塔里木盆地西北缘乌恰地区乌拉根铅锌矿床S-Pb同位素特征及其地质意义

摘要

乌拉根铅锌矿床产出于塔里木盆地西北缘喀什凹陷中—新生界中,成矿地质条件优越,资源潜力可观,具有超大型矿床找矿远景,但其成因一直存在较大争议.本次对乌拉根铅锌矿进行了详细的S、Pb同位素研究,探讨了其成矿物质来源和矿床成因.测试分析结果表明,乌拉根铅锌矿床矿石δ34S值为-26.09‰～+15.0‰,具有较宽的分布范围,显示出轻硫与重硫同时富集的特征,指示乌拉根铅锌矿床S主要来自海相硫酸盐的还原.乌拉根铅锌矿的206Pb/204Pb值为17.771～18.6413,207Pb/204Pb值为15.402～15.6454,208Pb/204Pb值为37.92～38.7507,Pb同位素组成变化较小,且集中于造山带铅演化线附近,推测本矿区Pb可能来自区域内的古老地层.综合前人研究和本次S、Pb同位素分析结果,认为乌拉根铅锌矿床是在南天山和西昆仑山两大造山带相互逆冲推覆背景下,盆地流体大规模运移,在油气还原条件下形成的一类赋存于沉积岩中的铅锌矿床.%Located in Wuqia area of western Xinjiang, the Wulagen lead-zinc deposit is hosted by Mesozoic-Cenozoic strata of Kashi depression in the northwestern margin of the Tarim Basin. Recent studies and prospecting have confirmed the favorable ore-forming conditions of this ore deposit, and the mineral potential should be very large. However, its genesis remains controversial for a long time. In this paper, S-Pb isotopic compositions of sulfides from ore bodies in the ore deposit were systematically determined so as to discuss the source of ore-forming material and the genesis or the ore deposit. The sulfur isotopic compositions δ34S in ore bodies are in a wide range of -26.09-+15.0‰. The sulfur-rich characteristics of two-terminal element indicated that the sulfur might have been derived from the marine sulfate thermal chemical reduction. The lead isotopic ratios are 206Pb/204Pb=17.771 -18.6413, 207Pb/204Pb = 15.402 -15.6454, and 208Pb/204Pb=37.92-38.7507, respectively, varying very narrowly and plotted near the orogenic belt evolution curve. It can be inferred that the ore-forming metals were probably derived from the the old stratum. These results and previous data Wulagen lead-zinc deposit was one of the sediment-Hosted lead-zinc deposits, related to the thrust-nappe setting of South Tian-shan-West Kunlun regional orogenic belt, large-scale migration of basin fluids and the reducing conditions from oil and gas.