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投稿时间：2018-10-26 修订日期：2019-04-11 网络发布日期：2019-07-03
中文摘要:樊岔金矿床位于小秦岭金矿田的娘娘山岩体西南侧，受观音堂剪切带控制，赋矿围岩为太华超群变质岩。根据矿物组合特征和脉体穿插关系，成矿可分为早、中、晚3个阶段，分别以石英+钾长石±黄铁矿、石英+多金属硫化物、石英+方解石±黄铁矿为标志，以中阶段矿化最为重要。热液石英发育纯CO2包裹体（PC型）、CO2-H2O包裹体（C型）、水溶液包裹体（W型）和含子晶多相包裹体（S型）。早阶段流体包裹体主要为C型，次为PC型及少量的W型和S型包裹体，均一温度的峰值为340~360℃，盐度w（NaCleq）峰值为14.0%~16.0%。与早阶段相比，中阶段PC型、C型包裹体数量减少，W型、S型包裹体数量增多，均一温度峰值为320~340℃，盐度w（NaCleq）峰值为12.0%~14.0%。晚阶段只发育W型包裹体，均一温度峰值为180~200℃，盐度w（NaCleq）峰值为2.0%~4.0%。激光拉曼探针显示早阶段流体包裹体富含CO2和CH4，中阶段包裹体中仅富含CO2，而晚阶段包裹体中不含CO2或CH4。结合氢、氧同位素研究，认为樊岔金矿床成矿流体由早阶段中温、中低盐度、富含CO2和CH4的变质热液逐渐向晚阶段低温、低盐度、贫CO2的大气降水热液演化，沸腾作用和混合作用是其主要演化机制。根据沸腾包裹体计算得出早阶段和中阶段包裹体的捕获压力分别介于108~295 MPa和97~261 MPa之间，对应的成矿深度分别约为10.8 km和9.7 km。矿石硫、铅同位素研究表明，成矿物质主要来自太华超群围岩而非燕山期岩浆。综合上述区域地质、矿床地质、包裹体和同位素地球化学资料，樊岔金矿床应是形成于侏罗纪-早白垩世华北与扬子大陆碰撞造山过程挤压向伸展转变体制的造山型金矿床。
Abstract:The Fancha gold deposit in Henan Province is located in southwestern Niangniangshan granite of eastern Xiaoqinling gold orefield. The orebodies are controlled by the Guanyintang shear zone and hosted in the metamorphic rocks of the Taihua Supergroup. Based on mineralogical assemblages and crosscutting relationships, the hydrothermal ore-forming process can be divided into early, middle and late stages, which are characterized by mineral assemblages of quartz+potash feldspar±pyrite, quartz+polymetallic sulfides, and quartz+carbonate±pyrite, respectively, with gold being introduced mainly at the middle stage. Quartz contains four types of fluid inclusions:pure carbonic (PC), carbonic-aqueous (C), aqueous (W) and solid-bearing (S) fluid inclusions. Fluid inclusions in early stage quartz are predominated by C-type, followed by PC-type, and then Sand W-types, and yield homogenization temperatures and salinities clustering around 340~360℃ and w(NaCleq) 14.0%~16.0%, respectively. Compared with quartz of the early stage, the middle stage quartz has less Cand PC-types, but more Wand S-types inclusions with homogenization temperatures and salinities ranging 320~340℃ and w(NaCleq) 12.0%~14.0%, respectively. Only the W-type inclusions can be observed at the late stage, with the lowest homogenization temperature and salinity w(NaCleq) peaks around 180~200℃ and 2.0%~4.0%, respectively. The laser Raman microspectroprobe detection proved that early stage inclusions contain both CO2 and CH4, middle stage inclusions contain only CO2, and late stage inclusions contain neither CO2 nor CH4, but H2O is always observed in inclusions of various stages. These data indicate that ore-forming fluids changed from early-stage metamorphicdevolatilized mesothermal, low to medium salinity, and CO2- and CH4-rich nature to late-stage meteoric-sourced low-temperature, low salinity and CO2-poor nature. Fluid boiling and mixing are the most favorable factors causing metal precipitation. This understanding is supported by the hydrogen and oxygen isotope data obtained from the Fancha gold deposit. Trapping pressures estimated from the boiling fluid inclusion associations are 108~295 MPa and 97~261 MPa for early and middle stages, respectively, suggesting that gold mineralization occurred at depths of~10.8 km and~9.7 km at early and middle stages, respectively. The sulfur and lead isotope ratios indicate that the host rocks within Taihua Supergroup served as a significant source of ore metals. Integrating the data obtained from the studies including regional geology, ore geology and fluid inclusion as well as H-O-S-Pb isotope geochemistry, the authors have reached the conclusion that the Fancha gold deposit is an orogenic-type system formed in the tectonic transition from compression to extension during the Jurassic-Early Cretaceous collision between the North China and Yangtze continents.
keywords:geochemistry fluid inclusions mineralization mechanism Xiaoqinling gold field Fancha gold deposit
ZHAN EnPeng,WANG Pin,QI Nan,XU Chen,HAO JiaoLong,LI ZongYan,CHEN YanJing.2019.Ore-forming fluid and isotope geochemical study of Fancha gold deposit in Lingbao County, Henan Province[J].Mineral Deposits(3):459~478