(1. 北京科技大学 土木与资源工程学院，北京 100083；
2. 南京地质矿产研究所，南京 210016)
摘 要: 汞洞冲铅锌矿床位于大别成矿带的东段，是该区内重要的角砾岩型多金属矿床。矿体受角砾岩体控制，赋存于早古生代佛子岭岩群诸佛庵组云母石英片岩和千枚岩之中。矿床经历他形石英-绢云母-黄铁矿阶段(Ⅰ)、自形石英-铁锰镁碳酸盐-多金属硫化物阶段(Ⅱ)和方解石-绿泥石-黄铁矿阶段(Ⅲ)，其中Ⅱ阶段为最主要的铅锌沉淀阶段。流体包裹体岩相学、显微测温、激光拉曼综合研究表明：Ⅰ阶段主要发育富CO2包裹体(均一温度为307~354 ℃，盐度(NaCleq)为0.6%~5.6%(质量分数))和含子晶多相包裹体(均一温度为323~377 ℃，盐度为38.2%~45.3%)；Ⅱ阶段主要发育气液相体积比变化很大的气液两相水溶液包裹体，及少量含CO2的包裹体，均一温度为249~315 ℃，盐度(NaCleq)为2.9%~6.9%；Ⅲ阶段主要发育气液两相水溶液包裹体，均一温度为242~280 ℃，盐度为1.4%~5.0%，其中Ⅰ阶段流体发生了沸腾作用。H、O同位素测试结果表明：Ⅰ阶段硅化细粒石英流体包裹体显示岩浆水来源，而Ⅱ阶段晶簇石英的流体包裹体则存在有大气水混入的特征。成矿流体由中高温、高盐度、富CO2的岩浆水向低温、低盐度、贫气富水的大气水方向演化。C-O同位素测试结果表明，与铅锌等金属共生的白云石中δ13CV-PDF值为-4.6×10-3~-1.2×10-3之间，相对变化较小，δ18OSMOW值为7.1×10-3~10.2×10-3，显示岩浆碳酸岩来源。金属硫化物的δ34SV-CDT值变化范围很窄，在2.5×10-3~4.5×10-3之间，也显示深源硫的特征。综合分析表明：汞洞冲铅锌矿床为一热液隐爆角砾岩型矿床，成矿流体和成矿物质主要来自深部的岩浆热液，矿床经历了隐爆作用和减压过程，使得流体发生了沸腾作用，此时气液相开始分离, CO2不断逃逸，成矿金属在残存的高盐度液相中富集，随后大气降水沿着隐爆作用所产生的裂隙加入热液中，流体混合使得体系盐度大幅降低，金属络合物失稳，最终铅锌大量沉淀。
关键字: 汞洞冲；隐爆角砾岩；沸腾作用；混合作用；岩浆热液
（1. School of Civil and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China;
2. Nanjing Institute of Geology and Mineral Resource, Chinese Academy of Geological Sciences, Nanjing 210016, China）
Abstract:The Gongdongchong Pb-Zn deposit located in Jinzhai County, Anhui Province, China, is one of the important breccia type lead-zinc polymetallic deposits in the east end of Qinling-Dabie metallogenic belt. Ore bodies are controlled by the breccia, hosted in Early Palaeozoic mica-quartz schist and phyllite of Zhufo’an Formation, Foziling Group. The ore-forming processes of Gongdongchong deposit can be divided into three stages, namely the anhedral quartz-sericite-pyrite stage (Ⅰ), the euhedral quartz-carbonate-polymetal sulfides stage (Ⅱ) and the calcite-chlorite-pyrite stage (Ⅲ), among which, the stage (Ⅱ) is the major mineralization stage. Studies of fluid inclusions show that the fluid inclusions trapped in stage (Ⅰ) including two-phase inclusions, as evidenced by the coexistence of CO2-rich(C-type) (Homogenization temperatures of 307-354 ℃, Salinity(NaCleq): 0.6%-5.6% and multi-phase(S-type) inclusions with daughter minerals (Homogenization temperature of 323-377 ℃, Salinity of 38.2%-45.3%. The fluid inclusions of stage (Ⅱ) are two-phase inclusions, as identified by the coexistence of L1- and L2-type fluid inclusions; L1-type inclusions homogenized is 249-315 ℃, with salinities of 2.9%-6.9%. The fluid inclusions formed in stage(Ⅲ) are dominated by vapor-liquid two phase inclusions, with the homogenization temperatures ranging from 242 ℃ to 280 ℃ and salinities between 1.4% and 5.0%. The fluid-boiling is evidenced by divergent-phase homogenizations of fluid inclusions with contrasting salinities at similar temperatures in stage (Ⅰ). The hydrogen and oxygen isotopes composition in quartz grains from different stages show that ore-forming fluid for stage (Ⅰ) is of magmatic origin, and is mixd by the meteoric water in stage (Ⅱ). The ore-forming fluid is characterized by medium-high temperature, high salinity and CO2-rich, and then evolved into low temperature, low salinity and CO2-release from early to late stage. The carbon and oxygen isotope composition in the dolomite in the deposit range from -4.6×10-3 to 1.2×10-3 and from 7.1×10-3 to 10.2×10-3, respectively, which is similar to those in magmatic carbonatite. The values of δ34SV-CDT in major sulfides have narrow variable range, from 2.5×10-3 to 4.5×10-3, indicating that the sulfur is derived from the mantle. All the data presented show that Gongdongchong Pb-Zn deposit belongs to the cryptoexplosion breccia-type deposit. The ore forming fluid and metallogenic materials come from magma in depth. The fluids boiling after cryptoexplosion and decompression result in gas-release. The metallogenic elements, such as Pb, Zn and Cu, concentrated in the solution with high salinity. The ore-forming hydrothermal solution migrated upwards along the tensional cracks with the sharply salinity decreasing by mixture with meteoric water, finally ore-forming materials are precipitated.
Key words: Gongdongchong; cryptoexplosion breccia; fluid boiling; mixing; magmatic hydrothermal
