渝东南秀山石堤铅锌矿S、Pb同位素地球化学特征与成矿物质来源探讨

Sulfur and Lead Isotopic Geochemistry and its Significance for Ore-forming Material of the Shidi Pb-Zn Deposit in Xiushan, Southeast Chongqing

石堤铅锌矿位于重庆市秀山县境内,紧邻湖南花垣铅锌矿,矿体赋存于中寒武统平井组碳酸盐岩中。本文对该矿床矿石进行了系统的硫、铅同位素研究,探讨了成矿物质来源。研究表明,石堤铅锌矿矿石中硫化物δ34S值变化范围为10.8‰~15.6‰,平均13.52‰,主要为海相硫酸盐的还原产物,硫酸盐的还原机制为热化学还原作用。矿石铅206Pb/204Pb为18.319~18.422,207Pb/204Pb为15.740~15.784,208Pb/204Pb为38.355~38.511,铅同位素组成较为均一,显示正常铅的组成特征,在Zartman铅同位素图解中,主要位于上地壳演化线之上,在Δβ-Δγ图解中,总体落入上地壳与地幔混合的俯冲带铅和上地壳铅的过渡范围内,因此认为石堤铅锌矿床成矿物质主要来源于上地壳物质,下寒武统牛蹄塘组黑色页岩可能是石堤铅锌矿床成矿物质的重要来源。

The Shidi lead-zinc deposit is located in Xiushan county in southeast Chongqing. Its orebodies occur in marine carbonates of the Cambrian Pingjing formation. The authors selected sulfide minerals from the deposit for sulfur and lead isotope compositional analyses. The δ34S values of these sulfide minerals vary from 10.8% to 15.6% and show an average value of 13.52%, indicating the sulfur was mainly derived from marine sulfate reduction and reduced sulfurs that were probably derived from thermo-chemical sulfate reduction. The 206Pb/204 Pb, 207Pb/204 Pb and 208Pb/204 Pb ratios for these sulfide minerals vary, ranging from 18.319 to 18.422, 15.740 to 15.784 and 38.355 to 38.511 respectively. The Zartman diagrams show the Pb isotope compositions of these sulfide minerals fall into the regional upper crustal lead zone. In the Δβ-Δγ diagram values fall into the upper crustal lead zone implying that Pb might have come from rocks in the upper crust. According to the geochemical characteristics of the sulfur and lead isotope compositions from the Shidi Pb-Zn deposit, the ore-forming materials might have come from the black shale of the Lower Cambrian Niutitang Formation.