| 大宝山铁-多金属矿床的海相火山热液沉积成因特征 |
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| 引用本文：.1986.Submarine Volcanic Hydrothermal Sedimentary Origin Of The Dabaoshan Iron And Polymetallic Sulfide Deposit[J].Mineral Deposits,5(1):1~12 |
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| Submarine Volcanic Hydrothermal Sedimentary Origin Of The Dabaoshan Iron And Polymetallic Sulfide Deposit |
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| Abstract:The Dabaoshan deposit, a large-sized iron and polymetallic sulfide deposit in China, is situated in the middle of the polymetaUic-sulfur metallogenic area of northern Guangdortg. It occurs in the Middle-Upper Devonian volcanic-sedimentary formation in which the orebody constitutes an inseparable part of the strata. Based on the systematic study of the formation, it can be further divided into five rock associations: (1) stratiform siderite-pyrite and intennediate-basic volcanic rocks; (2) altered tuff-shale-marble; (3) main ore belt consisting of polymetallic sulfides; (4) altered dacite; (5) bottom shale. The deposit consists of two parts, the upper part being limonite orebodies of weathering-leaching type and the lower part made up of primary Cu, Pb, and Zn sulfide orebodies. The primary orebodies, except for some veinlet-type orebodies in the altered dacite, have identical strikes and dips with their host rocks. The primary ores have typical striped structure and colloform and olitic textures, suggesting a syngenetic sedimentary origin. lt is particularly worth mentioning that fossils of microorganism have been found in pyrite of primary ores. A detailed study indicates that the taxitic ore, rather than being an original one, resulted from the late stage reformation of the primary ore. The deposit shows typical metallic zoning: along the strike of orebodies from north to south the Cu/(Cu+Zn+Pb) ratios vary from 0.95 to 0.21. Beneath the main orebody there exists an altered rock belt in which CaO and Na2O obviously decrease while K2O and MgO increase to some extent. From bottom to top the Co, Ni, Se concentrations and Co/Ni ratio of pyrite and pyrrhotite decrease whereas S/Se ratio increases This is quite like things for Kuroko ores. The formation temperature of the syngenetic massive ores is determined at about 1500. The temperatures obtained by geothermometry for the late reformed ores range 290-320℃, quite close to those of the altered rocks. The δ18O SMOW values of equilibrium water for syngenetic sedimentary ore average -2.25+0.99‰, which are rather similar to those for the Kuroko-type deposits, implying its volcanic-sedimentary origin. Theδ18O values of siderite in quartz-siderite ore average 18.47+0.43‰, andδ13C‰ PDB range from -2.55 to -5.80 when no influence of organism exists. Theδ13C values are similar to those of Red Sea hot brine (averaging -4.5‰). The Pb isotope ratios of the Dabaoshan ores are extremely stable: 206Pb/204Pb=18.6303+0.0314, 207Pb/204 Pb=15.6809+0.0250 and 208Pb/204Pb=38.8226+0.0809. |
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