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At least 883 records · Page 49Linked to original sources
USGS1960

The chief oxide-burgin area discoveries, East Tintic district, Utah; A case history

In 1955 exploration for base and precious metals was undertaken by Bear Creek Mining Company immediately north of the Main Tintic district , Utah . During the course of this work Bear Creek became interested in the East Tintic district , primarily as a result of the activities of the U.S. Geological Survey in that area . Data published on the East Tintic district by the Survey and others were studied and map data made available from various mining companies were compiled. Preliminary economic studies were made to determine the present day value of the type of ore body discovered previously in the district . Encouraging results from these investigations led to the selection of specific targets for exploration. Recommendations for a project program were made and approved. Negotiations were successfully concluded in mid-1956 for a unit lease agreement on lands in the East Tintic district owned by the Tintic Standard and Chief Consolidated mining companies and their subsidiaries. Of the targets selected for exploration, the Chief Oxide area seemed to be one of the most prominent. Our preliminary work in the Chief Oxide area corroborated the findings of the U.S. Geological Survey described in Part I of this paper. After careful consideration it was decided to gamble the cost of an exploration shaft in this area for the purpose of providing an underground drilling platform. We also hoped by means of underground workings to establish the existence and nature of the postulated fault. A limited amount of surface drilling was done prior to shaft sinking in order to locate a shaft site and also to obtain additional information of subvolcanic structure and alteration. Underground exploration in the Chief Oxide area was started in January, 1957. The Burgin shaft was sunk to a depth of 1,100 feet and by August, 1959, lateral development on the 1050 level totaled 4,721 feet and underground diamond drilling totaled 15,480 feet. Results of the work done to date are as follows: ( a ) Identification of the sedimentary rock section and an interpretation of the structure in the Burgin mine area . (b) Discovery by penetration of the previously postulated East Tintic thrust fault. (c) Discovery of large zones of manganese oxides and carbonates, which were found to be closely related to silver-lead-zinc mineralization. (d) Discovery of ore-grade lead-zinc mineralization within the footwall rocks of the East Tintic thrust. (e) Discovery of high-grade silver-lead ore within the thrust zone. Insofar as ore localization is concerned the most important structural feature in the Burgin mine area is the East Tintic thrust fault- a fact that opens up new ore potential over a large part of the East Tintic district not previously explored. Although the discoveries to date must be attributed essentially to the application of geology to exploration, the tools of geochemical prospecting and geophysics were also used, and the geochemical work, in particular, was found to be a definite aid in the selection of areas for further exploration.

Utah↗
USGS1989

Non-energy resources, Connecticut and Rhode Island coastal waters

Cores collected from Long Island Sound, Connecticut, were used to establish control on the geologic framework of the area. Lithologic and stratigraphic analyses verified the presence of the following units: (1) Cretaceous coastal plain, (2) Pleistocene glacial till, (3) late Pleistocene glacial lake, (4) late Pleistocene glacial outwash, and (5) Holocene fluvial, estuarine and marine deposits. Cores collected in Block Island Sound, Rhode Island, were obtained from inferred, relict shoreline features and were analyzed for heavy mineral content. Concentrations ranged from 0.3 to 3.4%; no significant downcore changes were found. The results indicated that surficial sediments in areas of high-velocity tidal flow yield greater amounts of heavy minerals than do inferred placer deposits. During the second phase of the program of study, Connecticut and Rhode Island pooled resources to develop a study plan for the comprehensive quantification of all non-energy resources in the adjacent waters of the states. A literature and data survey was conducted to assess the occurrence, extent, and accessibility of these resources. Sand and gravel and heavy minerals were found in concentrations offering potential for resource exploitation. Constraints on exploitation include (1) water depth restrictions for the protection of shellfish beds and public beaches, (2) fishing activities, (3) military, commercial, and fishing vessel traffic, (4) seafloor cable routes and (5) dump sites. Deposits composed of Pleistocene glacial sediments and/or Holocene marine sediments in regions of little or no user conflict were identified as sites potentially suitable for resource exploitation. The study plan stated additional data needs (geophysical profiling and vibracore sampling) at these sites. Subsequent to these recommendations, high-resolution seismic profiles and sidescan sonographs were obtained from these sites. Seismic stratigraphic analyses confirm the presence of extensive deposits of potential economic value.

Marine Geology↗
USGS1981

Geologic mapping of Kentucky: A history and evaluation of the Kentucky Geological Survey--U.S. Geological Survey Mapping Program, 1960-1978

In 1960, the U.S. Geological Survey and the Kentucky Geological Survey began a program to map the State geologically at a scale of 1:24,000 and to publish the maps as 707 U.S. Geological Survey Geologic Quadrangle Maps. Fieldwork was completed by the spring of 1977, and all maps were published by December 1978. Geologic mapping of the State was proposed by the Kentucky Society of Professional Engineers in 1959. Wallace W. Hagan, Director and State Geologist of the Kentucky Geological Survey, and Preston McGrain, Assistant State Geologist, promoted support for the proposal among organizations such as Chambers of Commerce, industrial associations, professional societies, and among members of the State government. It was also arranged for the U.S. Geological Survey to supply mapping personnel and to publish the maps; the cost would be shared equally by the two organizations. Members of the U.S. Geological Survey assigned to the program were organized as the Branch of Kentucky Geology. Branch headquarters, including an editorial staff, was at Lexington, Ky., but actual mapping was conducted from 18 field offices distributed throughout the State. The Publications Division of the U.S. Geological Survey established a cartographic office at Lexington to prepare the maps for publication. About 260 people, including more than 200 professionals, were assigned to the Branch of Kentucky Geology by the U.S. Geological Survey at one time or another. The most geologists assigned any one year was 61. To complete the mapping and ancillary studies, 661 professional man-years were required, compared with an original estimate of 600 man-years. A wide variety of field methods were used, but most geologists relied on the surveying altimeter to obtain elevations. Surface data were supplemented by drill-hole records, and several dozen shallow diamond-drill holes were drilled to aid the mapping. Geologists generally scribed their own maps, with a consequent saving of publication costs. Paleontologists and stratigraphers of the U.S. Geological Survey cooperated closely with the program. Paleontologic studies were concentrated in the Ordovician of central Kentucky, the Pennsylvanian of eastern and western Kentucky, and the Mesozoic and Cenozoic of westernmost Kentucky. In addition to financial support, the Kentucky Geological Survey provided economic data, stratigraphic support, and drillhole records to the field offices. Geologists of the State Survey made subsurface structural interpretations, constructed bedrock topography maps, and mapped several quadrangles. Some of the problems encountered were the inadequacy of much of the existing stratigraphic nomenclature, the uneven quality of some of the mapping, and the effects of relative isolation on the professional development of some of the geologists. The program cost a total of $20,927,500. In terms of 1960 dollars, it cost $16,035,000; this compares with an original estimate of $12,000,000. Although it is difficult to place a monetary value on the geologic mapping, the program has contributed to newly discovered mineral wealth, jobs, and money saved by government and industry. The maps are used widely in the exploration for coal, oil and gas, fluorspar, limestone, and clay. The maps are also used in planning highways and locations of dams, in evaluating foundation and excavation conditions, in preparing environmental impact statements, and in land-use planning.

Kentucky↗
USGS1963

Epigenetic, diplogenetic, syngenetic, and lithogene deposits

Much of the disagreement over " epigenetic " And " Syngenetic " Deposits Is Semantic; Some Ores And altered rocks are in part syngenetic and in part epigenetic and for them the term " diplogenetic " is proposed. All these terms are primarily time terms related to the contemporaneity of the deposit and the enclosing rock, but in a secondary sense they are space terms; they do not, however, imply process of formation or source of the chemical constituents. Process or source terms such as "magmatic," "hydro-thermal," "sedimentary" are generally satisfactory, but the process term "lateral secretion" is now vague in meaning. A more precise term is needed for the process of mobilization of elements from a solid rock and their transportation and redeposition elsewhere; for this process I propose the term " lithogene " ("stone-born"), to stress the source and process as do "magmatic" and "sedimentary." Such deposits could be derived from syngenetic , diplogenetic , or epigenetic deposits through the action of metamorphic, hydrothermal, supergene or other solutions. If one wishes, however, to emphasize the distance the mobilized elements have moved from the source rock, the resulting deposit can be described best as a locally derived lithogene deposit ("lateral secretion"), or as a regionally derived lithogene deposit ("product of regional metamorphism"). The classification of many deposits such as epigenetic replacement bodies of magnetite in limestone, and syngenetic gold in recent placers is not controversial; however, where large parts of the mineral deposit are made up both of syngenetic elements and introduced elements, the term " diplogenetic " is appropriate. Examples include mineral deposits in which syngenetic cations are united with epigenetic anions, as in fluorite replacements in limestones, or where the reverse relationship holds and epigenetic cations are united to syngenetic sulfur or other anions-as may be true of certain black cupriferous shales of the Mansfeld type. Guides for distinguishing the various types of mineral deposits are discussed at length and include: mineralogy; texture; isotopic composition of hydrogen, carbon, oxygen, sulfur, and perhaps other elements; form; age relations; alteration; zoning; position and quantitative adequacy of supposed source rocks; lithology; structural geology; paleogeography; and regional geologic relations. The criteria developed are used in a critical review of several examples of controversial deposits -including the African Copper-belt deposits and those of the graphitic schists of Fenno-Scandia.

Economic Geology↗
USGS1994

Lead isotope compositions as guides to early gold mineralization: The North Amethyst vein system, Creede district, Colorado

The North Amethyst vein system, which is hosted by approximately 27 Ma Carpenter Ridge Tuff and approximately 26 Ma Nelson Mountain Tuff, has two mineral associations separated by brecciation and sedimentation in the veins. The early association consists of quartz, rhodonite, hematite, magnetite, electrum (Au (sub 0.3-0.5) Ag (sub 0.7-0.5)) , and Mn carbonate, Au-Ag sulfide, Ag sulfosalt, and base metal sulfide minerals. The later mineral association cuts the Mn- and Au-bearing assemblages and consists of quartz, calcite, sericite, chlorite, hematite, adularia, fluorite, base metal sulfides, and Ag-bearing tetrahedrite.Our detailed studies show that the Pb isotope compositions of paragenetically early galenas associated with Au-rich mineralization in the North Amethyst vein system are relatively unradiogenic ( 206 Pb/ 204 Pb: 18.826-18.881, 207 Pb/ 204 Pb: 15.588-15.602, and 208 Pb/ 204 Pb: 37.790-37.926) compared to Pb isotope compositions of galenas formed later at about 25 Ma during Ag and base metal mineralization ( 206 Pb/ 204 Pb: 19.041-19.115, 207 Pb/ 204 Pb: 15.627- 15.672, and 208 Pb/ 204 Pb: 37.829-38.057). New Pb isotope data for the central and southern parts of the Creede district, which are located 5 to 7 km south of the North Amethyst area, agree with the results of a regional study by Doe et al. (1979) that included five samples from the main part of the Creede district. Galenas and adularia from the central and southern Creede district and galenas from the Bondholder district, 7 km north of the North Amethyst area, are similar to the Pb isotope compositions of galenas formed later in the North Amethyst area during Ag and base metal mineralization. Galenas from the Alpha-Corsair vein, which was mined for Ag prior to 1910, are isotopically similar to galenas associated with North Amethyst Au-stage mineralization. This isotopic similarity suggests that unexplored segments of the Alpha-Corsair structure may have the same mineralogy as the North Amethyst Au stage; thus, the Alpha-Corsair structure has the potential for high gold contents.Pb isotope compositions from the late stage of the North Amethyst vein system and from the Bondholder and central and southern Creede mining districts are more radiogenic than the host volcanic rocks of the central cluster of the San Juan volcanic field. Our Pb isotope results indicate that early Au mineralization of the North Amethyst area may represent the product of an older and relatively local hydrothermal system distinct from that of the younger base metal and Ag mineralization found throughout the region. Fluids that deposited Au minerals may have derived their Pb isotope composition by a greater degree of interaction with shallow, relatively less radiogenic volcanic wall rocks. The younger, base metal and Ag-rich mineralization that overprints the Au mineralization in the North Amethyst area clearly has a more radiogenic isotopic signature, which implies that the later mineralization derived a greater component of its Pb from Proterozoic source rocks, or sediments derived from them.Paragenetically early sulfide-rich vein assemblages have the least radiogenic galenas and generally also have the highest Au contents. Thus, identification of paragenetically early vein assemblages with relatively unradiogenic Pb isotope compositions similar to those of the North Amethyst area provides an additional exploration tool for Au in the central San Juan Mountains area.

Colorado↗
USGS1978

Remote-sensing and subsurface definition of facies and structure related to uranium deposits, Powder River Basin, Wyoming

Computer-enhanced Landsat images of the southern Powder River Basin have been used to define facies and linear structural features within the Wasatch Formation. The facies distribution is detectable primarily because of a relation of vegetation density and type to the local substrate. The surface indications of facies are confirmed by sandstone/ mudstone ratios determined from logs of abundant exploration drill holes. These newly defined geologic features are spatially related to known uranium mineral occurrences and are believed to be related to mineralization in the following ways. (1) Major uranium occurrences are virtually restricted to an intermediate grain-size facies of the Wasatch, probably marking the axial zone of the depositional basin. (2) The axial zone is also marked by a change from one structural lineament domain to another, and the structures may have influenced details of fluvial-system patterns and sedimentation and (subsequently) the flow of uranium-bearing ground water. (3) A recently active linear structure may mark the current basin axis; it appears to have some relationship both to groundwater chemistry and the distribution of uranium occurrences, suggesting structural influence on relatively modern ground-water transport and uranium deposition. © 1978 Society of Economic Geologists, Inc.

Wyoming↗
USGS2014

Geochemical and modal data for igneous rocks associated with epithermal mineral deposits

The purposes of this report are to (1) present available geochemical and modal data for igneous rocks associated with epithermal mineral deposits and (2) to make those data widely and readily available for subsequent, more in-depth consideration and interpretation. Epithermal precious and base-metal deposits are commonly associated with subduction-related calc-alkaline to alkaline arc magmatism as well as back-arc continental rift magmatism. These deposits form in association with compositionally diverse extrusive and intrusive igneous rocks. Temperature and depth regimes prevailing during deposit formation are highly variable. The deposits form from hydrothermal fluids that range from acidic to near-neutral pH, and they occur in a variety of structural settings. The disparate temperature, pressure, fluid chemistry, and structural controls have resulted in deposits with wide ranging characteristics. Economic geologists have employed these characteristics to develop classification schemes for epithermal deposits and to constrain the important genetic processes responsible for their formation.

Data Series↗
USGS1966

Isotopic study of galenas from the upper Mississippi Valley, the Illinois-Kentucky, and some Appalachian Valley mineral districts

Analyses of lead isotopes in galena in carbonate rock ore deposits collected from several mineralized districts in the Central and Eastern Interior of the United States support previous studies in establishing that the galena is anomalously radiogenic ("J"type")- This study , using care-fully selected samples to test some géologie relationships, shows region-wide and distrietwide systematic variations in isotope ratios. The genetic implications of thèse variations are discussed. Two mechanisms of origin are considered to explain thèse variations in isotopic ratios. One involves mixing of leads from multiple sources, the other calls for variable lead-isotope ratios originating from a single source. Several source materials for the lead ores have been suggested; whether a single source has predominated, or two or more main sources have predominated is still unresolved. Slopes from Pb206/Pb204 versus Pb207/Pb204 plot are compatible with a contribution of lead by the 1300 ± 300 m.y. basement rocks that underlie the deposits. The spatial relationships of alkaline igneous rocks to several of the minerai districts in the Mississippi Valley région suggest a possible mag-matic source for the lead. Isotopic analyses of galenas closely associated with several of the intrusive rocks are similar in isotopic composition to adjacent ore leads, but genetic implications are ambiguous. Galena oc-curring in shales in the Mississippi Valley région outside mineralized districts contains ordinary lead. Théories that call upon such shales to be the major source of the lead in the depoaits of the Mississippi Valley type must explain this distinct différence in isotopic compositions. Galena collected from districts within the Appalachian Ridge and Valley Province contains notably less radiogenic lead than that from the Mississippi Valley minerai districts , and the lead is of the ordinary type.

Illinois, Kentucky↗
USGS1989

Geologic setting, depths of emplacement, and regional distribution of fluid inclusions in intrusions of the central Wasatch Mountains, Utah

Nine mid-Tertiary calc-alkaline stocks, a subvolcanic porphyry system, and coeval volcanic rocks are exposed in a 45-km-long east-trending belt across the central Wasatch Mountains, Utah. The intrusions vary systematically from west to east in texture, style of emplacement, extent of contact metamorphism, hydrothermal alteration, and mineralization. Pressure-depth estimates based on metamorphic mineral assemblages, stratigraphic reconstructions, and fluid inclusion data indicate a regular variation in paleodepths ranging from about 11 km on the west to less than 1 km on the east. These data indicate that the central Wasatch Mountains have been tilted down to the east about 20 degrees during the late Cenozoic. Fluid inclusion populations in igneous quartz also vary systematically with paleodepth; high-salinity (halite-saturated) fluid inclusions are present in the eastern porphyry stocks and in the upper parts of the Alta and Clayton Peak stocks in the center of the belt but are absent in the deeper parts of the Alta and Clayton Peak stocks and in the Little Cottonwood stock on the west side of the belt. In the Alta and Clayton Peak stocks, nearly planar high-paleosalinity horizons, presently dipping 15 degrees to 20 degrees east, separate rocks containing high-salinity fluid inclusions (above the high-paleosalinity horizon) from those lacking such fluid inclusions. Comparison of fluid-inclusion populations in igneous and vein quartz in the Alta and Clayton Peak stocks indicates that high-salinity fluids predated most of the vein-forming hydrothermal activity and provide the earliest record of fluids to circulate in these stocks. High-salinity fluids probably formed either by boiling of fluids released during the late stages of crystallization in the parts of the intrusions where pressure was less than about 1,300 bars or by exsolution of immiscible high-salinity brines from the crystallizing magmas. Most hydrothermal mineralization associated with the intrusions, including Ag-Pb-Zn ores in the Park City district, are associated spatially with parts of the intrusions where high-salinity fluids were present. The major exception is the porphyry molybdenum system in the eastern part of the Little Cottonwood stock, which probably was at too great a depth (approximately 7 km) to form high-salinity brines and is dominated by low-salinity CO 2 -rich fluids.

Economic Geology↗
USGS1991

Oxygen, hydrogen, and sulfur isotope studies in the Juneau gold belt, southeastern Alaska: Constraints on the origin of hydrothermal fluids

The delta 18 O values of gold-bearing quartz from the Juneau gold belt range from 15.2 to 20.8 per mil, indicating that ore fluid values ranged from 7.2 to 12.8 per mil at an estimated temperature of 300 degrees C. Hydrothermal micas from many of the deposits are characterized by delta D values of -75 to -53 per mil, and ore fluids were calculated to have values of -35 to -15 per mil. In contrast, extracted fluid inclusion waters have a broad range of delta D values, from -48 in relatively undeformed quartz to about -110 per mil for some of the more deformed quartz veins. This range of more than 60 per mil reflects various mixtures from inclusions containing isotopically heavy, primary ore fluids and those containing low-temperature, isotopically light meteoric waters that were trapped in late fractures during uplift of the veins to shallow crustal levels. These results indicate a deep crustal source for the ore fluids, most likely of metamorphic origin. Values of delta D for muscovite, biotite, and hornblende from country rocks, as well as of delta 18 O for quartz-feldspar and quartz-plagioclase, provide little evidence of deep circulation of meteoric water along the length of the gold belt.The provinciality of delta 34 data suggests a regional metamorphic fluid of approximately -6 per mil that acquired much of its sulfur from lithologies near sites of ore deposition. Sulfur ratios of sulfide minerals from auriferous quartz range from -17.8 to -5.6 per mil in black phyllite hosts, from -6.0 to -1.3 per mil in less reduced metasedimentary rocks, and from -3.8 to +1.2 per mil in relatively oxidized igneous rocks. The regional fluid is interpreted to have driven desulfidation reactions in relatively 34 S-depleted sulfur reservoirs in the phyllites and 34 S-enriched reservoirs in the more oxidized lithologies.

Economic Geology↗
USGS2016

News from the seabed: Geological characteristics and resource potential of deep-sea mineral resources

Marine minerals such as manganese nodules, Co-rich ferromanganese crusts, and seafloor massive sulfides are commonly seen as possible future resources that could potentially add to the global raw materials supply. At present, a proper assessment of these resources is not possible due to a severe lack of information regarding their size, distribution, and composition. It is clear, however, that manganese nodules and Co-rich ferromanganese crusts are a vast resource and mining them could have a profound impact on global metal markets, whereas the global resource potential of seafloor massive sulfides appears to be small. These deep-sea mineral commodities are formed by very different geological processes resulting in deposits with distinctly different characteristics. The geological boundary conditions also determine the size of any future mining operations and the area that will be affected by mining. Similarly, the sizes of the most favorable areas that need to be explored for a global resource assessment are also dependent on the geological environment. Size reaches 38 million km 2 for manganese nodules, while those for Co-rich crusts (1.7 million km 2 ) and massive sulfides (3.2 million km 2 ) are much smaller. Moreover, different commodities are more abundant in some jurisdictions than in others. While only 19% of the favorable area for manganese nodules lies within the Exclusive Economic Zone of coastal states or is covered by proposals for the extension of the continental shelf, 42% of the favorable areas for massive sulfides and 54% for Co-rich crusts are located in EEZs

Marine Policy↗
USGS1998

International strategic mineral issues summary report– Tungsten

Scheelite and wolframite are the principal minerals currently mined for tungsten. Both occur in hard-rock deposits; wolframite is also recovered from placer deposits. Most current mine production of tungsten is from vein/stockwork, skarn, porphyry, and strata-bound deposits. Minor amounts are produced from disseminated, pegmatite, breccia, and placer deposits. Most tungsten is used to make tungsten carbide and tungsten alloys for use in machine tools and drilling equipment. Other important applications are in lamp filaments and cathodes, high-speed steels, textile dyes, paints, and catalysts. The world is well endowed with tungsten resources. China and the former Soviet Union have 8 of the world's 10 largest deposits; these 8 contain about half of the world's resources of tungsten. If economic conditions are suitable, world tungsten resources in known deposits and their extensions (categories R1 and R2), including economic, marginal, and subeconomic resources, are sufficient to permit world production to continue at 1995 levels until well into the 21st century. World tungsten resources in identified deposits and districts that are currently economically exploitable (category R1E) appear to be sufficient to meet world demand at 1995 levels only until the year 2007. However, the figure for resources of this kind does not include or reflect resources whose economic parameters are unknown in major producing areas in the former Soviet Union, China, and other nonmarket-economy countries and thus severely underestimates future tungsten availability. In 1995, China and the former Soviet Union accounted for over three-fourths of the world's mine production of tungsten. China alone produced about two-thirds of world output. Given its vast resources, China will likely maintain its prominent role in world tungsten supply. By the year 2020, changes in supply patterns are likely to result from declining output from individual deposits in Australia, Austria, and Portugal and the opening of new mines in Canada, China, and the United Kingdom.

Circular↗
USGS1955

A reconnaissance for uranium in carbonaceous rocks in southwestern Colorado and parts of New Mexico

Coal and carbonaceous shale of the Dakota formation of Cretaceous age were examined for radioactivity in the Colorado Plateau of southwestern Colorado and northwestern New l1exico during the summer of 1953. Older and younger sedimentary rocks and some igneous rocks also were examined, but in less detail, Weak radioactivity was detected at many places but no new deposits of apparent economic importance were discovered. The highest radioactivity of carbonaceous rocks was detected in black shale, siltstone, and sandstone of the Paradox member of the Hermosa formation of Pennsylvanian age. A sample collected from this member at the Bald Eagle prospect in Gypsum Valley, San Higuel County, Colo. contains 0.10. percent uranium. Carbonaceous rocks were investigated at several localities on the Las Vegas Plateau and the Canadian Escarpment in Harding and San Miguel Counties, northeastern New Mexico. Carbonaceous sandstone and siltstone in the middle sandstone member of the Chinle formation of Triassic age contain uranium at a prospect of the Hunt Oil Company southwest of Sabinoso in northeastern San Miguel County, N. Mex. A channel sample across 3.2 feet of mineralized rocks at this locality contains 0.22 percent uranium. Weak radioactivity was detected at two localities in carbonaceous shale of the Dakota and Purgatoire formations of Cretaceous age.

Trace Elements Memorandum↗
USGS2004

Stable isotopic constraints on fluid-rock interaction and Cu-PGE-S redistribution in the Sonju Lake intrusion, Minnesota

The Sonju Lake intrusion, part of the 1.1 Ga Midcontinent rift-related Beaver Bay Complex, is a 1,200-m-thick, strongly differentiated, layered sequence of mafic cumulates located in northeastern Minnesota. Basal melatroctolite and dunite layers are overlain by troctolite, gabbro, Fe-Ti oxide-rich gabbro, apatite diorite, and monzodiorite. Stratigraphic intervals rich in Pt + Pd, Cu, and S occur over ???500 m in the Fe-Ti oxide-rich gabbro and apatite diorite units. Peak concentrations show offsets that are similar to those found in other tholeiitic layered intrusions. Concentrations of Pd in excess of 100 ppb are confined to the lowermost 25 m of the interval. Copper shows a sharp increase to 630 ppm above the Pd-rich interval. Sulfur contents are low (<375 ppm) in the Cu-rich interval, but they increase to values as high as 3,150 ppm above in the apatite diorite. Disseminated sulfides in the intrusion have ??34S values that range from -2.2 to 3 per mil Vienna-Canyon Diablo Troilite (V-CDT) and suggest that contamination by country rock sulfur was not an important process in the formation of the metal-rich interval. ??18O values of plagioclase from the intrusion range from 5.6 to 12.0 per mil (V-SMOW) and indicate that a relatively low-18O fluid (??18O ???3-5 ???) interacted with the rocks of the intrusion at temperatures less than ???275??C. Clinopyroxene and Fe-Ti oxides (ilmenite with minor amounts of titanomagnetite) show much more restricted ranges in ??18O values (4.6-5.7 and 5.5-6.7 per mil, respectively) and attest to the kinetic control of the oxygen isotope exchange process. The externally derived fluid that interacted with rocks now enriched in platinum group elements (PGE) + Cu- and Fe-sulfide minerals locally liberated sulfur and replaced chalcopyrite and pyrite with goethite. In the Cu-rich zone, goethite that replaces chalcopyrite may contain up to 8.5 weight percent Cu. It is evident that hydrothermal alteration resulted in a decoupling of copper and sulfur, with sulfur being transferred out of the Cu-rich interval. Interaction between rocks in the PGE-Cu-S interval of the Sonju Lake intrusion and an externally derived fluid at low temperatures modified what appears to have been a primary stratigraphic metal-sulfur zonation. The effects of hydrothermal alteration on PGE and base-metal sulfide mobility and redistribution must be understood before models of primary zonation processes can be meaningfully applied. ?? 2004 by Economic Geology.

Economic Geology↗
USGS1946

Structural control of ore bodies in the Jefferson City area, Tennessee

The zinc deposits of the Jefferson City area are confined to the lower half of the Kingsport formation of the Knox group of rocks. They are on the southeast flank of a northeast-trending anticline which is partially overridden from the southeast by the Bays Mt. thrust sheet. The beds show low dips. The area is transected by a series of high angle strike-slip faults having relatively small displacement and striking essentially parallel to the dominant northeast structure. Minor cross folds running transversely to the regional structure are numerous. Three sets of fractures trending N. 45-50 degrees W., N. 30-40 degrees E., and N. 60-70 degrees E. are well developed. The ore bodies are irregular but generally have a distinct elongation. The vertical extent may be limited to a single bed or may include several beds, depending upon local structural conditions. All ore bodies are confined to zones of pre-mineral deformation. The linear trends of the ore bodies show a remarkable parallelism to the axes of the cross folds. Ore occurs on any part of the flexures but maximum concentration is on the anticlinal crests and synclinal troughs: the ore attains greatest thickness on the anticlines. Fractures associated with the folding exhibit local ore control. Faults are poor sites for ore, but fracturing and drag folding accompanying faulting produce conditions favorable to ore deposition.

Tennessee↗
USGS1947

The beryl resources of Connecticut

In 1942-44, about 120 Connecticut pegmatites were examined for beryl and other minerals during investigations by the Federal Geological Survey. Most of the pegmatites lie in the Middletown district, occurring principally in the Bolton schist and Monson gneiss. The pegmatites range from distinctly zoned bodies to those that are essentially uniform mixtures of the component minerals. Beryl in the zoned pegmatites commonly is present in greater concentration in one or more zones than in others. It occurs in the majority of pegmatites examined, but on the basis of crystal counts only 10 pegmatites, either in whole or in sizable part, average 0.2% or more beryl. Six structural types of beryl deposits are described and illustrated: border-zone, wall-zone, intermediate-zone, pod, fracture-controlled, and disseminated. Some pegmatites contain two or more types.Grades and tonnages of 14 beryl-bearing pegmatites are tabulated. Total indicated and inferred beryl-bearing pegmatite is 207,885 tons containing 859 + tons of beryl. Most of the beryl is in crystals too small to be economically separable by hand sorting, and barring a marked increase in the price of beryl, milling operations would have to be supported primarily by the yield of salable feldspar, scrap mica, and possibly quartz.

Connecticut↗
USGS1955

Geochemistry and mineralogy of a uraniferous sub bituminous coal

A sample of subbituminous uraniferous coal from the Red Desert, Sweetwater County, Wyo., has been studied mineralogically. The coal contains gypsum (6 percent), kaolinite (1 percent), quartz (0.3 percent), calcite (trace), and limonite (trace). This suite of minerals and the absence of pyrite show that the coal has been subjected to weathering and oxidation. No uranium minerals have been found; mechanical fractionation has indicated that the uranium is associated with the organic constituents of the coal. The minerals that have been isolated contain 0.0006 percent uranium, a content that is to be expected for nonuraniferous sedimentary rocks. The organic components of the coal contain approximately 0.002 percent uranium. On the basis of material-balance calculations, the organic components carry 98 percent of the uranium in the coal. Batch extraction of the Wyoming coal with 6 N hydrochloric acid leads to the solution of almost 90 percent of its uranium. Recovery of uranium is independent of the particle size of the coal between - 4 and - 20 mesh, and is accompanied by the solution of approximately 70 percent of the inorganic constituents (ash) of the coal. The extract contains, together with uranium, a concentration of several elements such as manganese, cerium, and vanadium that are present in the coal. Fischer assays of this weathered coal from the Red Desert indicate a yield of 16.7 gallons of tar per ton. Yields of both tar and char are about 15 percent lower if the coal is first treated with 6 N hydrochloric acid to extract the uranium. It is suggested that uranium was introduced into the coal by means of ground water carrying soluble alkaline or alkaline-earth uranyl carbonate complexes. The mineral schroeckingerite-a similar complex-is found near this subbituminous coal in the Red Desert of Wyoming. These complexes, which are unstable in acid medium, release the uranyl ion (U02++), which may then react with organic constituents of the coal to form ionic uranyl-organic compounds that are insoluble above a pH of about 2.2. Preliminary data indicate that the uranium is associated with various humic components of the coal. The distribution of uranium among the components of the subbituminous coal from Wyoming is similar to the distribution in a lignite from South Dakota. There is no indication that uranium was introduced into or retained by the two coals by appreciably different geochemical processes. © 1955 Society of Economic Geologists, Inc.

Wyoming↗
USGS1957

Eastern and central Montana as a possible source area of uranium

Geologic settings in central and eastern Montana and in a few places in southwestern Montana are similar to the settings in areas favorable for the occurrence of uranium deposits. Several areas in Montana seem especially favorable for the occurrence of uranium.The alkalic igneous rock province of central Montana is similar to the one of the Colorado Plateau. On the basis of this analogy, certain areas in Montana, where the lithology and (or) structure are considered favorable for the occurrence of uranium, are suggested for prospecting. Seleniferous plants, similar to those that are uranium indicators on the Colorado Plateau, might be used as an aid in prospecting for uranium provided that the seleniferous shale areas are taken into account.Uranium deposits, similar to those in North and South Dakota, may be found in Cretaceous and Tertiary sandstones, lignites, and low-grade coals of eastern Montana; also, the magnetite-bearing beds of certain Cretaceoussandstones may contain fossil placer deposits of radioactive black minerals. Theoccurrence of uranium in basal conglomerates, quartzites, and sandstones in Africa and Ontario suggests that similar basal sedimentary rocks in central Montana may contain uranium.Many of the radioactivity anomalies in Montana found from the air are closely associated with the Eagle sandstone; others are associated with Precambrian basement rocks, Upper Cretaceous and Lower Tertiary igneous rocks, or sedimentary rocks of Jurassic and Cretaceous age. Glacial cover and lack of outcrops locally may hinder prospecting for uranium.

Montana↗