Ali A.A.,Moscow State University |
Prokofief V.Y.,RAS Institute of Geology and Mineralogy |
Kryazhev S.G.,Central Research Institute of Geological Exploration for Base and Precious Metals
Moscow University Geology Bulletin | Year: 2014
The fluid inclusions in minerals and isotope composition of sulfur in sulfides and carbon and oxygen in carbonates are studied for the Novoshirokinskii gold-polymetallic deposit. The ore-forming fluids are characterized by the following physico-chemical and isotope-geochemical parameters: temperature of 290-100°C, salinity of 13-2.5 wt % NaCl-equiv., δ18O from +8 to 0‰, δ13C of 2.5 ± 0.5‰, and δ34S of 10.5 ± 1.0‰. It is concluded that the Late Proterozoic-Early Cambrian carbonaceous-terrigenous and carbonate rocks were involved in the Late Jurassic ore-magmatic system. © 2014 Allerton Press, Inc.
Diamonds from the Poiskovaya, Zapolyarnaya, and Leningrad kimberlite pipes, Northern Yakutia: Correlation of carbon isotopic composition and nitrogen content as an indicator of fluid diamond formation
Ukhanov A.V.,RAS Vernadsky Institute of Geochemistry and Analytical Chemistry |
Khachatryan G.K.,Central Research Institute of Geological Exploration for Base and Precious Metals
Geology of Ore Deposits | Year: 2011
Compared to most studied kimberlite pipes of the Yakutian province, diamonds from the Poiskovaya, Zapolyarnaya, and Leningrad pipes (about 100 determinations) are characterized by a decrease in the average δ 13C (-4. 59, -4. 50,-4. 04%) and by relatively low average nitrogen contents (93, 254, 304 ppm, respectively). These pipes also differ in the relative abundance of alpha-1 group crystals in Galimov's classification. Based on a stable combination of morphology and properties, we distinguished diamond populations of the common origin. All of them have significant a negative correlation between δ 13C and the nitrogen content. This correlation is considered to be a result of synchronous and progressive loss of nitrogen and the light isotope 12C in the medium during the diamond formation. The conclusion is drawn that the alpha-1 crystals were formed in the open fluid system. The pyrolysis of ethane-C 2H 6 → CH 4 + H 2 + C diam-is assumed to be a model of diamond precipitation from fluid. The pressure release due to extension deformation of the mantle under tectonic action might be a factor shifting this reaction toward diamond formation. © 2011 Pleiades Publishing, Ltd.
Prokof'ev V.Y.,RAS Institute of Geology and Mineralogy |
Bortnikov N.S.,RAS Institute of Geology and Mineralogy |
Kovalenker V.A.,RAS Institute of Geology and Mineralogy |
Vinokurov S.F.,RAS Institute of Geology and Mineralogy |
And 5 more authors.
Geology of Ore Deposits | Year: 2010
The chemistry, REE patterns, and carbon and oxygen isotopic compositions of carbonates from ore veins of the Darasun deposit are discussed. In addition to the earlier described siderite, calcite, and carbonates of the dolomite-ankerite series, kutnahorite is identified. The total REE content in Fe-Mg carbonates of the dolomite-ankerite series (2.8-73 ppm) is much lower than in later calcite (18-390 ppm). δ 13C of Fe-Mg carbonates and calcite varies from +1.1 to -6.7‰ and from -0.9 to -4.9‰, respectively. δ 18O of Fe-Mg carbonates and calcite varies from +17.6 to 3.6‰ and from +15.7 to -0.5‰, respectively. The REE sum and carbon and oxygen isotopic compositions reveal zonal distribution relative to the central granodiorite porphyry stock. The correlation between the carbon and oxygen isotopic compositions and REE sum reflects variations in the physicochemical formation conditions and composition of ore-forming fluid. The isotopic composition of fluid is calculated, and possible sources of its components are considered. Earlier established evidence for a magmatic source of ore-forming fluid and participation of meteoric water in ore formation is confirmed. Geochemical evidence for interaction of ore-forming fluid with host rocks is furnished. The relationships between the REE sum, on the one hand, and carbon and oxygen isotopic compositions of hydrothermal ore-forming fluid, on the other, are established. © Pleiades Publishing, Ltd., 2010.
Obushkov A.V.,Central Research Institute of Geological Exploration for Base and Precious Metals |
Struzhkov S.F.,Central Research Institute of Geological Exploration for Base and Precious Metals |
Natalenko M.V.,Central Research Institute of Geological Exploration for Base and Precious Metals |
Ryzhov O.B.,Central Research Institute of Geological Exploration for Base and Precious Metals |
And 2 more authors.
Geology of Ore Deposits | Year: 2010
The Engteri is a new hidden Au-Ag deposit in the Russian segment of the Pacific ore belt. The discovery of this deposit merits special attention, because it involves repeated attempts to reappraise a lowprospective ore occurrence, which were crowned with success as a result of fulfillment of large-scale drilling project. The average Au grade is 18.6 gpt. The deposit is classified as the gold geochemical type of Au-Ag deposits. The major ore mineral is pyrite, which amounts to no less than 95% of the total ore minerals. The native phases comprise electrum and to a lesser extent native gold of low fineness (730). The homogenization temperature of fluid inclusions is 125-255°C with a distinct maximum at 145-150°C. Despite blind localization of some orebodies, the Engteri deposits bears evidence for a deep erosion level: (1) small vertical range of economic mineralization (50-100 m); (2) predominant occurrence of massive sugarlike quartz with a low sulfide content; (3) prevalence of massive and brecciated textures above rhythmically banded textures; and (4) lack of low-temperature propylites. The southern part of the ore field distinguished by occurrence of rhythmically banded, framework-tabular, and brecciated texture has the best prospect for revealing new orebodies. The Engteri deposit allowed us to outline the following prospecting guides and methods of prospecting for hidden Au-Ag deposits: (1) these deposits are regularly arranged in ore clusters between heavy concentrate anomalies of cinnabar and gold-silver or silver-base-metal occurrences (method of missed link); (2) findings of fragments of ore mineral assemblages with sporadically high Au and Ag contents in barren calcite-quartz veins (method of indicators); (3) linear zones of ankeritization in the fields of low- and mediumtemperature propylites (mapping of metasomatic rocks); and (4) pyrite-quartz veinlets with rhythmically banded pockets (mineralogical mapping of halos of stringer-disseminated mineralization). © 2010 Pleiades Publishing, Ltd.