| 胶西北寺庄金矿床红化蚀变过程及其对金成矿贡献 |
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| 引用本文： | 汪浩,杨立强,王偲瑞,张良,魏瑜吉,吕广耀.胶西北寺庄金矿床红化蚀变过程及其对金成矿贡献[J].岩石学报,2020,36(5):1515-1528. |
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| 作者姓名： | 汪浩 杨立强 王偲瑞 张良 魏瑜吉 吕广耀 |
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| 作者单位： | 中国地质大学地质过程与矿产资源国家重点实验室, 北京 100083;山东黄金矿业(莱州)有限公司焦家金矿, 莱州 261400 |
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| 基金项目： | 本文受国家重点研发计划（2019YFA0708603、2016YFC0600107-4）、国家自然科学基金项目（41230311、41572069）、高等学校学科创新引智计划（BP0719021）和地质过程与矿产资源国家重点实验室科技部专项经费（MSFGPMR201804）联合资助. |
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| 摘 要： | 胶东是我国最重要的金矿集区,其内金矿床均赋存于沿NE-NNE向断裂带展布的大规模红化蚀变带中;然而对红化蚀变是钾长石化还是赤铁矿-金红石化,及其对金成矿的贡献尚存争议。寺庄超大型金矿床的红化蚀变沿NE-NNE向焦家断裂带及其次级断裂-裂隙系统发育,占已探明资源储量70%的Ⅲ号矿体群即赋存于红化蚀变带内,是研究红化蚀变与金成矿关系的理想对象。本文以该金矿床红化蚀变花岗岩为研究对象,通过对比新鲜花岗岩与强、弱红化蚀变岩内矿物组合和地球化学组成,探讨红化蚀变对于金成矿的贡献。矿物学研究表明,弱红化蚀变岩内的蚀变发生在斜长石核部,以钠长石化为主,同时形成绢云母和少量热液钾长石,且赤铁矿在此阶段沉淀;而弱红化蚀变岩进一步水岩反应成为强红化蚀变岩的过程中出现大量热液钾长石。质量平衡计算表明,红化蚀变过程中SiO_2、K_2O迁入,而Na_2O、CaO、Al_2O_3、FeO~T、MgO迁出;红化流体由早期富Na向后期富K转变。岩石地球化学与氢氧同位素综合示踪显示,红化流体为高温、高氧逸度、富K的玲珑岩浆期后热液,与胶东金矿床中-低温、还原性、富CO_2成矿流体性质相反,表明红化流体未直接参与成矿过程。综合研究揭示,流体交代斜长石后形成贯通性孔隙提高红化蚀变岩的渗透性;热液钾长石交代斜长石导致岩石体积膨胀而破裂,降低岩石抗压强度;这些为成矿期断裂活动以及成矿流体的运移和成矿物质的沉淀提供了极为有利的围岩条件,可能是巨量金聚集成矿的关键因素之一。
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| 关 键 词： | 胶东 寺庄金矿床 红化蚀变 矿物组合 抗压强度 |
| 收稿时间： | 2019/12/2 0:00:00 |
| 修稿时间： | 2020/3/30 0:00:00 |
The process of rubefication and its relationship with gold mineralization of Sizhuang gold deposit, northwestern Jiaodong Peninsula, eastern China |
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| Institution: | State Key Laboratory of Geological Process and Mineral Resources, China University of Geosciences, Beijing 100083, China; Shandong Gold Mining(Laizhou) Limited Company Jiaojia Gold Deposit, Laizhou 261400, China |
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| Abstract: | The Jiaodong gold province is the most important gold producer in China. Gold deposits in the province are mainly located in the NE-NNE trending massive rubefication zone. The formation of rubefication has long been problematic. The foci of the dispute are whether the nature of rubefication is K-feldspar alteration or hematite-rutile alteration and how the rubefication contributes to gold mineralization. The rubefication zone of Sizhuang gold deposit, which occupies 70% gold resources, along NE-NNE Jiaojia Fault and its secondary fractures provides an opportunity to study such topic. In order to constrain the nature of rubefication and its role in the gold mineralization, the comparation of mineral assemblage and geochemistry of unaltered granites and intense and weak rubeficated granites was carried out in this study. Mineralogical studies indicate that the alteration of feldspars initiated from the formation of significant albitization and little sericite and hydrothermal K-feldspar. This indicates a Na-rich fluid. Hematite was also precipitated at this early stage in the weakly rubefication area. As the water-rock reaction proceeded, large amounts of hydrothermal K-feldspar formed. Mass-balance calculations between altered and unaltered rocks indicate complex behaviors of major elements: SiO2 and K2O were brought in from fluid, and Na2O, CaO, Al2O3, FeOT and MgO were brought out from fresh biotite granite, indicating that the transformation from Na fluid to K fluid. Combined with hydrogen and oxygen isotopic data, the bulk geochemistry of rocks with different alteration degrees reveals that fluids which resulted in the rubefication were derived from Linglong magmatic water (high T and fO2, rich K), and is different from the ore-forming fluid (moderate-low T and fO2, rich CO2). Thus, the fluids forming the rubefication played no genetic role in gold mineralization. Comprehensive study reveals that the formation of penetrating pores during rubefication improves the porosity of red alteration rock. The process of rubefication also led to rock volume expansion and fracture, which reduced rock compressive strength. Thus, the Jiaodong gold province owes its giant gold endowment to a conjunction of previously enhanced porosity and reduced compressive strength of the rubeficated granites. |
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| Keywords: | Jiaodong Sizhuang gold deposit Rubefication Mineral assemblage Compressive strength |
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