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listelement.badge.dso-typeЭлемент, Chemical Compositions of Fluid Inclusions in Intrusion-Related Gold Systems, Alaska and Yukon, Using PIXE Microanalysis(2006) Baker T.; Ebert S.; Rombach C.; Ryan C.G.Proton-induced X-ray emission (PIXE) has been used to characterize the multielement chemistry of the diverse fluid inclusions found in intrusion-related gold systems in the Tintina gold province, Yukon and Alaska. The studied samples are from shallow-level examples that contain coexisting brine (type 3) and carbon dioxide-bearing vapor (type 4) inclusions (e.g., Shotgun, Donlin Creek Dome area, Mike Lake, and Brewery Creek) and deeper level deposits (e.g., Pogo, Dublin Gulch, and Emerald Lake) that contain low-salinity carbon dioxide- (type 1) and/or methane-rich (type 5) inclusions, which locally are overprinted by late secondary type 3 inclusions (e.g., Pogo and Emerald Lake). Major element ratios, K/Ca and Mn/Fe, of both synore high-salinity (type 3) and low-salinity (types 1, 4, and 5) inclusions are >1 and 0.24), and at Pogo low K/Ca ratios (<0.2). Chlorine and bromine data have been used to trace the source of salinity. Two distinct groups of Br/Cl mol ratio are recognized. Group 1 includes type 3 inclusions from the Pogo region, Mike Lake, Brewery Creek, and Emerald Lake, which have Br/Cl mol ratios consistent with typical magmatic values, mostly above 0.5 x 10–3 and below 1.54 x 10–3 (seawater). Group 2 comprises type 3 inclusions from Donlin Creek and Shotgun in southwestern Alaska, which have Br/Cl mol ratios from 2.34 x 10–3 to 6.37 x 10–3, potentially reflecting a halogen contribution from the local sedimentary crust (the Kuskokwim basin) considered to be the primary source of the granite melts. The data also provide insights into important metal contents of the fluid inclusions, including copper, zinc, lead, tungsten, and arsenic; however, gold, bismuth and antimony were all below the detection limits for these elements by the PIXE technique.listelement.badge.dso-typeЭлемент, REE in fluid inclusions of quartz from gold deposits of north-eastern Russia(2012) Vikent’eva O.V.; Gamyanin G.N.; Bortnikov N.S.Inductively coupled plasma-mass spectrometry (ICP-MS) has been used to determine rare earth element concentrations in aqueous solutions extracted from fluid inclusions. Quartz has been sampled from ores of three major types of polygenic gold hydrothermal systems of North-Eastern Russia: (1) gold-quartz-sulphide (Au-Q, Nezhdaninsk); (2) gold-antimony (Au-Sb, Sarylakh) and (3) intrusion-related gold-bismuth-siderite-polysulphide (Au-Bi-Sid, Arkachan) large deposits located in terrigenous rocks of the Verkhoyansk fold belt. The total concentration of REE in the fluid inclusions is not high (up to 52 ppm). The contribution of LREE dominates in REE balance (ΣLREE/ΣHREE=7.4–112.1). The chondrite-normalized REE patterns of inclusion fluids for the Au-Q and Au-Bi-Sid deposits are characterized by LREE enrichment with a positive or negative Eu anomaly. REE patterns for the regenerated quartz from Au-Sb deposits are characterized by pronounced differentiation between light and heavy lanthanides in fluid inclusions. Significant total REE concentration decreasing (on 1–2 order) from early to late stages of Nezhdaninsk and Arkachan deposits is revealed. The positive correlations of total REE concentrations with Rb, Cs, Li and B contents in fluid inclusions are shown. The REE distribution in fluid inclusions can be used as indicators of the contribution of magmatic fluid in the hydrothermal system.listelement.badge.dso-typeЭлемент, RB-SR-ИЗОТОПНАЯ СИСТЕМАТИКА ГИДРОТЕРМАЛЬНЫХ МИНЕРАЛОВ, ВОЗРАСТ И ИСТОЧНИКИ ВЕЩЕСТВА ЗОЛОТОРУДНОГО МЕСТОРОЖДЕНИЯ НЕЖДАНИНСКОЕ (ЯКУТИЯ)(2010) Чугаев А.В.; Чернышев И.В.; Гамянин Г.Н.; Бортников Н.С.; Баранова А.Н.Проблема связи орогенных (мезотермальных) золоторудных месторождений с магматическими и метаморфическими процессами наиболее дискуссионна. Типичным и крупным объектом указанного типа является месторождение Нежданинское, поэтому возраст гидротермальной минерализации и источники металлов относятся к числу ключевых вопросов в изучении конкретно этого месторождения и в разработке указанной выше проблемы в целом. Наиболее актуальной сейчас является задача прямого датирования гидротермальных образований месторождения Нежданинское. Такие изотопно-геохронологические данные отсутствуют, что оставляет открытым вопрос о временно&й корреляции рудообразующих и магматических процессов, проявленных на этом месторождении.listelement.badge.dso-typeЭлемент, Mineralogy, Geochemistry, and Origin of the Nezhdaninsk Gold Deposit (Sakha-Yakutia, Russia)(1998) Bortnikov N.S.; Gamyanin G.N.; Alpatov V.A.; Naumov V.B.; Nosik L.P.; Mironova O.F.The Nezhdaninsk gold deposit is located at a junction of four regional faults in the South Verkhoyansk synclinorium. The ore bodies are the mineralized cataclitic zones and the veins. They are hosted by meta-morphosed terrigenous sandstone-slate sequences intruded by stocks and dikes of silicic and intermediate rocks. The age of the magmatic rocks was found to vary from 154 to 94 Ma. The deposit was formed during three stages. Gold-bearing ore bodies were formed during the second stage. A regeneration of quartz and sulfides, and a crystallization of silver-bearing mineral assemblages occurred during the third stage. The gold deposition began at the metasomatic alteration of the host rocks. The altered rocks consist of quartz, sericite, carbonates, and disseminated pyrite and arsenopyrite. These sulfides contain "invisible" chemically bound gold. Native gold crystallized in quartz veins. The native gold is associated with coarse-grained arsenopyrite and pyrite, and is coeval with sphalerite-galena-sulfosalt aggregates. The fluid inclusion study showed that the ore formation occurred from two immiscible fluids. One of them was a H 2O + CO 2-dominated fluid with N 2, CH 4, and soluble chlorides (up to 4.5 wt % equiv NaCl). The second fluid was a vapor phase consisting mainly of CO 2 and CH 4. The stable isotope (S, C, and O) study in the minerals suggests that sulfur, water, and CO 2 of magmatic origin prevailed in fluids. They were mixed with components incorporated from the host rocks. The magmatic and host rocks interacted with the isotopically light and possibly meteoric waters. The mineral crystallization occurred at temperatures of 360 to 175°C, and under pressures of 1.2 to 1.7 kbar from mineral-forming fluids with a pH equal to 5.5-6.1. The CO 2 mole fraction of the fluids was from 0.25 to 0.3. The formation of the economic gold ores was linked with the postaccretion tectono-magmatic activation of the South Verkhoyansk synclinorium in the Early to Late Cretaceous.listelement.badge.dso-typeЭлемент, GARNET-BEARING XENOLITHS FROM SALT LAKE CRATER, OAHU, HAWAII: HIGH-PRESSURE FRACTIONAL CRYSTALLIZATION IN THE OCEANIC MANTLE(2007) Keshav S.; Sen G.; Presnall D.C.The focus of this study is a suite of garnet-bearing mantle xenoliths from Oahu, Hawaii. Clinopyroxene, olivine, and garnet constitute the bulk of the xenoliths, and orthopyroxene is present in small amounts. Clinopyroxene has exsolved orthopyroxene, spinel, and garnet. Many xenoliths also contain spinel-cored garnets. Olivine, clinopyroxene, and garnet are in major element chemical equilibrium with each other; large, discrete orthopyroxene does not appear to be in major-element chemical equilibrium with the other minerals. Multiple compositions of orthopyroxene occur in individual xenoliths. The new data do not support the existing hypothesis that all the xenoliths formed at 1.6–2.2 GPa, and that the spinel-cored garnets formed as a consequence of almost isobaric subsolidus cooling of a spinel-bearing assemblage. The lack of olivine or pyroxenes in the spinel–garnet reaction zones and the embayed outline of spinel grains inside garnet suggest that the spinel-cored garnets grew in the presence of a melt. The origin of these xenoliths is interpreted on the basis of liquidus phase relations in the tholeiitic and slightly silica-poor portion of the CaO–MgO–Al 2 O 3 –SiO 2 (CMAS) system at pressures from 3.0 to 5.0 GPa. The phase relations suggest crystallization from slightly silica-poor melts (or transitional basaltic melts) in the depth range ∼110–150 km beneath Oahu. This depth estimate puts the formation of these xenoliths in the asthenosphere. On the basis of this study it is proposed that the pyroxenite xenoliths are high-pressure cumulates related to polybaric magma fractionation in the asthenosphere, thus making Oahu the only locality among the oceanic regions where such deep magmatic fractional crystallization processes have been recognized.