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At least 487 records · Page 27Linked to original sources
USGS1969

Micromineralogy of silver-bearing sphalerite from Flat River, Missouri

Detailed mineralogical and chemical study of sphalerite-rich lead ores from Flat River, Mo., confirms the presence of anomalous amounts of silver in the sphalerite. Although silver is closely associated with chlorine and no silver sulfide minerals were identified, geochemical considerations indicate the silver may be in the form of discrete submicron-size grains of sulfide rather than chloride. However, the close correlation between abundance variations in silver, chlorine, cadmium, iron, and minor lead suggests the possible existence of submicron-size grains of a complex chloride or oxychloride. Results from detailed chemical study of sphalerite show: (1) chlorine is present in areas containing silver and changes in abundance of both elements are similar; (2) the mole ratio of chlorine to silver varies from approximately 3:1 to 6:1 with an approximate average of 5:1 and the total content of each element varies widely between grains and within the same grain; (3) taking total silver in any analysis and calculating the amount of chlorine required for silver chloride leaves an excess of chlorine; (4) in chlorine-deficient areas the amounts of iron and cadmium substituting for zinc in the sphalerite structure vary widely; and (5) in areas containing chlorine, changes in abundance of iron and cadmium vary directly with that of chlorine. The fine-grained dusty opaque inclusions characterize sphalerite from this area; they were identified as mainly galena with lesser amounts of pyrite and cassiterite. Galena is silver-free (<0.02 weight percent Ag) and is essentially pure lead sulfide. Other sulfides identified include pyrite, a cobalt-nickel-iron sulfide of composition Co (sub 0.55) Ni (sub 0.25) Fe (sub 0.20) S (sub 2.00), and an iron-cobalt-nickel sulfide containing 22-28 weight percent Fe, 10-15 weight percent Co, and 3-5 weight percent Ni. Anomalous amounts of tin present as cassiterite are associated with the gangue minerals quartz, potash feldspar, a kaolinite-type clay, and trace amounts of cuprite. Carbonate gangue minerals include calcite, dolomite, ankerite, magnesite, and minor amounts of cerussite. Chemical analyses were made of many minerals and physical and textural relationships examined.

Missouri↗
USGS1953

Geology of the Plumtree area, Spruce Pine district, North Carolina

This report describes the results of study and geologic mapping (1:12,000) in the 70-square-mile Plumtree area in the northeastern part of the Spruce Pine pegmatite district, on the Blue Ridge upland in western North Carolina. The district has been the chief domestic source of feldspar and sheet mica. The mining belt just west of the Blue Ridge Front trends northeast and is 25 miles long and 10 miles wide. The center of the Plumtree area lies 10 miles northeast of Spruce Pine pegmatite district, on the Blue Ridge upland in western North Carolina. The district has been the chief domestic source of feldspar and sheet mica. The mining belt just west of the Blue Ridge Front trends northeast and is 25 miles long and 10 miles wide. The center of the Plumtree area lies 10 miles northeast of Spruce Pine and includes parts of Mitchell and Avery Counties shown on the portions of the 7.5-minute Spruce Pine, Linville Falls, Newland, North Carolina, and Carvers Gap, North Carolina and Tennessee quadrangle. The topography varies from rugged mountains to rounded or flat topped hills near the entrenched, meandering master streams. Old erosion surfaces are approximately 600,1,100, 1,500, and 2,500 feet above the present master stream level. The area is in late youth or early maturity after rejuvenation.. The regionally metamorphosed rocks of the amophibolite facies form three mappable units: mica gneiss, mica schist, and hornblende rock. These rocks, perhaps of Precambrian age, are intimately interlayered with thicknesses of the individual layers ranging from less than one inch to several tons of feet. Field relationships and chemical data suggest that the mica (Carolina-type) rocks were derived from sandstones, graywackes, and shales and that the hornblende-rich (Roan-type) layers were derived from impure carbonate rocks. The igneous rocks include alaskite and associated pegmatite of early Paleozoic age (?), dunite and associated soapstone of a prepegmatite age, and a few diabasic dikes of post-pegmatite age (Triassic?). The alaskite and pegmatite have similar bulk compositions, notably low in iron (0.3 percent). The major constituents in order of decreasing abundance are plagioclase, perthitic microcline, quartz, and muncovite. All of these minerals, as well as clay deposits derived from the weathering of alaskite under old terraces, have economic value. The zoned pegmatites contain fewer zones which are less complex mineralogically than those in the pegmatites of many other areas. These essentially unmetamorphosed bodies were intruded approximately at the peak of the regional metamorphism. Their emplacement was controlled by local structure and rock type. The source of this igneous material may have been the mobilized portions of the Cranberry gneiss which underlies the area. The dunite bodies were intruded early in the metamorphic cycle. The bodies are commonly zoned: from the wall rock inwards (1) talc-antrophyllite-serpentine fringe, (3) serpentinized dunite, (3) granular olivine core. Dunite, chromite, vermiculite, and anthophyllite are the major economic commodities. Extensive hydrothermal alteration of dunite bodies produced soapstone. The area is the northeast end of a southwest plunging synclinorium about 20 miles wide with the steeper limb on the northwest side. There are three structural zones: zone I on the northwest is characterized by the northeast-trending isoclinal folds with steep southeast dips; zone II on the southwest includes an area of rocks with low and variable dip; zone III is the complex central core. In the extreme northeast zones I and II have an indistinct boundary where they coalesce along the rim of the synclinorium. Six stratigraphic units are exposed totaling approximately 10,500 feet of metamorphic rocks. Small scale structural features include a foliation, and a lineation in the planes of the foliation. Minor folding reflects the trends of the major structures. There are randomly orient

Open-File Report↗
USGS1981

Sediment parameters for a fine-grained sediment deposit on the southeastern New England continental shelf

An area of fine-grained sediments south of Martha's Vineyard, Massachusetts, has been interpreted as a contemporary deposit. Textural analysis of cores from this area indicates that the deposit consists of sandy to clayey silts overlying a well sorted relict sand. The maximum thickness of the fine sediments is about 6 meters as determined from a core near the center of this deposit. The mineralogy of the <2 um size fraction is similar in both the fine sediments of the contemporary deposit and the underlying coarse sands. The assemblage consists of about 60% illite, 20% chlorite, and 10% kaolinite with minor amounts of mixed-layered clay and smectites. Heavy mineral analysis from a core near the center of the deposit reveals that opaque minerals, framboidal pyrite, muscovite, hornblende, garnet, and tourmaline constitute over 65% of the total downcore assemblage. Pyrite concentrations vary widely at some intervals and may reflect areas of micro-reducing conditions within the core or changes in source area with time. A persistent mica content indicates the presence of a low-energy environment throughout the depositional history of these fine sediments. Downcore organic carbon concentrations are generally uniform in the fine sediments and average about 1.5 percent. Surficial concentration from a core near the center of this feature is about 10 times greater than concentrations for coarse-grained sands on the surrounding shelf.

New England continental shelf↗
USGS1955

Geology and ground-water resources of Webster County, Iowa

Webster County, comprising an area of 718 square miles just northwest of the center of Iowa, had a population of 44,241 in 1950, with 25,115 in Fort Dodge, the principal city. Some 94.4 percent of the county is in farm land; corn is the principal crop and is used in the raising of hogs and cattle, an important occupation in this part of the country. Mineral products include gypsum, clay, coal, sand, gravel and limestone. The mean annual precipitation at Fort Dodge is 31.21 inches, of which more than 3 inches normally occurs during each of the months May, June, July, August, and September. The average number of growing days is 150. The warmest month generally is July; during December, January, and February the average temperature normally is below freezing. The upland area, comprising over 80 percent of the county, is mostly a gently undulating, slightly eroded glacial-drift plain. Morainal hills of low relief occur in the extreme southern and northern parts of the county. The Des Moines River flows through the county from north to south and, together with its tributaries, drains the entire county except the southwestern part, which is tributary to the Raccoon River. The Des Moines River has cut a deep, narrow valley about 90 feet below the upland in the northern part of the county and about 220 feet below the upland in the southern part. The tributary streams commonly have shallow valleys more than a few miles back from the Des Moines River. Glacial deposits of Pleistocene age, ranging in thickness from 50 feet in the north to 175 feet in the south, mantle the indurated rocks over all the upland area, but indurated rocks ranging in age from Mississippian to Cretaceous are exposed in places along the valleys of the Des Moines River and its tributaries.

Iowa↗
USGS2016

Aptian ‘Shale Gas’ Prospectivity in the Downdip Mississippi Interior Salt Basin, Gulf Coast, USA

This study evaluates regional ‘shale gas’ prospectivity of the Aptian section (primarily Pine Island Shale) in the downdip Mississippi Salt Basin (MSB). Previous work by the U.S. Geological Survey estimated a mean undiscovered gas resource of 8.8 trillion cubic feet (TCF) in the chronostratigraphic-equivalent Pearsall Formation in the Maverick Basin of south Texas, where industry has established a moderately successful horizontal gas and liquids play. Wells penetrating the downdip MSB Aptian section at depths of 12,000-15,000 ft were used to correlate formation tops in a 15-well cross-section extending about 200 miles (mi) east-southeastward from Adams Co. to Jackson Co. Legacy cuttings from these wells were analyzed for thermal maturity and source rock quality. Bitumen reflectance (n=53) increases with increasing present-day burial depth in the east-central study area from 1.0% to 1.7%. As the Aptian section shallows in Adams Co. to the west, bitumen Ro values are higher (1.7-2.0%), either from relatively greater heat flux or greater mid-Cenomanian uplift and erosion in this area. Total organic carbon (TOC) content ranges 0.01-1.21 and averages 0.5 wt.% (n=51); pyrolysis output (S2; n=51) averages 0.40 mg HC/g rock, indicating little present-day hydrocarbon-generative potential. Bitumen reflectance is preferred as a thermal maturity parameter as Tmax values are unreliable. Normalized X-ray diffraction (XRD) mineral analyses (n=26) indicate high average clay abundance (53 wt.%) relative to quartz (29%) and carbonate (18%). Mineral content shows a spatial relationship to an Appalachian orogen clastic sediment source, with proximal high clay and quartz and distal high carbonate content. Clastic influx from the Appalachian orogen is confirmed by detrital zircon U-Pb ages with dominant Grenville and Paleozoic components [105 ages from a Rodessa sandstone and 112 ages from a Paluxy (Albian) sandstone]. Preliminary information from fluid inclusion microthermometry (41 aqueous measurements from calcite cements in one argillaceous James Limestone sample) indicates homogenization temperatures (Th) of 120-135°C, consistent with present-day bottom-hole conditions and measured bitumen Ro values towards the western end of the MSB. Downdip in the central MSB, microthermometry (26 aqueous measurements from quartz dust rims in one Paluxy sandstone sample) and measured bitumen Ro values indicate maximum temperatures may have been significantly higher (~25°C) than present-day conditions. High inclusion salinities (15-25 wt.% salt) at both locations suggest interaction of pore fluids with evaporites. Mercury injection capillary pressure (MICP) analyses (n=3) indicate porosity ranges 1.3-2.1% and permeability 0.006-0.02 µD for Pine Island and Rodessa shales. Overall, results from this work indicate generally poor ‘shale gas’ prospectivity compared to other shale reservoirs based primarily on depth, low organic content, low porosity, and high clay content. However, thickness and thermal maturity are appropriate, moderate reservoir pressures are present, and petroleum systems modelling by others has indicated high undiscovered gas potential for the basin as a whole.

Conference Paper↗
USGS1998

Clays, specialty

Part of a special section on the state of industrial minerals in 1997. The state of the specialty clay industry worldwide for 1997 is discussed. The specialty clays mined in the U.S. are ball clay, fuller's earth, bentonite, fire clay, and kaolin. Sales of specialty clays in the U.S. were around 17 Mt in 1997. Approximately 53 kt of specialty clays were imported.

Mining Engineering↗
USGS1998

Clays, common

Part of a special section on the state of industrial minerals in 1997. The state of the common clay industry worldwide for 1997 is discussed. Sales of common clay in the U.S. increased from 26.2 Mt in 1996 to an estimated 26.5 Mt in 1997. The amount of common clay and shale used to produce structural clay products in 1997 was estimated at 13.8 Mt.

Mining Engineering↗
USGS2001

Common clay and shale

Part of the 2000 annual review of the industrial minerals sector. A general overview of the common clay and shale industry is provided. In 2000, U.S. production increased by 5 percent, while sales or use declined to 23.6 Mt. Despite the slowdown in the economy, no major changes are expected for the market.

Mining Engineering↗
USGS2019

Rare earth element mineral deposits in the United States

Because of their unique special chemical properties, many of the metals in the group of rare earth elements (REEs) have essential applications in 21st century technologies. Examples of products that use REEs are cell phones, computers, fluorescent and light-emitting-diode lights, flat-screen television and computer monitors, and in high-strength magnets used by clean energy technologies such as the generators of wind turbines and batteries of hybrid and electric vehicles. REEs are used in many defense applications, such as in components of jet engines, missile guidance systems, antimissile defense systems, satellites, and communication systems. The rare earth elements have become vital to manufacturing numerous high-tech products, which has been accompanied by a large increase in their demand. At the same time, there has been concern by the United States and many other Nations about the near-monopoly of mining, processing, and supply of REEs from one Nation, China. Between 2011 and 2017, China produced approximately 84 percent of the world’s REEs, and during this time the United States only produced REEs between 2012 and 2015. The U.S. production came entirely from the Mountain Pass mine in California, providing only about 4 percent of the world REE supply. Because REEs are essential for technological applications and are primarily supplied by one Nation, there has been an increased concern in identifying new sources of REEs, including economic REE deposits. In response to these concerns, since 2009, the U.S. Geological Survey (USGS) has conducted numerous studies focused on the distribution, geology, and potential resources for the REE-bearing mineral deposits in the United States. The basic characteristics of mineral deposit types that host REE enrichments in the United Sates are summarized in this report, with selected examples. Several types of REE-enriched mineral deposits are reviewed, including deposits in carbonatites, alkaline igneous rocks, sedimentary phosphate-rich rocks (phosphorite), regions containing REE-rich veins, iron oxide deposits containing REE-bearing apatite, monazite-xenotime-bearing placer deposits (heavy-mineral sands), and ion-adsorption clay deposits (REE in granite-derived regolith). A better understanding of these mineral deposits will assist in identifying domestic resources to help alleviate the dependence on imported REEs. The economic development of REE mineral deposits is affected by many factors beyond mining, such as commodity prices and mineral processing costs. Most of the REEs are hosted by minerals that have complex chemical formulas; this presents more challenges to process and extract the REEs. Continued advancements and refinements in mineral processing techniques may allow REE deposits with complex mineralogy to be economically developed in the future.

Circular↗
USGS1903

The clays of the United States east of the Mississippi River

NATURE OF CLAY. The term clay is applied to a natural substance or rock which, whenfinely ground and mixed with water, forms a pasty, moldable mass that preserves its shape when air dried, and when burned changes to a hard, rock-like substance by the coalescence of its particles, through softening under the action of heat. A microscopic examination of clay shows that it is made up of a great number of small mineral fragments of many different kinds and of varying shape, ranging in size from. those which are under 1/1000 mm. in diameter (known as clay) up to grains of sand which are sufficiently large to be easily visible to the naked eye. The smaller particles predominate. Since clays vary mineralogically they vary also chemically, but the plasticity may remain the same through a wide range of chemical composition, and this property is evidently not dependent on the chemical composition alone, but is due rather to some physical cause. The plasticity may be destroyed by heating the clay to a sufficiently high temperature to drive off the chemically combined water. Although varying in their mineral composition, most clays are supposed to contain more or less of the mineral kaolinite (a hydrated silicate of alumina), which is commonly referred to as the clay base or clay substance. The adoption of the latter term has probably arisen from the fact that many have 'considered this mineral to be the cause of plasticity, an idea now known to be somewhat incorrect, because some of the most plastic clays contain but small quantities of kaolinite, and vice versa.

Professional Paper↗
USGS1982

Geologic factors that control mineral matter in coal

Elements other than organically derived and bound C, H, N, O, and S constitute mineral matter in coal. Mineral matter may consist of discrete minerals such as calcite, quartz, clays, and pyrite, and/or organic compounds that contain organically bonded elements such as Ca and CI. Processes that may affect the association and content of mineral matter are operable from the initial peat-forming stage to the time of utilization of the coal. However, the objective of this paper is to discuss some of the various geologic processes that may influence content and associations in unmined coal.

Book chapter↗
USGS1979

Analyses of surficial deposits, central Brooks Range, Alaska

Seventy-nine sediment samples from the central Brooks Range were analyzed for grain-size distribution, shape and composition of grains, and other physical properties. Four statistical measures (sorting, mean diameter, skewness, and kurtosis) were then computed for the sand-to-clay size fraction of all samples. Fan sediments resemble the other alluvial-gravel deposits in consisting of sand and gravel from which very fine sand and the smaller size fractions have been removed by running water. Sorting and rounding of particles is best at the distal ends of large fans. Modern alluvium is better sorted than most fan deposits, with more rounded clasts and generally higher ratios of sand to gravel. Other alluvial deposits from terraces and heavily dissected erosion remnants generally are comparable to modern alluvium. All classes of alluvial gravel are characterized by removal of fines and by decreasing values of mean 0, kurtosis, and skewness as sorting increases. Most samples also have high clay/silt ratios that probably were caused by deflation on windswept bars and floodplains. Lacustrine deposits have clay percentages ranging from about 85 to 35, with silt predominant in more than one-half of the samples. Several samples contain sand and gravel that presumably were ice rafted. Clay-sized particles are unweathered mineral grains, implying that glacial abrasion was their primary source. Flow-slide deposits are very poorly sorted mixtures of gravel, sand, and silt, with clay content averaging only about one percent. Clasts consist of angular fragments of local bedrock, usually schist and phyllite, and matrix materials usually are highly micaceous. Although related flow types, a mud-flow and a debris-flow in till, are generally similar to flow-slide deposits, the mudflow has been modified by running water and the debris flow reflects the composition of its parent till. Other colluvial deposits commonly have high silt and low clay contents, but one solifluction deposit has abundant clay derived from till. Several of the flow-slides and other colluvial deposits are polygenetic, having undergone several episodes of flow that incorporated different types of sediment. Sand deposits include silty floodplain and basin-fill deposits as well as five relatively pure and well sorted dunal and river-bar sands. The silt-rich deposits probably contain large amounts of loess that fell into late-Pleistocene basin fillings and muskegs and later was redeposited on Holocene floodplains. The five dunal and bar sands are dominantly medium to fine sand; relatively well sorted, symmetric to coarse skewed, and leptokurtic. The dunal sands can be distinguished by the presence of very fine sand: wind apparently is less effective than flowing water in removing the finest sand fraction. The glacial deposits consist of till, ice-content stratified drift, and outwash. Till is a poorly sorted mixed sediment that resembles many flow de-posits but typically contains more clay. Two clay-deficient tills resemble fan deposits, implying effective washing by meltwater during glacial transport or deposition of these deposits. The ice-contact stratified drift varies in character from fan-like gravel deposits to sand accumulations nearly as well sorted as those of river bars. Almost all samples reflect some restriction in washing of fines by meltwater, probably owing to irregular topography and resulting poor drainage on and around stagnating glaciers. Most outwash deposits have less fine sand than modern alluvium, probably reflecting the generally high energy of glacial meltwater streams and the absence of vegetation from their floodplains. Samples from the southern Brooks Range are better sorted than those from northern Brooks Range valleys, and their statistical values lie close to those of modern alluvium. Comparisons between the different classes of sediments are facilitated by combining them into (1) gravel, (2) sand, silt, and clay, and (3) mixed deposits. Deposits of unknown or uncertain origin may then be compared directly against sediments from modern streams, dunes, flow-slides and other known sources, and alternative origins of aberrant samples in each of the sediment classes can also be examined. Several samples that initially were classed as fan, lacustrine, or glacial proved to be mixed deposits created by frost-churning, frost-lifting of stones, flowage down faces of river bluffs, and other postdepositional processes. Sorting and mean ϕ of matrix materials were useful in distinguishing the different sediment classes, separating them into contrasting subgroups, and identifying atypical samples. Skewness and kurtosis were generally less useful in this study.

Alaska↗
USGS1949

Vestigial zinc in surface residuum associated with primary zinc ore in East Tennessee

A series of samples of residual clay at the Friends Station zinc deposit, Tenn., was collected and analyzed for zinc. Results indicate that residuum containing 0.05 percent Zn and more is the product of weathering of limestone and dolomite containing zinc mineralization. Chemical analysis of residual clays for zinc shows promise as a method of prospecting for zinc in the limestone valleys of the southern Appalachians.

Tennessee↗
USGS2022

The Coles Hill uranium deposit, Virginia, USA: Geology, geochemistry, geochronology, and genetic model

The Coles Hill uranium deposit with an indicated resource of about 130 million lbs. of U 3 O 8 is the largest unmined uranium deposit in the United States. The deposit is hosted in the Taconian (approximately 480 – 450 Ma) Martinsville igneous complex, which consists of the Ordovician Leatherwood Granite (granodiorite) and Silurian Rich Acres Formation (diorite). The host rock was metamorphosed to orthogneiss during the Alleghanian orogeny (approximately 325 – 260 Ma) when it also underwent dextral strike-slip movement along the Brookneal shear zone. During the Triassic, extensional tectonics led to the development of the Dan River Basin that lies east of Coles Hill. The mineralized zone is hosted in brittle structures in the footwall of the Triassic Chatham fault that forms the western edge of the basin. Within brittle fracture zones, uranium silicate and uranium-bearing fluorapatite with traces of brannerite form veins and breccia fill with chlorite, quartz, calcite, titanium oxide, pyrite, and calcite. Uranium silicates also coat and replace primary titanite, zircon, ilmenite, and sulfides. Sodium metasomatism preceded and accompanied uranium mineralization, pervasively altering host rock, and forming albite from primary feldspar, depositing limpid albite rims on feldspar, altering titanite to titanium oxide and calcite and forming riebeckite. Various geothermometers suggest temperatures of less than approximately ~200°C during mineralization. In situ U-Pb analyses of titanite, Ti-oxide, and apatite, and Rb/Sr and U/Pb isotope-systematics of whole rock samples resolve the timing of geologic processes affecting Coles Hill. The host Leatherwood granite containing primary euhedral titanite is dated at 450 – 445 Ma, in agreement with previously obtained ages from zircon in the Martinsville igneous complex. A regional metamorphic event at 330 – 310 Ma formed anhedral titanite and some apatite, re-equilibrated whole rock Rb/Sr and U-Pb isotopes and is interpreted to have coincided with movement along the Brookneal shear zone. During shearing and metamorphism primary refractory uranium-bearing minerals including titanite, zircon, and uranothorite were recrystallized and uranium was liberated and incorporated locally into hematite, clay, and other fine-grained minerals. Uranium mineralization was accompanied by a metasomatic episode between 250 and 200 Ma that reset the Rb-Sr and U-Pb isotope systems, forming titanite and apatite that are associated and in places intimately intergrown with uranium silicate dating mineralization. This event coincides with rifting that formed the Dan River Basin and was a precursor to the breakup of Pangea. Based on the close spatial and temporal association of uranium with apatite, we conclude that uranium was carried as a uranyl-phosphate complex. The release of calcium during sodium metasomatic alteration of primary calcic feldspar and titanite in the host rock initiated successive reactions in which uranium and phosphate in mineralizing fluids combined with calcium to form U-enriched fluorapatite. Excess uranium was locally reduced by coupled redox reactions involving ferrous iron and sulfide minerals in the host rock, forming uranium silicates. Based on the deposit mineralogy, oxygen isotope geochemistry and trace element characteristics of uranium silicate and gangue minerals the primary mineralizing fluids likely included connate and/or meteoric water sourced from the local Dan River Basin. High heat flow related to Mesozoic rifting may have driven these (P-Na-F-rich) brines through local aquifers and into basin margin faults, transporting uranium from the basin or mobilizing uranium from previously formed U-minerals in the Brookneal shear zone, or from U-enriched older basement rock.

Virginia↗
USGS2017

Multiscale hyperspectral imaging of the Orange Hill Porphyry Copper Deposit, Alaska, USA, with laboratory-, field-, and aircraft-based imaging spectrometers

In the past decade, use of hyperspectral imaging (imaging spectroscopy) for mineral exploration and mining operations has been increasing at different spatial scales. In this paper, we focus on recent trends in applying imaging spectrometer data to: 1) airborne imaging of high latitude deposits, 2) field-based imaging of outcrops, and 3) laboratory-level imaging of geologic samples. Comparing mineral information derived from imaging spectrometer data acquired at these three scales in Alaska in areas of exposed porphyry Cu-Au-Mo deposits, Orange Hill and Bond Creek, we find notable consistency in identifications of spectrally predominant minerals, including white mica, chlorite, clays, and gypsum. Variations in the wavelength position of white mica 2200 nm Al-OH absorption seen at the airborne level are echoed by finerscale field and laboratory imaging, with wavelength positions spanning the 2199 to 2207 nm range. The longerwavelength micas associated with porphyry formation are more phengitic in composition, and thus distinct from mica in plutonic and volcanic arc rocks not affected by magmatic-hydrothermal fluids. The hillside imagery, collected on a cloudy day that would have precluded aircraft survey, gave comparable result to airborne and laboratory data, indicating field-based imaging spectroscopy can be a feasible alternative to airborne survey for accessible targets. Direct spectral observation of molybdenite in rocks collected from the Orange Hill deposit demonstratesthat additional important mineral information can be revealed with laboratory level imaging spectroscopy that is difficult to obtain in coarser scale data, commonly due to low areal extent of target minerals. The spatial association of the clinochlore + white mica and long wavelength white mica spectral classes to multi-element Cu-Mo-Au anomalies from geochemical analyses of rocks and sediments support a causative relationship with magmatic-hydrothermal alteration. Mineral maps from the airborne data were used to guide field sampling that found additional CuMo-Au mineralized areas, which were previously unknown or unreported. The results from this study provide support for utilization of imaging spectroscopy for assisting mineral exploration in other portions of the state of Alaska as well as other areas at high latitudes. Imaging spectroscopy has the potential to provide targeting information for follow-up sampling and investigations, potentially reducing subsequent exploration costs.

Alaska↗
USGS2005

Remote sensing characterization of the Animas River watershed, southwestern Colorado, by AVIRIS imaging spectroscopy

Visible-wavelength and near-infrared image cubes of the Animas River watershed in southwestern Colorado have been acquired by the Jet Propulsion Laboratory's Airborne Visible and InfraRed Imaging Spectrometer (AVIRIS) instrument and processed using the U.S. Geological Survey Tetracorder v3.6a2 implementation. The Tetracorder expert system utilizes a spectral reference library containing more than 400 laboratory and field spectra of end-member minerals, mineral mixtures, vegetation, manmade materials, atmospheric gases, and additional substances to generate maps of mineralogy, vegetation, snow, and other material distributions. Major iron-bearing, clay, mica, carbonate, sulfate, and other minerals were identified, among which are several minerals associated with acid rock drainage, including pyrite, jarosite, alunite, and goethite. Distributions of minerals such as calcite and chlorite indicate a relationship between acid-neutralizing assemblages and stream geochemistry within the watershed. Images denoting material distributions throughout the watershed have been orthorectified against digital terrain models to produce georeferenced image files suitable for inclusion in Geographic Information System databases. Results of this study are of use to land managers, stakeholders, and researchers interested in understanding a number of characteristics of the Animas River watershed.

Scientific Investigations Report↗
USGS1984

Coalification of organic matter in coal balls of the Pennsylvanian (upper Carboniferous) of the Illinois Basin, United States

An evaluation was made of the degree of coalification of two coal balls from the Illinois Basin of the Pennsylvanian (upper Carboniferous) of the United States. Previous interpretations are mainly misleading and contradictory, primarily because of the assumption that the brown color and exceptional cellular and subcellular preservation typical of American coal balls imply chemical preservation of cellulose and lignin, the primary components of peat. Xylem tissue from a medullosan seed fern contained in a coal ball and the coal attached to the coal ball from the Calhoun coal bed, Mattoon Formation, Illinois, was analyzed by elemental, petrographic, and nuclear magnetic resonance (NMR) techniques to determine the degree of coalification. The NMR and elemental data indicate the lack of cellulose and lignin and a probable rank of high-volatile C bituminous coal. These data corroborate data for a coal ball from the Herrin (No. 6) coal bed (Carbondale Formation, Middle Pennsylvanian) and support our hypothesis that the organic matter in coal balls of the Pennsylvanian strata of the United States is coalified to about the same degree as the surrounding coal. Data presented show a range of lower reflectances for xylem tissue and vitrinite in the analyzed coal balls compared with vitrinite in the attached coal. The data reported indicate that physical preservation of organic matter in coal balls does not imply chemical preservation. Also our study supports the hypothesis that compactional (static load) pressure is not a prerequisite for coalification up to a rank of high-volatile C bituminous coal. A whole-rock analysis of the Calhoun coal ball indicates a similarity to other carbonate coal balls from the United States. It consists primarily of calcium carbonate and 1–2% organic matter; silica and alumina together make up less than 0.5%, indicating the lack of minerals such as quartz and clays.

Illinois, Indiana, Kentucky↗