closed basins is sufficient to produce world-class Li brine resources. After each eruption, meteoric water leaches Li from tuff, which drains into playas, where it is concentrated by evaporation. The localized occurrence of Li-enriched rhyolites may explain why brines in arid lacustrine basins seldom have economic concentrations of Li. Considering that hydrothermal deposits of Sn, Mo, Be, U, and F may indicate potential for Li brines in nearby basins, we surmise that the world’s largest Li brine resource in the Salar de Uyuni (10 Mt) received Li from nearby rhyolite tuffs in the Bolivian tin belt.

California;Colorado;New Mexico;Utah↗

USGS1996

Data base for a national mineral-resource assessment of undiscovered deposits of gold, silver, copper, lead, and zinc in the conterminous United States

For this assessment, the conterminous United States was divided into 12 regions Adirondack Mountains, Central and Southern Rocky Mountains, Colorado Plateau, East Central, Great Basin, Great Plains, Lake Superior, Northern Appalachians, Northern Rocky Mountains, Pacific Coast, Southern Appalachians, and Southern Basin and Range. The assessment, which was conducted by regional assessment teams of scientists from the USGS, was based on the concepts of permissive tracts and deposit models. Permissive tracts are discrete areas of the United States for which estimates of numbers of undiscovered deposits of a particular deposit type were made. A permissive tract is defined by its geographic boundaries such that the probability of deposits of the type delineated occurring outside the boundary is neglible. Deposit models, which are based on a compilation of worldwide literature and on observation, are sets of data in a convenient form that describe a group of deposits which have similar characteristics and that contain information on the common geologic attributes of the deposits and the environments in which they are found. Within each region, the assessment teams delineated permissive tracts for those deposit models that were judged to be appropriate and, when the amount of information warranted, estimated the number of undiscovered deposits. A total of 46 deposit models were used to assess 236 separate permissive tracts. Estimates of undiscovered deposits were limited to a depth of 1 km beneath the surface of the Earth. The estimates of the number of undiscovered deposits of gold, silver, copper, lead, and zinc were expressed in the form of a probability distribution. Commonly, the number of undiscovered deposits was estimated at the 90th, 50th, and 10th percentiles. A Monte Carlo simulation computer program was used to combine the probability distribution of the number of undiscovered deposits with the grade and tonnage data sets associated with each deposit model to obtain the probability distribution for undiscovered metal.

conterminous United States↗

USGS1976

Medicine Lodge thrust system, east-central Idaho and southwest Montana

The Medicine Lodge thrust system, exposed in east-central Idaho and southwest Montana, is a major segment of the North America Cordilleran fold and thrust belt on which Precambrian and Paleozoic rocks have been telescoped and transported far east of their depositional area. The fault has overlapped rocks that initially were deposited in differing sedimentary environments on opposite sides of the northwest-trending geanticlinal Lemhi arch. The nature of the arch itself has been obscured by later thrusting, but it can be roughly reconstructed as a major landmass recurrently uplifted from Precambrian Y time at least through the Mesozoic. Although sections of the large landmass have been identified in the past as small islands, it was instead a southern extension of Belt island, and exerted a major influence on sedimentation patterns. The thrust has obscured recognition of correlative sedimentary rock units. It also appears to have controlled the distribution of volcanic rocks in satellite centers of the main field of Challis Volcanics. The thrust system has exerted a major influence on the emplacement of granodiorite-quartz monzonite stocks and related mineral deposits in east-central Idaho. Recognition of the fault as a major influence in intrusive activity and deposition of metallic mineral deposits suggests new possibilities for mineral resource exploration in this region. And consideration of the stratigraphic, paleogeographic, and structural framework of sedimentary rocks beneath the thrust suggests the possibility of petroleum and natural gas resources in the region north of the Snake River Plain.

Idaho, Montana↗

USGS2010

Mg isotope constraints on soil pore-fluid chemistry: Evidence from Santa Cruz, California

Mg isotope ratios ( 26 Mg/ 24 Mg) are reported in soil pore-fluids, rain and seawater, grass and smectite from a 90 kyr old soil, developed on an uplifted marine terrace from Santa Cruz, California. Rain water has an invariant 26 Mg/ 24 Mg ratio (expressed as δ26 Mg> δ26 Mg ) at −0.79 ± 0.05‰, identical to seawater δ26 Mg> δ26 Mg . Detrital smectite (from the base of the soil profile, and therefore unweathered) has a δ26Mg"> δ26Mg value of 0.11‰, potentially enriched in 26 Mg by up to 0.3‰ compared to the bulk silicate Earth Mg isotope composition (although within the range of all terrestrial silicates). The soil pore-waters show a continuous profile with depth for δ26 Mg> δ26 Mg , ranging from −0.99‰ near the surface to −0.43‰ at the base of the profile. Shallow pore-waters (<1 m) have δ26 Mg> δ26 Mg values that are similar to, or slightly lower than the rain waters. This implies that the degree of biological cycling of Mg in the pore-waters is relatively small and is quantified as <32%, calculated using the average Mg isotope enrichment factor between grass and rain ( δ26 Mggrass- δ26 Mgrain> δ26 Mggrass- δ26 Mgrain ) of 0.21‰. The deep pore-waters (1–15 m deep) have δ26 Mg> δ26 Mg values that are intermediate between the smectite and rain, ranging from −0.76‰ to −0.43‰, and show a similar trend with depth compared to Sr isotope ratios. The similarity between Sr and Mg isotope ratios confirms that the Mg in the pore-waters can be explained by a mixture between rain and smectite derived Mg, despite the fact that Mg and Sr concentrations may be buffered by the exchangeable reservoir. However, whilst Sr isotope ratios in the pore-waters span almost the complete range between mineral and rain inputs, Mg isotopes compositions are much closer to the rain inputs. If Mg and Sr isotope ratios are controlled uniquely by a mixture, the data can be used to estimate the mineral weathering inputs to the pore-waters, by correcting for the rain inputs. This isotopic correction is compared to the commonly used chloride correction for precipitation inputs. A consistent interpretation is only possible if Mg isotope ratios are fractionated either by the precipitation of a secondary Mg bearing phase, not detected by conventional methods, or selective leaching of 24 Mg from smectite. There is therefore dual control on the Mg isotopic composition of the pore-waters, mixing of two inputs with distinct isotopic compositions, modified by fractionation. The data provide (1) further evidence for Mg isotope fractionation at the surface of the Earth and (2) the first field evidence of Mg isotope fractionation during uptake by natural plants. The coherent behaviour of Mg isotope ratios in soil environments is encouraging for the development of Mg isotope ratios as a quantitative tracer of both weathering inputs of Mg to waters, and the physicochemical processes that cycle Mg, a major cation linked to the carbon cycle, during continental weathering.

California↗

USGS2013

Geologic occurrences of erionite in the United States: an emerging national public health concern for respiratory disease

Erionite, a mineral series within the zeolite group, is classified as a Group 1 known respiratory carcinogen. This designation resulted from extremely high incidences of mesothelioma discovered in three small villages from the Cappadocia region of Turkey, where the disease was linked to environmental exposures to fibrous forms of erionite. Natural deposits of erionite, including fibrous forms, have been identified in the past in the western United States. Until recently, these occurrences have generally been overlooked as a potential hazard. In the last several years, concerns have emerged regarding the potential for environmental and occupational exposures to erionite in the United States, such as erionite-bearing gravels in western North Dakota mined and used to surface unpaved roads. As a result, there has been much interest in identifying locations and geologic environments across the United States where erionite occurs naturally. A 1996 U.S. Geological Survey report describing erionite occurrences in the United States has been widely cited as a compilation of all US erionite deposits; however, this compilation only focused on one of several geologic environments in which erionite can form. Also, new occurrences of erionite have been identified in recent years. Using a detailed literature survey, this paper updates and expands the erionite occurrences database, provided in a supplemental file (US_erionite.xls). Epidemiology, public health, and natural hazard studies can incorporate this information on known erionite occurrences and their characteristics. By recognizing that only specific geologic settings and formations are hosts to erionite, this knowledge can be used in developing management plans designed to protect the public.

Arizona;California;Colorado;Idaho;Montana;New Mexi↗

USGS2012

Using hydrogeology to identify the source of groundwater to Montezuma Well, a natural spring in central Arizona: part 1

Montezuma Well is a natural spring located within a “sinkhole” in the desert environment of the Verde Valley in Central Arizona. It is managed by the National Park Service as part of Montezuma Castle National Monument. Because of increasing development of groundwater in the area, this research was undertaken to better understand the sources of groundwater to Montezuma Well. The use of well logs and geophysics provides details on the geology in the area around Montezuma Well. This includes characterizing the extent and position of a basalt dike that intruded a deep fracture zone. This low permeability barrier forces groundwater to the surface at the Montezuma Well “pool” with sufficient velocity to entrain sand-sized particles from underlying bedrock. Permeable fractures along and above the basalt dike provide conduits that carry deep sourced carbon dioxide to the surface, which can dissolve carbonate minerals along the transport path in response to the added carbon dioxide. At the ground surface, CO 2 degasses, depositing travertine. Geologic cross sections, rock geochemistry, and semi-quantitative groundwater flow modeling provide a hydrogeologic framework that indicates groundwater flow through a karstic limestone at depth (Redwall Limestone) as the most significant source of groundwater to Montezuma Well. Additional groundwater flow from the overlying formations (Verde Formation and Permian Sandstones) is a possibility, but significant flow from these units is not indicated.

Arizona↗