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At least 451 records · Page 25Linked to original sources

Mineral resources of the Sagebrush Focal Areas of Idaho, Montana, Nevada, Oregon, Utah, and Wyoming

Scientific Investigations Report 2016–5089 and accompanying data releases are the products of the U.S. Geological Survey (USGS) Sagebrush Mineral-Resource Assessment (SaMiRA). The assessment was done at the request of the Bureau of Land Management (BLM) to evaluate the mineral-resource potential of some 10 million acres of Federal and adjacent lands in Idaho, Montana, Nevada, Oregon, Utah, and Wyoming. The need for this assessment arose from the decision by the Secretary of the Interior to pursue the protection of large tracts of contiguous habitat for the greater sage-grouse ( Centrocercus urophasianus ) in the Western United States. One component of the Department of the Interior plan to protect the habitat areas includes withdrawing selected lands from future exploration and development of mineral and energy resources, including copper, gold, silver, rare earth elements, and other commodities used in the U.S. economy. The assessment evaluates the potential for locatable minerals such as gold, copper, and lithium and describes the nature and occurrence of leaseable and salable minerals for seven Sagebrush Focal Areas and additional lands in Nevada (“Nevada additions”) delineated by BLM. Supporting data are available in a series of USGS data releases describing mineral occurrences (the USGS Mineral Deposit Database or “USMIN”), oil and gas production and well status, previous mineral-resource assessments that covered parts of the areas studied, and a compilation of mineral-use cases based on data provided by BLM, as well as results of the locatable mineral-resource assessment in a geographic information system. The present assessment of mineral-resource potential will contribute to a better understanding of the economic and environmental trade-offs that would result from closing approximately 1 0 million acres of Federal lands to mineral entry.

Idaho, Montana, Nevada, Oregon, Utah, Wyoming↗

Hyperspectral (VNIR-SWIR) analysis of roll front uranium host rocks and industrial minerals from Karnes and Live Oak Counties, Texas Coastal Plain

VNIR-SWIR (400–2500 nm) reflectance measurements were made on the surfaces of various cores, cuttings and sample splits of sedimentary rocks from the Tertiary Jackson Group, and Catahoula, Oakville and Goliad Formations. These rocks vary in composition and texture from mudstone and claystone to sandstone and are known host rocks for roll front uranium occurrences in Karnes and Live Oak Counties, Texas. Spectral reflectance profiles, 569 in total, were reduced to 125 representative spectral signatures, which were analyzed using the U.S. Geological Survey's (USGS) Material Identification and Characterization Algorithm (MICA). MICA uses an automated continuum-removal procedure together with a least-squares linear regression to determine the fit of observed sample spectral absorption features to those of reference mineral standards in a spectral library. The reference minerals include various clay, mica, carbonate, ferric and ferrous iron minerals and their mixtures. In addition, absorption feature band-depth analysis was done to identify rock surfaces exhibiting absorption features related to uranium and zeolite minerals, which were not included in the command files used to execute MICA. Rocks from each of the four geologic units produced broadly similar spectral signatures as a result of comparable mineral compositions, but there were some notable differences. For example, Ca- and Na-montmorillonite was matched most frequently to the spectral absorption features in 2-μm (∼2000–2500 nm) wavelengths, while goethite occurred often at 1-μm (∼400–1000 nm) wavelengths. The latter is related to limonitic iron-staining in and around oxidized zones of the uranium roll front as described in previous papers. Rocks of the Jackson Group differed from those of the Catahoula, Oakville and Goliad units in that the former exhibited spectral features we interpret as being due to the presence of lignite-bearing mudstone layers. Goliad rocks exhibit spectral features related to dolomite, gypsum, anhydrite, and an unidentified green clay mineral that is possibly glauconite . Jackson Group rocks also exhibit weak but well-resolved absorption features at 964 and 1157 nm related to either or both zeolite minerals clinoptilolite and heulandite. These zeolite minerals and a few spectra exhibiting hydrous silica absorption features are indicative of alteration of volcanic glass in tuffaceous mudstone and claystone layers. A few sample spectra exhibited strong absorption features at around 1135 nm related to the uranium mineral coffinite. Both the 1135 nm coffinite and 1157 nm zeolite absorption features overlap somewhat, potentially making them difficult to distinguish without additional hyperspectral field, laboratory or remote sensing data. The results of this study were compared to mixtures of minerals described for ore, gangue and alteration minerals in deposit models for sandstone-hosted uranium, sedimentary bentonite and sedimentary zeolite. Use of these spectra can help facilitate mapping of both waste materials from the legacy mining of the above commodities, as well as future exploration and resource assessment activities.

Texas↗

Top-down targeted network analysis of critical mineral commodities applied to international geochemistry database

The global demand for critical mineral commodities is rapidly increasing, making domestic production an important factor in supporting the economy and national security. Large scale, publicly available geochemical databases allow for the application of data informatics methods to interrogate critical mineral commodities data for correlations in deposit formation and distribution, particularly for identifying enrichment of multiple critical mineral commodities at the same deposit. In this study, we applied network analysis to the Critical Minerals Mapping Initiative (CMMI) ore geochemistry (Critical Minerals in Ores, CMiO) database to identify the high concentration (defined as 10× bulk crustal abundance) co-occurrence of different critical mineral commodities across a mineral system hierarchy from deposit environments to individual deposits. Identifying patterns or unique outliers in enrichment in network communities will allow for the location of secondary critical mineral commodity resources from under-utilized deposits. We find trends in the enrichment of critical mineral commodities in network-communities between the elements praseodymium (Pr), neodymium (Nd), terbium (Tb), and dysprosium (Dy) across multiple CMiO database deposit environments and groups down to specific deposit types and sites. A separate trend in network community deposition is observed as well between iridium (Ir) and platinum (Pt) in deposit environments, groups, types, and sites. Network analysis focused on critical minerals in magmatic-hydrothermal deposits identified multiple deposit sites from different deposit types within the CMiO database with concentrations of Dy, Nd, Tb, Pr, Ir, and Pt that are at least ten times greater than the crustal average. This approach can be applied to any target element(s) or deposit(s) of interest, allowing broad investigation of co-enriched critical mineral commodities.

Journal of Geochemical Exploration↗

Heavy-mineral suites in unconsolidated Paleocene and younger sands, western Tennessee

Heavy-mineral suites from unconsolidated sands of Wilcox and Claiborne age (Eocene) in the subsurface of western Tennessee were tabulated and compared with heavy-mineral suites obtained from outcropping sands known to be of Midway (Paleocene) and Wilcox age and younger. In the subsurface at Memphis, both pink and colorless garnet are relatively abundant in the Claiborne but rare in the Wilcox. Garnet, however, is very rare in both the Claiborne and the Wilcox in the subsurface 35 miles northeast of Memphis. The mineral is very rare also in the terrace sands of western Tennessee and in samples of the Pliocene(?) and Pleistocene deposits of the Tennessee River in eastern and western Tennessee. It is possible, therefore, that the relative abundance of the mineral garnet is related to the quantity of sediment received from differing source areas in Wilcox and Claiborne times, but that, owing to the shifting of the axis of the embayment, no one source area furnished all the sediment for any formation. Heavy-mineral suites from Pliocene(?) and Pleistocene terrace deposits of the Tennessee River in both eastern and western Tennessee, and heavy-mineral suites from Pliocene(?) deposits of the Mississippi River are much alike, and the only isotropic mineral noted in these sediments was a very rare green mineral. Heavy-mineral suites from Recent deposits of the Mississippi River at Memphis and reported heavy-mineral suites from Cambrian sandstones of Wisconsin and Minnesota differ greatly from heavy-mineral suites of Pliocene(?) terrace deposits of the Tennessee and Mississippi Rivers and include much pink and colorless garnet. The possibility, therefore, is suggested that the Pliocene(?) terrace deposits of the Mississippi River in western Tennessee were derived largely from the basin of the Tennessee River.

Tennessee↗

Metamorphism and gold mineralization in the Blue Ridge, southernmost Appalachians

Lode gold mineralization in the Blue Ridge of the southernmost Appalachians is hosted by metavolcanic rocks (e.g., Anna Howe mine, AL; Royal Vindicator mine, GA), metaplutonic rocks (e.g., Hog Mountain mine, AL), and metasedimentary rocks (e.g., Lowe, Tallapoosa, and Jones Vein mines, AL). Most gold occurs in synkinematic quartz + or - plagioclase + or - pyrite + or - pyrrhotite + or - chlorite veins localized along polydeformational faults that juxtapose rocks with significantly different peak metamorphic mineral assemblages.Mineralogy, chemistry, and O and H isotope studies suggest that the three types of host rocks have undergone differing amounts and types of alteration during mineralization. Limited wall-rock alteration in metavolcanic- and metasediment-hosted deposits, and relatively extensive wall-rock alteration in granitoid-hosted deposits, suggests that most deposits formed from fluids that were close to equilibrium with metavolcanic and metasedimentary rocks. Stable isotope compositions of the fluids calculated from vein minerals and vein selvages are consistent with a predominantly metasedimentary fluid source, but vary from deposit to deposit (-22 to -47ppm delta D, 4-5ppm, delta 18 O, and 5-7ppm delta 34 S at Anna Howe and Royal Vindicator; -48 to -50ppm delta D, 9-13ppm delta 18 O, and ca. 19ppm delta 34 S at Lowe and Jones Vein; and -22 to -23ppm delta D, 8-11ppm delta 18 O, 9-10ppm delta 34 S, and -6 delta 13 C at Hog Mountain). Silicate mineral thermobarometry of vein, vein selvage, and wall-rock mineral assemblages indicate that mineralization and regional metamorphism occured at greenschist to amphibolite facies (480 degrees + or - 75 degrees C at Anna Howe, 535 degrees + or - 50 degrees C at 6.4 + or - 1 kbars at Lowe, 530 degrees + or - 50 degrees C at 6.9 + or - 1 kbars at Tallapoosa, and 460 degrees + or - 50 degrees C at 5.5 + or - 1 kbars at Hog Mountain). Oxygen isotope fractionation between vein minerals and selvage minerals consistently records equilibration temperatures that are similar to or slightly lower than those estimated from silicate thermometry.Auriferous veins contain numerous fluid inclusions that were emplaced in several stages and can be subdivided into five compositional types based on salt and CO 2 concentrations. Fluid inclusion isochores for early formed inclusions from these veins intercept the pressure and temperature conditions estimated from silicate mineral thermobarometry and stable isotope thermometry, and are compatible with entrapment at those conditions. These fluids exhibit significant variation in salinity (X (sub NaCl equiv ) ) = 0.0-0.2) and CO 2 (X (sub CO 2 ) = 0.0-0.2), suggesting variation in fluid-wall-rock interaction that accompanied gold deposition during declining temperatures. Less abundant and later fluids within the veins are dominantly CO 2 .The association of gold mineralization with structurally controlled concordant and discordant quartz sulfide veins, and the temperatures and pressures of wall-rock alteration and regional metamorphism indicate that the present distribution of gold is a result of metamorphism during progressive D 2 -D 3 deformation. Isotopic data for alteration envelopes date this event as Alleghanian: 279 + or - 14 Ma (K-Ar whole rock) and 343 + or - 18 Ma (K-Ar biotite) at Lowe; and 315 + or - 18 Ma (Rb-Sr whole-rock isochron; 87 Sr/ 86 Sr i = 0.7061 + or - 0.0008) and 294 + or - 16 Ma (K-Ar whole-rock) at Hog Mountain. Available data are compatible with development of the lodes during early Alleghanian overthrusting of allochthons over sedimentary rocks of the autochthonous North American margin. The implication is that the fluids were derived from metasedimentary and/or metavolcanic formations in the lower parts of the crystalline thrust stack (or possibly from underlying autochthonous sedimentary formations), ascended along permeable fault zones, and were emplaced as veins into dilatent areas in and adjacent to the fault zones.

Economic Geology↗

Summary mineral resource appraisal of the Richfield 1° x 2° quadrangle, west-central Utah

The mineral resource potential of the Richfield 1° x 2° quadrangle, Utah, has been appraised using geological, geophysical, geochemical, and remote-sensing techniques. These studies have led to many publications giving basic data and interpretations; of these, a series of 18 maps at 1:250,000 and 1:500,000 scales summarizing aspects of the geology, geophysics, geochemistry, and remote sensing is designated the CUSMAP (Conterminous United States Mineral Appraisal Program) folio. This circular uses the data shown on these maps to appraise the mineral resource potential of the quadrangle. The oldest rocks exposed in the Richfield quadrangle are small patches of Early Proterozoic (1.7 billion years old) gneiss and schist on the west side of the Mineral Mountains. These rocks presumably formed the basement on which many thousands of meters of Late Proterozoic, Paleozoic, and lower Mesozoic sedimentary strata were deposited. These rocks were deformed during the Late Cretaceous Sevier orogeny when Precambrian and Paleozoic strata in the western part of the quadrangle were thrust relatively eastward across Paleozoic and Mesozoic strata in the eastern part of the quadrangle. Late Cretaceous and early Tertiary highlands above the overthrust belt were eroded and much of the debris was deposited in broad basins east of the belt. Volcanism in Oligocene and earliest Miocene time formed an east-northeast-trending belt of calcalkalic volcanoes across the southern half of the quadrangle. In early Miocene time, the composition of the volcanic rocks changed to a bimodal assemblage of mafic rocks and high-silica alkali rhyolite that has been erupted episodically ever since. Syngenetic mineral resources developed during formation of both sedimentary and volcanic rocks. These include limestone and dolomite, silica-rich sandstone, metalliferous black shale, evaporite deposits, zeolite deposits, pumice, cinders and scoria, and evaporitic or diagenetic deposits in playa environments. Most of these deposits need to have markets established, or extraction and fabrication techniques developed, for them to be utilized. Most epigenetic deposits are of volcanogenic-hydrothermal origin. Deposits associated with calc-alkalic igneous activity largely contain Cu, Pb, Zn, Au, and Ag, and occur in a variety of types zoned around core intrusions. Younger deposits are mostly associated with silicic igneous centers belonging to the bimodal mafic-silicic igneous association. Resources associated with this latter group are likely to contain one or more of the elements Mo, W, U, Sn, Be, and F, as well as Pb, Zn, Au, and Ag. Alunite and kaolinite deposits are found at many mineralized centers. Most epigenetically mineralized areas expose only the upper, near-surface parts of the different hydrothermal systems; most of whatever mineral deposits formed in these systems probably still exist at depth, awaiting discovery. Our conclusion is that many mineralized areas have excellent possibilities for the occurrence of mineral resources. Each of the many identified centers of mineralization is discussed briefly in this report and an estimate made of its resource potential.

Utah↗

Conflict minerals from the Democratic Republic of the Congo—Tin processing plants, a critical part of the tin supply chain

Summary The U.S. Geological Survey (USGS) analyzes mineral and metal supply chains to identify and describe major components of material flows from ore extraction, through intermediate forms, to a final product. Supply chain analyses may be used (1) to identify risks to the United States associated with the supply of critical and strategic minerals and metals and (2) to provide greater supply chain transparency so that policymakers have the fact-based information needed to formulate public policy. This fact sheet focuses on the post-mining/pre-consumer-product part of the tin supply chain. The USGS National Minerals Information Center (NMIC) has been asked by governmental and non-governmental organizations to provide information about tantalum, tin, tungsten, and gold (collectively known as “3TG minerals”) processing facilities worldwide in response to U.S. legislation aimed at identifying and removing the supply chain links between the trade in these minerals and civil unrest in the Democratic Republic of the Congo (DRC) and adjacent countries. Post-beneficiation processing plants (generally called smelters and refineries) for 3TG mineral ores and concentrates were identified by company and industry association representatives as being a link in the 3TG mineral supply chain through which these minerals can be traced to their source of origin (mine). The determination of the source of origin is critical to the development of a complete and transparent conflict-free mineral supply chain. Tungsten processing plants were the subject of the first fact sheet in this series published by the USGS NMIC in August 2014. Background information about historical conditions and multinational stakeholders’ voluntary due diligence guidance for minerals from conflict-affected and high-risk areas was presented in the tungsten fact sheet. Tantalum processing plants were the subject of the second fact sheet in this series published by the USGS NMIC in December 2014. This fact sheet, the third in the series about 3TG minerals, focuses on the tin supply chain by listing selected processors that produced tin materials commercially worldwide during 2013–14. It does not provide any information regarding the sources of the material processed in these facilities.

Fact Sheet↗

Geochemistry, geochronology, mineralogy, and geology suggest sources of and controls on mineral systems in the southern Toquima Range, Nye County, Nevada

Geochemistry maps showing the distribution and abundance of 18 elements in about 1,400 rock samples, both mineralized and unmineralized, from the southern Toquima Range, Nev., indicate major structural and lithologic controls on mineralization, and suggest sources of the elements. Radiometric age data, lead mineralogy and paragenesis data, and lead-isotope data supplement the geochemical and geologic data, providing further insight into timing, sources, and controls on mineralization. Major zones of mineralization are centered on structural margins of calderas and principal northwest-striking fault zones, as at Round Mountain, Manhattan, and Jefferson mining districts, and on intersections of low-angle and steep structures, as at Belmont mining district. Paleozoic sedimentary rocks, mostly limestones (at Manhattan, Jefferson, and Belmont districts), and porous Oligocene ash-flow tuffs (at Round Mountain district) host the major deposits, although all rock types have been mineralized as evidenced by numerous prospects throughout the area. Principal mineral systems are gold-silver at Round Mountain where about 7 million ounces of gold and more than 4 million ounces of silver has been produced; gold at Gold Hill in the west part of the Manhattan district where about a half million ounces of gold has been produced; gold-mercury-arsenic-antimony in the east (White Caps) part of the Manhattan district where a few hundred thousand ounces of gold has been produced; and silver-lead-antimony at Belmont where more than 150,000 ounces of silver has been produced. Lesser amounts of gold and silver have been produced from the Jefferson district and from scattered mines elsewhere in the southern Toquima Range. A small amount of tungsten was produced from mines in the granite of the Round Mountain pluton exposed east of Round Mountain, and small amounts of arsenic, antimony, and mercury have been produced elsewhere in the southern Toquima Range. All elements show unique distribution patterns that suggest specific sources and lithologic influences on deposition, as well as multiple episodes of mineralization. Principal episodes of mineralization are Late Cretaceous (molybdenum and tungsten in and near granite; silver at Belmont and Silver Point mines), early Oligocene [tourmaline and base- and precious-metals around the granodiorite of Dry Canyon stock as well as at Manhattan(?)], late Oligocene (gold at Round Mountain and Jefferson), and Miocene (gold at Manhattan). Most likely principal sources of molybdenum, tungsten, silver, and bismuth are Cretaceous granites; of antimony, arsenic, and mercury are intermediate-composition early Oligocene intrusives; and of gold are early and late Oligocene and early Miocene magmas of the volcanic cycle. Lead may have been derived principally from Cretaceous granitic magma and Paleozoic sedimentary rocks. Several areas prospective for undiscovered mineral deposits are suggested by spatial patterns of element distributions related to geologic features. The Manhattan district in the vicinity of the White Caps mine may be underlain by a copper-molybdenum porphyry system related to a buried stock; peripheral high-grade gold veins and skarn deposits may be present below deposits previously mined. The Jefferson district also may be underlain by a copper-molybdenum porphyry system related to a buried stock, it too with peripheral high-grade gold deposits. The Bald Mountain Canyon belt of small gold veins has potential for deeper deposits in buried porous ash-flow tuff similar to the huge Round Mountain low-grade gold-silver deposit. Several other areas have potential for a variety of mineral deposits. Altogether the geochemical, geochronologic, mineralogic, and geologic evidence suggests recurring mineralizing episodes of varied character, from Late Cretaceous to late Tertiary time, related to a long-lived hot spot deep in the crust or in the upper mantle. Granite plutons of Late Cretaceous age were minerali

Nevada↗

Investigations needed to stimulate the development of Jordan's mineral resources

The level of living that any society can attain is a direct function of the use it makes of all kinds of raw materials (soil, water, metals, nonmetals, etc.), all kinds of energy (both animate and inanimate), and all kinds of human ingenuity; and is an inverse function of the size of the population that must share the collective product. The relation between raw materials, energy and ingenuity is such that use of a large amount of one may offset the need for large amounts of others. The most vital raw materials are water, soil, and construction materials, for these are needed in large quantities and are hard to import. Metals, chemicals, and inanimate energy are necessary for industrialization. The more of these minerals a nation possess, the better, but not nation can hope to be self-sufficient in all of the m and therefore must trade for some essential materials. Jordan’s natural resources have been little explored. The grantitc-metamorphic terrane in the southeastern part of the Kingdom could contain deposits of tungsten, rare earths, feldspar, mica, fluorite etc. and the sedimentary terrane over much of the rest of the county is favorable for the occurrence of oil. Even if none of these minerals is found, however, Jordan’s other mineral resource, if fully explored and developed in the light of modern technology, will support a far higher level of living than her people now enjoy. Very likely she can increase her rainfall by about 10 percent by cloud seeding, and she undeveloped supplies in both surface and ground water that are sufficient to nearly double her usable water supply. Even if she does not have oil or have it in large quantities, she can buy it cheaply from neighboring counties, and in addition has undeveloped sources of hydroelectric power, large reserves of bituminous limestone, large reserves of nuclear power as uranium in phosphate rock, and can use solar and wind power for special purposes. Her large supplies of construction, fertilizer, and other chemical raw materials will not only satisfy her own needs, but will yield both raw materials and some manufactured products for export. And she has valuable resource of touristic interest in the form of incomparable scenery, antiquities, and holy places, which, if properly advertised, could well become her largest single source of foreign currency. Revenues obtained from this source and from the export of agricultural products, nonmetallic minerals, and mineral products should support foreign oil purchase of oil, machinery, and other products not mined or produced internally. Full development of Jordan’s economic potential will take years to achieve and involves many complex activities. One of the most essential is one that can be pressed in the early years, namely the gathering of facts and basic data concerning the character, extent, and distribution of her resources, and the uses that can be made of them. Without each fundamental data or the understanding of their meaning or the ways to use and apply them, costly developmental projects and similar efforts to raise the level of living are likely to have limited success at best. Basic data and mineral resources are best gathered and published by permanent government agencies, for private organizations and individual cannot afford to take the risks involved in gathering data that may not have an immediate economic return; and even if private parties do collect such data they are not likely to make them general available. Of the activities needed in the field of mineral resources, some are already underway as the established function of government agencies. No bureau however, seems to have responsibility for making geologic maps and for gathering data on such things as steam flow, composition and properties of minerals and rocks, or for investigating the uses to which Jordan’s minerals might be put. To satisfy these needs, a Geological Survey and a Bureau of Mineral Industries should be formed and placed in operation as quickly as possible. The task of collecting and interpreting basic data or mineral resources must be done largely by Jordanians, for only in this way will Jordan acquire the technical competence needed to use the information. Few Jordanians have enough training or experience to work independently in these fields now, however, so help from outside technicians would be necessary over an initial training period of several years. But the number of outside technicians should never exceed the number of Jordanian technicians, and for this reason, neither organization could have a staff of more than a few people during the early years of operation.

Open-File Report↗

The study of the undiscovered mineral resources of the Tongass National Forest and adjacent lands, Southeastern Alaska

The quantitative probabilistic assessment of the undiscovered mineral resources of the 17.1-million-acre Tongass National Forest (the largest in the United States) and its adjacent lands is a nonaggregated, mineral-resource-tract-oriented assessment designed for land-planning purposes. As such, it includes the renewed use of gross-in-place values (GIPV's) in dollars of the estimated amounts of metal contained in the undiscovered resources as a measure for land-use planning. Southeastern Alaska is geologically complex and contains a wide variety of known mineral deposits, some of which have produced important amounts of metals during the past 100 years. Regional geological, economic geological, geochemical, geophysical, and mineral exploration history information for the region was integrated to define 124 tracts likely to contain undiscovered mineral resources. Some tracts were judged to contain more than one type of mineral deposit. Each type of deposit may contain one or more metallic elements of economic interest. For tracts where information was sufficient, the minimum number of as-yet-undiscovered deposits of each type was estimated at probability levels of 0.95, 0.90, 0.50, 0.10, and 0.05. The undiscovered mineral resources of the individual tracts were estimated using the U.S. Geological Survey's MARK3 mineral-resource endowment simulator; those estimates were used to calculate GIPV's for the individual tracts. Those GIPV's were aggregated to estimate the value of the undiscovered mineral resources of southeastern Alaska. The aggregated GIPV of the estimates is $40.9 billion. Analysis of this study indicates that (1) there is only a crude positive correlation between the size of individual tracts and their mean GIPV's: and (2) the number of mineral-deposit types in a tract does not dominate the GIPV's of the tracts, but the inferred presence of synorogenic-synvolcanic nickel-copper, porphyry copper skarn-related, iron skarn, and porphyry copper-molybdenum deposits does. The influence of this study on the U.S. Forest Service planning process is yet to be determined. ?? 1992 Oxford University Press.

Nonrenewable Resources↗

Hydrogeomorphology influences soil nitrogen and phosphorus mineralization in floodplain wetlands

Conceptual models of river–floodplain systems and biogeochemical theory predict that floodplain soil nitrogen (N) and phosphorus (P) mineralization should increase with hydrologic connectivity to the river and thus increase with distance downstream (longitudinal dimension) and in lower geomorphic units within the floodplain (lateral dimension). We measured rates of in situ soil net ammonification, nitrification, N, and P mineralization using monthly incubations of modified resin cores for a year in the forested floodplain wetlands of Difficult Run, a fifth order urban Piedmont river in Virginia, USA. Mineralization rates were then related to potentially controlling ecosystem attributes associated with hydrologic connectivity, soil characteristics, and vegetative inputs. Ammonification and P mineralization were greatest in the wet backswamps, nitrification was greatest in the dry levees, and net N mineralization was greatest in the intermediately wet toe-slopes. Nitrification also was greater in the headwater sites than downstream sites, whereas ammonification was greater in downstream sites. Annual net N mineralization increased with spatial gradients of greater ammonium loading to the soil surface associated with flooding, soil organic and nutrient content, and herbaceous nutrient inputs. Annual net P mineralization was associated negatively with soil pH and coarser soil texture, and positively with ammonium and phosphate loading to the soil surface associated with flooding. Within an intensively sampled low elevation flowpath at one site, sediment deposition during individual incubations stimulated mineralization of N and P. However, the amount of N and P mineralized in soil was substantially less than the amount deposited with sedimentation. In summary, greater inputs of nutrients and water and storage of soil nutrients along gradients of river–floodplain hydrologic connectivity increased floodplain soil nutrient mineralization rates.

Maryl;Virginia↗

Thermochronology of the Cornubian batholith in southwest England: Implications for pluton emplacement and protracted hydrothermal mineralization

The metalliferous ore deposits of southwest England are associated with biotite-muscovite granites that intruded upper Paleozoic sediments and volcanic rocks at the end of the Hercynian Orogeny. The hydrothermal mineralization can be subdivided into four stages: 1. exoskarns 2. high-temperature tin and tungsten oxide-bearing sheeted greisen bordered veins and Sn-bearing tourmaline veins and breccias 3. polymetallic quartz-tourmaline-chlorite-sulfide-fluorite-bearing fissure veins, which represent the main episode of economic mineralization 4. late-stage, low-temperature polymetallic fluorite veins. U-Pb dating of monazite and xenotime and 40 Ar 39 Ar "> 40 Ar 39 Ar dating of muscovite were used to determine emplacement ages and cooling times for individual plutons within the Cornubian batholith, as well as separate intrusive phases within the plutons. In addition, 40 Ar 39 Ar "> 40 Ar 39 Ar ages from hornblende and secondary muscovite and Sm-Nd isochron ages from fluorite were employed to determine the relationship between pluton emplacement and different stages of mineralization. The U-Pb ages indicate that granite magmatism was protracted from ~300 Ma down to ~275 Ma with no evidence of a major hiatus. There is no systematic relation between the age of a pluton and its location within the batholith. The U-Pb ages for separate granite phases within a single pluton are resolvable and indicate that magma emplacement within individual plutons occurred over periods of as much as 4.5 myrs. Felsic porphyry dike emplacement was coeval with plutonism, but continued to ~270 Ma. The geochronologic data suggest that the Cornubian batholith originated from repeated melting events over 30 myrs and was formed by a series of small coalescing granitic bodies. Cooling rates of the main plutons are unrelated to emplacement age, but decrease from the southwest to the northeast from ~210°C myr −1 to ~60°C myr −1 with a mean of 100°C myr −1 . These slow cooling rates appear to reflect the addition of heat from multiple intrusive episodes. The mineralization history is distinct for each pluton and ranges from coeval with, to up to 40 myrs younger than the cooling age for the host pluton. Stage 2 mineralization is broadly synchronous with the emplacement of granite magmas, is dominated by fluids expelled during crystallization, and may be repeated by the emplacement of younger magmas within the same pluton. Sm-Nd isochrons for fluorite from stage 3 polymetallic mineralization give ages of 259 ± 7, 266 ± 3 and 267 ± 12 Ma, postdating stage 2 mineralization by up to 25 myrs within the same deposit. The similarity in age of the main polymetallic mineralization hosted by the oldest and youngest plutons, suggests that this stage of mineralization is unlikely to be related to hydrothermal circulation driven by the emplacement and cooling of the host granite. The mineralization is more likely the product of regional hydrothermal circulation driven by heat from the emplacement and crystallization of younger buried pulses of magma.

Cornubian Batholith↗

Mineralogical, magnetic and geochemical data constrain the pathways and extent of weathering of mineralized sedimentary rocks

The oxidative weathering of sulfidic rock can profoundly impact watersheds through the resulting export of acidity and metals. Weathering leaves a record of mineral transformation, particularly involving minor redox-sensitive phases, that can inform the development of conceptual and quantitative models. In sulfidic sedimentary rocks, however, variations in depositional history, diagenesis and mineralization can change or overprint the distributions of these trace minerals, complicating the interpretation of weathering signatures. Here we show that a combination of bulk mineralogical and geochemical techniques, micrometer-resolution X-ray fluorescence microprobe analysis and rock magnetic measurements, applied to drill core samples and single weathered fractures, can provide data that enable the development of a geochemically consistent weathering model. This work focused on one watershed in the Upper Colorado River Basin sitting within the Mesaverde Formation, a sedimentary sandstone bedrock with disseminated sulfide minerals, including pyrite and sphalerite, that were introduced during diagenesis and subsequent magmatic-hydrothermal mineralization. Combined analytical methods revealed the pathways of iron (Fe), carbonate and silicate mineral weathering and showed how pH controls element retention or release from the actively weathering fractured sandstone. Drill core logging, whole rock X-ray diffraction, and geochemical measurements document the progression from unweathered rock at depth to weathered rock at the surface. X-ray microprobe analyses of a 1-cm size weathering profile along a fracture surface are consistent with the mobilization of Fe(II) and Fe(III) into acidic pore water from the dissolution of primary pyrite, Fe-sphalerite, chlorite, and minor siderite and pyrrhotite. These reactions are followed by the precipitation of secondary minerals such as of goethite and jarosite, a Fe-(oxyhydr)oxide and hydrous Fe(III) sulfate, respectively. Microscale analyses also helped explain the weathering reactions responsible for the mineralogical transformations observed in the top and most weathered section of the drill core. For example, dissolution of feldspar and chlorite neutralizes the acidity generated by Fe and sulfide mineral oxidation, oversaturating the solution in both Fe-oxides. The combination of X-ray spectromicroscopy and magnetic measurements show that the Fe(III) product is goethite, mainly present either as a coatings on fracture surfaces in the actively weathering region of the core or more homogeneously contained within the unconsolidated regolith at the top of the core. Low-temperature magnetic data reveal the presence of ferromagnetic Fe-sulfide pyrrhotite that, although it occurs at trace concentrations, could provide a qualitative proxy for unweathered sulfide minerals because the loss of pyrrhotite is associated with the onset of oxidative weathering. Pyrrhotite loss and goethite formation are detectable through room-temperature magnetic coercivity changes, suggesting that rock magnetic measurements can determine weathering intensity in rock samples at many scales. This work contributes evidence that the weathering of sulfidic sedimentary rocks follows a geochemical pattern in which the abundance of sulfide minerals controls the generation of acidity and dissolved elements, and the pH-dependent mobility of these elements controls their export to the ground- and surface-water.

Colorado↗

Temporal and spatial distribution of alteration, mineralization and fluid inclusions in the transitional high-sulfidation epithermal-porphyry copper system at Red Mountain, Arizona

Red Mountain, Arizona, is a Laramide porphyry Cu system (PCD) that has experienced only a modest level of erosion compared to most other similar deposits in the southwestern United States. As a result, the upper portion of the magmatic–hydrothermal system, which represents the transition from shallower high-sulfidation epithermal mineralization to deeper porphyry Cu mineralization, is well preserved. Within the Red Mountain system, alteration, mineralization and fluid inclusion assemblages show a systematic distribution in both time and space. Early-potassic alteration (characterized by the minerals biotite and magnetite) is paragenetically earlier than late-potassic alteration (K-feldspar–anhydrite) and both are followed by later phyllic (sericite–pyrite) alteration. Advanced argillic alteration (pyrophyllite–alunite–other clay minerals) is thought to be coeval with or postdate phyllic alteration. Minerals characteristic of advanced argillic alteration are present in the near surface. Phyllic alteration extends to greater depths compared to advanced argillic alteration. Early-potassic and late-potassic alteration are only observed in the deepest part of the system. Considerable overlap of phyllic alteration with both early-potassic and late-potassic alteration zones is observed. The hypogene mineralization contains 0.4–1.2% Cu and is spatially and temporally related to the late-potassic alteration event. Molybdenum concentration is typically < 300 ppm but positive anomalies (between 600 and 1200 ppm) occur, and typically correlate with the zones of higher Cu grades. Silver and Au range up to 50 ppm and 1 ppm, respectively, and mostly occur in the deeper parts of the system. Individual assays of up to 18 ppm Au and 274 ppm Ag in the shallower part of the system are interpreted to be associated with areas of highly focused fluid flow (i.e., breccias and thick veins). A near-surface, discontinuous chalcocite blanket is represented by scattered Cu anomalies within the mixed oxide/sulfide zone and its discontinuous nature may reflect differential permeability along fractures and faults. In the deepest part of the system, an early generation of low-to-moderate density and salinity liquid + vapor inclusions with opaque daughter minerals is followed in time by halite-bearing inclusions that also contain opaque daughter minerals indicating that an early intermediate-density magmatic fluid evolved to a high-density, high-salinity mineralizing fluid. The increase in density and salinity of fluids with time observed in the deeper parts of the system may be the result of immiscibility (“boiling”) of the earlier magmatic fluids or may reflect the compositional evolution of fluids that exsolved from the magma. Trails of inclusions consisting of only vapor-rich inclusions are common in the shallow parts of the system, and are associated with advanced argillic alteration, suggesting that intense boiling (“flashing”) occurred at (or below) this level. Fluid inclusion assemblages consisting of coexisting vapor-rich and halite-bearing inclusions are observed in samples extending from the surface to the upper part of the late-potassic zone, indicating that fluid immiscibility occurred within this depth interval.

Arizona↗

Framework for assessing intranational risk of critical mineral sectors: Case study of India

Recent geopolitical actions regarding the supply of critical minerals have highlighted both the threats posed by countries dominating a critical mineral supply chain, and the potential mitigations served by alternative supplier countries. However, no systematic quantification exists for the intranational factors that determine such threats or mitigations. This study outlines a methodological framework for quantifying the intranational risk profile of critical mineral sectors and compares them with the sector's international potential for leverage. The four intranational factors of concentration, synchronization, private sector involvement, and regulatory obstacles were analyzed across multiple scales in order to determine an intranational risk score that quantifies the resilience or fragility of the critical mineral sector in question. Network analysis was also separately conducted to identify the most important entities operating across all critical mineral sectors. Finally, this study assessed the critical mineral sector's global share of reserves and production to determine an international risk score that quantifies the country's critical mineral sector's leverage potential. A case study of India showed that two critical mineral sectors with high leverage potential, chromite and barite, were respectively intranationally resilient and fragile. Of the remaining sectors with minimal leverage, five sectors such as aluminum were intranationally resilient and may serve as viable mitigation options for future critical mineral supply. Three sectors such as titanium were intranationally fragile, but recent regulatory developments may both decrease intranational risk and increase international risk, potentially making them major critical mineral sectors in the future.

Resources Policy↗

Characterizing regional soil mineral composition using spectroscopyand geostatistics

This work aims at improving the mapping of major mineral variability at regional scale using scale-dependent spatial variability observed in remote sensing data. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data and statistical methods were combined with laboratory-based mineral characterization of field samples to create maps of the distributions of clay, mica and carbonate minerals and their abundances. The Material Identification and Characterization Algorithm (MICA) was used to identify the spectrally-dominant minerals in field samples; these results were combined with ASTER data using multinomial logistic regression to map mineral distributions. X-ray diffraction (XRD)was used to quantify mineral composition in field samples. XRD results were combined with ASTER data using multiple linear regression to map mineral abundances. We testedwhether smoothing of the ASTER data to match the scale of variability of the target sample would improve model correlations. Smoothing was donewith Fixed Rank Kriging (FRK) to represent the mediumand long-range spatial variability in the ASTER data. Stronger correlations resulted using the smoothed data compared to results obtained with the original data. Highest model accuracies came from using both medium and long-range scaled ASTER data as input to the statistical models. High correlation coefficients were obtained for the abundances of calcite and mica (R2 = 0.71 and 0.70, respectively). Moderately-high correlation coefficients were found for smectite and kaolinite (R2 = 0.57 and 0.45, respectively). Maps of mineral distributions, obtained by relating ASTER data to MICA analysis of field samples, were found to characterize major soil mineral variability (overall accuracies for mica, smectite and kaolinite were 76%, 89% and 86% respectively). The results of this study suggest that the distributions of minerals and their abundances derived using FRK-smoothed ASTER data more closely match the spatial variability of soil and environmental properties at regional scale.

Remote Sensing of Environment↗

Effect of contaminant concentration on aerobic microbial mineralization of DCE and VC in stream-bed sediments

Discharge of DCE and VC to an aerobic surface water system simultaneously represents a significant environmental concern and, potentially, a non-engineered opportunity for efficient contaminant bioremediation. The potential for bioremediation, however, depends on the ability of the stream-bed microbial community to efficiently and completely degrade DCE and VC over a range of contaminant concentrations. The purposes of the studies reported here were to assess the potential for aerobic DCE and VC mineralization by stream-bed microorganisms and to evaluate the effects of DCE and VC concentrations on the apparent rates of aerobic mineralization. Bed-sediment microorganisms indigenous to a creek, where DCE-contaminated groundwater continuously discharges, demonstrated rapid mineralization of DCE and VC under aerobic conditions. Over 8 days, the recovery of [1,2-14C]DCE radioactivity as 14CO2 ranged from 17% to 100%, and the recovery of [1,2- 14C]VC radioactivity as 14CO2 ranged from 45% to 100%. Rates of DCE and VC mineralization increased significantly with increasing contaminant concentration, and the response of apparent mineralization rates to changes in DCE and VC concentrations was adequately described by Michaelis-Menten kinetics.Discharge of DCE and VC to an aerobic surface water system simultaneously represents a significant environmental concern and, potentially, a non-engineered opportunity for efficient contaminant bioremediation. The potential for bioremediation, however, depends on the ability of the stream-bed microbial community to efficiently and completely degrade DCE and VC over a range of contaminant concentrations. The purposes of the studies reported here were to assess the potential for aerobic DCE and VC mineralization by stream-bed microorganisms and to evaluate the effects of DCE and VC concentrations on the apparent rates of aerobic mineralization. Bed-sediment microorganisms indigenous to a creek, where DCE-contaminated groundwater continuously discharges, demonstrated rapid mineralization of DCE and VC under aerobic conditions. Over 8 days, the recovery of [1,2-14C]DCE radioactivity as 14CO2 ranged from 17% to 100%, and the recovery of [1,2-14C]VC radioactivity as 14CO2 ranged from 45% to 100%. Rates of DCE and VC mineralization increased significantly with increasing contaminant concentration, and the response of apparent mineralization rates to changes in DCE and VC concentrations was adequately described by Michaelis-Menten kinetics.

Environmental Science & Technology↗

Selective sediment transport during Hurricane Sandy on Fire Island (New York, USA): Inferences from heavy-mineral assemblages

In October 2012, Hurricane Sandy caused severe erosion on beaches and dunes of Fire Island (New York, USA). Major shoreline changes occurred with erosional dominance in the upper shoreline and aggradation in the lowermost section of the beach due to the deposition of eroded upper beach and dune sediment. Sand laminations with a high concentration of heavy minerals (“black sand laminations”) were observed in three excavated trenches located on a washover terrace and fan on the east side of Fire Island. The mineralogical composition of these laminations reveals the presence of high quantities of magnetite, ilmenite (as opaque minerals), and garnet (as main translucent mineral). These heavy mineral enriched laminations were formed as waves eroded and transported sand from the primary dune and smaller relict dunes under specific hydrodynamic conditions that promoted grain sorting according to differences in size and specific gravity. Based on the concentrations of certain heavy minerals, the threshold for primarily density-driven sorting probably lies between the specific gravity of a less dense mineral (ilmenite, 4.7) and Garnet almandine (4.3), the most common transparent heavy mineral. The number of laminations and concentrations of heavy minerals vary between trenches on the overwash terrace and appear to be controlled by their distance from sediment sources. The trench with a greatest number of laminations and higher heavy mineral concentrations is located furthest from the main dune but is just 10 m inland of a relict dune that acts as the primary source of sediment of the washover deposit in this trench. A conceptual model for heavy mineral layer deposition is presented based on geomorphological and sedimentological evidences allowing the definition of a density threshold.

New York↗