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81.
This paper analyzes literature data on physicochemical parameters and chemical composition of fluids of Precambrian endogenous gold deposits. The average values and ranges of temperature, pressure, and salinity of fluids from the Archean and Proterozoic gold deposits are estimated. It is revealed that fluids of Archean deposits are dominated by methane, while those of Proterozoic deposits, by nitrogen. It is proposed that the accumulation of nitrogen in the atmosphere is related to the intense nitrogen degassing from the Earth’s interior. The highest pressures of endogenous fluids in this period could reflect specifics of deep geodynamics of the planet in the Proterozoic. The large gold deposits (>100 tons) are characterized by narrower range of physicochemical parameters as compared to small deposits. The contribution of heated chloride brines in the formation of majority of large Proterozoic deposits is established. 相似文献
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M. L. Tolstykh V. B. Naumov M. G. Gavrilenko A. Yu. Ozerov N. N. Kononkova 《Geochemistry International》2012,50(6):522-550
Melt inclusions in olivine and plagioclase phenocrysts from rocks (magnesian basalt, basaltic andesite, andesite, ignimbrite,
and dacite) of various age from the Gorely volcanic center, southern Kamchatka, were studying by means of their homogenization
and by analyzing the glasses in 100 melt inclusions on an electron microprobe and 24 inclusions on an ion probe. The SiO2 concentrations of the melts vary within a broad range of 45–74 wt %, as also are the concentrations of other major components.
According to their SiO2, Na2O, K2O, TiO2, and P2O5 concentrations, the melts are classified into seven groups. The mafic melts (45–53 wt % SiO2) comprise the following varieties: potassic (on average 4.2 wt % K2O, 1.7 wt % Na2O, 1.0 wt % TiO2, and 0.20 wt % P2O5), sodic (3.2% Na2O, 1.1% K2O, 1.1% TiO2, and 0.40% P2O5), and titaniferous with high P2O5 concentrations (2.2% TiO2, 1.1% P2O5, 3.8% Na2O, and 3.0% K2O). The melts of intermediate composition (53–64% SiO2) also include potassic (5.6% K2O, 3.4% Na2O, 1.0% TiO2, and 0.4% P2O5) and sodic (4.3% Na2O, 2.8% K2O, 1.3% TiO2, and 0.4% P2O5) varieties. The acid melts (64–74% SiO2) are either potassic (4.5% K2O, 3.6% Na2O, 0.7% TiO2, and 0.15% P2O5) or sodic (4.5% Na2O, 3.1% K2O, 0.7% TiO2, and 0.13% P2O5). A distinctive feature of the Gorely volcanic center is the pervasive occurrence of K-rich compositions throughout the whole
compositional range (silicity) of the melts. Melt inclusions of various types were sometimes found not only in a single sample
but also in the same phenocrysts. The sodic and potassic types of the melts contain different Cl and F concentrations: the
sodic melts are richer in Cl, whereas the potassic melts are enriched in F. We are the first to discover potassic melts with
very high F concentrations (up to 2.7 wt %, 1.19 wt % on average, 17 analyses) in the Kuriles and Kamchatka. The average F
concentration in the sodic melts is 0.16 wt % (37 analyses). The melts are distinguished for their richness in various groups
of trace elements: LILE, REE (particularly HREE), and HFSE (except Nb). All of the melts share certain geochemical features.
The concentrations of elements systematically increase from the mafic to acid melts (except only for the Sr and Eu concentrations,
because of active plagioclase fractionation, and Ti, an element contained in ore minerals). The paper presents a review of
literature data on volcanic rocks in the Kurile-Kamchatka area in which melt inclusions with high K2O concentrations (K2O/Na2O > 1) were found. K-rich melts are proved to be extremely widespread in the area and were found on such volcanoes as Avachinskii,
Bezymyannyi, Bol’shoi Semyachek, Dikii Greben’, Karymskii, Kekuknaiskii, Kudryavyi, and Shiveluch and in the Valaginskii and
Tumrok Ranges. 相似文献
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V. B. Naumov V. A. Dorofeeva A. V. Girnis V. V. Yarmolyuk 《Geochemistry International》2014,52(5):347-364
Using our database on major, trace, and volatile element contents in melt inclusions in minerals and quenched glasses of volcanic rocks reported in the literature, we compared the mean contents of 71 chemical elements in melts from the mid-ocean ridges (MORB) of the Atlantic, Pacific, and Indian oceans and determined the mean MORB composition for all the oceans of the Earth (global MORB composition). Mean ratios of incompatible trace and volatile components (H2O/Ce, K2O/Cl, Nb/U, Ba/Rb, Ce/Pb, Nb/U, etc.) were calculated for magmatic melts from all the oceans. Variations of these parameters were estimated, and significant differences between the melts of the Atlantic and Pacific oceans were established. 相似文献
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V. I. Vasil’ev N. V. Pervukhina S. V. Borisov S. A. Magarill D. Yu. Naumov N. V. Kurat’eva 《Geology of Ore Deposits》2010,52(7):656-661
The composition and structure of aktashite from the Aktash deposit, Gorny Altai, Russia, have been studied by electron microprobe and X-ray structural analysis. On the basis of close compositions and crystal structures, the identity of aktashite from the Gal-Khaya and Aktash deposits has been demonstrated. Crystals of aktashite are of trigonal symmetry; the unit-cell dimensions are: a = 13.7500(4), c = 9.3600(3) Å, V = 532.54(8) Å3, space group R3, Z = 3 for the composition of Cu6Hg3As4S12, R = 0.043. The structure of aktashite as a framework of vertex-shared HgS4? and CuS4? tetrahedrons of the same orientation is intimately related to the sphalerite-type structure. The earlier identified uncommon cluster group [As4] has been verified and its parameters have been refined. It is shown that the structure may be represented as construction blocks (As4S12)12? packed according to the law of the distorted cubic I-cell. 相似文献