| 西秦岭小沟里石英脉型金矿床成矿地质特征及成因 |
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| 引用本文：.2002.Geology and Genesis of Xigouli Quartz Vein Type Gold Deposit, West Qinling Mountain[J].Mineral Deposits,21(2):159~167 |
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| 基金项目:国家重点基础研究项目(编号：G1999043213)和国家科技攻关项目(编号：96_914_01_04) |
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| 中文摘要:本文通过石英脉Ar-Ar法和花岗岩单颗粒锆石U-Pb法定年、氢氧同位素测定、微量元素测定及含矿岩石中斑点构造显微镜研究，结合矿床地质特征和区域地质环境分析，探讨了花岗岩与金矿床的关系以及矿床成因。含金石英脉Ar_Ar坪年龄为197 Ma，等时线年龄为193 Ma。大山花岗岩U-Pb年龄为201 Ma。石英包裹体水的δ18O为8.15‰～12.82‰，δD为-58‰～-77‰，热液水来源以岩浆水为主。岩石中发育斑点构造，斑点为黄铁矿、绿泥石、石英、黑云母等热液交代蚀变矿物。矿区内脉岩发育，组成矿体的上下盘，花岗岩体和脉岩含金可达240×10-9。大山岩体中心相含金1.7×10-9，边缘相含金6.3×10-9，从岩体到矿区脉岩含金量增加。研究表明，大山花岗岩与矿床有密切的时间、空间及成因关系，并提供了热源、水源和部分成矿物质。矿床类型为岩浆热液型。 |
| 中文关键词:秦岭造山带 小沟里金矿 岩浆作用 成岩成矿年代学 |
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| Geology and Genesis of Xigouli Quartz Vein Type Gold Deposit, West Qinling Mountain |
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| Abstract:Qinling is one of the most famous orogenic belts in the world, where a series of Carlin_type gold deposits have been discovered. Nevertheless, the Xiaogouli gold deposit discovered in Gansu Province in recent years is different from Carlin_type in many aspects. It is characterized by Au_bearing quartz lodes with the presence of visible and coarse_grained gold. Au_bearing quartz veins extend steadily in siltstone, phyllite, and silicalite of Mid_Devonian Xihanshui Formation. Ores are composed of pyrite, pyrrhotite, arsenopyrite, sphalerite, and galena. Unlike things with Carlin type, visible or coarse gold is commonly present, up to 3 mm in diameter at most. This paper deals with Ar_Ar dating of Au_bearing quartz, U_Pb dating of zircon from granite, stable isotope analysis, trace element analysis, and mineralogy and texture of spots developed in the Au_bearing rocks, aiming at clarifying relations between granite and Au mineralization as well as metallogenesis based on geology of the deposit and regional geological environment. Studies show that dykes are well developed and commonly constitute the footwall and hang wall of orebodies. Spots developed well in the Au_bearing rocks are composed of pyrite, pyrrhotite, arsenopyrite, chlorite, quartz, sericite, biotite, cordierite, andalusite, tourmaline and carbonates, which suggests that they resulted from thermal alteration and hydrothermal fluid metasomatism. A geological section from Dashan granitic intrusive to the mine indicates that Au content of granitic veins intends to increase from 6.3×10-9 to 240×10-9. The Ar_Ar dating of Au_bearing quartz veins yields (197±1)Ma of Ar_Ar plateau age and (193±1)Ma of Ar_Ar isochron age. The single zircon of granite is dated by U_Pb method at (201±1)Ma. Accordingly, it is considered that metallization is temporally consistent with or slightly later than intrusion of granite. Stable isotope analyses show that sulfur is a mixed sulfur of sulfate and sulfur from deep magma. Si isotope of quartz is similar to that of granite. Dashan intrusive and granitic veins have higher Au content. δD values range from -58‰ to -77‰ and δ18O water from 8.2‰ to 12.8‰. On the δD-δ18O water diagram these data are plotted near the field of magmatic water, which implies that fluids were derived from magmatism. It is thought that Dashan granite has close temporal, spatial and genetic relationship with the Xiaogouli gold deposit and provides heat source, water source and partial ore_forming material for the formation of the deposit. The Xiaogouli gold deposit is genetically of magmatic hydrothermal type. |
| keywords:Qinling orogen, Xiaogouli gold deposit, magmatism, diagenetic and metallogenic geochronology |
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