黔西北云炉河坝铅锌矿集区成矿物质来源—S、Pb同位素制约

Sources of the Ore-forming Material from Yunluheba Ore Field in Northwest Guizhou Province, China: Constraints from S and Pb Isotope Geochemistry

川滇黔铅锌成矿域位于扬子克拉通的西南缘,是我国十分重要的铅锌成矿区带之一,相关成矿物质来源认识长期存在较大争议。本文以该区研究程度较低的黔西北云炉河坝矿集区为研究对象,对矿集区内典型的铅锌矿床（包括,昊星、富强、顺达和狮子洞等）进行了硫、铅同位素研究,以探讨其成矿物质的来源。硫同位素分析结果表明,昊星矿区硫化物的δ34S值变化范围很小（-1.5‰～2.7‰）,且集中于零值附近,暗示矿区硫可能主要来自于幔源岩浆硫的贡献,另外还发现一件黄铁矿样品具有较低的δ34S值（-18.1‰）,反映矿区可能还存在细菌还原硫的贡献。铅同位素数据表明,不同矿区不同类型矿石的Pb同位素组成十分均一,206Pb/204Pb介于18.196～18.525,207Pb/204Pb为15.645～15.731,208Pb/204Pb为38.415～39.058,且不同样品之间的Pb同位素不存在明显差别,表明云炉河坝矿集区中的众多铅锌矿床（点）可能具有统一的铅金属来源,且后期的氧化淋滤作用并未导致明显的铅同位素分馏。通过与区域上不同时代地层以及邻区铅锌矿床综合对比,我们初步认为矿区铅可能主要源于该区基底岩石,而非其赋矿地层和二叠纪玄武岩。

The Sichuan-Yunnan-Guizhou Pb-Zn metallogenic domain, located on the southwest margin of Yangtze craton, is one of most important lead-zinc mineralization belts in China. However, there is still a strong debate on the source of ore-forming materials. In this paper, we focus on the Yunluheba Pb-Zn ore field（including Haoxing, Shunda, Fuqiang and Shizdong Pb-Zn deposits） in the northwest of Guizhou Province, which has not been well studied until now, and try to determine the source of ore-forming materials by analysing the sulphur and lead isotopic compositions for different sulfides. The analytical results of sulphur isotopes show that most sulphides from the Haoxing mining area have a narrow δ34S range（-1.5‰–2.7‰）, suggesting that sulphur mainly originated from the mantle. Moreover, one pyrite sample has a very low δ34S value（i.e.-18.1‰）, which could have resulted from the reduction of bacterial sulphur. Lead isotope data show that different types of ore from different deposits all has uniform Pb isotopic composition, i.e. 206Pb/204 Pb = 18.196–18.525, 207Pb/204 Pb = 15.645–15.731, and 208Pb/204 Pb = 38.415–39.058, respectively. Furthermore, the oxidized ores generally have similar Pb isotopes with those of sulphide ores, which indicates that later oxidation leaching action did not cause lead isotope fractionation. Based on a comparison of the Pb isotopic data for different strata and deposits from Yunluheba and its adjacent regions, we proposed that the lead metal could be mainly derived from the basement rocks, rather than the wall rocks and/or Permian basalts.