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Volcanogenic massive sulfide (VMS) Zn-Pb-Cu-Ag-Au deposits of the Bonnifield mining district formed during Late Devonian-Early Mississippian magmatism along the western edge of Laurentia. The largest deposits, Dry Creek and WTF, have a combined resource of 5.7 million tonnes at 10% Zn, 4% Pb, 0.3% Cu, 300 grams per tonne (g/t) Ag, and 1.6 g/t Au. These polymetallic deposits are hosted in high field strength element (HFSE)- and rare-earth element (REE)-rich peralkaline (pantelleritic) metarhyolite, and interlayered pyritic argillite and mudstone of the Mystic Creek Member of the Totatlanika Schist Formation. Mystic Creek metarhyolite and alkali basalt (Chute Creek Member) constitute a bimodal pair that formed in...
Categories: Publication; Types: Citation; Tags: Economic Geology
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The Copley Greenstone, Balaklala Rhyolite, and Mule Mountain stock in the West Shasta Cu-Zn district, California, have Rb-Sr, Sm-Nd, U-Pb, and K-Ar systematics that indicate they are a cogenetic suite of ensimatic island-arc rocks about 400 Ma. Pervasive alteration and mineralization of these rocks, for the most part, was syngenetic and the major component of the mineralizing fluid was Devonian seawater. K-Ar ages of quarz-sericite concentrates from ore horizons and Rb-Sr systematics of a few rock and ore specimens record a later thermal and mineralizing event in the district of about 260 Ma. Contamination of some rocks with pelagic sediments is indicated by the Sm-Nd data. -Authors
Categories: Publication; Types: Citation; Tags: Economic Geology
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The gold deposits at Alleghany, California, are typical of many epigenetic gold-bearing hydrothermal vein systems in metamorphic terranes worldwide. Detailed analyses of alteration halos in serpentinite, mafic amphibolite, and granite wall rocks at Alleghany indicate that widely contrasting deposit types, ranging from fuchsite-carbonate schists to pyrite-albitites, resulted when different wall rocks interacted with the same externally derived CO2-rich hydrothermal vein fluid. Patterns of element redistribution within halos and among lithologic units suggest a complex process involving fluid flow along vein fractures and diffusion (?? infiltration) normal to the veins. Wall rocks locally controlled both the directions...
Categories: Publication; Types: Citation; Tags: Economic Geology
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The Stillwater, Fiskenaesset and Bushveld complexes have many similarities. The trends of the Pt/(Pt + Pd) and its correlation with Mg/(Mg + Fe2+) are presented. Presumably the Pt/(Pt + Pd) variations are related to changes in major mineral compositions. -K.A.R.
Categories: Publication; Types: Citation; Tags: Economic Geology
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Fluids extracted from aqueous fluid inclusions in epigenetic gangue and ore minerals record the migration of huge volumes of highly saline fluids throughout the stratigraphic section of the Ozark region. The extracted fluids share many similarities regionally, but there are significant temporal differences which define two geochemically distinct end-member ore-forming fluids, referred to as the Viburnum Trend main stage or Viburnum Trend type and the Tri-State type. Possible explanations for the origins of these two end-member fluids are discussed. -from Authors
Categories: Publication; Types: Citation; Tags: Economic Geology
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Geologic studies during recent open-pit mining at Summitville, Colorado, have provided new information on an epithermal acid sulfate Au-Ag-Cu deposit formed in a volcanic dome. Geologic mapping, geochemical studies of whole-rock samples from blast holes, and geologic and geochemical traverse studies refine the details of the evolution of the Summitville deposit. Six distinct events followed emplacement of the quartz latite volcanic dome and define the development of the Summitville deposit: 1) an early stage of acid sulfate alteration, 2) subsequent Cu sulfide and gold mineralization, 3) widespread hydrothermal brecciation, 4) volumetrically minor, base metal sulfide-bearing barite veining, 5) volumetrically minor,...
Categories: Publication; Types: Citation; Tags: Economic Geology
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Cleat and clastic dikes of Middle Pennsylvanian-age coal beds of the Illlinois and Forest City basins of Illinois, Iowa, Missouri, and Kansas locally contain appreciable amounts of sphalerite within a kaolinite-pyrite-sphalerite (?? pyrite)-calcite paragenetic sequence. The sphalerite and associated minerals are of interest as a partial record of the history of fluids in the sedimentary basin and as possible indicators of Mississippi Valley-type mineralization. Moreover, zinc from the sphalerite may represent an exploitable by-product of coal mining and combustion. -Authors
Categories: Publication; Types: Citation; Tags: Economic Geology
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Analysis of in situ reflectance spectra of native vegetation was used to interpret airborne MSS data. Representative spectra from three plant species in the E Tintic Mountains, Utah, were used to interpret the color components on a color ratio composite image made from MSS data in the visible and near-infrared regions. A map of plant communities was made from the color ratio composite image and field checked. -from Author
Categories: Publication; Types: Citation; Tags: Economic Geology
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Presents a quantitative simulation of regional groundwater flow during uranium deposition in the Westwater Canyon Member and Jackpile Sandstone Member of the Upper Jurassic Morrison Formation in the San Juan basin. Topographic slope, shoreline position, and density contrasts in the lake and pore fluids controlled the directions of flow and recharge-discharge areas. The most important results for uranium ore deposit formation are that regional groundwater discharged throughout the basin, regional discharge was concentrated along the shore line or playa margin, flow was dominantly gravity driven, and compaction dewatering was negligible. A strong association is found between the tabular sandstone uranium deposits...
Categories: Publication; Types: Citation; Tags: Economic Geology
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The thick (≤8 km), regionally extensive section of Neoproterozoic siliciclastic strata (terrigenous detrital succession, TDS) in the central and eastern Great Basin contains sedimentary pyrite characterized by mostly high δ34S values (−11.6 to 40.8‰, >70% exceed 10‰; 51 analyses) derived from reduction of seawater sulfate, and by markedly radiogenic Pb isotopes (207Pb/204Pb >19.2; 15 analyses) acquired from clastic detritus eroded from Precambrian cratonal rocks to the east-southeast. In the overlying Paleozoic section, Pb-Zn-Cu-Ag-Au deposits associated with Jurassic, Cretaceous, and Tertiary granitic intrusions (intrusion-related metal deposits) contain galena and other sulfide minerals with S and Pb isotope compositions...
Categories: Publication; Types: Citation; Tags: Economic Geology
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The thermal history of the Oquirrh Mountains, Utah, indicates that hydrothermal fluids associated with emplacement of the 37 Ma Bingham Canyon porphyry Cu-Au-Mo deposit extended at least 10 km north of the Bingham pit. An associated paleothermal anomaly enclosed the Barneys Canyon and Melco disseminated gold deposits and several smaller gold deposits between them. Previous studies have shown the Barneys Canyon deposit is near the outer limit of an irregular distal Au-As geochemical halo, about 3 km beyond an intermediate Pb-Zn halo, and 7 km beyond a proximal pyrite halo centered on the Bingham porphyry copper deposit. The Melco deposit also lies near the outer limit of the Au-As halo. Analysis of several geothermometers...
Categories: Publication; Types: Citation; Tags: Economic Geology
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The mercury-gold deposits of the Ivanhoe mining district in northern Nevada formed when middle Miocene rhyolitic volcanism and high-angle faulting disrupted a shallow lacustrine environment. Sinter and replacement mercury deposits formed at and near the paleosurface, and disseminated gold deposits and high-grade gold-silver veins formed beneath the hot spring deposits. The lacustrine environment provided abundant meteoric water; the rhyolites heated the water; and the faults, flow units, and lakebeds provided fluid pathways for the hydrothermal fluids. A shallow lake began to develop in the Ivanhoe area about 16.5 Ma. The lake progressively expanded and covered the entire area with fine-grained lacustrine sediments....
Categories: Publication; Types: Citation; Tags: Economic Geology
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The experimental metal solubilities for rock-buffered hydrothermal systems provide important insights into the acquisition, transport, and deposition of metals in real hydrothermal systems that produced base metal ore deposits. Water-rock reactions that determine pH, together with total chloride and changes in temperature and fluid pressure, play significant roles in controlling the solubility of metals and determining where metals are fixed to form ore deposits. Deposition of metals in hydrothermal systems occurs where changes such as cooling, pH increase due to rock alteration, boiling, or fluid mixing cause the aqueous metal concentration to exceed saturation. Metal zoning results from deposition occurring at...
Categories: Publication; Types: Citation; Tags: Economic Geology
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The final event in a complicated hydrothermal history at the Meikle gold deposit was gold deficient but caused extensive postore dissolution of carbonate, collapse brecciation, and precipitation of calcite and barite crystals in the resulting cavities. Although previously interpreted to be part of the Carlin-type hydrothermal system, crosscutting relationships and U-Th-Pb geochronology constrain this hydrothermal event to late Pliocene time (ca. 2 Ma), nearly 36 Ma after ore formation. Mineralogic, fluid inclusion, and stable isotope data indicate that postore hydrothermal fluids were reduced, H2S-rich, unevolved meteoric waters ((??18O = -17???) of low temperature (ca. 65??C). The ??18O values of barite and calcite...
Categories: Publication; Types: Citation; Tags: Economic Geology
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Analysis of the heavy metal content in a Holocene-Pliocene red bed sequence near San Felipe in N Baja California, Mexico, has yielded new information on the mobility and distribution of these metals during ageing of iron oxyhydroxides from the amorphous to the crystalline state. Whole-rock samples (27) and a series of successive leachates were analysed for V, Al, Cr, Mn, Fe, Co, Ni, Cu and Zn by ICP spectrometry and for U by a delayed neutron technique. These data are supported by a variety of other mineralogical and petrographical observations. The results indicate that the metal content of the samples is predominantly inherited from the constituent detrital minerals. Reddening of the whole-rock samples does not...
Categories: Publication; Types: Citation; Tags: Economic Geology
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The Laramide San Manuel-Kalamazoo porphyry system of Arizona has been pivotal in concepts of both extensional tectonics and alteration-mineralization zoning. This paper reexamines the tilting history in light of new work in the region and reinterprets the geometry of the deposit. The porphyry mineralization occurs in and near an intrusion of Laramide San Manuel porphyry in Precambrian Oracle Granite. The area has an extremely complicated history of Tertiary crustal extension and fanglomerate deposition, but the blocks containing the two main fragments of the original orebody were involved in only the later parts of this history and are less tilted than other nearby blocks. Originally horizontal features of mid-Tertiary...
Categories: Publication; Types: Citation; Tags: Economic Geology
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Two major periods of uranium mineralization are indicated by U-Pb isotope dating of uranium ores from collapse breccia pipes in the Grand Canyon region, northern Arizona. The Hack 2 and 3, Kanab North, and EZ 1 and 2 orebodies apparently formed in the interval of 200 ?? 20 Ma, similar to ages inferred for strata-bound, Late Triassic-hosted uranium deposits in southern Utah and northern Arizona. Samples from the Grand Canyon and Pine Nut pipes, however, indicate a distinctly older age of about 260 Ma. The clustering in ages for a variety of uranium deposits at about the age of the lower part of the Chinle Formation (Late Triassic) suggests that uranium in these deposits may have been derived by leaching from volcanic...
Categories: Publication; Types: Citation; Tags: Economic Geology
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Lead from galena of massive sulphide deposits in the metavolcanic belt of northern Wisconsin was probably derived from 3700 m.y. old source material 1800-1900 m.y. ago. Approximately 3500 m.y. old rocks occur within 100-300 km to the north and west. The U-Th-Pb systems of the metavolcanic and granitic rocks in the belt were reset about 1600 m.y. ago during retrogressive metamorphism. The ages from lead isotope data are in accord with Rb/Sr whole-rock, Rb/Sr and K/Ar mineral, and U-Th-Pb zircon dating. A concordia plot of whole-rock lead data shows that many of the rocks lost lead 200-400 m.y. ago during uplift and erosion. Meta-volcanic rocks near Crandon, Wisconsin, had lead isotope compositions 20 m.y. ago that...
Categories: Publication; Types: Citation; Tags: Economic Geology