新疆彩霞山铅锌矿硫化物原位硫同位素特征及对成矿机制的指示

The giant Caixiashan Zn-Pb deposit is the largest Zn-Pb deposit that hosted in the Precambrian basement of the northern Tarim Basin, which shows great advantage of ore-forming condition and potential of Zn-Pb deposit exploration. But the sulfur source(s) and ore forming mechanism of Caixiashan are still in great controversy due to the traditional sulfide isotope techniques are unable to reveal the nature sources of these sulfides at Caixiashan, as the sulfides are locally characterized by growth zonation and/or recrystallization resulted from multiple stages of mineralization overprinting. In situ sulfur isotope analysis by the Secondary Ion Mass Spectroscopy (SIMS) can be used to observe intra- and inter-grain sulfur isotope variability at scales of a few to tens of μm, which can provide not only ideal information for revealing the sulfur sources and evolutionary process, but also help us understand the sulfide precipitation regime as well as the ore genesis, unfortunately, systematic in situ sulfur isotope study of the time and spatial variations in Caixiashan have not been systematic studied yet. In this study, the SIMS is applied for in situ sulfides sulfur isotope from multiple stages and different spatial positions based on detailed field and indoor geological investigation and observation of Caixiashan Zn-Pb deposit, trying to clarify the sulfur sources, the evolutionary process and spatial variation of ore-forming fluid during upwelling, those of which enable us to comprehended the ore fluid generating, migration and precipitation regime etc., so as to identify the ore genesis of Caixiashan Zn-Pb deposit. This study will not only be able to shed light upon the sulfur sources and time and spatial variations of the ore fluid, but also has suitable value for the ore genesis classification based on the in situ sulfur isotopes.

彩霞山超大型铅锌矿是塔里木北缘前寒武纪基底中最大的铅锌矿，显示出优越的成矿条件和巨大的资源潜力，但由于其硫化物具有明显生长环带或重结晶等现象，传统硫同位素研究难以揭示成矿作用多期叠加的本质特征，其硫源特征和矿床成因研究一直存在争议。二次离子质谱仪能够有效获得矿物晶格内和共生矿物数微米内硫同位素的变化特征，不仅能揭示多期硫源和演化，还为硫化物沉淀机制和矿床成因研究提供借鉴。目前彩霞山铅锌矿硫化物原位硫同位素特征和空间变化规律尚未被系统研究，故本项目拟选择彩霞山铅锌矿为研究对象，对不同阶段（时间）和空间位置的硫化物样品开展原位硫同位素研究，还原硫化物硫源、演化特征及成矿流体上涌过程中的空间变化规律；辅助推断成矿流体形成、运移和沉淀等精细演化过程；并判定矿床成因类型。本研究不仅能揭示彩霞山铅锌矿硫化物硫源及时空变化规律，对原位硫同位素在铅锌矿成因机制的应用也具有较为重要的科学意义。

塔里木北缘前寒武纪基底中近年来发现了一批重要的铅锌矿床，如卡瓦布拉克–星星峡地块中的彩霞山超大型铅锌矿床（~131 Mt @ 3.95wt.% Zn + Pb）、宏源铅锌矿（60,000 t Zn @ 3.17wt.%和28,100 t Pb @ 1.10wt.%）等，引起了国内外学者的广泛关注并开展大量研究，但这些铅锌矿床的成矿流体来源、成矿作用过程、矿床成因及其与前寒武纪基底的内在联系等问题尚未被很好解决。彩霞山铅锌矿作为塔里木北缘最大的铅锌矿，储量可达超大型，在塔里木北缘乃至全国都占有重要的地位，是研究和探讨以上问题的理想对象。前人对彩霞山的区域地质、成矿流体、同位素和成矿年龄做了大量研究和总结，认为彩霞山具有多期成矿作用叠加的特征，这些成果为深入研究彩霞山铅锌矿阶段性成矿流体性质、来源和硫化物沉淀机制奠定了良好基础。然而在彩霞山铅锌矿硫同位素研究方面，前人仅限于对单矿物粉末的硫同位素进行了初步研究，但对共生硫化物和普遍发育的硫化物环带硫同位素分布特征，以及阶段性硫化物沉淀过程中硫同位素分馏规律及控制因素等方面还未有研究。这些问题的解决，是揭示彩霞山成矿流体演变过程和成矿机理的基础，可为塔里木北缘铅锌找矿勘查提供线索。