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Kiseleva G. D. Yazykova Yu. I. Trubkin N. V. Kovalenker V. A. 《Doklady Earth Sciences》2021,500(1):728-733
Doklady Earth Sciences - Tungstenite of unusual shapes (spheroids, rings, threads, spirals, etc.) was found in scheelite of gold-bearing quartz–carbonate–pyrite–chalcopyrite... 相似文献
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I. S. Krassivskaya E. V. Sharkov N. S. Bortnikov A. V. Chistyakov N. V. Trubkin T. I. Golovanova 《Petrology》2010,18(3):263-277
Altered variolites described for the first time in the axial zone of the Mid-Atlantic Ridge are represented by rounded globules
of andesite (icelandite) composition with light trachyandesite rim embedded in a picrobasaltic matrix. The globules were transferred
with picrobasaltic melt and then floated to the surface of lava flow, while formation of leucocratic rims was presumably related
to thermodiffusion (Soret effect) in a cooling heterogeneous melt. This heterogeneous melt was formed by penetration of ascending
column of picrobasaltic magma in already existing small intracructsal magmatic chamber filled with residual icelanditetype
andesite melt and involvement of the latter into a general upward movement. The rapid ascent of the melts in the oceanic spreading
zones by means of turbulent flowing caused dispersion of the extragenous melt into small drops in a jet of picrobasaltic magma,
without their interaction. Variolites were formed during cooling of such heterogeneous lava flow. No signs of liquid immiscibility
were found in the studied variolites. 相似文献
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E. V. Sharkov K. N. Shatagin I. S. Krassivskaya I. V. Chernyshev N. S. Bortnikov A. V. Chistyakov N. V. Trubkin A. Yu. Kramchaninov 《Petrology》2008,16(4):335-352
Based on detailed petrological, geochemical, and isotope-geochemical study, fragments of fresh pillow lavas with chilled glass margins dredged at the Sierra-Leone test site in the axial MAR rift zone between 5° and 7°N correspond to MORB tholeiites, which are not primitive mantle melts but were differentiated in intermediate magmatic (intrusive) chambers. Small-scale geochemical and Sr-Nd isotope heterogeneities were established for the first time in the basalts and their glasses. It was shown that some samples show significant nonsystematic differences in the 87Sr/86Sr ratio between the basalts and their chilled glasses and less significant difference in ?Nd; higher Sr ratios can be observed both in the glasses and basalts of the same lava fragments. No significant correlation is observed between the isotope characteristics of the samples and their geochemistry; it was also shown that seawater did not affect the Sr and Nd isotope composition of the chilled glasses of the studied pillow lavas. It is suggested that such differences in isotope ratios are related to a small-scale heterogeneity of the melts owing to incomplete homogenization during their rapid ascent to the surface. The heterogeneity of the basaltic melts is explained by their partial contamination by the older plutonic rocks (especially gabbroids) of the lower oceanic crust, through which they ascended to the ocean floor surface. The wider scatter of the Sr isotopic ratios relative to Nd is related to the presence of xenocrysts of calcic plagioclase; correspondingly, the absence of a Nd mineral carrier in the rocks results in less distinct Nd isotope variations. It was shown that all of the studied basalts define a single trend along the mantle correlation array in the Sr-Nd isotope diagram. The causes of this phenomenon remain unclear. 相似文献
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Marina A. Yudovskaya Vadim V. Distler Ilya V. Chaplygin Andrew V. Mokhov Nikolai V. Trubkin Sonya A. Gorbacheva 《Mineralium Deposita》2006,40(8):828-848
The distribution of gold in high-temperature fumarole gases of the Kudryavy volcano (Kurile Islands) was measured for gas, gas condensate, natural fumarolic sublimates, and precipitates in silica tubes from vents with outlet temperatures ranging from 380 to 870°C. Gold abundance in condensates ranges from 0.3 to 2.4 ppb, which is significantly lower than the abundances of transition metals. Gold contents in zoned precipitates from silica tubes increase gradually with a decrease in temperature to a maximum of 8 ppm in the oxychloride zone at a temperature of approximately 300°C. Total Au content in moderate-temperature sulfide and oxychloride zones is mainly a result of Au inclusions in the abundant Fe–Cu and Zn sulfide minerals as determined by instrumental neutron activation analysis. Most Au occurs as a Cu–Au–Ag triple alloy. Single grains of native gold and binary Au–Ag alloys were also identified among sublimates, but aggregates and crystals of Cu–Au–Ag alloy were found in all fumarolic fields, both in silica tube precipitates and in natural fumarolic crusts. Although the Au triple alloy is homogeneous on the scale of microns and has a composition close to (Cu,Ni,Zn)3(Au,Ag)2, transmission electron microscopy (TEM) shows that these alloy solid solutions consist of monocrystal domains of Au–Ag, Au–Cu, and possibly Cu2O. Gold occurs in oxide assemblages due to the decomposition of its halogenide complexes under high-temperature conditions (650–870°C). In lower temperature zones (<650°C), Au behavior is related to sulfur compounds whose evolution is strongly controlled by redox state. Other minerals that formed from gas transport and precipitation at Kudryavy volcano include garnet, aegirine, diopside, magnetite, anhydrite, molybdenite, multivalent molybdenum oxides (molybdite, tugarinovite, and ilsemannite), powellite, scheelite, wolframite, Na–K chlorides, pyrrhotite, wurtzite, greenockite, pyrite, galena, cubanite, rare native metals (including Fe, Cr, Mo, Sn, Ag, and Al), Cu–Zn–Fe–In sulfides, In-bearing Pb–Bi sulfosalts, cannizzarite, rheniite, cadmoindite, and kudriavite. Although most of these minerals are fine-grained, they are strongly idiomorphic with textures such as gas channels and lamellar, banded, skeletal, and dendrite-like crystals, characteristic of precipitation from a gas phase. The identified textures and mineral assemblages at Kudryavy volcano can be used to interpret geochemical origins of both ancient and modern ore deposits, particularly gold-rich porphyry and related epithermal systems. 相似文献
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A. V. Volkov N. V. Cherepanova V. Yu. Prokof’ev N. E. Savva S. V. Smil’gin N. V. Trubkin V. Yu. Alekseev 《Geology of Ore Deposits》2013,55(3):185-206
The Butarny gold deposit is situated in the central part of the Khurchan-Orotukan Zone of tectonomagmatic activation, which is traced for 150 km in the near-meridional direction, and localized in the slightly eroded Late Jurassic granitoid stock of the same name. The explored orebodies are quartz veins and pinnate veinlets with low-grade pocket-disseminated sulfide (mainly arsenopyrite) mineralization containing native gold. The Bi-bearing gold-pyrite-arsenopyrite and the quartz-löllingite-arsenopyrite-stibnitejamesonite stages of the veined low-sulfide ore formation have been distinguished. The main mineral assemblage consists of arsenopyrite, native gold, and native bismuth. The minerals-carriers of gold were deposited during the final stage of ore-bearing quartz crystallization at 334?245°C from low-concentrated pneumatolytic-hydrothermal carbonated fluid containing CO2 and CH4 (5.8?2.2 and 1.6?0.5 mol/kg of solution, respectively). The ore-bearing fluid had variable salinity (5.3?2.2 wt % NaCl equiv). It is quite probable that the gas-saturated fluid participated in transport and precipitation of ore matter. Its density varies from 1.02 to 0.77 g/cm3. The pressure is estimated at 1600 to 780 bar. The fluid regime of ore formation at the Butarny deposit is similar to that of typical intrusion-related gold deposits. The Au tenor of beresitized granodiorite, numerous quartz veinlets, and extensive Au-bearing weathering mantle allow us to suggest stockwork mineralization. 相似文献
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The paper considers the localization of potassic and propylitic hydrothermal alteration zones in the domal volcanic-plutonic structure controlling the position of the Dukat ore field with the eponymous unique epithermal Au-Ag deposit. Comprehensive mineralogical and geochemical data on rocks and minerals in hydrothermal alteration zones and associated intrusions have shown that quartz-jarosite-sericite, quartz-pyrite-sericite, and quartz-adularia-chlorite alterations were formed with the participation of fluid flows related to a fingerlike projection of a high-K leucogranite porphyry intrusion with large phenocrysts. These hydrothermal alterations developed in the rifted graben under conditions of divergent plate boundaries, whereas quartz-clinozoisite-calcite, epidote-chlorite, and garnet-calcite-chlorite alterations were linked to K-Na leucogranite intrusive bodies and developed under conditions of convergent plate boundaries reactivated as a result of formation of the marginal Okhotsk-Chukotka volcanic belt. Phase separation and coagulation of specific portions of ascending fluids resulted in the formation and stabilization of small-sized particles of native silver and other ore components, which enabled involvement in flows of secondary geothermal solutions and ore-forming fluids. The Sr, Nd, and Pb isotopic compositions of rocks and minerals from the hydrothermal alteration zones, associated intrusions, and economic orebodies at the Dukat deposit indicate that their components have been derived from the juvenile continental crust, which was altered in pre-Cretaceous periods of endogenic activity. The components of gangue minerals of potassic and propylitic hydrothertmal alterations and associated intrusions have been taken from deep sources differing in 87Sr/86Sr and 143Nd/144Nd at similar U/Pb and Th/Pb ratios. Chalcophile lead in products of hydrothermal activity and melanocratic inclusions in leucogranite has been taken from regions with elevated U/Pb and Th/Pb ratios. 相似文献
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V. A. Kovalenker N. V. Trubkin V. D. Abramova O. Yu. Plotinskaya G. D. Kiseleva S. E. Borisovskii Yu. I. Yazykova 《Geology of Ore Deposits》2018,60(1):62-81
The paper presents pioneering data on the composition, texture, and crystal structure of molybdenite from various types of molybdenum mineralization at the Bystrinsky Cu–Au–Fe porphyry–skarn deposit in the eastern Transbaikal region, Russia. The data were obtained using electron microprobe analysis (EMPA), laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS), and high-resolution transmission electron microscopy (HRTEM). Molybdenite found at the deposit in skarn, sulfide-poor quartz veins, and quartz–feldspar alteration markedly differs in the concentrations of trace elements determined by their species in the mineral, as well as in its structural features. Molybdenite-2H from skarn associated with phyllosilicates occurs as ultrafine crystals with uniform shape and texture; no dislocations or inclusions were found but amorphous silica was. The molybdenite composition is highly contrasting in the content and distribution of both structure-related (Re, W, and Se) and other (Mn, Co, Ni, Cu, Zn, As, Ag, Cd, Sb, Te, Ag, Pd, Au, Hg, Pb, and Bi) metals. In the sulfide-poor quartz veins, highly structurally heterogeneous (2H + 3R) molybdenite microcrystals with abundant defects (dislocations and volumetrically distributed inclusions) are associated with illite, goethite, and barite. Some single crystals are unique three-phase (2H + 3R polytypes + amorphous MoS2). The mineral has a low concentration of all trace elements, which are uniformly distributed. However, individual domains with uniquely high Pd, Te, Ni, Hg, and W concentrations caused by mineral inclusions are found in some grains. Molybdenite from quartz–feldspar alteration is characterized by low concentrations of all trace elements except for Re and Se, which enrich some domains of the grains. Our data indicate that the compositional and structural heterogeneity of molybdenite from the Bystrinsky deposit are its crucial features, which obviously correlate with the types of Mo mineralization. 相似文献
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Data on the morphology and crystal structure of micro- and nanoparticles of zincite and native zinc that occur among the newly formed minerals of metasomatic rocks in the Dukat ore field are presented. The origin of minute particles in the discharge areas of hydrothermal fluids is caused by the specific dynamics of the heterogeneous mineral-forming environment, resulting in the formation of ultralocal zinc concentrations. In propylite and greisen, the minute particles, which are products of the earliest stages of ore deposition, arise at the front of growing Fe-chlorite and apophyllite crystals. Aggregation of zincite nanoparticles with formation of metalliferous inclusions and fibrous native zinc proceeds in the greisen zones during aggradation recrystallization of a finely dispersed mineral system under the effect of additional portions of reduced fluids. In the zone of argillic alteration, dendritic zincite crystals result from crystallization of gels formed during coagulation of colloid solutions. 相似文献