流体包裹体和C-H-O同位素对湘中古台山金矿床成因制约  

Constraint on the genesis of Gutaishan gold deposit in central Hunan Province:Evidence from fluid inclusion and C-H-O isotopes

作　　者：李伟[1,2] 谢桂青[2,3] 张志远[2] 张兴康[4] 

机构地区：[1]中国地质大学资源学院,武汉430074 [2]中国地质科学院矿产资源研究所,北京100037 [3]国土资源部成矿作用与资源评价重点实验室,北京100037 [4]河北省地质调查院,石家庄050081

出　　处：《岩石学报》2016年第11期3489-3506,共18页Acta Petrologica Sinica

基　　金：国家"973"项目(2014CB440902)资助

摘　　要：古台山金矿是湘中盆地最典型的高品位石英脉型金矿床,主要赋存于新元古界和震旦系板岩-千枚岩中。为了探明古台山金矿的成矿物质和成矿流体来源,本次工作对其开展了详细的野外地质考察,对不同阶段石英进行了系统的包裹体岩相学观察、显微测温、激光拉曼探针及H-O同位素分析,对与金矿化密切相关的铁白云石进行了C-O同位素分析。包裹体岩相学及测温结果显示,不同阶段石英主要发育CO_2三相和水溶液两相包裹体,金沉淀阶段CO_2三相包裹体丰度最高,包裹体均一温度集中在180~320℃之间,盐度集中在0~13%NaCleqv之间。激光拉曼显示不同阶段石英包裹体成分主要为H_2O、CO12及少量的CH_4和N_2。不同阶段石英的δ^(18)O_(V-SMOW)变化范围为15.6‰~17.9‰,对应的δ8OH_2O变化范围为4.5‰~8.3‰,δD_(V-SMOW)变化范围-78‰^-49‰,显示成矿过程中有岩浆水参与。铁白云石的δ^(13)C_(PDB)集中在-10.3‰^-8.6‰,δ^(18)O_(V-SMOW)分布在13.9‰~15.7‰之间,暗示成矿流体中的碳主要来自深部岩浆。流体不混溶、CH_4气体存在、围岩及脉体发生硫化-碳酸盐化等因素是导致古台山矿床Au沉淀富集的重要机制。综合上述分析,推测古台山金矿可能是一个非典型的造山型金矿床。The Gutaishan high-grade gold deposit, located in the Xiangzhong basin, is hosted within Neoproterozoic to Sinian slate and phyllite rocks. Petrographic observation, microthermometric measurements, Raman spectroscopy and H-O isotopes on the fluid inclusions for different stages quartz from the Gutaishan Au deposit were carried out in this study, aiming to show new insights into the origin of ore-forming fluids and understand on ore genesis. Additionally, C-O isotopic analyses of representative hydrothermal ankerite samples were also presented. Fluid inclusions of different stages are generally characterized by two major types ： carbon dioxide-bearing inclusions and brine inclusions, and the former type is of the highest abundance within the Au mineralization stage. The homogenization temperature and salinity range from 180℃ to 320℃, and 0 to 13 % NaCleqv, respectively. Raman spectroscopy analyses show that H20 and CO2 are main components in the measured fluid inclusions, with minor CH4 and N2. δ18 OV.SMOW, δ18 OH20 and 8DV-SMOW of quartz range from 15.6‰to 17.9‰, 4. 5‰ to 8. 3‰, -78‰ to -49‰, respectively, indicating magmatic fluid was possible involved in the ore-forming process. Homogenized carbon （δ13CVDB = -10. 3%0 --8. 6%0） and oxygen （δ18OV-SMOW = ＋ 13. 9%0 - ＋ 15. 7%0） of ankerite collectively suggest a magmatic source. Fluid immiscibility, existence of CH4, together with sulfidation and carbonation in the wallrock and veins, are the key factors to the precipitation of Au. These syntheses of available information lead to the proposal that the Gutaishan gold deposit may represent an atypical orogenic gold deposit.

关 键 词：流体包裹体 C-H-O同位素 矿床成因 古台山金矿床 湘中Au-Sb矿集区 

分 类 号：P597.2[天文地球—地球化学] P618.51[天文地球—地质学]