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At least 739 records · Page 41Linked to original sources
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↗
USGS2016

Ferromanganese crusts and nodules, rocks that grow

Ferromanganese (Fe-Mn) crusts and nodules are marine sed- imentary mineral deposits, composed mostly of iron and manganese oxides. They precipitate very slowly from seawa- ter, or for nodules also from deep-sea sediment pore waters, recording the chemical signature of these source waters as they grow. Additional elements incorporate via sorption pro- cesses onto the Fe-Mn oxides, including rare and valuable metals that can reach concentrations that are economically valuable.

Book chapter↗
USGS2006

Geology and reconnaissance stable isotope study of the Oyu Tolgoi porphyry Cu-Au system, South Gobi, Mongolia

The Oyu Tolgoi porphyry Cu-Au system in the South Gobi desert, Mongolia, comprises five deposits that extend over 6 km in a north-northeast-oriented zone. They occur in a middle to late Paleozoic are terrane and are related to Late Devonian quartz monzodiorite intrusions. The Hugo Dummett deposits are the northernmost and deepest, with up to 1,000 m of premineral sedimentary and volcanic cover rock remaining. They are the largest deposits discovered to date and characterized by high-grade copper (>2.5% Cu) and gold (0.5-2 g/t) mineralization associated with intense quartz veining and several phases of quartz monzodiorite intruded into basaltic volcanic host rocks. Sulfide minerals in these deposits are zoned outward from a bornite-dominated core to chalcopyrite, upward to pyrite ?? enargite and covellite at shallower depth. The latter high-sulfidation-state sulfides are hosted by advanced argillic alteration mineral associations. This alteration is restricted mainly to dacitic ash-flow tuff that overlies the basaltic volcanic rock and includes ubiquitous quartz and pyrophyllite, kaolinite, plus late dickite veins, as well as K alunite, Al phosphate-sulfate minerals, zunyite, diaspore, topaz, corundum, and andalusite. A reconnaissance oxygen-hydrogen and sulfur isotope study was undertaken to investigate the origin of several characteristic alteration minerals in the Oyu Tolgoi system, with particular emphasis on the Hugo Dummett deposits. Based on the isotopic composition of O, H, and S (??18O(SO4) = 8.8-20.1???, ??D = -73 to -43???, ??34S = 9.8-17.9???), the alunite formed from condensation of magmatic vapor that ascended to the upper parts of the porphyry hydrothermal system, without involvement of significant amounts of meteoric water. The isotopic data indicate that pyrophyllite (??18O = 6.5-10.9???, ??D = -90 to -106???) formed from a magmatic fluid with a component of meteoric water. Muscovite associated with quartz monzodiorite intrusions occurs in the core of the Hugo Dummett deposits, and isotopic data (??18O = 3.0-9.0???, ??D = -101 to -116%o) show it formed from a magmatic fluid with water similar in composition to that which formed the pyrophyllite. Mg chlorite (??18O = 5.5???, ??D = -126???) is a widespread mineral retrograde after hydrothermal biotite and may have formed from fluids similar to those related to the muscovite during cooling of the porphyry system. By contrast, paragenetically later and postmineralization alteration fluid, which produced dickite (??18O = -4.1 to +3.3???, ??D = -130 to -140???), shows clear evidence for mixing with substantial amounts of meteoric water. Relatively low ??D values (-140???) for this meteoric water component may indicate that its source was at high elevations. The geologic structure, nature of alteration, styles of mineralization, and stable isotope data indicate that the Oyu Tolgoi deposits constitute a typical porphyry system formed in an island-arc setting. The outward zonation of sulfide minerals for the Hugo Dummett deposits, from a bornite-dominated core to chalcopyrite and pyrite-enargite, can be interpreted to be related to a cooling magmatic hydrothermal system which transgressed outward over enclosing advanced argillic alteration. This resulted in some unusual alteration and sulfide parageneses, such as topaz, or pyrite, enargite, and tennantite, entrained by high-grade bornite. ?? 2006 by Economic Geology.

Economic Geology↗
USGS1954

The occurrence of cobalt and nickel in the Silver Summit Mine, Coeur d'Alene district, Idaho

Cobalt and nickel of possible commercial interest have been discovered in the Silver Summit mine, Coeur d'Alene district, Idaho. Assay data indicate that an ore shoot contained about 0.40 percent cobalt and about 1.0 percent nickel in addition to the copper and rich silver ores. The cobalt-nickel mineral gersdorffite occurs in tetrahedrite-siderite veins. Gersdorffite is widespread in small amounts and appears to have been the first of the "ore shoot" minerals. The known occurrence of either cobalt bloom or gersdorffite in other properties of the Coeur d'Alene district Silver Belt suggests that other ore shoots may exist that contain commercial quantities of cobalt and nickel.

Idaho↗
USGS1968

Borax solution at Kramer, California

Material of obscure structure that forms part of the hanging wall of the great sodium borate ore body at Kramer, Kern County, Calif., is interpreted herein as collapsed insoluble claystone layers left where interbedded borax has been dissolved. Nodular ulexite in such collapsed material is secondary; relationships between primary borax and contemporaneous ulexite or other syngenetic borate minerals remain unestablished. The effects of solution also leave unestablished the original limits of borax deposition. It is suggested that collapsed claystone layers containing ulexite might be used as an indicator of proximity to borax elsewhere in the district.

California↗
USGS2003

Crustal structure in the Elko-Carlin Region, Nevada, during Eocene gold mineralization: Ruby-East Humboldt metamorphic core complex as a guide to the deep crust

The deep crustal rocks exposed in the Ruby - East Humboldt metamorphic core complex , northeastern Nevada , provide a guide for reconstructing Eocene crustal structure ∼50 km to the west near the Carlin trend of gold deposits. The deep crustal rocks, in the footwall of a west-dipping normal-sense shear system, may have underlain the Piñon and Adobe Ranges about 50 km to the west before Tertiary extension, close to or under part of the Carlin trend. Eocene lakes formed on the hanging wall of the fault system during an early phase of extension and may have been linked to a fluid reservoir for hydrothermal circulation. The magnitude and timing of Paleogene extension remain indistinct, but dikes and tilt axes in the upper crust indicate that spreading was east -west to northwest-southeast, perpendicular to a Paleozoic and Mesozoic orogen that the spreading overprinted. High geothermal gradients associated with Eocene or older crustal thinning may have contributed to hydrothermal circulation in the upper crust . Late Eocene eruptions, upper crustal dike intrusion, and gold mineralization approximately coincided temporally with deep intrusion of Eocene sills of granite and quartz diorite and shallower intrusion of the Harrison Pass pluton into the core - complex rocks. Stacked Mesozoic nappes of metamorphosed Paleozoic and Precambrian rocks in the core complex lay at least 13 to 20 km deep in Eocene time, on the basis of geobarometry studies. In the northern part of the complex , the presently exposed rocks had been even deeper in the late Mesozoic, to >30 km depths, before losing part of their cover by Eocene time. Nappes in the core plunge northward beneath the originally thicker Mesozoic tectonic cover in the north part of the core complex . Mesozoic nappes and tectonic wedging likely occupied the thickened midlevel crustal section between the deep crustal core - complex intrusions and nappes and the overlying upper crust . These structures, as well as the subsequent large-displacement Cenozoic extensional faulting and flow in the deep crust , would be expected to blur the expression of any regional structural roots that could correlate with mineral belts. Structural mismatch of the mineralized upper crust and the tectonically complex middle crust suggests that the Carlin trend relates not to subjacent deeply penetrating rooted structures but to favorable upper crustal host rocks aligned within a relatively coherent regional block of upper crust .

Nevada↗
USGS1986

Prospects for mineral resource assessments on public lands: Proceedings of the Leesburg workshop

Modern geological surveys pursue a wide spectrum of research activities in the earth sciences. From the beginning, however, one of the core tasks of any national geological survey has been the assessment and evaluation of its nation's mineral and fuel resources. The methods by which such assessments are carried out have become more sophisticated over time, in keeping with advancing geoscientific knowledge and the development and application of new concepts and technologies. However, the basic objectives of such work have changed little, and the fundamental goal remains the construction of the best possible base of information on the nature, distribution and economic potential of the resources within a nation's landmass and its offshore jurisdictions.

Circular↗
USGS1977

Uranium and thorium in the middle Precambrian Estes Conglomerate, Nemo District, Lawrence County, South Dakota: a preliminary report

The Estes Conglomerate, which is exposed in the Nemo District on the northeastern flank of the Black Hills, South Dakota, is inferred to be of early middle Precambrian age (early Precambrian X or Paleoaphebian) and to be resting on late early Precambrian (late Precambrian W) granitic continental crust. The Estes contains beds of quartzite and quartz-pebble conglomerate (oligomictic conglomerate) with matrices of micaceous quartzite that locally contain 5 to 25 percent dispersed pyrite. Highly oxidized outcrop samples of the oligomictic conglomerate have anomalously high contents of both uranium (10 to 40 ppm) and thorium (20 to 800 ppm). High thorium values in the oligomictic conglomerate favor a placer mechanism for the concentration of radioactive minerals and appear to eliminate the possibility of epigenetic processes, such as reduction of uranium by pyrite. The presence of abundant old prospect pits and of several abandoned mines suggests that these conglomerates may also contain some gold. Early prospectors may have been attracted by the gossan produced by oxidation of pyrite. Uranium in the Estes Conglomerate may be of similar origin to the economically very important uranium deposits in the Matinenda Formation of the Elliot Lake District, Ontario. Because uranium is rapidly dissolved in acidic, oxygenated ground water, such as is present where pyrite is weathering, most of the uranium originally present in the analyzed samples has probably been leached out. Conglomerate located below the zone of weathering and oxidation has good potential for economic uranium deposits.

Open-File Report↗
USGS2017

Selenium

Selenium (Se) was discovered in 1817 in pyrite from copper mines in Sweden. It is a trace element in Earth’s crust, with an abundance of three to seven orders of magnitude less than the major rock-forming elements. Commercial use of selenium began in the United States in 1910, when it was used as a pigment for paints, ceramic glazes, and red glass. Since that time, it has had many other economic uses—notably, in the 1930s and 1940s, when it was used in rectifiers (which change alternating current to direct current), and in the 1960s, when it began to be used in the liner of photocopier drums. In the 21st century, other compounds have replaced selenium in these older products; modern uses for selenium include energy-efficient windows that limit heat transfer and thin-film photovoltaic cells that convert solar energy into electricity. In Earth’s crust, selenium is found as selenide minerals, selenate and selenite salts, and as substitution for sulfur in sulfide minerals. It is the sulfide minerals, most commonly those in porphyry copper deposits, that provide the bulk of the selenium produced for the international commodity market. Selenium is obtained as a byproduct of copper refining and recovered from the anode slimes generated in electrolytic production of copper. Because of this, the countries that have the largest resources and (or) reserves of copper also have the largest resources and (or) reserves of selenium. Because selenium occurs naturally in Earth’s crust, its presence in air, water, and soil results from both geologic reactions and human activity. Selenium is found concentrated naturally in soils that overlie bedrock with high selenium concentrations. Selenium mining, processing, use in industrial and agricultural applications, and disposal may all contribute selenium to the environment. A well-known case of selenium contamination from agricultural practices was discovered in 1983 in the Kesterson National Wildlife Refuge in California. There, waters draining from agricultural fields created wetlands with high concentrations of dissolved selenium in the water. The selenium was taken up by aquatic wildlife and caused massive numbers of embryonic deformities and deaths. Regulatory agencies have since worked to safeguard ecological and human health by creating environmental exposure guidelines based upon selenium concentrations in water and in fish tissue. Any attempt to regulate selenium concentrations requires a delicate balance because selenium occurs naturally and is also a vital nutrient for the health of wildlife, domestic stock, and humans. Selenium is commonly added as a vitamin to animal feed, and in some regions of the United States and the world, it is added as an amendment to soils for uptake by agricultural crops. The important role of selenium in economic products, energy supply, agriculture, and health will continue for well into the future. The challenge to society is to balance the benefits of selenium use with the environmental consequences of its extraction. Increased understanding of the elemental cycle of selenium in the earth may lead to new (or unconventional) sources of selenium, the discovery of new methods of extraction, and new technologies for minimizing the transfer of selenium from rock to biota, so to protect environmental and human health.

Professional Paper↗
USGS1968

Uranium deposits in the Jackpile Sandstone, New Mexico

Ultimate sources of uranium are believed to be either fluids from Morrison volcanoes (not demonstrable) or labile constituents in the Jackpile Sandstone. Petrographic studies indicate considerable pre-Dakota diagenesis, which would have made uranium in feldspars, heavy minerals, and volcanic debris available. Deposition of uranium occurred while host sandstone was near the surface during the pre-Dakota hiatus. Sedimentary permeability was the principal factor in distribution of ore and of the organic decomposition products that precipitated it.

New Mexico↗
USGS1980

Textural and structural evidence for a predeformation hydrothermal origin of the Tungsten Queen Deposit, Hamme District, North Carolina

The Hamme tungsten district is composed of a series of steeply dipping quartz-wolframite veins in the Piedmont of North Carolina. Veins are concentrated near the border of the lower Paleozoic Vance County pluton, along its western contact with green-schist-facies metapelites and metavolcanic rocks of the Carolina slate belt. One of these quartz veins, the Snead-Walker, hosts the Tungsten Queen deposit. The vein is 0 to 10 m thick and trends N 35 degrees E for approximately 3,500 m through slate belt rocks and the granitic pluton. The deposit has been worked to a depth of nearly 520 m and contains eight en echelon ore lodes that plunge 42 degrees to 65 degrees between S 10 degrees E and S 10 degrees W. Ore lodes commonly are encased in thin lenses of quartz-sericite greisen. The principal ore mineral is huebnerite and is accompanied by scattered occurrences of pyrite, sphalerite, galena, chalcopyrite, and tetrahedrite. The gangue is predominantly quartz with minor amounts of fluorite, sericite, and carbonate.Studies of minor structures and mineral textures indicate that both the wall rock and the ore and gangue minerals within the vein have been deformed by at least two events. The first event produced relatively gentle, open, and shallow-plunging folds; later, an intense episode of right-lateral shearing developed steeply plunging, tight folds and numerous northeast-trending shears. This latter deformation also developed a prominent alignment of ore and gangue minerals oblique to the vein walls and may have formed the en echelon distribution of ore lodes.In relatively undeformed parts of the vein, clusters of euhedral huebnerite crystals are oriented perpendicular to vein layering. Some prismatic crystals have terminations with cappings of sulfides and in polished thin section show concentric growth zones. These features are similar to textures found in unmetamorphosed tungsten-bearing hydrothermal vein deposits such as those at Pasto Bueno, Peru; Carrock Fell, England; and Panasqueria, Portugal. The relationships of mineral textures and minor structures indicate that the Tungsten Queen deposit formed by open-space fillings of linear faults or fractures and was subsequently deformed by at least two episodes of folding and shearing.

North Carolina↗
USGS1983

Sequence of mineral assemblages in differentiated granitic pegmatites

Revised sequence is (1) plagioclase, quartz, muscovite, (2) plagioclase, quartz, (3) quartz, perthite, plagioclase, (4) perthite, quartz, (5) quartz, plagioclase, perthite, spodumene (or petalite), amblygonite, (6) quartz, spodumene (or petalite), (7) quartz, microcline or perthite, (8) quartz, and (9) lepidolite or lithian mica, plagioclase, quartz, microcline.

Economic Geology↗
USGS1946

Preliminary chemical correlation of chromite with the containing rocks

Chromite investigations of the U. S. Geological Survey since 1939 indicate that economic deposits of chromite rich in normative spinel ((Mg, Fe)Al 2 O 4 ) occur in peridotites which are closely associated with gabbro; high-chrome chromites occur in feldspar-free peridotites; and chromites rich in both normative chromite ((Mg, Fe)Cr 2 O 4 ) and magnetite (FeFe 2 O 4 ) are found in the pyroxene-rich stratiform complexes. Reaction of high-alumina chromite with diopsidic gabbro to form anorthite, olivine, and enstatite is described, and some probable equilibria between chromite and silicate minerals are discussed. A plot of 63 complete analyses on a triangular prism of composition shows that chromites from different geologic provinces in the Western Hemisphere vary consistently and fall in overlapping, but distinct, fields. The chromites of the Caribbean Province, which occur in dunite and troctolite, have the general formula Cr (sub 25-80) Al (sub 15-75) Fe (sub 1-5) (Mg (sub 65-75) ) and average about Cr 50 Al 47 (Mg 70 ). The chromites of the Pacific Coast, which occur in dunite and saxonite, average about Cr 70 Al 24 (Mg 60 ) in the range Cr (sub 60-77) Al (sub 16-35) Fe (sub 3-12) (Mg (sub 45-75) ). The stratiform deposits of the Stillwater and Bushveld complexes occur in harzburgite and bronzitite, and are very much alike, averaging Cr 60 Al 32 (Mg 52 ) and Cr 58 Al 34 (Mg 44 ) respectively. Chromites from gabbroic facies of the Bushveld complex are much richer in normative magnetite, presumably reflecting a higher CaO: Al 2 O 3 ratio in the silicate environment.

Economic Geology↗
USGS1952

Geology of the Iron King Mine, Yavapai county, Arizona

The Iron King mine is about 2,000 feet west-northwest of the intersection of the 112 15 west meridian and the 34 30 north parallel in the Humboldt region in central Yavapai County , Arizona . The mine is approximately in the geographical center of the Humboldt region. Precambrian rocks form the bedrock. Late Cenozoic unconsolidated river wash and valley fill with some interbedded basalt locally mantle the Precambrian rocks, especially in the north-central part of the region. The Precambrian rocks consist of two metamorphosed volcanic formations and intrusive rocks that range in composition from quartz porphyry to gabbro. The volcanic formations originally were flows, volcanic breccias, and tuffaceous sedimentary rocks. Dynamothermal metamorphism of these rocks formed textures, structures, and mineral assemblages characteristic of low-grade ;riietamorphic rocks, but sufficient relict textures and structures remain to permit delineation of formations on the bases of their original nature. All the Precambrian rocks are foliated, except those in the interior parts of the larger intrusive masses. This foliation has two major trends, (1) north to N 20° W, and (2) N 20° E. The northeast-trending foliation is younger and locally is superimposed on the north- to northwest-trending foliation. The Precambrian rocks strike north to northwest and dip steeply, chiefly westward. Duplication of stratigraphic units and determination of tops suggest two major northeast-trending folds, which probably plunge southward. The northeast-trending foliation appears to bear an axial-plane relationship to these folds. Some masses of igneous rock probably were intruded during development of foliation. The Iron King deposit supports the only active mine in the Humboldt region. It consists of 12 steeply plunging echelon veins arranged along the footwall of a sheared and altered zone in the metamorphosed andesitic tuffaceous sedimentary rocks. Narrow zones of more intense shear probably localized the veins. Solutions first introduced quartz, pyrite, ankerite, and sericite, forming a sporadically mineralized zone (in the hanging wall of the deposit) and probably veins in the Iron King fracture system. Intra-mineralization shear strongly brecciated these early minerals and formed the structures that localized and distributed the ore minerals in the veins. After this deformation, sphalerite, galena, chalcopyrite, tennantite, arsenopyrite, pyrite, quartz, and ankerite were deposited; the last three minerals may have formed through solution and the redeposition of earlier minerals. Formation of sericite either accompanied or followed the deposition of ore-forming minerals. Silver is related closely in distribution to copper and probably is in the tennantite. Gold occurs chiefly in the pyrite. Banding, mimetic after foliation and planes developed by shearing, is pronounced in much of the vein material. Mineral zoning, generally similar in each vein, is a characteristic of the deposit. High-angle reverse faults of about 100 feet in maximum vertical separation offset the veins. These faults are nearly parallel to the veins in strike and dip.

Arizona↗
USGS1978

Origin of a South Texas roll-type deposit; II, Sulfide petrology and sulfur isotope studies

Petrologic and sulfur isotopic studies have been carried out on drill core samples from a roll-type uranium deposit in the mid-Tertiary Catahoula Tuff, Webb County, south Texas. Epigenetic iron disulfide minerals formed in two distinct stages. The first stage involved sulfidization of the host rock by sulfide (H 2 S, HS-)-bearing solutions that emanated from a fault about 1.5 km downdip from and subparallel to the orebody. Pyrite was the dominant iron disulfide mineral formed from this fault sulfide. The isotopic composition (delta 34 S) of first-stage iron disulfide is quite heavy (>0 per mil), in part because the fault-derived H 2 S was isotopically heavy. The development of the second-stage sulfides was related to processes that formed the uranium roll. Iron disulfide minerals produced during this second stage commonly occur as rims around the first-stage sulfides. The rims are exclusively marcasite in and adjacent to ore, but the pyrite content in these rims increases with increasing distance from ore. The sulfur of the second-stage sulfides in the vicinity of the roll front is isotopically light (--25 to --40 per mil). The virtual absence of organic carbon in the host sand precludes a bacterial origin for the ore-stage iron disulfide minerals and, therefore, eliminates bacterial metabolism as the mechanism for isotopic fractionation. Instead, the sulfur source for ore-stage sulfides was preore (first stage) sulfides, remobilized via partial oxidation to soluble metastable sulfur oxyanions.

Texas↗
USGS2018

The Central African Republic Diamond Database—A geodatabase of archival diamond occurrences and areas of recent artisanal and small-scale diamond mining

The alluvial diamond deposits of the Central African Republic (CAR) are mined almost exclusively by way of informal artisanal and small-scale mining (ASM) methods. ASM sites range in diameter from a few meters to 30 meters or more, and are typically excavated by crews of diggers using hand tools, sieves, and jigs. CAR’s reported annual production has ranged from 300,000 to 470,000 carats over the past decade. This production is significant for CAR because it accounts for a large portion of the country’s export income and employs an estimated 60,000 to 90,000 miners nationally. Diamond production has also been linked to the violent conflict and political instability which have plagued the country for decades. The most recent conflict began in 2012 and resulted in an international embargo on the export of rough diamonds from CAR. This embargo was followed by a ceasefire and a return of peace in certain zones of the country in 2015; however, political and economic instability continues to afflict many areas of the country. International efforts to restore peace in CAR have included United Nations support as well as international technical assistance in tracking, assessing, and monitoring diamond production. In 2015, the Kimberley Process (KP) developed an operational framework allowing for legitimate exports from five subprefectures in CAR that were deemed to be compliant with KP internal controls and which were also considered to be free from systematic violence or control of armed groups. The goal of this study was to address information gaps regarding the location and extent of diamond occurrences and mining activity through the integration of geologic research with remote sensing, geographic information systems analysis, and fieldwork. Effective and efficient monitoring of diamond mining activity using satellite imagery requires detailed understanding of the geographic distribution of diamond sources and mining activities. A two-phase methodology was developed to address the knowledge gaps. The first phase consisted of the creation of a comprehensive geospatial catalogue of diamond mining and occurrence locations from archival records such as historical maps, mining reports, academic publications, and field data. Building upon this locational database, the second phase consisted of the creation of a geospatial dataset cataloguing current mining activity locations through manual interpretation of recently acquired satellite imagery. The accuracy of this second geospatial dataset was then assessed using field observations made between 2016 and 2017 by the U.S. Agency for International Development’s Property Rights and Artisanal Diamond Development II project. This report presents a two-part geodatabase: part 1 contains the locations of diamond mine sites and occurrences from archival sources, and part 2 indicates areas of current or recent mining activity. This geodatabase is unique in its temporal and spatial extent and may be used to analyze the geographic distribution of CAR’s known diamond resources, to assess the effect of recent violent conflicts and KP actions on diamond produc-tion, to provide decision makers with information regarding small-scale diamond mining, and to improve the monitoring of mining in regions of the country prone to conflict.

Open-File Report↗
USGS1978

Principal uranium deposits of the world

The geology of the principal world uranium deposits that have identified uranium reserves and production, as described in published literature, is summarized briefly, including such features as type of deposit, host rock and age of host roc, age of mineralization, depositional environment, and mineralogy. The deposits are located on four maps with the deposit grouped according to age of host rocks?Precambrian, Paleozoic, Mesozoic, and Cenozoic?and further subdivided into types of deposits and size categories. Types of deposits are penecordant sandstone, quartz-pebble conglomerate, vein and vein-type, marine black shale, phosphate deposits, coaly carbonaceous rocks, and pegmatic and alaskitic rocks. The economically most significant deposits of uranium known in 1975 are in quartz-pebble conglomerates and sandstones, which together represented about 75 percent of the world?s total production. The largest deposits occur in quartz-pebble conglomerate at the Elliot Lake-Blind River area, Canada (average grade 0.12 percent U3O8), and at the Witwatersrand basin area in the Republic of South Africa (average grade 0.025 percent U3O8), where uranium is produced principally as a byproduct or coproduct of gold mining; and in medium-grained sandstones in the Colorado Plateau, USA (average grade 0.2 percent U3O8). Other economically significant concentrations are vein, pegmatite or contact metamorphic types, containing smaller but relatively high-grade tonnages and representing about 20 percent of the world?s total production. At Vastergotland (Billingen) and Narke in Sweden, uranium has been recovered on a pilot-plant basis from black shale deposits having an uncommonly high grade for black shale of 0.03 percent U3O8. ?Recoverable reserves? in the near future (40 year period, lifetime of nuclear plants) is on the order of 50,000 metric tons U. Over 50 percent of the world?s total uranium reserves is located on or near the trend of the iron deposits in the Precambrian iron formation, referred to as the ?iron band?.

Open-File Report↗
USGS2011

Cobalt mineral exploration and supply from 1995 through 2013

The global mining industry has invested a large amount of capital in mineral exploration and development over the past 15 years in an effort to ensure that sufficient resources are available to meet future increases in demand for minerals. Exploration data have been used to identify specific sites where this investment has led to a significant contribution in global mineral supply of cobalt or where a significant increase in cobalt production capacity is anticipated in the next 5 years. This report provides an overview of the cobalt industry, factors affecting mineral supply, and circumstances surrounding the development, or lack thereof, of key mineral properties with the potential to affect mineral supply. Of the 48 sites with an effective production capacity of at least 1,000 metric tons per year of cobalt considered for this study, 3 producing sites underwent significant expansion during the study period, 10 exploration sites commenced production from 1995 through 2008, and 16 sites were expected to begin production by 2013 if planned development schedules are met. Cobalt supply is influenced by economic, environmental, political, and technological factors affecting exploration for and production of copper, nickel, and other metals as well as factors affecting the cobalt industry. Cobalt-rich nickel laterite deposits were discovered and developed in Australia and the South Pacific and improvements in laterite processing technology took place during the 1990s and early in the first decade of the 21st century when mining of copper-cobalt deposits in Congo (Kinshasa) was restricted because of regional conflict and lack of investment in that country's mining sector. There was also increased exploration for and greater importance placed on cobalt as a byproduct of nickel mining in Australia and Canada. The emergence of China as a major refined cobalt producer and consumer since 2007 has changed the pattern of demand for cobalt, particularly from Africa and Australasia. Chinese companies are increasingly becoming involved in copper and cobalt exploration and mining in Congo (Kinshasa) and Zambia as well as nickel, copper, and other mining in Australia and the South Pacific. Between 2009 and 2013, mines with a cumulative capacity of more than 100,000 metric tons per year of cobalt were proposed to come into production if all sites came into production as scheduled. This additional capacity corresponds to 175 percent of the 2008 global refinery production level. About 45 percent of this cobalt would be from primary nickel deposits, about 32 percent from primary copper deposits, and about 21 percent from primary cobalt deposits. By 2013, about 40 percent of new capacity was expected to come from the African Copperbelt; 38 percent, from Australia and the South Pacific countries of Philippines, Indonesia, New Caledonia, and Papua New Guinea; 11 percent, from other African countries; 5 percent, from North America; and 6 percent, from other areas.

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