江苏栖霞山铅锌矿成矿物质来源与成矿过程:S-C-O同位素证据

Source and Ore-forming Process of the Qixiashan Lead-zinc Ore Deposit,Jiangsu Province:Evidences from S-C-O Isotopes

为揭示江苏栖霞山矿床成矿物质来源与成矿过程,对取自该矿床两个深钻孔的岩芯样品进行了电子探针及S、C、O稳定同位素分析。电子探针分析结果显示,矿化早期的磁铁矿具有Ag-Pb-Zn热液矿床特征;不同成矿期的闪锌矿中的Fe含量有从成矿早期到晚期逐渐降低的趋势,暗示成矿是一降温过程。同位素分析样品采用微钻取样,测试结果表明矿石中的铅锌硫化物的δ^34S值为-4.44‰~7.22‰,表明硫主要为岩浆来源;围岩中硫化物的δ^34S值较矿石的δ^34S值要小,结合地层中存在沉积型黄铁矿,推测部分硫来自地层。脉石矿物的C、O同位素数据表明,成矿期流体主要来源于岩浆,运移过程中与围岩发生水-岩反应;晚期方解石脉的C、O同位素更接近岩浆范围,表明随着温度的降低,热液与围岩的反应强度降低。栖霞山铅锌矿床的成矿物质与成矿流体主要来自深部岩浆热液,温度、围岩性质是制约矿质沉淀的重要因素。

In this paper,the authors have studied samples from cores of two deep boreholes in the Qixiashan Pb-Zn deposit using electron probe microanalysis and sulfur-carbon-oxygen stable isotope analysis,in order to reveal the source of metallogenic materials and ore-forming process of the deposit.The results of electron probe microanalysis show that magnetite of the early ore stage of the Qixiashan lead-zinc deposit has characteristics of that of the Ag-Pb-Zn hydrothermal deposit;The Fe contents in sphalerites are gradually decreased from the early to late ones,indicating a cooling mineralization process.The overallδ34S values of sulfides,ranging from-4.44‰to 7.22‰,indicate a mainly magmatic source for sulfur.Theδ34S values of sulfides from lead-zinc ore body are much higher than those of sulfides in the wall rock.Considering there are sedimentary pyrites in the wall rock,it is inferred that a little sulfur could be sourced from the wall rock.The CO isotopic data of gangue minerals at different stages show that the ore-forming fluid could be mainly derived from magma.The water-rock reaction occurred between the magmatic hydrothermal fluid and the wall rock during the fluid migration process.The C-O isotopic data of calcite veins of late stage are much closer to the value of magma than those of the early stage calcite veins,indicating that the reaction intensity of hydrothermal fluid and the wall rock was decreased with the decrease of temperatures.In summary,we believe that the ore-forming materials and fluid of the Qixiashan lead-zinc deposit were mainly derived from deep magmatic hydrothermal fluid,with important factors of temperature and wall rock property for restricting the precipitation of ore-forming materials.