Bonanza-grade accumulations of gold tellurides in the Early Cretaceous Sandaowanzi deposit,northeast China |
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| Affiliation: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. Centre for Tectonics, Resources and Exploration (TRaX), School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia;3. Geological Survey of Heilongjiang Province, Harbin 150036, China;1. College of Earth Sciences, Jilin University, Changchun, China;2. Far East Geological Institute, Far Eastern Branch of Russian Academy of Sciences, Vladivostok, Russia;3. School of Engineering, Far Eastern Federal University, Vladivostok, Russia;4. Changchun Gold Research Institute, China;5. Shanghai Municipal Engineering Design Institute (Group) Co., Ltd., China;1. Institute of Mineralogy, Ural Branch, Russian Academy of Sciences, Miass, Chelyabinsk District 456317, Russia;2. Department of Geology, South Urals State University, 8 Oktyabrya str. 16, Miass 456301, Russia;3. ARC Centre of Excellence in Ore Deposits, University of Tasmania, Hobart, Australia;4. Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom;5. Institute of Oceanology, Russian Academy of Sciences, Nakhimosvsky av., 36, Moscow 117997, Russia;6. John de Laeter Centre, Department of Imaging and Applied Physics, Curtin University, GPO Box U 1987, Perth 6845, Western Australia, Australia |
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| Abstract: | The Sandaowanzi epithermal gold deposit (0.5 Moz or ca. 14 tons), located at the northern edge of the Great Xing'an range, NE China, is unique in that nearly all the gold (> 95%) is contained in gold tellurides mostly in bonanza grade ore shoots (the highest grade being up to 20,000 g/t). The bonanza ores are hosted in the central parts of large-scale (> 3 m wide, 200 m long) quartz veins which crosscut Early Cretaceous andesitic trachyte and trachytic andesite, and are, in turn, crosscut by diabase dykes of similar age. There are two ore types: low-grade disseminated ores and high-grade vein ores. In the former, very fine grains of Ag-rich tellurides (mainly hessite and petzite) coexist with sulfides (pyrite, sphalerite, galena and chalcopyrite), occurring as disseminated grains or sometimes as grain aggregates. In the high-grade vein ores, coarse-grained Au–(Ag)–tellurides (calaverite, sylvanite, krennerite, and petzite) form a major part of quartz–telluride veins. Chalcopyrite forms separate monomineralic veins emplaced within the quartz–telluride veins. Spectacular textures among coarse-grained (up to 3 cm in diameter) tellurides, and micron-scale bamboo shoot-like grains are observed. Two- and three-phase telluride symplectites are common in the vein ores.Fluid inclusion studies suggest that the mineralizing fluids are a mixture of magmatic and meteoric fluids, that homogenized in the temperature range of 260–280 °C. Sulfur isotope compositions of pyrite and chalcopyrite (δ34S − 1.64 to 1.91‰) support the origin of fluids from a deep source. It is suggested that faulting, temperature changes and variation in fS2 and fTe2 were major factors contributing to the two main types of mineralization and the differences between them. Early rapid cooling and subsequent slow cooling of the later fluids along fault and fracture zones were instrumental in formation of the two superposed ore types. Open-space filling and crack-sealing along fractures predominates over replacement during telluride mineralization. The Sandaowanzi deposit is a unique bonanza-grade accumulation of gold tellurides genetically related to subalkaline magmatism, which was genetically associated with Early Cretaceous regional extension. |
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