湘南王仙岭与荷花坪花岗岩成因及其钨锡成矿作用

This proposal deals with studies on the petrological, geochemical and isotopic features and timing of the Hehuaping and Wangxianling granites associated with W-Sn deposits and probe to their source material nature and origin. The evolution of these two granite magmas and enrichment of ore-forming element W and Sn during this process are traced by investigations into the chemical features, morphology and paragenesis of rock-forming minerals and accessory minerals. The spacial distribution of ore bodies, alteration zoning, assemblage of the alteration minerals and ore-forming stage of the W and Sn deposits associated with these two granites are studied. On the basis of analysis of the O-H-S-Pb isotopic compositions of ores and fluid inclusions, property, source and evolution of ore-forming fluids are discussed. Dating of both the W- and Sn-deposits will be carried out and combined with timing of the granites, the corresponding relationship between the granites and the W- and Sn- deposit will be revealed. By the overall contrast of the geological and geochemical characters of the the Hehuaping and Wangxianling granites and also the associated W- and Sn-deposits the relationship between the genetic type of these two granites and the W- and Sn-deposits will be elucidated. The differences of formation conditions and origin between these two granites also are discussed. This proposal will discuss how the evolution and formation process of the granite magmas control W- and Sn-mineralization. The mineralogical and geochemical indicators of W-bearing and Sn-bearing granites will be established. This study not only deepens understanding the relationship between granite and W- and Sn-metallogeny, but also benefits exploration for W- and Sn-deposits.

本项目选择湘南荷花坪与王仙岭花岗岩及其有钨锡关矿床，系统开展花岗岩的岩石学、地球化学、同位素和年代学研究，探讨花岗岩的源区特征和成因。通过花岗岩的造岩矿物和副矿物的矿物化学与岩相学特征示踪岩浆演化过程和该过程中成矿元素钨锡的富集规律。研究与花岗岩有关的钨锡矿床矿体的空间分布特征、蚀变分带、蚀变矿物组合、蚀变期次和成矿阶段。通过O-H-S-Pb同位素和包裹体研究，探讨成矿流体的性质、来源和演化。查明矿床的形成时代，结合岩石定年研究，从年代学方面揭示钨、锡成矿与两个花岗岩的对应关系。综合对比两个花岗岩及有关矿床的地质和地球化学特征，探讨花岗岩成因与钨、锡成矿关系，分析两个花岗岩形成条件和成因差异，查明花岗岩演化与形成对钨锡成矿的制约作用，建立含钨和含锡花岗岩的地球化学和矿物学标志。这项研究不仅可以丰富花岗岩成岩成矿理论，加深对花岗岩成矿的理解，而且对指导找矿也具有重要的意义。

首次对荷花坪锡矿进行了锡石ICP-MS-LA U-Pb定年研究，构建了王仙岭-荷花坪地区成岩成矿年代学格架，确定该地区存在晚印支期和早燕山期两期成岩成矿作用。原位锆石和锡石U-Pb定年、辉钼矿Re-Os定年和白云母40Ar/39Ar测年显示，王仙岭花岗岩形成于约224Ma，钨成矿年龄为214Ma~224Ma，荷花坪黑云母花岗岩形成年龄约156Ma，锡成矿年龄约156Ma。定年结果显示钨成矿作用与晚印支期花岗岩有关，而锡成矿与早燕山期荷花坪花岗岩有关。王仙岭晚印支期钨矿化的确定进一步证实南岭晚印支期钨成矿作用值得重视，晚印支期花岗岩具有成矿和找矿潜力。荷花坪锡矿是一个典型的镁质矽卡岩型矿床，矽卡岩以镁橄榄石、尖晶石、透辉石、透闪石、蛇纹石、滑石和金云母等富镁矿物组合为特征。依据岩相学研究和矿物组合特征，可以进一步划分出三类矽卡岩：镁橄榄石-尖晶石-透辉石矽卡岩、金云母-绿泥石-蛇纹石矽卡岩和锡石-磁铁矿-透辉石矽卡岩。成矿可划分为四个阶段：进变质、退变质、锡石-硫化物和碳酸盐阶段。矽卡岩矿物成分研究显示，从早期矽卡岩到晚期矽卡岩，矽卡岩矿物的镁含量呈降低趋势，Fe和锰呈升高趋势。S和Pb同位素研究表明成矿物质主要来自地壳，H和O同位素特征揭示进变质阶段成矿流体主要来自岩浆，退变质阶段和晚阶段有大量大气降水参与成矿。流体包裹体研究表明，随成矿作用进行，流体温度和盐度逐渐，主成矿阶段成矿温度和盐度较低，岩浆流体与大气降水混合可能是导致锡成矿的有效机制。岩石化学、微量元素和同位素研究表明，王仙岭含钨花岗岩属属高分异过铝质S型花岗岩，由古元古代变质基底部分熔融形成；荷花坪含锡花岗岩属铝质A型花岗岩~，是由麻粒岩化的中元古代变质基底部分熔融形成。这两类花岗岩具有不同的地球化学特征，表现出明显的成矿专属性。南岭分布有较多的铝质A型花岗岩，因此，在华南要注意寻找与A型花岗岩有关的锡矿。