湖南省留书塘铅锌矿床S、Pb同位素特征及意义

摘要

The discovery of the Liushutang lead-zinc deposit is one of the major breakthroughs of prospecting in the Nanling metal?logenic belt in recent years. The lead-zinc lodes are strictly controlled by the shattered fracture zones along the western margin of Hengyang basin. Field observation shows that the related mineralization can be divided into three stages of quartz-pyrite, quartz-sphalerite-galena and barite. In this paper, systematic research on S, Pb isotopes based on different stages of ores were conducted to explain the origin of ore-forming materials and ore genesis. The result shows that sulfur isotopes of 17 sulfide samples vary in a wide range (δ34S value being-12.8‰~4.6‰) with a dynamic evolution of gradual increasing of δ34S values from early to late. This can be probably explained by a mixing process of organic sulfur (~-13‰) and magmatic sulfur (~5‰). Sulfur of latest barite ore (δ34S is 14.7‰~24.4‰) might have been provided by the strata sulfate. 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb ratios of 13 sulfide ore samples vary in the range of 18.627~18.942, 15.670~15.804 and 38.366~38.912, with the average value being 18.747, 15.705 and 38.614, respec?tively. These values are very similar to values of Pb isotopes of magmatic feldspar in southern Hu'nan and also have weak linear rela?tion with Pb isotopes of regional Cambrian strata, suggesting that ore materials might have mainly originated from magmatic pluton in the depth, and subordinately from the Cambrian strata. Based on the above results and geological evidence, the authors put forward a model of magma-related hydrothermal mineralization with multiple sources of ore-forming materials, which may be suitable for explaining the ore genesis of the Liushutang deposit.%对湖南省留书塘铅锌矿床不同阶段矿石硫化物进行的S、Pb同位素研究表明,17件矿石样品硫化物的S同位素组成变化范围较宽(δ34S=-12.8‰~4.6‰),具有地层有机硫(约-13‰)与岩浆硫(约5‰)混合特征.从早阶段到晚阶段,硫化物呈现出δ34S值逐渐升高、极差逐渐增大的演化趋势.最晚形成的重晶石矿石硫由地层硫酸盐提供.13件硫化物样品的Pb同位素组成比较稳定,206Pb/204Pb、207Pb/204Pb、208Pb/204Pb值变化范围分别为18.627~18.942、15.670~15.804和38.366~38.912,平均值分别为18.747、15.705和38.614.与区内新元古界—寒武系基底、邻区湘南与铅锌矿相关的岩浆岩钾长石Pb同位素进行的对比表明,矿石铅主要来源于矿区深部岩浆岩,少部分可能来自于基底寒武纪地层.结合宏观地质特征分析,留书塘矿床可能是与岩浆岩有关的热液充填交代矿床,其成矿物质具有多来源特征.