四川盆地富硫天然气与盆地周缘铅锌铜矿的成因联系

金属元素的搬运和沉淀是热液矿床成矿机理研究的重要方面。目前人们普遍认为热液矿床中金属元素主要呈硫的络合物和卤素络合物形式搬运。MVT铅锌矿床等硫化物矿床盐度较高,包裹体成分中阳离子以Na+、K+、Ca2+、Mg2+为主,阴离子以Cl-、F-、CO2-3为主,很少有HS-、S2-,表明金属元素主要以氯的络合物形式搬运,外来硫的加入是导致铅锌成矿物质以硫化物形式沉淀成矿的关键。四川盆地天然气中富含H2S,其与周缘MVT铅锌矿床具有密切的时空关系,据此推测天然气中的H2S可能是导致铅锌硫化物沉淀形成MVT铅锌矿床的主要硫源,天然气中的H2S与铅锌成矿流体在古油藏中作用形成含沥青的铅锌矿床;当含硫化氢的天然气运移离开古油藏后与含矿流体混合时,形成不含沥青的铅锌矿床。另外,石油热裂解产生的不含H2S的天然气使得含铜热液中的铜还原,以自然铜形式沉淀形成含沥青的玄武岩铜矿;石油热化学硫酸盐还原(TSR)过程中,还会发生溶蚀作用,扩大碳酸盐岩孔隙,为成矿提供空间。

The Genetic Relationship between the H2S-bearing Gas in Sichuan Basin and Lead—Zinc—Copper Deposits around the Basin

The migration and precipitation of metal elements are key factors in the formation of hydrothermal deposits. By far, metallic ions in ore-forming fluid is considered migrating as complex of S and halogen elements. The metallic ions in the fluid forming MVT lead—zinc deposits is considered migrating as complex of halogen element, because the ore forming fluids are rich in Na+、K+、Ca2+、Mg2+ and Cl-、F-、CO2-3, poor in HS- and S2-. Therefore, import of H2S is indispensable in deposition of lead and zinc sulfides in MVT lead—zinc deposits. There are close temporal and spatial relationships between the H2S-rich gas in Sichuan basin and the MVT lead—zinc deposits around the basin. This implies that the S in the MVT lead—zinc deposits probably comes from the H2S-rich gas. The bitumen-bearing lead—zinc sulfide deposits are formed within the oil reservoir. The lead—zinc sulfide deposits without bitumen are formed outside the oil reservoir. When copper-bearing hydrothermal fluid mixed with petroleum, the petroleum becomes into H2S-poor gas and bitumen by the heat of the hydrothermal fluid. The reduction of the gas results in the deposition of the copper ion in the hydrothermal fluids as native copper, forming the bitumen-bearing native copper deposits in the Emeishan basalts. More over, the corrosion from H2S can provide the space for Zn—Pb—Cu deposition.