湘西唐家寨铅锌矿床锶、硫同位素及其对成矿物质来源的指示意义

Strontium and sulfur isotopic characteristics of the Tangjiazhai Pb-Zn deposit in western Hunan Province, China:Denotative significance for ore-forming materials Source

唐家寨铅锌矿床位于湘西龙山—洛塔铅锌矿区的中部。对闪锌矿开展了锶同位素测试分析,通过成矿年龄(372Ma)的校正,得到初始(^(87)Sr/^(86)Sr)i的范围为0.70904~0.71143,平均值为0.70998(n=10),大于矿床形成时的海水Sr同位素,远小于富含有机质的下寒武统石牌组页岩层的Sr同位素,推测成矿流体中的Sr,可能是由具有较低Sr同位素组成的成矿期的海水混染了具有高Sr同位素的下寒武统石牌组页岩层而致。9件闪锌矿和方铅矿样品的δ^(34)SV-CDT值介于14.78‰~17.21‰,平均值为15.84‰,比同期(早奥陶世)海相硫酸盐硫同位素组成的平均值(29.5‰)低13.66‰,符合该矿床成矿温度(100~200℃)条件下硫同位素的分馏效应(10‰~20‰),表明硫化物中还原硫可能主要来源于赋矿地层中海相硫酸盐的热化学还原作用(TSR)。

The Tangjiazhai Pb-Zn deposit is located in the middle of the Longshan-Luota mining field in western Hunan Province,China, and is an important lead and zinc reserve base for Hunan Province. Sr isotope compositions measured for sphalerite were age-corrected by 372 Ma. As a result, the（^87Sr/^86Sr）ivalues range from 0.70904 to 0.71143 with an average value of 0.70998（n=10） which is higher than that of the seawaterin the mineralized age（372 Ma）,and lower than that of Lower Cambrian Shipai Formation shale enriched in organic matter. Speculation can be made is that Sr in ore-forming fluids is sourced from seawater（372 Ma） with relatively lower Sr contaminated high Sr Lower Cambrian Shipai Formation shale. Sphalerite and galena are measured for sulfur isotope composition. The δ^34SV-CDTvalues of them have a range from 14.78‰ to 7.21‰ with a mean of 15.84‰（n=9） which is lower13.66‰ than that of the Early Ordovician seawater sulfate. This variation conforms to sulfur isotope fractionation of 10‰-20‰ when the mineralized temperature is from 100 ℃ to 200 ℃.These evidences indicate that the reduced sulfur in the sulfides probably derive from the Thermochemical Sulfate Reduction（TSR） of seawater sulfate within the ore-bearing strata.