云南会泽铅锌矿灯影组矿石硫、铅同位素组成及找矿意义

Sulfur and lead isotopic compositions of ores from the Dengying Formation and their prospecting implications in the Huize Pb–Zn deposit, Yunnan Province

关键词:  LA-MC-ICP-MS  硫、铅同位素组成  灯影组  会泽铅锌矿  “新层位”找矿

Key words:  LA-MC-ICP-MS  S-Pb isotopic compositions  Dengying Formation  Huize lead–zinc deposit  "New formation" prospecting

摘要:

会泽超大型铅锌矿床位于川滇黔铅锌成矿带的核心部位，矿体主要赋存于下石炭统大埔组白云岩中，少量产于上泥盆统宰格组白云岩中，近年来在深部上震旦统灯影组白云岩中新发现了铅锌矿化线索。本文在详细的野外地质调查与矿相学显微观察的基础上，针对灯影组矿石开展了系统的硫化物微区LA-MC-ICP-MS原位硫、铅同位素分析。结果表明，灯影组矿石的硫同位素值集中于－29.6‰~－22.2‰和+6.3‰~+18.8‰两个变化范围，表明硫主要来自碳酸盐岩地层中海相硫酸盐的热化学还原反应，少量由细菌化学还原反应生成。灯影组矿石的铅同位素比值²⁰⁶Pb/²⁰⁴Pb、²⁰⁷Pb/²⁰⁴Pb、²⁰⁸Pb/²⁰⁴Pb分别介于18.480~18.909、15.714~15.747、38.427~38.959，暗示铅为单一来源或混合较为均一的多源，并具有壳源特征。综合前人研究成果及成矿地质与地球化学特征，本文认为，会泽铅锌矿床应归属于MVT矿床。灯影组矿石的硫、铅同位素组成特征指示会泽铅锌矿床在“新层位”灯影组具有较好的找矿潜力。

Abstract:

The giant Huize lead-zinc deposit is situated at the core area of the Sichuan-Yunnan-Guizhou lead-zinc metallogenic province. The mineralization is mostly hosted in the dolomite of the Lower Carboniferous Dapu Formation and minor orebodies occur in the dolomite of the Upper Devonian Zaige Formation. The mineralization has been newly discovered in the dolomite of the Upper Sinian Dengying Formation. In this paper, on the basis of detailed field investigation and microscopic observation on ore minerals, we conducted systematic LA-MC-ICP-MS sulfur and lead isotopic analyses on sulfides from ores hosted in the Dengying Formation. The δ³⁴S values of the sulfides have two variation ranges, which are -29.6‰~-22.2‰ and +6.3‰~+18.8‰, respectively. The results indicate that most of the sulfur was sourced from thermal reduction of marine sulfates in the carbonates, and a little of the sulfur was generated from bacterial sulfate reduction. The ratios of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb vary in narrow ranges of 18.480~18.909, 15.714~15.747, 38.427~38.959, respectively, which suggests a single source or multiple sources with homogeneous mixing and an upper crust source for the lead. In combination with previous studies, and geological and geochemical characteristics, we suggest that the Huize lead-zinc deposit should be assigned as a MVT deposit. The ores hosted in the Dengying Formation imply a good prospecting potential in the Dengying Formation.