Mechanical transport of metallogenic materials in endogenic hydrothermal solutions: evidence from the microspherules in micro-disseminated gold deposits,northwestern Sichuan,China |
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| Institution: | 1. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China;2. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510275, China;3. School of Earth Science and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China;4. South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510006, China;1. Montanuniversität Leoben, Department of Applied Geosciences and Geophysics, Chair of Resource Mineralogy, Peter Tunner Straße 5, 8700 Leoben, Austria;2. Johann Wolfgang von Goethe University Frankfurt, Institute of Geosciences, Mineralogy, Altenhöferallee 1, 60438 Frankfurt, Germany;1. Geology Department, University of Otago, PO Box 56, Dunedin 9054, New Zealand;2. OceanaGold Ltd, 22 McLaggan St, Dunedin 9016, New Zealand;1. Key Laboratory of Orogen and Crust Evolution, Peking University, Beijing 100871, China;2. Twelfth Gold Team of Chinese People''s Armed Police, Chengdu 611732, China;3. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;4. School of Earth Sciences and Resources, China University of Geoscience (Beijing), Xueyuan Road, Beijing 100083, China |
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| Abstract: | Numerous steel-gray microspherules were recently unexpectedly discovered in ore and rock samples from several disseminated gold deposits hosted in Middle–Upper Triassic turbidites in northwestern Sichuan Province, China. Both nature surfaces and part sections of 227 microspherules have been observed by reflected light microscope, scanning electron microscope (SEM), electron microprobe analyses, X-ray energy spectra, X-ray powder patterns, the results reveal them to be cosmic dust. It is the first discovery of cosmic dust in this kind of deposits in China.The size of the microspherules ranges from 25 to 185 μm and generally is less than 100 μm. According to their composition, they belong to chromium-rich iron cosmic dust. The microspherules have complex, diverse and diagnostic microscope structures and textures, and such as very distinct airprint structure that are compatible with extraterrestrial material. Variation of geochemical content of the microspherules in the gold deposits in generally positively correlates with both the Ir content of the enclosing strata and the intensity of mineralization and hydrothermal alteration. The abnormally high content of Ir is important evidence for an extraterrestrial source for the microspherules. The fact that a geological body with strong alteration and mineralization is rich in microspherules may raise a new concept: Under endogenic conditions, it is not only possible but also realistic for mineralized material to be transported mechanically, in addition to the generally accepted chemical transport of ore constituents in hydrothermal solution because it is obviously impossible for cosmic spherules to fall directly from space into cemented hydrothermal ore veins more than 1 km deep in the earth. |
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