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Minerals & deposits

Find USGS publications on mineral resources and deposits. Search commodities and geographic names, then check source reports for geology and assessment methods.

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USGS1987

Isotope geochemistry of minerals and fluids from Newberry volcano, Oregon

Isotopic compositions were determined for hydrothermal quartz, calcite, and siderite from core samples of the Newberry 2 drill hole, Oregon. The ??15O values for these minerals decrease with increasing temperatures. The values indicate that these hydrothermal minerals precipitated in isotopic equilibrium with water currently present in the reservoirs. The ??18O values of quartz and calcite from the andesite and basalt flows (700-932 m) have isotopic values which require that the equilibrated water ??18O values increase slightly (- 11.3 to -9.2???) with increasing measured temperatures (150-265??C). The lithic tuffs and brecciated lava flows (300-700 m) contain widespread siderite. Calculated oxygen isotopic compositions of waters in equilibrium with siderite generally increase with increasing temperatures (76-100??C). The ??18O values of siderite probably result from precipitation in water produced by mixing various amounts of the deep hydrothermal water (- 10.5 ???) with meteoric water (- 15.5 ???) recharged within the caldera. The ??13C values of calcite and siderite decrease with increasing temperatures and show that these minerals precipitated in isotopic equilibrium with CO2 of about -8 ???. The ??18O values of weakly altered (<5% alteration of plagioclase) whole-rock samples decrease with increasing temperatures above 100??C, indicating that exchange between water and rock is kinetically controlled. The water/rock mass ratios decrease with decreasing temperatures. The ??18O values of rocks from the bottom of Newberry 2 show about 40% isotopic exchange with the reservoir water. The calculated ??18O and ??D values of bottom hole water determined from the fluid produced during the 20 hour flow test are -10.2 and -109???, respectively. The ??D value of the hydrothermal water indicates recharge from outside the caldera. ?? 1987.

Journal of Volcanology and Geothermal Research↗

USGS1990

Enzyme leaching of surficial geochemical samples for detecting hydromorphic trace-element anomalies associated with precious-metal mineralized bedrock buried beneath glacial overburden in northern Minnesota

One objective of the International Falls and Roseau, Minnesota, CUSMAP projects was to develop a means of conducting regional-scale geochemical surveys in areas where bedrock is buried beneath complex glacially derived overburden. Partial analysis of B-horizon soils offered hope for detecting subtle hydromorphic trace-element dispersion patterns. An enzyme-based partial leach selectively removes metals from oxide coatings on the surfaces of soil materials without attacking their matrix. Most trace-element concentrations in the resulting solutions are in the part-per-trillion to low part-per-billion range, necessitating determinations by inductively coupled plasma/mass spectrometry. The resulting data show greater contrasts for many trace elements than with other techniques tested. Spatially, many trace metal anomalies are locally discontinuous, but anomalous trends within larger areas are apparent. In many instances, the source for an anomaly seems to be either basal till or bedrock. Ground water flow is probably the most important mechanism for transporting metals toward the surface, although ionic diffusion, electrochemical gradients, and capillary action may play a role in anomaly dispersal. Sample sites near the Rainy Lake-Seine River fault zone, a regional shear zone, often have anomalous concentrations of a variety of metals, commonly including Zn and/or one or more metals which substitute for Zn in sphalerite (Cd, Ge, Ga, and Sn). Shifts in background concentrations of Bi, Sb, and As show a trend across the area indicating a possible regional zoning of lode-Au mineralization. Soil anomalies of Ag, Co, and Tl parallel basement structures, suggesting areas that may have potential for Cobalt/Thunder Baytype silver viens. An area around Baudette, Minnesota, which is underlain by quartz-chlorite-carbonate-altered shear zones, is anomalous in Ag, As, Bi, Co, Mo, Te, Tl, and W. Anomalies of Ag, As, Bi, Te, and W tend to follow the fault zones, suggesting potential for lode-Au deposits. Soil anomalies of Co, Mo, and Tl appear to follow northwest-striking structures that cross the shear zones, suggesting that Thunder Bay-type mineralization may have overprinted earlier mineralization along the shear zones.

Conference Paper↗

USGS1994

McCrillisite, NaCs(Be,Li)Zr2(PO4)4.1-2H2O, a new mineral species from Mount Mica, Oxford County, Maine, and new data for gainesite

McCrillisite, a member of the gainesite group, occurs in the Mount Mica granitic pegmatite, South Paris, Oxford County, Maine. The mineral is a product of late-stage hydrothermal alteration and is associated with approximately 20 other silicate, oxide, carbonate, arsenite and phosphate minerals. Crystals occur in mm- to cm-sized cavities, and individuals are up to 1.2 mm in maximum dimension. The crystallography and mineral chemistry of McCrillisite are described. -from Authors

Canadian Mineralogist↗

USGS1993

Kosnarite, KZr2(PO4)3, a new mineral from Mount Mica and Black Mountain, Oxford County, Maine

Kosnarite, ideally KZr2(PO4)3, has been identified as part of a late-stage, secondary phosphate mineral assemblage from the Mount Mica pegmatite at Paris, and from the Black Mountain pegmatite, Rumford, Oxford County, Maine. Kosnarite from Mount Mica occurs as pseudocubic rhombohedral crystals, as much as 0.9 mm in maximum dimension, that display the dominant {102} form. Color ranges from pale blue to blue-green to nearly colorless. The mineral has a white streak, is transparent, has a vitreous luster, and is nonfluorescent in ultraviolet light. It has a hardness of 4.5, is brittle with a conchoidal fracture, and has perfect {102} cleavage. Kosnarite from Black Mountain is almost pure KZr2(PO4)3 with only trace amounts of Hf, Mn, Na, and Rb. The mineral is one of three known alkali zirconium phosphates; the others are gainesite and the Cs analogue of gainesite. -from Author

American Mineralogist↗

USGS1995

Impedance spectra of hot, dry silicate minerals and rocks: qualitative interpretation of spectra

Impedance spectroscopy helps distinguish the contributions that grain interiors and grain boundaries make to electrical resistance of silicate minerals and rocks. Olivine, orthopyroxene, clinopyroxenes, and both natural and synthetic clinopyroxenite were measured. A network of electrical elements is presented for use in interpreting impedance spectra and conductive paths in hot or cold, wet or dry, minerals and rocks at any pressure. In dry rocks, a series network path predominates; in wet rocks, aqueous pore fluid and crystals both conduct. Finite resistance across the sample-electrode interface is evidence that electronic charge carriers are present at the surface, and presumably within, the silicate minerals and rocks measured. -from Authors

American Mineralogist↗

USGS1998

Needle twins and right-angled twins in minerals: comparison between experiment and theory

Transformation twinning in minerals forms isolated twin walls, intesecting walls with corner junctions, and wedge-shaped twins as elements of hierarchical patterns. When cut perpendicular to the twin walls, the twins have characteristic shapes, right-angled and needle-shaped wall traces, which can be observed by transmission electron microscopy or by optical microscopy. Theoretical geometries of wall shapes recently derived for strain-related systems should hold for most displacive and order-disorder type phase transitions: 1) right-angled twins show curved junctions; 2) needle-shaped twins contain flat wall segments near the needle tip if the elastic behaviour of the mineral is dominated by its anisotroyp; 3) additional bending forces and pinning effects lead to curved walls near the junction that make the needle tip appear more blunt. Bent right-angled twins were analyzed in Gd2(MoO4)3. Linear needle tips were found in WO3, [N(CH3)4]2.ZnBr4 CrAl, BiVO4, GdBa2Cu3O7, and PbZrO. Parabolic tips occur in K2Ba(NO2)4, and GeTe whereas exponential curvatures appear in BaTiO3, KSCN, Pb3(PO4)2, CaTiO3, alkali feldspars, YBa2Cu3O7, and MnAl. The size and shape of the twin microstructure relates to its formation during the phase transition and the subsequent annealing history. The mobility of the twin walls after formation depends not only on the thermal activation but also on the structure of the wall, which may be pinned to impurities on a favorable structural site. Depinnign energies are often large compared with thermal energies for diffusion. This leads to kinetic time scales for twin coarsening that are comparable to geological time scales. Therefore, transformation twins that exhibit needle domains not only indicate that the mineral underwent a structural phase transition but also contain information about its subsequent geological history.

American Mineralogist↗

USGS1999

Evolution of composition of major mineral phases in layered complex of ophiolite assemblage: Evidence for the Voykar ophiolites (Polar urals, Russia)

We present a detailed study of compositional variation of major minerals through a cross section of the layered complex of the Late Devonian Voykar ophiolite assemblage (Polar Urals). The principal characteristics of this layered complex suggest crystallization from a periodically replenished open magma system in a tectonically dynamic, oceanic environment. The complex may be described in terms of two sequences of cumulus rocks, or megarhythms, that each display an upward progression from ultramafic to gabbroic composition. A transitional zone between the megarhythms is characterized by an upwardly reverse lithologic progression from gabbroic to ultramafic composition. Broad cryptic variation in mineral composition over intervals >100 m parallel changes in the lithologic abundances and suggest changes in the rate of magma supply relative to crystallization and(or) tapping of different mantle sources that had been previously depleted to different degrees. The mineralogy, mineral compositions and isotopic composition of the layered complex coupled with the association of the Voykar ophiolite with island-arc complexes suggest that it most likely formed in a back-arc basin.

Conference Paper↗

USGS2003

Comment on "Evaluation of X-ray diffraction methods for determining the crystal growth mechanisms of clay minerals in mudstones, shales and slates," by L. N. Warr and D. R. Peacor

A recent paper by Warr and Peacor (2002) suggested that our use of the Bertaut-Warren-Averbach technique (MudMaster computer program) for studying changes in crystallite thickness distributions (CTDs) of clay minerals during diagenesis and very low-grade metamorphism is not reliable because it is dependent on many variables which can not be fully controlled. Furthermore, the authors implied that the measured shapes of CTDs cannot be used with confidence to deduce crystal growth mechanisms and histories for clays, based on our CTD simulation approach (using the Galoper computer program). We disagree with both points, and show that the techniques are powerful, reliable and useful for studying clay mineral alteration in rocks. ?? 2003 Schweiz. Mineral. Petrogr. Ges.

Schweizerische Mineralogische und Petrographische ↗

USGS2003

Goldquarryite, a new Cd-bearing phosphate mineral from the Gold Quarry mine, Eureka County, Nevada

Goldquarryite, idealized formula CuCd2Al3(PO44F2(H2O)10(H2O 2, structure-derived formula (Cu0.70???0.30??1.00(Cd1.68Ca0.32??2.00Al3 (PO44F2(H2O)10[(H2O 1.60F0.40]??2.00, is triclinic, space group P1, with unit-cell parameters derived from crystal structure: a = 6.787(1), b = 9.082(2), c = 10.113(2) A??, ?? = 101.40(1)??, ?? = 104.27(1)??, ?? = 102.51(1)??, V = 568.7(3) A??3, a:b:c: = 0.7473:1:1.1135, Z = 1. The strongest seven reflections in the X-ray powder-diffraction pattern are [d(A??)(I)(hkl)]: 9.433(100)(001); 4.726(30)(002); 3.700(30)(022); 3.173(30b)(122, 113, 120, 003); 3.010(30)(122, 212); 2.896(30)(211); 2.820(50)(022). The mineral occurs on a single specimen collected from the 5,425-foot bench, Gold Quarry mine, Eureka County, Nevada, as isolated clusters of radiating sprays of crystals and as compact parallel crystal aggregates, which are both found on and between breccia fragments. Sprays and aggregates never exceed 3 mm in longest dimension and typically average about 0.5 mm in size. Goldquarryite is a late-stage supergene mineral associated with opal, carbonate-fluorapatite and hewettite, on a host rock composed principally of brecciated and hydrothermally rounded jasperoid fragments which have been lightly cemented by late-stage silicification. Individual euhedral crystals are acicular to bladed, elongate [100], with a length-to-width ratio of approximately 20:1; the maximum size is 1.5 mm but most crystals do not exceed 0.4 mm in length. Forms are {010}, {001} major and {100} very minor. The mineral is pleochroic; translucent (masses) to transparent (crystals); very pale blue to blue-gray (crystals) or blue (masses); with a white streak and a vitreous to glassy luster. Goldquarryite is brittle, lacks cleavage, has an irregular fracture, and is nonfluorescent; hardness (Mohs') is estimated at 3-4; measured density is 2.78(1) g/cm3 (sink-float techniques using methylene iodide-acetone mixtures), calculated density is 2.81 g/cm3 (for formula and unit-cell parameters derived from crystal structure). Optically, it is biaxial positive, ?? = 1.570, ?? = 1.573, ?? = 1.578; 2V (meas.) = ???30??, 2V (calc.) = 76??; dispersion r < v, strong. Average electron-microprobe analysis: K2O = 0.17, CuO = 5.33, CaO = 1.25, NiO = 0.23, ZnO = 0.05, CdO = 26.24, Al2O3 = 15.22, V2O3 = 0.05, P2O5 = 28.04, F = 3.63, H2O (calculated assuming stoichiometry) = [22.19], -O = F = -1.53, total = 100.87 weight %, corresponding to [(Cu0.66Ni0.03Zn0.01) ??0.70.

Mineralogical Record↗

USGS2003

Fluid inclusion and noble gas studies of the Dongping gold deposit, Hebei Province, China: A mantle connection for mineralization?

The Dongping gold deposit (>100 t Au) occurs about 200 km inboard of the northern margin of the North China craton. The deposit is mainly hosted by syenite of a middle Paleozoic alkalic intrusive complex that was emplaced into Late Archean basement rocks. Both groups of rocks are intruded by Late Jurassic to Early Cretaceous crustal-melt granite dikes and stocks, some within a few kilometers of the deposit. The gold ores were deposited during this latter magmatic period at about 150 Ma, a time that was characterized by widespread regional north-south compression that formed the east-west-trending Yanshan deformational belt. The ores include both the telluride mineral-bearing, low sulfide quartz veins and the highly K-feldspar-altered syenite, with most of the resource concentrated in two orebodies (1 and 70). Fluid inclusion microthermometry indicates heterogeneous trapping of low-salinity (e.g., 5-7 wt % NaCl equiv) fluids that varied from a few to 60 mole percent nonaqueous volatile species. Laser Raman spectroscopy confirms that the vapor phase in these inclusions is dominated by CO2, but may be comprised of as much as 9 mole percent H2S and 20 mole percent N2; methane concentrations in the vapor phase are consistently <1 mole percent. The variable phase ratios are consistent with fluid immiscibility during ore formation. Fluid inclusion trapping conditions are estimated to be 250?? to 375??C and 0.6 to 1.0 kbar. Helium isotope studies of fluid inclusions in ore-stage pyrites indicate He/He ratios of 2.1 to 5.2 Ra (Ra = 1.4 x 10-6 for air) for orebody 1 and 0.3 to 0.8 Ra for orebody 70. The former data suggest that at least 26 to 65 percent mantle helium occurs in the fluids that deposited the veins in orebody 1. The lower values for orebody 70, which is characterized by a more disseminated style of gold mineralization, are interpreted to reflect an increased interaction of ore fluids with surrounding crustal rocks, which may have contributed additional He to the fluids. A mantle source for at least some of the components of the gold-forming fluid is consistent with upwelling of hot asthenosphere and erosion of as much as 100 to 150 km of cool Archean lithosphere beneath the craton during this time. The Dongping deposit is located along the 100-km-wide north-south gravity lineament, which marks the western border of the thinned crust. As both regional metamorphism of Mesoproterozoic and younger cover rocks, and widespread granite magmatism, also occurred at ca. 150 Ma, it is unclear as to whether one or both of these also contributed fluid and/or metals to the hydrothermal system. Importantly, these new data suggest that economically significant gold deposits of similar mineral style and fluid composition, which are scattered along the margins of the craton, may all be products of a fluid originally partly sourced within the mantle.

Economic Geology↗

USGS2011

An open-water electrical geophysical tool for mapping sub-seafloor heavy placer minerals in 3D and migrating hydrocarbon plumes in 4D

Conference Paper↗

USGS1987

New techniques for the quantification and modeling of remotely sensed alteration and linear features in mineral resource assessment studies

Linear structural features and hydrothermally altered rocks that were interpreted from Landsat data have been used by the U.S. Geological Survey (USGS) in regional mineral resource appraisals for more than a decade. In the past, linear features and alterations have been incorporated into models for assessing mineral resources potential by manually overlaying these and other data sets. Recently, USGS research into computer-based geographic information systems (GIS) for mineral resources assessment programs has produced several new techniques for data analysis, quantification, and integration to meet assessment objectives.

Pecora XI Symposium↗

USGS2011

An open-water electrical geophysical tool for mapping sub-seafloor heavy placer minerals in 3D and migrating hydrocarbon plumes in 4D

A towed-streamer technology has been developed for mapping placer heavy minerals and dispersed hydrocarbon plumes in the open ocean. The approach uses induced polarization (IP), an electrical measurement that encompasses several different surface-reactive capacitive and electrochemical phenomena, and thus is ideally suited for mapping dispersed or disseminated targets. The application is operated at sea by towing active electrical geophysical streamers behind a ship; a wide area can be covered in three dimensions by folding tow-paths over each other in lawn-mower fashion. This technology has already been proven in laboratory and ocean settings to detect IP-reactive titanium- and rare-earth (REE) minerals such as ilmenite and monazite. By extension, minerals that weather and accumulate/concentrate by a similar mechanism, including gold, platinum, and diamonds, may be rapidly detected and mapped indirectly- even when dispersed and covered with thick, inert sediment. IP is also highly reactive to metal structures such as pipelines and cables. Currently, the only means for mapping an oil-spill plume is to park a large ship in the ocean and drop a sampling string over the side, requiring hours of time per sampling point. The samples must then be chemically analyzed, adding additional time and expense. We believe that an extension of the marine IP technology could also apply to rapidly mapping both seafloor- blanket and disseminated hydrocarbon plumes in the open ocean, as hydrocarbon droplets in conductive seawater are topologically equivalent to a metal-plates-and-dielectric capacitor. Because the effective capacitance would be frequency-dependent on droplet size, the approach we advocate holds the potential to not only map, but also to characterize the evolution and degradation of such a plume over time. In areas where offshore oil field development has been practiced for extended periods, making IP measurements from a towed streamer may be useful for locating buried - nd exposed pipelines, as well as pipeline leaks. We believe this technique will be a more cost-effective method than drop-sampling to map and monitor hydrocarbon plumes in open ocean settings. A marine induced polarization system was used successfully to map a 15 km × 45 km swath of the ocean floor off eastern South Africa with 3-meter sampling along 200-meter-separated profiles. The survey detected titanium-bearing sands up to 15 meters below the seafloor. From preliminary laboratory work it is apparent that we can extend this technology to monitor significant environmental problems including anthropogenic and industrial waste washed into sensitive estuaries and sounds during storm-water runoff episodes, and also to map and characterize dispersed oil plumes in the seawater column in three dimensions, as well as movement and dispersal of both over time.

Conference Paper↗

USGS1977

Chemical dissolution of sulfide minerals

Chemical dissolution treatments involving the use of aqua regia, 4 N HNO 3 , H 2 O 2 -ascorbic acid, oxalic acid, KClO 3 +HCl, and KClO 3 +HCl followed by 4 N HNO 3 were applied to specimens of nine common sulfide minerals (galena, chalcopyrite, cinnabar, molybdenite, orpiment, pyrite, stibnite, sphalerite, and tetrahedrite) mixed individually with a clay loam soil. The resultant decrease in the total sulfur content of the mixture, as determined by using the Leco induction furnace, was used to evaluate the effectiveness of each chemical treatment. A combination of KClO 3 +HCl followed by 4 N HNO 3 boiling gently for 20 min has been shown to be very effective in dissolving all the sulfide minerals. This treatment is recommended to dissolve metals residing in sulfide minerals admixed with secondary weathering products, as one step in a fractionation scheme whereby metals in soluble and adsorbed forms, and those associated with organic materials and secondary oxides, are first removed by other chemical extractants.

Journal of Research of the U.S. Geological Survey↗

USGS1990

Metallic-mineral assessment of the Aban Al Ahmar quadrangle, sheet 25F, Kingdom of Saudi Arabia

Comprehensive detailed interdisciplinary study assesses the metallic-mineral-resource potential in the Aban Al Ahmar Quadrangle of the Kingdom of Saudi Arabia, located in the eastern margin of the northeastern Arabian Shield, utilizing techniques of geophysics, geologic mapping, remote sensing and geochemistry. The landscape of the study area is characterized by isolated mountain groups, inselbergs, and local tracts of dissected hills separated by broad, low-relief peneplain. Topics covered include mining and exploration history; geological setting; interpretation of geophysical anomalies; limonitic hydrothermally altered and mineralized rocks; geochemical interpretation; mineral resource potential; skarn deposiits associated with intermediate igneous rocks; gold deposits; tin/tungsten skarn deposits; etc.

Aban Al Ahmar quadrangle↗

USGS2000

Three archives of the U. S. Geological Survey's Western Mineral Resources Team

The Western Mineral Resources Team of the U.S. Geological Survey (USGS) has three archives , which hold unpublished or difficult-to-obtain records and literature. The Technical Data Unit in Anchorage, Alaska, holds maps, field notes, and other records of the USGS work in Alaska. The USGS Field Office in Spokane, Washington, houses the more than 5,000 files from Federal government exploration programs that contracted to fund exploration for some commodities from 1950 until 1974. The Latin American Archive in Tucson, Arizona, holds material on Latin American mineral resources collected by the Center for Inter-American Mineral Resources Investigations.

Conference Paper↗

USGS2014

Mineral resource of the month: Mica

The mica mineral group includes 34 phyllosilicate minerals, all with a layered, platy texture. The mineral has been known for millennia: Mica was first mined in India about 4,000 years ago, where it was used primarily in medicines. The Mayans used it for decorative effect in stucco to make their temples sparkle in the sun. Today it is used in everything from electrical products to makeup.

Earth↗

USGS2017

Iron isotope systematics of shale-derived soils as potentially influenced by small mineral particle loss

Loss of small mineral particles from soil has been suggested as a process that can produce net isotopic fractionation in the remaining soil. We extracted water dispersible colloids (WDCs) from bulk soil collected at the Susquehanna/Shale Hills Critical Zone Observatory (SSHO) and measured their Fe isotopic composition for comparison to published data from the site. The goal was to explain soil δ56Fe values that become lighter as Fe is lost from soil. The range of δ56Fe values for WDCs was 0.22 to 0.59 ‰, barely intersecting the value of ~0.8 ± 0.3‰ predicted by mass balance for particulate Fe loss by a previous study. The WDCs extracted likely represent a mixture of unfractionated Fe inherited from shale minerals and secondary Fe fractionated by weathering zone processes. Thus, although the WDC compositions do not confirm small mineral particle losses as causing overall Fe isotope fractionation in SSHO soils, they are compatible with that interpretation.

Conference Paper↗