| 阿尔金北缘大平沟金矿床成因 |
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| 引用本文：.2005.Origin of Dapinggou gold deposit in Northern Altun area, northwestern China[J].Mineral Deposits,24(2):168~178 |
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| 基金项目:中国地质调查局国土资源调查项目(K1.1.2.3) 和(200110000001_5)及国家305项目(96_915_06_01) |
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| 中文摘要:大平沟金矿是阿尔金北缘地区近年来新发现的一个中型金矿床。它受韧性剪切带构造的控制，矿化类型为蚀变糜棱岩型夹少量钾长石石英脉型。文章通过地质地球化学的研究，探讨了该矿床的成因。稀土元素、硫同位素、铅同位素和锶同位素地球化学特征反映成矿物质主要来源于变质岩；流体包裹体和氢氧同位素反映成矿流体主要来源于变质水，有少量重熔岩浆水和大气降水的混入，成矿温度198～290℃，成矿流体密度0.791～0.971 g/cm3；盐度w(NaCleq)=2.03%～5.5%，成矿压力(420～720)×105 Pa，成矿深度为1.61～2.68 km。石英流体包裹体Rb-Sr等时线年龄表明成矿时代为加里东期。大平沟金矿床属于中温动力变质热液成因矿床。 |
| 中文关键词:地质学 动力变质热液型 成因 加里东期 大平沟金矿床 阿尔金北缘地区 |
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| Origin of Dapinggou gold deposit in Northern Altun area, northwestern China |
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| Abstract:The Dapinggou ore deposit, the only medium_size gold deposit recently found in northern Altun Mountain, is situated in Ruoqiang County, 620 km south-east-south of Urumqi. It is tectonically located in the northeastern margin of Qinghai-Tibet plateau, and also at the compounding site of Altun strike-slip fault and western Qilianshan structural zone. Regionally it lies in the Archaeozoic uplifted area within the middle part of northern Altun structural zone. The gold deposit is controlled by a ductile shear zone and characterized by altered mylonite-type mineralization intercalated with minor K-feldspar quartz vein-type mineralization. There mainly crop out meso-hypo-metamorphic rocks of Late Archaeozoic Gelagebulake Group (Ar3dg), with small amounts of Caledonian moyite. In this paper, the origin and ore_forming epoch of the gold deposit is determined on the basis of geological and geochemical studies. Characteristics and main parameters of REE in the altered mylonite type ore and K-feldspar quartz vein-type ore are identical with those of metamorphic rocks (K-feldspar gneiss), suggesting the same source. The δ34S values (5.8‰～6.2‰) show an orthometamorphite-derived sulfur source. The average Pb isotopic contents of three samples from the Dapinggou gold deposit are 208Pb/204Pb=38.4371, 207Pb/204Pb=15.6819 and 206Pb/204Pb=18.7314, which implies that Pb of the ore came mostly from the orogenic belt, and was formed by the mixture of the crust-source lead and the mantle_source lead at a certain proportion. The initial strontium ratio 〔(87Sr/86Sr)0〕is 0.71006, also indicating that the ore-forming material might have been derived from the crust rocks. All the REE, sulfur, lead and strontium isotopic information shows that the source materials of the deposit were derived mainly from the metamorphic rocks (K-feldspar gneiss). On the other hand, the inclusion study and the average hydrogen-oxygen isotopic contents of three samples (δ18OH2O=2.7‰，δD=-58‰) indicate that ore fluids came mainly from the dynamic metamorphic water source with an insignificant influence of remelting magmatic water and meteoric water. The ore fluids are 0.791～0.971 g/cm3 in density and 2.03%～5.5% in salinity. The gold deposit was formed 1.61～2.68 km below the surface with temperature of 198～290℃ and pressure of (420～720)×105 Pa. Rb-Sr isochron age of the quartz fluid inclusion is 〔(487±21) Ma〕, indicating that mineralization occurred in Caledonian. It is therefore concluded that the Dapinggou gold deposit is a medium-temperature dynamic metamorphic hydrothermal type deposit. |
| keywords:geology, dynamic metamorphic hydrothermal type, origin, Caledonian, Dapinggou gold deposit, northern Altun Mountain |
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