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At least 343 records · Page 19Linked to original sources
USGS1995

Industrial minerals of the Midcontinent: Proceedings of the Midcontinent industrial minerals workshop

The Midcontinent Industrial Minerals Workshop, in St. Louis, Missouri, September 16-17, 1991, was the fourth U.S. Geological Survey-sponsored meeting on the essential role of industrial rocks and minerals in the Nation's social and economic framework. The meeting was organized, supported, and the agenda was determined by a group from the USGS, the U.S. Bureau of Mines, and the State geological surveys of Arkansas, Illinois, Kansas, Kentucky, Missouri, Nebraska, and Oklahoma, with early assistance in planning from the Iowa and Tennessee surveys. As the major industrial rocks and minerals used in the nine-State area of the Midcontinent are construction materials, the Workshop focused on sand and gravel and limestone-dolomite resources and the extraction industry for those materials. Because active audience participation was considered vital, representatives from industry, universities, geological surveys, planning groups, regulatory agencies, and State legislatures were invited. The audience consisted of 87 attendees out of 120 invited participants (no legislators attended).

Bulletin↗
USGS2019

Carbon dioxide mineralization feasibility in the United States

Geologic carbon dioxide (CO 2 ) storage is one of many methods for stabilizing the increasing concentration of CO 2 in the Earth’s atmosphere. The injection of CO 2 in deep subsurface sedimentary reservoirs is the most commonly discussed method; however, the potential for CO 2 leakage can create long-term stability concerns. This report discusses the feasibility of an alternative form of geologic CO 2 storage: CO 2 mineralization. In this method, CO 2 reacts with rocks and minerals to form solid and stable carbonate rocks. New pilot projects and laboratory-based kinetics experiments have revealed that this method, both in situ and ex situ, may be a viable option for storage. In situ storage targets in-place rocks at the surface or subsurface. Ex situ storage targets industrial byproducts at the surface like mine tailings. Environmental risks include induced seismicity for in situ methods if pressure is not managed properly, as well as potential water and land use effects. However, there are fewer long-term CO 2 -leakage concerns for mineralization methods compared to saline storage methods and therefore potentially lower long-term monitoring costs. The costs and benefits of CO 2 mineralization are compared to those of CO 2 storage in saline reservoirs using estimates of pressure-limited dynamic storage capacity. This report highlights the regional potential of areas in the United States for in situ and ex situ storage, as well as their proximity to potential sources of CO 2 . Especially suitable targets include asbestos or other ultramafic mine tailings, in situ ultramafic rocks on the East and West Coasts, the Columbia River basalts in the Pacific Northwest, the Midcontinent Rift basalts in the midcontinent, and the basaltic Hawaiian Islands.

Scientific Investigations Report↗
USGS1984

Fission-track dating applied to mineral exploration

The partial to total resetting of fission-track ages of minerals in country rock near a mineralized area can be used to (1) locate a thermal anomaly, and (2) date the mineralizing event. Two mining districts in Colorado have been studied - Rico and Gilman. Rico is a precious- and base-metal mining district. Initial fission-track dating of a sill located about 6 km from the center of the district gave ages of 20 Myr and 65 Myr for apatite and zircon, respectively. The Eagle Mine in the Gilman District is the largest producer of zinc in the state of Colorado. Fission-track dating of zircon from a 70 Myr-old sill shows partial resetting of the zircon (45 Myr). The thermal anomaly identified by fission-track dating is seen in both districts far outside the area affected by obvious alteration. Based on the results of these two pilot studies, fission-track dating can be a useful exploration method for thermal anomalies associated with buried or otherwise poorly expressed mineral deposits.

Nuclear Tracks and Radiation Measurements (1982)↗
USGS2000

Regoliths of the middle-Atlantic Piedmont and evolution of a polymorphic landscape

The regolith overlying the alumino-silicate rocks of the middle-Atlantic Piedmont Province consists primarily of saprolite with a thin veneer of diamictons of colluvial origin. Thickness and distribution of the saprolite is related to landform and lithology. For example, on uplands isovolumetric weathering of the Loch Raven Schist produces saprolite averaging 55 ft (17 m) thick. On Port Deposit Gneiss, saprolite beneath uplands averages 42 ft (13 m) in thickness. The saprolite results from the reaction of alumino-silicate rocks with through-flowing groundwater. Chemical weathering of the rock results in clay and resistate minerals, residual rock layers, corestones, and pinnacles. Surface erosion of saprolite with quartzite and metagraywacke residual layers may produce a 'washboard' topography. Surface erosion of a metagabbro saprolite containing corestones and pinnacles results in a surface with lag deposits of corestones and emergent pinnacles. The diamicton material comes from the underlying saprolite, weathered rock and bedrock. Generally, diamictons are thinner on uplands and upper slopes, and thicker at the base of slopes and in hollows and gathering areas of first-order streams. The saprolite and colluvium reflect response of geomorphic processes (chemical weathering, fluvial incision, and periglacial processes) to rock lithology and landscape. The modifications to the landscape have been driven by neotectonic crustal warping and alternating periglacial-humid temperate climates. Altogether these varied interactions have resulted in a Holocene polymorphic landscape.

Southeastern Geology↗
USGS1982

Mineral resource potential map of the Shining Rock Wilderness, Haywood County, North Carolina

The Shining Rock Wilderness is in the Blue Ridge Mountains of Haywood County, N. C., and is underlain by complexly folded, high-grade metamorphic rocks. These rocks contain a few small, subeconomic deposits of sheet muscovite mica that have a small potential for scrap mica. Quartz as a source of silica (SiO2) and gneiss and schist suitable for common building stone and crushed rock are the only identified economic mineral resources. Other minerals and rocks, including kaolin, soapstone, copper, corundum, and dunite, have been prospected or mined nearby, but either they do not occur or have no current economic potential in the wilderness. A possibility exists for the presence of natural gas at depths greater than 5,000 ft (1,500 m).

North Carolina↗
USGS2021

Origin of the J-M Reef and Lower Banded series, Stillwater Complex, Montana, USA

The origin and parental magma for layered cumulates in the Lower Banded series (LBS) and the J-M Reef Pd-Pt deposit of the Stillwater Complex remains poorly constrained. We present whole-rock lithogeochemistry and mineral chemistry from LBS rocks collected from drill holes and surface samples from the Mountain View area of the complex that in total span nearly the entirety of the LBS stratigraphy. Excess S, Pt, and Pd in the noritic and gabbronoritic cumulates of the LBS indicate that small amounts of high tenor sulfide liquid generated at very low degrees of sulfide oversaturation were ubiquitous parts of the cumulate assemblage. We show that a simple two-stage thermodynamic model of assimilation-batch crystallization of a komatiitic parental magma in the lower crust, produces a close match to a common suite of fine-grained gabbronorite dikes and sills that intrude both the complex and its footwall. After fractionating ultramafic cumulates in the lower crust, the model contaminated komatiitic liquid produces upper crustal cumulates by batch crystallization en route to or at the level of the intrusion. The modeled rocks have compositions and mineral assemblages closely resembling pyroxenite of the Bronzitite zone and both norite and gabbronorite cumulates in the lower LBS. The trends from the Bronzitite zone through Norite zone I and Gabbronorite zone I can be understood as the result of deposition of crystals from successive batches of the same contaminated parental magma, with an upward trend toward greater amounts of cooling before the separation of crystals from liquid. The olivine-bearing suite of Olivine-bearing zone I, which includes the J-M Reef, can be modeled by partial remelting of the same norite and gabbronorite cumulates due to a temporarily increased flux of hot, moderately less contaminated LBS parental magma that infiltrated partially molten cumulates because its density exceeded that of the interstitial liquid. This model suggests that infiltration of hot Mg-rich parental liquid into moderately PGE-enriched footwall cumulates may be fundamental to the formation of the extremely high tenor sulfide mineralization in the J-M Reef ore zone, and perhaps other reef-type deposits worldwide. The same metal tenors that would require silicate/sulfide mass ratios (i.e., R-factors) of 10 5 to 10 6 in a single stage of equilibration would be attained during this second stage of interaction by the incremental infiltration and passage of LBS parental magma through previously sulfide saturated cumulate mush.

Montana↗
USGS1968

O18/O16 ratios of coexisting minerals in glaucophane-bearing metamorphic rocks

Oxygen isotope analyses have been obtained for coexisting minerals in several blue-schist-facies metamorphic rocks from California, Oregon, and New Caledonia. Detailed isotopic studies were made on a continuous exposure of schist in Ward Creek, California, previously described by Coleman and Lee (1962). The oxygen isotope fractionations among coexisting minerals in a variety of rock types, including metasediments and metabasalts, are systematic and larger than those measured in pelitic schists metamorphosed at the grade of biotite zone or higher. Therefore, these Ward Creek rocks (termed Type III) must have formed at lower temperatures than have such pelitic schists. Evidence for significant isotopic equilibration and homogenization is observed in the Ward Creek sequence. Six different metasediments and metavolcanics collected within 25 m of one another show almost identical mineral δ; -values: quartz (15.8 to 16.3), aragonite (13.1 to 13.3), glaucophane (9.8 to 10.0), muscovite (10.9 to 11.3), lawsonite (9.3 to 9.5), and garnet (8.0 to 8.4), given as per mil enrichment in O 18 relative to mean ocean water. These rocks seem to have reached equilibrium at about the same temperature in contact with abundant metamorphic pore fluids. Not all the Ward Creek rocks have completely equilibrated with the postulated metamorphic pore fluids. In particular, the metacherts seem to have been relatively impermeable to the aqueous fluids during metamorphism, as indicated by the large δ -values of quartz in such rocks (17 to 19.2) and by their appreciably higher Fe +3 /Fe +2 ratios. Gradients in O 18 /O 16 and Fe +3 /Fe +2 have been generally “smoothed out” in the rocks during metamorphism, but the process has gone to completion only locally. Cherts and limestones have apparently been lowered in O 18 content by 10 to 15 per mil, and the metabasalts are enriched by 3 to 4 per mil over their unmetamorphosed parent rocks. Using the calibrated quartz-muscovite and quartz—CaCO 3 geothermometers, the measured quartz-muscovite and quartz-aragonite fractionations indicate essentially “concordant” temperatures of formation for the Type III rocks of 270° to 315° C. Inasmuch as aragonite is part of the equilibrium assemblage, these rocks must therefore have been metamorphosed at pressures of at least 6.4 to 7.0 kb. Oxygen isotope fractionations for the mineral pairs aragonite-lawsonite, quartz-muscovite, and quartz-glaucophane progressively decrease from Type II (low-grade) through Type III to Type IV (high-grade tectonic blocks) metabasalts. The higher-grade blueschists from New Caledonia exhibit quartz-muscovite and quartz-glaucophane fractionations similar to the Type IV metabasalts at Ward Creek, indicating temperatures of formation of 400° to 550° C. Thus, glaucophane-bearing metamorphic rocks apparently form over a temperature range of 200° C to 550° C, encompassing the probable temperature range of the entire greenschist and epidote-amphibolite facies. This suggests that glaucophane schists should be separated into at least two metamorphic facies, a lower-grade, lawsonite-aragonite blueschist facies and a higher-grade, epidote-rutile blueschist facies, both representing higher pressures than are attained during ordinary low-rank and middle-rank regional metamorphism.

California, Oregon↗
USGS2007

Mapping known and potential mineral occurrences and host rocks in the Bonnifield Mining District using minimal cloud- and snow-cover ASTER data: Chapter E in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

On July 8, 2003, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor acquired satellite imagery of a 60-kilometer-wide swath covering a portion of the Bonnifield mining district within the southernmost part of the Tintina Gold Province, Alaska, under unusually favorable conditions of minimal cloud and snow cover. Although rocks from more than eight different lithotectonic terranes are exposed within the extended swath of data, we focus on volcanogenic massive sulfides (VMS) and porphyry deposits within the Yukon-Tanana terrane (YTT), the largest Mesozoic accretionary terrane exposed between the Denali fault system to the south of Fairbanks and the Tintina fault system to the north of Fairbanks. Comparison of thermal-infrared region (TIR) decorrelation stretch data to available geologic maps indicates that rocks from the YTT contain a wide range of rock types ranging in composition from mafic metavolcanic rocks to felsic rock types such as metarhyolites, pelitic schists, and quartzites. The nine-band ASTER visible-near-infrared region--short-wave infrared region (VNIR-SWIR) reflectance data and spectral matched-filter processing were used to map hydrothermal alteration patterns associated with VMS and porphyry deposit types. In particular, smectite, kaolinite, opaline silica, jarosite and (or) other ferric iron minerals defined narrow (less than 250-meter diameter) zonal patterns around Red Mountain and other potential VMS targets. Using ASTER we identified some of the known mineral deposits in the region, as well as mineralogically similar targets that may represent potential undiscovered deposits. Some known deposits were not identified and may have been obscured by vegetation or snow cover or were too small to be resolved.

Alaska;Yukon↗
USGS2002

Ultraviolet spectrophotometric determination of tantalum with pyrogallol

In a search for a more rapid method for the determination of tantalum in rocks and minerals, an intensive study was made of the tantalum-pyrogallol reaction recommended by Platanov and Krivoshlikov, and a better modified spectrophotometric procedure is given. The improved method consists in measuring the absorbancy of the tantalum-pyrogallol complex at 325 m μ in 4 N hydrochloric acid and a fixed concentration (0.0175 M ) of ammonium oxalate. Beer's law is followed for the concentration range up to 40 γ per ml. Sensitivity in terms of molar absorbancy index is 4775. Most interferences are additive in character and readily correctable. Separations or major corrections are required in the presence of significant amounts of molybdenum, tungsten, antimony, and uranium. The method has been successfully applied to three ores previously analyzed by gravimetric techniques. The method affords greater speed, sensitivity, and reproducibility in the determination of tantalum in rocks and minerals. A more reliable technique for preparing standard solutions of tantalum has been developed.

Analytical Chemistry↗
USGS1981

Sm-Nd systematics of a tonalitic augen gneiss and its constituent minerals from northern Michigan

The Sm-Nd isotopic system of a tonalitic augen gneiss and its constituent minerals from northern Michigan was disturbed during metamorphism. Sm-Nd zircon ages are lower than the wholerock Sm-Nd model age. However, closely associated pairs of minerals (for example, sphene and biotite or apatite and plagioclase) retain their apparent metamorphic ages. The Sm-Nd model age for the tonalitic augen gneiss of 3919 ± 30 myr , appears to reflect open system behavior during metamorphism. A mineralogically different gneiss from the same location has a Sm-Nd model age of 3520 ± 70 myr . The two whole rocks differ in their Sm-Nd and Rb-Sr systematics and in their chondrite-normalized rare earth element (REE) patterns. The whole-rock-normalized mineral REE patterns show the contribution of the major and trace minerals to the REE content of the whole rock. The trace minerals contain a significant amount of the total REE.

Geochimica et Cosmochimica Acta↗
USGS2004

Basis for paleoenvironmental interpretation of magnetic properties of sediment from Upper Klamath Lake (Oregon): Effects of weathering and mineralogical sorting

Studies of magnetic properties enable reconstruction of environmental conditions that affected magnetic minerals incorporated in sediments from Upper Klamath Lake. Analyses of stream sediment samples from throughout the catchment of Upper Klamath Lake show that alteration of Fe-oxide minerals during subaerial chemical weathering of basic volcanic rocks has significantly changed magnetic properties of surficial deposits. Titanomagnetite, which is abundant both as phenocrysts and as microcrystals in fresh volcanic rocks, is progressively destroyed during weathering. Because fine-grained magnetite is readily altered due to large surface-to-volume ratios, weathering causes an increase in average magnetic grain size as well as reduction in the quantity of titanomagnetite both absolutely and relative to hematite. Hydrodynamic mineralogical sorting also produces differences in magnetic properties among rock and mineral grains of differing sizes. Importantly, removal of coarse silicate and Fe-oxide grains by sorting concentrated extremely fine-grained magnetite in the resulting sediment. The effects of weathering and sorting of minerals cannot be completely separated. These processes combine to produce the magnetic properties of a non-glacial lithic component of Upper Klamath Lake sediments, which is characterized by relatively low magnetite content and coarse magnetic grain size. Hydrodynamic sorting alone causes significant differences between the magnetic properties of glacial flour in lake sediments and of fresh volcanic rocks in the catchment. In comparison to source volcanic rocks, glacial flour in the lake sediment is highly enriched in extremely fine-grained magnetite.

Journal of Paleolimnology↗
USGS1974

40Ar/39Ar age spectra of some undisturbed terrestrial samples

40 Ar/ 39 Ar age spectra and 40 Ar/ 36 Ar vs 39 Ar/ 36 Ar isochrons were determined by incremental heating for 11 terrestrial rocks and minerals whose geology indicates that they represent essentially undisturbed systems. The samples include muscovite, biotite, hornblende, sanidine, plagioclase, dacite, diabase and basalt and range in age from 40 to 1700 m.y. For each sample, the 40 Ar/ 39 Ar ratios, corrected for atmospheric and neutron-generated argon isotopes, are the same for most of the gas fractions released and the age spectra, which show pronounced plateaus, thus are consistent with models previously proposed for undisturbed samples. Plateau ages and isochron ages calculated using plateau age fractions are concordant and appear to be meaningful estimates of the crystallization and cooling ages of these samples. Seemingly anomalous age spectrum points can be attributed entirely to small amounts of previously unrecognized argon loss and to gas fractions that contain too small (less than 2 per cent) a proportion of the 39 Ar released to be geologically significant. The use of a quantitative abscissa for age spectrum diagrams is recommended so that the size of each gas fraction is readily apparent. Increments containing less than about 4–5 per cent of the total 39 Ar released should be interpreted cautiously. Both the age spectrum and isochron methods of data reduction for incremental heating experiments are worthwhile, as each gives slightly different but complementary information about the sample from the same basic data. Use of a least-squares fit that allows for correlated errors is recommended for 40 Ar/ 36 Ar vs 39 Ar/ 36 Ar isochrons. The results indicate that the 40 Ar/ 39 Ar incremental heating technique can be used to distinguish disturbed from undisturbed rock and mineral systems and will be a valuable geochronological tool in geologically complex terranes.

Geochimica et Cosmochimica Acta↗