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USGS1977

Oil-shale resource investigations of the U.S. Geological Survey

The decade of the 1970's so far has been marked by a sharply increased dependence by the United States on foreign sources of energy. Although this dependence had been growing for the previous 20 years, it was made clearly visible to the American public by the Arab oil embargo of 1973. Since then, energy has remained a topic of public discussion and concern. The current imbalance between U.S. energy supply and demand and the generally recognized need to increase the domestic production of energy make it appropriate to review our present knowledge of U.S. mineral fuel resources--coal, oil, natural gas, oil shale, and uranium--which in 1975 provided 95 percent of the energy produced in the United States. These conditions also warrant a description of the research that is being done to improve our understanding of these resources, and to determine the effects on the environment of their development. This is one of four reports on the energy resource investigations being conducted by the U.S. Geological Survey to assess the Nation's coal, oil and gas, oil shale, and uranium and thorium resources. Two other reports provide information about the Geological Survey's programs for assessing the petroleum resources of the U.S. Outer Continental Shelf and for identifying the environmental factors that could affect their development. The description of the Geological Survey's oil-shale investigations is presented in this report in the context of the underlying socio-economic problem of expanding the domestic production of oil and gas while maintaining acceptable environmental standards. This orientation toward a national mission characterizes each segment of the Geological Survey's energy resources and marine geology programs. Readers who want information about the individual projects that comprise the Oil-Shale Program will find it in the appendices, which also include a bibliography. It is hoped that this report will give scientists, science administrators, and policy makers, both in government and in the private sector, as well as the general public, a better understanding of the relation of oil shale resources to the Nation's requirements for energy and of the importance of a carefully planned research program of resource assessment and environmental research on this future energy commodity.

Open-File Report↗
USGS1978

Methods for regional assessment of geothermal resources

A consistent, agreed-upon terminology is prerequisite for geothermal resource assessment. Accordingly, we propose a logical, sequential subdivision of the "geothermal resource base", accepting its definition as all the thermal energy in the earth's crust under a given area, measured from mean annual temperature. That part of the resource base which is shallow enough to be tapped by production drilling is termed the "accessible resource base", and it in turn is divided into "useful" and "residual" components. The useful component (i.e. the thermal energy that could reasonably be extracted at costs competitive with other forms of energy at some specified future time) is termed the "geothermal resource". This in turn is divided into "economic" and "subeconomic" components, based on conditions existing at the time of assessment. In the format of a McKelvey diagram, this logic defines the vertical axis (degree of economic feasibility). The horizontal axis (degree of geologic assurance) contains "identified" and "undiscovered" components. "Reserve" is then designated as the identified economic resource. All categories should be expressed in units of thermal energy, with resource and reserve figures calculated at wellhead, prior to the inevitable large losses inherent in any practical thermal use or in conversion to electricity. Methods for assessing geothermal resources can be grouped into 4 classes: (a) surface thermal flux, (b) volume, (c) planar fracture and (d) magmatic heat budget. The volume method appears to be most useful because (1) it is applicable to virtually any geologic environment, (2) the required parameters can in Sprinciple be measured or estimated, (3) the inevitable errors are in part compensated and (4) the major uncertainties (recoverability and resupply) are amenable to resolution in the foreseeable future. The major weakness in all the methods rests in the estimation of how much of the accessible resource base can be extracted at some time in the future. In a manner similar to mineral and fuel assessment, this recoverability is expressed as a "recovery factor". For an ideally permeable hot-water system, the recovery factor may be as much as 50% and seems to be independent of temperature. It must decrease as effective porosity (??e) decreases, but the relation between the two is little more than a guess. On the other hand, for favorable systems like Larderello that produce steam by a mechanism of intergranular vaporization, the recovery factor is probably around 15-20%, decreasing to zero at an effective porosity of zero. According to the anlysis of Bodvarsson (1974), it increases with decreasing reservoir temperature, and as pointed out by Nathenson (1975a) is limited at low temperatures by the need to have sufficient reservoir pressure for extraction and use. The extent to which a geothermal reservoir can be resupplied with heat during "industrial" times of 10-100 yr can be evaluated using simple analytical models. The results, combined with gravity and levelling data of Hunt (1977) for Wairakei and Isherwood (1977) for The Geysers, confirm earlier conclusions by Ramey (1970) and Nathenson (1975a) that resupply to reservoirs producing only steam can be neglected, and the conclusion of Nathenson (1975a) that it may be significant for hot-water systems of high natural discharge. Major subjects that demand continuing investigation include: 1. 1. Determination of recovery factors as functions of temperature and effective porosity, particularly for hot-water systems. 2. 2. Evaluation of fluid recharge and heat resupply by repetitive gravity, levelling and underground temperature surveys in producing geothermal fields. 3. 3. Analysis of the extent to which a recovery factor can be enhanced by stimulation and by use of confined circulation loops. ?? 1979.

Geothermics↗
USGS1999

Mapping the glacial geology of the Central Great Lakes region in three dimensions: A model for state-federal cooperation

Planners need to evaluate complex and competing public-policy options for managing water, land, and biological resources; they must ensure economic growth, meet the needs of an increasing population, assess hazards, and manage the environment in a sustainable manner. The State Geological Surveys of Illinois, Indiana, Michigan, and Ohio and the U.S. Geological Survey (USGS) receive many requests from local, State, and Federal planners and officials for geologic information. Thick and complex layers of glacial and related sediments blanket the bedrock of these States: a three-dimensional understanding of these deposits is critical to making informed resource-management and other planning decisions. At two recent forums (in Indianapolis, March 1997, and Columbus, Ohio, February 1999), more than 200 attendees from more than 60 local, State, and Federal agencies provided a clear message. They need three-dimensional geologic information to use in making decisions on the following issues: • Quality, quantity, distribution, and accessibility of surface and ground water • Aggregate sources and land-use conflicts • Energy and mineral resource management • Environmental management and mitigation of land and water contamination • Acceleration of the permitting processes of regulatory agencies • Industrial, commercial, residential, and infrastructure siting and construction • Agricultural land loss, erosion, sedimentation, and agrichemical use • Waste-disposal planning and mitigation • Habitat alteration and biodiversity • Coastal erosion, landslides, radon, floods, and earthquakes

Illinois, Indiana, Michigan, Ohio↗
USGS2005

Geochemistry and jasper beds from the Ordovician Løkken ophiolite, Norway: origin of proximal and distal siliceous exhalites

Stratiform beds of jasper (hematitic chert), composed essentially of SiO 2 (69–95 wt %) and Fe 2 O 3 (3–25 wt %), can be traced several kilometers along strike in the Ordovician Løkken ophiolite, Norway. These siliceous beds are closely associated with volcanogenic massive sulfide (VMS) deposits and are interpreted as sea-floor gels that were deposited by fallout from hydrothermal plumes in silica-rich seawater, in which plume-derived Fe oxyhydroxide particles promoted flocculation and rapid settling of large (~200 μm) colloidal particles of silica-iron oxyhydroxide. Concentrations of chalcophile elements in the jasper beds are at the parts per million level implying that sulfide particle fallout was insignificant and that the Si-Fe gel-forming plumes were mainly derived from intermediate- (100°–250°C) to high-temperature (>250°C) white smoker-type vents with high Fe/S ratios. The interpreted setting is similar to that of the Lau basin, where high-temperature (280°–334°C) white smoker venting alternates or overlaps with sulfide mound-forming black smoker venting. Ratios of Al, Sc, Th, Hf, and REE to iron are very low and show that the detrital input was <0.1 percent of the bulk jasper. Most jasper beds are enriched in U, V, P, and Mo relative to the North American Shale Composite, reflecting a predominantly seawater source, whereas REE distribution patterns (positive Eu and negative Ce anomalies) reflect variable mixing of hydrothermal solutions with oxic seawater at dilution ratios of ~10 2 to 10 4 . Trace element variations in the gel precursor to the jasper are thought to have been controlled by coprecipitation and/or adsorption by Fe oxyhydroxide particles that formed by the oxidation of hydrothermal Fe 2+ within the variably seawater-diluted hydrothermal plume(s). Thick jasper layers near the Høydal VMS orebody show distinct positive As/Fe and Sb/Fe anomalies that are attributed to near-vent rapid settling of Si-Fe particles derived from As- and Sb-rich hydrothermal fluids prior to extensive mixing with seawater in the buoyant plume. Particles that formed later in the highly diluted nonbuoyant plume formed relatively As and Sb poor distal jasper. The large particle sizes and accordingly high settling rates of the particles, together with mass-balance calculations based on modern vent field data, suggest that individual meter-thick jasper beds formed within a plume lifetime of 200 years or less. The lack of thick jasper beds near the Løkken VMS orebody, which is larger than the Høydal orebody by more than two orders of magnitude, probably reflects a shift to anoxic conditions during Løkken mineralization. This environment limited oxidation of iron in the hydrothermal plume and formation of the ferric oxyhydroxides necessary for the flocculation of silica and sea-floor deposition of the gel precursor of the jasper beds. Distal pyritic and iron-poor cherts are more common than jasper in ancient VMS-hosting sequences. The origin of these other types of siliceous exhalite is enigmatic but at least in some cases involved sulfidation, reduction to magnetite, or dissolution of the original ferric iron in precursor Si-rich gels, either by hydrothermal or diagenetic processes.

Economic Geology↗
USGS1962

Metallogenetic provinces of Chile, S. A

The metalliferous deposits of Chile tend to be restricted to well denned metallogenetic provinces, each characterized by a dominant mineral or mineral assemblage. The most important ore deposits are those of copper, iron, silver, gold, and manganese. The primary minerals are few in number and most are simple sulfides and oxides; more complex sulfosalts are scarce. Secondary minerals in great variety are important constituents of the ores. Many of the ore deposits are situated along well defined structural lines, several hundred kilometers long, that parallel the structural grain of the Andes.The deposits, with few exceptions, are found in sedimentary or volcanic rocks that range in age from Jurassic to Late Cretaceous or in intrusive rocks of Late Jurassic to Late Cretaceous age. Most deposits are genetically related to intrusive bodies, which have an average composition within the range of granite-diorite.The metalliferous deposits can be classed as hydrothermal, sedimentary, contact-metasomatic and magmatic. Copper deposits are typically hydro-thermal, manganese deposits are sedimentary, and most of the iron ore deposits are contact-metasomatic. A unique group of iron ore deposits apparently formed by near-surface intrusion and surface flows of a magma consisting of iron oxides. Hydrothermal deposits, the most abundant and most important economically, were formed under conditions ranging from low to high temperature and pressure. © 1962 Society of Economic Geologists, Inc.

Economic Geology↗
USGS1987

Age of uranium mineralization at the Jabiluka and Ranger deposits, Northern Territory, Australia: New U-Pb isotope evidence

The Ranger and Jabiluka uranium deposits are the largest in the Alligator Rivers uranium field, which contains at least 20 percent of the world's low-cost uranium reserves. Ore occurs in early Proterozoic metasediments, below an unconformity with sandstones of the 1.65-b.y.-old Kombolgie Formation. This study has used U-Pb isotope data from a large number of whole-rock drill core samples with a variety of mineral assemblages and textures. Ranger samples indicate a well-defined age of 1,737 + or - 20 m.y., consistent with earlier suggestions of the antiquity of this deposit. This age is distinctly pre-Kombolgie, so the Ranger deposit cannot have been formed by processes requiring its presence. The age is consistent, however, with mineralization related to heating associated with either the emplacement of early postmetamorphic granites, or possibly, with intrusion of the nearby Oenpelli Dolerite. In contrast, data for the least-altered Jabiluka ores yield a concordia intercept age of 1,437 + or - 40 m.y.--significantly younger than the Ranger age and also younger than the Kombolgie Formation. This age may correspond to a regional thermal event, as indicated both by mafic dikes of roughly this age and a zircon lower intercept age from a nearby granite-gneiss. Thus our data indicate that there must be at least three distinct periods of major U mineralization in the Alligator Rivers uranium field (including the previously determined approximately 900-m.y. age of the Nabarlek deposit), despite the fact that all of the deposits share strong similarities in their host rock, mineralogy, alteration, and geologic setting.Both Ranger and Jabiluka reflect a common, profound isotopic disturbance at about 400 to 600 m.y. This disturbance, which was especially pronounced at Jabiluka, may correspond to the development of basins and associated basalt flows to the west and southwest, as suggested by Crick et al. (1980).

Economic Geology↗
USGS1962

Geology and refractory clay deposits of the Haldeman and Wrigley quadrangles, Kentucky, with a section on coal resources

The Haldeman and Wrigley 7th-minute quadrangles are near the western edge of the eastern Kentucky coal field and cover an area of approximately 117 square miles in parts of Carter, Rowan, Elliott, and Morgan Counties, Ky. The rocks exposed in the two quadrangles are of Early and Late Mississippian and Early and Middle Pennsylvanian age. The Mississippian rocks are composed of the thick Brodhead formation, which consists of siltstone and shale, and eleven thin marine limestone and shale formations, having an aggregate thickness of about 150 feet. The Lee and Breathitt formations, of Pennsylvanian age, consist of sandstone, siltstone, and shale; they also contain thin beds of coal and several beds of underclay, including the economically important Olive Hill clay bed of Crider, 1913. Pennsylvanian rocks include beds of both continental and marine origin. The eleven thin Mississippian formations and the upper-most part of the thick Brodhead formation are truncated by a prominent unconformity on which rocks of Pennsylvanian age rest. The rocks occupy a region of gentle dips between the Cincinnati arch and the Appalachian Mountains. Refractory clay deposits are in the Olive Hill clay bed, which occurs in the lower part of the Lee formation. The Olive Hill clay bed is discontinuous and consists of a series of irregularly shaped lenses. The bed is approximately two-thirds semifiint clay and one-third flint clay, and it contains minor amounts of plastic clay. Some of the flint clay is nearly pure kaolinite, but the semi flint and plastic clay consists of mixtures of kaolinite, illite, and mixed-layer clay minerals. The structure of the kaolinite ranges from highly crystalline to very poorly crystalline 'fireclay' type. The degree of crystallinity of the kaolinite and the hardness of the clay vary inversely with the amount of illite and mixed-layer clay minerals present. The nearly pure kaolinite is believed to have formed by the removal of alkalies and some silica fram mixtures of kaolinite, illite, and mixed-layer clays by leaching in swamps to the deposition of the beds overlying the clay. The refractory properties of the clay vary directly with the purity of the kaolinite, and refractoriness decreases as the proportions of illite and mixed-layer clays increase. Certain nonclay minerals, chiefly siderite, pyrite, and iron oxide-bearing minerals, also act as fiuxes, reducing the refractory properties of the clay. The entire resources of clay in the Olive Hill clay bed are roughly and tentatively estimated to include 105,000,000 tons in the Haldeman quadrangle and 175,000,000 tons in the Wrigley quadrangle. Much of this clay is of poor quality and the amount that is better than the minimum requirements for use in refractories is probably about 30,000,000 tons. Only a fraction of this tonnage is suitable for superheat-duty products. Limestone is the only nonmetallic mineral resource other than refractory clay that has been developed in the two quadrangles, but 1arge amounts of shale suitable for use in making lightweight aggregate and structural clay products may also be present. Most of the limestone, which is quarried. in both quadrangles, is used for road-metal, concrete aggregate, and agriculture stone, but some of the limestone is of the quality that would be suitable for other uses. Virtually all the Mississippian Beech Creek limestone of Malott, 1919 which is as much as 18 feet thick, consists of high-calcium limestone. Shale beds that appear most favoralble for making lightweight aggregate are in the shale facies of the Lee formation of Pennsylvanian age. Shale that is probably suitable for structural clay products is present in the shale flacles of the Lee formation and in the Muldraugh formation of Mississippian age. Several dry holes have been drilled in search for oil and gas within the area of the two quadrangles. Though no commercial production was ever attained, one well furnished a supply of gas f

Kentucky↗
USGS1982

Characteristics and description of cores from the USGS core hole CRU-1, Parachute Creek Member, Green River Formation, east-central Uinta Basin, Utah

Oil-yield, lithologic, and mineral distribution data were determined for cores taken from a 497.7-foot drill hole in the upper part of the Parachute Creek Member of the Eocene Green River Formation. The drill hole, 1050 feet FEL, 700 feet FNL, sec. 3, T. 12 S., R. 24 E., Uintah County, Utah, started slightly below the contact between the Uinta Formation, also of Eocene age, and the underlying Green River Formation. It ended 32 feet below the base of the Mahogany bed (the richest oil-shale bed between A groove and B groove--which define the upper and lower boundaries, respectively, of the Mahogany zone). Most of the interval studied is kerogen- or carbonate-rich, commonly tuffaceous, and is very fine grained. Several thin (<3 feet) oil-shale beds which yield as much as 25 gallons of oil per ton occur above the Mahogany zone, but are probably not of economic interest. The cored sequence contains several tuff beds. The thickest of these beds is approximately 2 feet thick; the average thickness is rarely greater than 0.5 feet. Two oil-saturated tuff beds occur approximately 65 feet above the Mahogany oil-shale bed. Although these two tuffs are exposed on nearby surface outcrops, no evidence of oil is seen on outcrop. The Mahogany zone is approximately 69 feet thick at the drill site; the lowermost few feet were not penetrated. At the site cored, the Mahogany zone is overlain by 435 feet of overburden. Fischer assays indicate that 42.3 feet of oil shale within the Mahogany zone could yield at least 25 gallons of oil per ton from beds at least 10 feet thick.

Open-File Report↗
USGS1982

Geology of the Jabal Riah area, Kingdom of Saudi Arabia

The Jabal Riah area is in the southern part of the Jibal al Hamdah quadrangle (lat 19?00'00'' to 19?07'S0'' N., long 45?37'30'' to 43?45'00' E.) in the southeastern Precambrian Shield, Asir Province, Kingdom of Saudi Arabia. The Jabal Mahanid group of ancient gold mines, which is part of the Jabal Ishmas-Wadi Tathlith gold belt, is in the west-central part of the area. Rocks in the Jabal Riah area consist of Precambrian layered metasedimentary and metavolcanic rocks intruded by Precambrian igneous rocks. The metamorphic rocks are, from oldest to youngest, interlayered hornblende and biotite schist, quartz-biotite schist, hornblende schist, serpentinite, and chlorite schist. The igneous rocks are, from oldest to youngest, diorite-gabbro including dikes, granodiorite, monzogranite-granodiorite, leucocratic quartz porphyry, rhyolite, and aplite and pegmatite dikes. A large area of jasper replaces serpentinite. On the valley floors, recent alluvium and pediment deposits overlie the bedrock. The structure of the area is dominated by a dome centered over the eastern border of the area; leucocratic quartz porphyry forms the core of the dome. Minor folds and faults are present. The Jabal Mahanid group of ancient gold mines is on a northwest-trending vein system, and major ancient mine areas are found where the system splits or changes direction. The veins consist of zones of brecciated and crushed rock, which are generally less than 0.5 m wide but may be as wide as 1 m. These zones contain quartz and calcite stringers and commonly are along hornblende schist-serpentinite contacts; however, they also cut both units. Most aplite, pegmatite, and quartz dikes in the area are thin and discontinuous and are intruded along the vein trend. Similar veins, at the same stratigraphic interval, have been found beyond the northeastern part of the map area. The veins contain detectable gold and silver (median gold, approximately 0.14 ppm; median silver, approximately 1 ppm). Gold and silver are most abundant in calcium-rich rocks and veins; silver was not detected in igneous rocks. Altered wall-rock zones are mineralized as much as 10 m away from the veins. Away from the Jabal Mahanid vein-system, silver was detected in the jasper. Gold and silver were detected in minor brecciated and sheared structures and in metasedimentary rocks. Gold was detected in sericitized margins of the leucocratic quartz porphyry, in unaltered rhyolite, and in aplite dikes. The presence of unusual amounts of gold and silver over a wide area is indicated by the ancient gold mines along veins at or near the hornblende schist-serpentinite contact in the map area and to the south in the Hajrah-Hamdah area and by the widespread evidence of precious metals in igneous rocks and other vein structures. A domed-shaped area, approximately 30 km in diameter, is outlined by the hornblende schist-serpentinite contact and has leucocratic quartz prophyry in the middle. Additional study of this area might reveal economic concentrations of gold and silver.

Open-File Report↗
USGS1970

Mineral resources of parts of the Departments of Antioquia and Caldas, Zone II, Colombia

The mineral resources of an area of 40,000 sq km, principally in the Department of Antioquia, but including small parts of the Departments of Caldas, C6rdoba, Risaralda, and Tolima, were investigated during the period 1964-68. The area is designated Zone II by the Colombian Inventario Minero Nacional(lMN). The geology of approximately 45 percent of this area, or 18,000 sq km, has been mapped by IMN. Zone II has been a gold producer for centuries, and still produces 75 percent of Colombia's gold. Silver is recovered as a byproduct. Ferruginous laterites have been investigated as potential sources of iron ore but are not commercially exploitable. Nickeliferous laterite on serpentinite near Ure in the extreme northwest corner of the Zone is potentially exploitable, although less promising than similar laterites at Cerro Matoso, north of the Zone boundary. Known deposits of mercury, chromium, manganese, and copper are small and have limited economic potentia1. Cement raw materials are important among nonmetallic resources, and four companies are engaged in the manufacture of portland cement. The eastern half of Zone II contains large carbonate rock reserves, but poor accessibility is a handicap to greater development at present. Dolomite near Amalfi is quarried for the glass-making and other industries. Clay saprolite is abundant and widely used in making brick and tiles in backyard kilns. Kaolin of good quality near La Union is used by the ceramic industry. Subbituminous coal beds of Tertiary are an important resource in the western part of the zone and have good potential for greater development. Aggregate materials for construction are varied and abundant. Deposits of sodic feldspar, talc, decorative stone, and silica are exploited on a small scale. Chrysotils asbestos deposits north of Campamento are being developed to supply fiber for Colombia's thriving asbestos-cement industry, which is presently dependent upon imported fiber. Wollastonite and andalusite are potential resources not exploitable now.

Open-File Report↗
USGS1962

Trace element distribution in the searchlight, Nevada quartz monzonite stock

Gold, silver, copper, and lead-bearing veins, non-radially zoned, occur just beyond the southern and western margins of the Searchlight , Nevada , quartz monzonite stock . Seven samples of the quartz monzonite and purified individual constituent minerals of the rock, representing apophyses and marginal and interior parts of the intrusive mass, were analyzed petrographically and spectrographically. A semiquantitative total-energy spectrographic method proved satisfactory for Cu, Pb, Ni, Co, Ga, Mo, Mn, Ti, V, Cr, Sr, and Zr, but too insensitive for Zn, Ag, and Au. A synthetic silicate base was used for preparation of standards and working curves. The modal trace element content of unaltered (hypothetical) quartz monzonite samples was determined from the trace element content of the purified minerals. Ferromagnesian minerals contain concentrations of Cu, Pb, Ni, Co, Mn, and Cr. Felsic minerals are low in these but high in Sr and Ga. Cu appears to have been partly released during chloritization of the mafic minerals. Ni, Cr, Zr show little difference between the unaltered (hypothetical) and actual rock. Ga, V, Mn, Sr are in lesser quantities in the altered rock. Pb and Cu also show a loss, especially nearest largest Pb and Cu producers. Pb, Cu, V occur in the spatially related veins, but Sr or Ga have not been reported to date. Pb/Cu in unaltered rock compared to altered rock is 1.6/1; past mining production ratio of Pb/Cu is 2.6/1. While further work is needed, the trace element pattern suggests a possible means of identifying a "productive" intrusive body.

Economic Geology↗
USGS1986

Genesis of the Spar Lake strata-bound copper-silver deposit, Montana: Part I. Controls inherited from sedimentation and preore diagenesis

Mineable zones of the Spar Lake deposit occur where argentiferous copper sulfides and native silver formed cements and replaced certain earlier cements and clasts in the gently dipping middle quartzite beds of the upper member of the Revett Formation, middle Proterozoic Belt Supergroup. The copper sulfides and native silver are part of a large, zoned system of authigenic ore and gangue minerals at Spar Lake. Mineral zone boundaries of ore and gangue phases cross all five stratigraphic units of the upper member.Deduced depositional environments for the host sedimentary rocks include beach and near-shore slope environments for the lower quartzite beds and subtidal(?) channels for the middle quartzite beds. The deposit must be epigenetic because mineral zone boundaries cross every facies in the sequence of beach and nearshore slope sediments.Mineral zonation has been mapped, and seven major associations, each named for its most abundant sulfide and/or most characteristic gangue cement, are recognized. Zones that appear to be developed on a regional scale include, in spatial order, pyrite-calcite, chalcopyrite-ankerite, and the lavender (hematitic) zone. Minor concentrations of base and precious metals occur along boundaries between the hematite and chalcopyrite-ankerite zones, and between the chalcopyrite-ankerite and pyrite-calcite zones; however, at the major concentrations of metals in the Revett Formation, including the Spar Lake deposit, additional mineral zones are developed between the chalcopyrite-ankerite and pyrite-calcite regional zones. Mineral zones at the deposit are, from northwest to southeast: pyrite-calcite, galena-calcite, chalcopyrite-calcite, bornite-calcite, chalcocite-chlorite, and chalcopyrite-ankerite. Gangue minerals, including carbonates, Fe-Ti oxides, chlorite, barite, authigenic feldspars, and apatite, are zonally distributed with boundaries parallel to the sulfide-mineral zone boundaries. Bornite-calcite and chalcocite-chlorite zones form ore grades in certain, but not all, quartzite intervals.As observed at unmetamorphosed deposits where sulfide-mineral zonation is similar, some pyrite-calcite-zone minerals were probably replaced by galena-calcite-zone minerals, which were probably succeeded, in sequence, by minerals of the chalcopyrite-calcite, bornite-calcite, and chalcocite-chlorite zones. This inferred paragenesis suggests that the chalcocite-chlorite zone is more proximal to the source of ore solutions than the galena-calcite or pyrite-calcite zones. The subeconomic chalcopyrite-ankerite zone, found farthest to the southeast at the Spar Lake deposit, was apparently even more proximal to the source than ore. Ore deposition took place during diagenesis from solutions that migrated upward and laterally through the sediments from a southeasterly source.The distributions of mineral zones and ore grades were controlled by two factors, one inherited from sedimentation and the other from preore diagenesis. All mineral zones spread out within coarser grained portions of quartzite units, suggesting that lateral migration of ore solutions was controlled by primary permeability of the sediments. However, high grades of copper and silver are found only in certain of the coarser grained beds. The distributions of higher grades suggest that ore mineral abundances reflect the abundances of preore diagenetic phases which were involved in the ore precipitation reactions. Preore reactant phases were evidently more abundant in sandstones deposited in subtidal(?) channels (the ore-grade middle quartzite beds) than in sandstones deposited in beach and nearshore slope environments (the lower quartzite beds). The identity of the reactant phases and the processes that resulted in their concentration at the site of later ore deposition remain unknown, although a preore sulfide- and hydrocarbon-bearing pore fluid appears to be the best hypothesis as to the identity of the reactants.

Economic Geology↗
USGS2004

40 Ar/ 39 Ar Dating of Zn-Pb-Ag Mineralization in the Northern Brooks Range, Alaska

The 40 Ar/ 39 Ar laser step-heating method potentially can be used to provide absolute ages for a number of formerly undatable, low-temperature ore deposits. This study demonstrates the use of this method by determining absolute ages for Zn-Pb-Ag sediment-hosted massive sulfide deposits and vein-breccia occurrences found throughout a 300-km-long, east-west-trending belt in the northern Brooks Range, Alaska. Massive sulfide deposits are hosted by Mississippian to Pennsylvanian(?) black carbonaceous shale, siliceous mudstone, and lesser chert and carbonate turbidites of the Kuna Formation (e.g., Red Dog, Anarraaq, Lik (Su), and Drenchwater). The vein-breccia occurrences (e.g., Husky, Story Creek, West Kivliktort Mountain, Vidlee, and Kady) are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine clastic rocks (the Endicott Group) that stratigraphically underlie the Kuna Formation. The vein-breccias are mineralogically similar to, but not spatially associated with, known massive sulfide deposits. The region's largest shale-hosted massive sulfide deposit is Red Dog; it has reserves of 148 Mt grading 16.6 percent zinc, 4.5 percent lead, and 77 g of silver per tonne. Hydrothermally produced white mica in a whole-rock sample from a sulfide-bearing igneous sill within the Red Dog deposit yielded a plateau age of 314.5 Ma. The plateau age of this whole-rock sample records the time at which temperatures cooled below the argon closure temperature of the white mica and is interpreted to represent the minimum age limit for massive sulfide-related hydrothermal activity in the Red Dog deposit. Sulfide-bearing quartz veins at Drenchwater crosscut a hypabyssal intrusion with a maximum biotite age of 337.0 Ma. Despite relatively low sulfide deposition temperatures in the vein-breccia occurrences (162&deg;-251&deg;C), detrital white mica in sandstone immediately adjacent to large vein-breccia zones was partially to completely recrystallized. The 40 Ar/ 39 Ar age spectra and inverse isochron plots of the multicomponent whole-rock sandstone samples are more complex than those of single minerals. However, different minerals have different Ca/K and Cl/K ratios and closure temperatures, and these properties were used to identify portions of spectra dominated by argon release from specific minerals. 40 Ar/ 39 Ar laser step-heating analyses of Late Devonian sandstone whole rocks produced spectra that record a two-stage resetting history: a Carboniferous hydrothermal event first and later Mesozoic to Tertiary events, which are in agreement with geologic constraints. The 40 Ar/ 39 Ar ages and the similar mineralogy, lead isotope composition, and relative stratigraphic positions support the interpretation that the shale-hosted massive sulfide deposits and most vein-breccia occurrences are temporally and genetically related, and that they are different expressions of Carboniferous basinal dewatering.

Alaska↗
USGS1944

The fluorspar deposits of Saint Lawrence, Newfoundland

Fluorspar from Newfoundland, eighth ranking producer of the world, comes entirely from the St. Lawrence district. Here pre-Cambrian lavas and pyroclastics, Cambrian sedimentary rocks, Ordovician (?) volcanic and sedimentary rocks, and a Paleozoic alaskite-granite comprise the bedrock.Epithermal fluorite veins occupy steeply dipping fault fissures in granite, rhyolite porphyry, and lamprophyre. Eleven veins show walls bearing nearly horizontal striations; one vein bears only vertical striations; and the walls of three veins show both horizontal and vertical striations. The strikes of nearly all veins are within 45 degrees of the normal to the walls of the elongated granite mass. Some veins are more than a mile long and contain numerous workable lenses. Veins are of two types: high-grade containing over 95 per cent CaF 2 and averaging about 5 feet thick, and lower grade containing about 75 per cent CaF 2 and averaging between 15 and 20 feet thick.Sulphides, present in small quantities, include pyrite, chalcopyrite, sphalerite, and argentiferous galena. Non-metallic gangue minerals are quartz, calcite, and rarely barite. "Blastonite," a local name for material composed of microcrystalline quartz and brecciated fluorite, in some places forms as much as 10 per cent of a vein. A nodular type of fluorspar probably formed by alternate rotation of fragments of breccia and deposition of fluorite.Regional zoning is shown by the distribution of barite and green fluorite. Barite shows a distinct zone of localization, and green fluorite predominates in veins both near the granite margins and farther from the granite body.This district will undoubtedly occupy a still more prominent position among producers of fluorspar.

Newfoundland↗
USGS1984

Hydrology of area 53, northern Great Plains and Rocky Mountain coal provinces, Colorado, Wyoming, and Utah

Hydrologic information and analysis are needed to aid in decisions to lease Federally owned coal and for the preparation of the necessary Environmental Assessments and Impact Study Reports. This need has become even more critical with the enactment of the Surface Mining Control and Reclamation Act of 1977 (Public Law 95-87). This report, one in a series of nationwide coal province reports, presents information thematically by describing single hydrologic topics through the use of brief texts and accompanying maps, graphs, or other illustrations. The report broadly characterizes the hydrology of Area 53 in northwestern Colorado, south-central Wyoming, and northeastern Utah. The report area, located primarily in the Wyoming Basin and Colorado Plateau physiographic provinces, consists of 14,650 square miles of diverse geology, topography, and climate. This diversity results in contrasting hydrologic characteristics. The two major rivers, the Yampa and the White Rivers, originate in humid granitic and basaltic mountains, then flow over sedimentary rocks underlying semiarid basins to their respective confluences with the Green River. Altitudes range from 4,800 to greater than 12,000 feet above sea level. Annual precipitation in the mountains, as much as 60 inches, is generally in the form of snow. Snowmelt produces most streamflow. Precipitation in the lower altitude sedimentary basins, ranging from 8 to 16 inches, is generally insufficient to sustain streamflow; therefore, most streams originating in the basins (where most of the streams in coal-mining areas originate) are ephemeral. Streamflow quality is best in the mountains where dissolved-solids concentrations generally are small. As streams flow across the sedimentary basins, mineral dissolution from the sedimentary rocks and irrigation water with high mineral content increase the dissolved-solids concentrations in a downstream direction. Due to the semiarid climate of the basins, soils are not adequately leached; consequently, flows in the ephemeral streams usually have larger concentrations of dissolved solids than those in perennial streams. Ground-water supplies are restricted by the low yields of wells due to small permeability. Most ground-water use is for domestic and stock-watering purposes; it is limited by the amount and type of dissolved material. The ground-water ionic composition is highly variable. Dissolved-solids concentrations for aquifers sampled in Area 53 range from a minimum of 46 milligrams per liter to a maximum of 109,000 milligrams per liter. Trace element concentrations generally are not a problem. An estimated 82 billion tons of coal exist above a depth of 6,000 feet in the Colorado parts of the area. The coal beds of greatest economic interest occur in the sedimentary deposits of the Upper Cretaceous Iles and Williams Fork Formations of the Mesaverde Group and the Upper Cretaceous Lance Formation and the Fort Union and Wasatch Formations of Tertiary age. The coal characteristically has a low sulfur content. Hydrologic problems related to surface mining are erosion, sedimentation, decline in water levels, disruption of aquifers, and degradation of water quality. Because the semiarid mine areas have very little runoff and the major streams have large buffer and dilution capacities, the effects of mining on surface water are minimal. However, effects on ground water may be much more severe and long lasting.

Colorado, Wyoming and Utah↗
USGS2011

The efficacy of salvage logging in reducing subsequent fire severity in conifer-dominated forests of Minnesota, USA

Although primarily used to mitigate economic losses following disturbance, salvage logging has also been justified on the basis of reducing fire risk and fire severity; however, its ability to achieve these secondary objectives remains unclear. The patchiness resulting from a sequence of recent disturbances—blowdown, salvage logging, and wildfire—provided an excellent opportunity to assess the impacts of blowdown and salvage logging on wildfire severity. We used two fire‐severity assessments (tree‐crown and forest‐floor characteristics) to compare post‐wildfire conditions among three treatment combinations (Blowdown–Salvage–Fire, Blowdown–Fire, and Fire only). Our results suggest that salvage logging reduced the intensity (heat released) of the subsequent fire. However, its effect on severity (impact to the system) differed between the tree crowns and forest floor: tree‐crown indices suggest that salvage logging decreased fire severity (albeit with modest statistical support), while forest‐floor indices suggest that salvage logging increased fire severity. We attribute the latter finding to the greater exposure of mineral soil caused by logging operations; once exposed, soils are more likely to register the damaging effects of fire, even if fire intensity is not extreme. These results highlight the important distinction between fire intensity and severity when formulating post‐disturbance management prescriptions.

Minnesota↗
USGS1997

Element distribution patterns in the ordovician Galena group, Southeastern Minnesota: Indicators of fluid flow and provenance of terrigenous material

As part of a regional geochemical investigation of lower Paleozoic strata in the Hollandale embayment of southeastern Minnesota, elemental concentrations in acid-insoluble residues were determined for carbonate rock in the Middle Ordovician Galena Group. Elemental distribution patterns within the insoluble residues, particularly those of Ti, Al, and Zr, show that the Wisconsin dome and the Wisconsin arch, which contributed sediment to the embayment prior to Galena time, continued as weak sources of sediment during this period. In contrast, trace metals commonly associated with Mississippi Valley-type lead-zinc mineralization, including Pb, Zn, Cu, Ag, Ni, Co, As, and Mo, show dispersal patterns that are independent of those associated with primary depositional phenomena. These trace metals are concentrated in southern Minnesota in carbonate rocks near the interface between limestone- and dolostone-dominated strata. Dispersal patterns imply that the metals were carried by a north-flowing regional ground-water system. The results show that the geochemical attributes of insoluble residues can be used to distinguish provenance and transport directions of primary sediments within a depositional basin from effects of subsequent regional ground-water flow systems.

Economic Geology↗
USGS1926

Ore deposits of the Jerome and Bradshaw Mountains quadrangles, Arizona

In the summer of 1922, at the request of the Director of the United States Geological Survey, I undertook an examination of the ore deposits in the Jerome and Bradshaw Mountains quadrangles, Ariz. (See fig. 1.) The object of this work was not a detailed investigation of each deposit but rather a coordination and classification of the occurrences and an attempt to ascertain their origin and economic importance. Almost all the deposits occur in pre-Cambrian rocks or in rocks that are not readily differentiated from the pre-Cambrian. In the northern part of the Jerome quadrangle there are large areas of almost horizontal Paleozoic beds, and in both quadrangles there are also large areas of lava flows of Tertiary age. Finally there are wide spaces occupied by Tertiary tuff and limestone, or by Tertiary and Quaternary wash filling the valleys between the mountain ranges. But all these rocks except the pre-Cambrian are practically barren of ore deposits, and the problem therefore narrowed itself to an examination of the pre-Cambrian areas. This task was greatly facilitated by the careful work of Jaggar and Palache, set forth in the Bradshaw Mountains folio,l in which the southern quadrangle of the two under present consideration is mapped geologically and described, and which also includes a comprehensive though brief discussion of the mineral deposits. There is no published geologic map of the Jerome quadrangle, but I had the opportunity through the courtesy of Dr. G. M. Butler, Director of the Arizona Bureau of Mines, to use a manuscript map of this area prepared for the State by Mr. L. E. Reber, jr., and Mr. Olaf Jenkins.

Arizona↗