西藏那茶淌铅锌矿床S-Pb同位素组成及其示踪成矿物质来源

Sulfur and lead isotope composition tracing for the ore-forming material source of Nachatang Pb-Zn deposit in Tibet

关键词:  S-Pb同位素  矽卡岩型矿床  那茶淌铅锌矿床  冈底斯–念青唐古拉成矿带  西藏

Key words:  S-Pb isotope  Skarn deposit  Nachatang Pb-Zn deposit  Gangdese-Nyainqêntanglha Metallogenic belt  Tibet

摘要:

那茶淌矿床位于西藏冈底斯–念青唐古拉成矿带东段，为近年发现的具中—大型远景规模的矽卡岩型铅锌矿床，其成矿物质来源及其成矿背景还缺乏详细调查，制约了矿床成因的深入研究。本文在矿床地质特征研究基础上，对矽卡岩型矿石中主要金属矿物闪锌矿、方铅矿、磁黄铁矿的S、Pb同位素组成进行分析，探讨矿床成矿物质来源，并与区域上典型铅锌矿床进行对比，总结区域成矿规律。结果显示，那茶淌矿床金属硫化物的δ³⁴S（‰）值变化于－1.6‰～4.2‰之间，平均值为1.4‰，其频率直方图呈正太分布形式，具幔源硫特征。金属硫化物的²⁰⁶Pb/²⁰⁴Pb值为18.548～18.792，平均值为18.691；²⁰⁷Pb/²⁰⁴Pb值为15.683～15.856，平均值为15.755；²⁰⁸Pb/²⁰⁴Pb值为39.049～39.685，平均值为39.331；铅同位素特征值μ的变化范围为9.61～9.93，平均值为9.74，所有样品μ值均高于9.58，显示铅源具有上地壳源区物质的特征。通过区域成矿作用对比研究，那茶淌矿床S、Pb同位素组成与念青唐古拉带东段典型矽卡岩型铅锌矿床具有相似的特征，成矿物质主要来源于念青唐古拉群结晶基底物质的重熔。

Abstract:

The Nachatang deposit, which discovered in recent years with a medium-large prospective scale, is located in the eastern segment of Gangdese-Nyainqêntanglha metallogenic belt in Tibet. The lack of detailed investigation of mineral origin and metallogenic background restricts the further study of genesis of the deposit. Based on the study of the geological characteristics of the deposit, the S and Pb isotopic characteristics of the main metal minerals in skarn ore (such as sphalerite, galena and pyrrhotite) are analyzed in this paper, and the source of ore-forming materials of the deposit is discussed. The regional metallogenic regularity is summarized by comparing with the regional typical lead-zinc deposits. The results show that the δ³⁴S(‰) value of metal sulfide varies from -1.6‰ to 4.2‰, with an average value of 1.4‰. The frequency histogram has the characteristics of normal distribution and mantle sulfur source. The ²⁰⁶Pb/²⁰⁴Pb value of metal sulfide ranges from 18.548 to 18.792, with an average of 18.691. The ²⁰⁷Pb/²⁰⁴Pb values range from 15.683 to 15.856, with an average of 15.755. ²⁰⁸Pb/²⁰⁴Pb values range from 39.049 to 39.685, with an average of 39.331. The characteristic μ values of Pb isotope range from 9.61 to 9.93, with an average value of 9.74. The μ values of all samples are higher than 9.58, indicating that the lead source has the characteristics of upper crustal source. Based on the comparative study of regional mineralization, it is concluded that the S and Pb isotope characteristics of the Nachatang deposit are similar to those of the typical skarn Pb-Zn deposits in the eastern segment of Nyainqêntanglha lead-zinc metallogenic belt, and the ore-forming materials are mainly derived from the remelting of crystalline basement materials of the Nyainqêntanglha Group.