胶东玲珑金矿田早白垩世中-基性脉岩硫化物和硅酸盐熔体包裹体研究及其对成矿的启示

Close spatial and temporal associations between lode gold deposits and intermediate to mafic dykes are well recognized features of the North China Craton (NCC) and some Archean terranes worldwide. However, whether they have possible genetic relationships still remains poorly understood due to lack of convincing evidence. Silicate melt compositions and metals and volatiles dissolved in igneous systems prior to degassing and crystallization can be recorded in sulfide and silicate melt inclusions. Thus investigation on sulfide and silicate melt inclusions is an important approach to improve our understanding of the relation between magmatism and ore formation. In this proposed project, the early Cretaceous intermediate to mafic dykes from the Linglong gold ore field are selected. Systematic petrological and mineralogical studies will be conducted on the basis of detailed field investigation to better understand the internal mineral structure and occurrence of melt inclusions, and systematical in-situ sulfur isotope and elemental analyses will be further conducted on sulfide and silicate melt inclusions hosted by hornblende, clinopyroxene and plagioclase. These new data allow us to reveal whether geochemical signatures of the intermediate to mafic dykes are consistent with those of bulk ores and sulfides in the Linglong gold ore field. This project will not only assist to better understand whether gold deposits have direct genetic associations with intermediate to mafic dykes and related underlying magma chamber in the Jiaodong Peninsula and the formation of the giant late Mesozoic gold province in the NCC, but also may establish a possible relationship between lode gold deposits in the NCC and Archean terranes worldwide.

华北克拉通和国外前寒武纪变质地体中脉状金矿床与中-基性脉岩在时间和空间上高度耦合是一个普遍现象，可目前仍然缺乏有效的证据来揭示两者之间是否存在直接的成因联系。硫化物和硅酸盐熔体包裹体能够记录岩浆结晶和脱气之前岩浆的成分和成矿金属等关键信息，因而对熔体包裹体开展研究是理解岩浆与成矿之间联系的重要手段。本申请拟以玲珑金矿田及其外围早白垩世中-基性脉岩为对象，在详细的野外地质调查和室内微观鉴定基础上，开展脉岩内角闪石、单斜辉石和斜长石等斑晶硫化物和硅酸盐熔体包裹体原位微区主-微量元素和硫同位素组成研究，并与玲珑金矿田矿石的地球化学特征进行对比。预期研究成果不仅有助于揭示胶东地区金矿床与中-基性脉岩（及其深部岩浆房）之间是否存在直接的成因联系，对于正确理解华北克拉通脉状金矿床巨量金的聚集成矿有重要的理论意义，还有可能为我国该类型矿床与世界范围内其他地区脉状金矿床之间的联系建立纽带。

华北克拉通和国外前寒武纪变质地体中脉状金矿床是世界范围内一种重要的金矿床类型，但是关于金成矿的来源研究，以及金成矿与同时期中-基性脉岩之间的联系，仍然存在较大的争议。华北克拉通周缘（包括胶东、小秦岭、华北北缘等）产出的晚中生代金矿床是我国十分重要的黄金资源，对上述几个主要矿集区金矿床成矿作用进行研究，对于正确理解华北克拉通脉状金矿床巨量金的聚集成矿有重要的理论意义。本项目选取胶东半岛典型矿床（三山岛、九曲、玲珑、金翅岭、岭南），华北北缘典型矿床（柏杖子、金厂沟梁、铧尖），以及区域分布的脉岩和变质基底为研究对象，在详细的野外地质调查和室内微观观察基础上，开展了详细的微区地球化学、矿物学及全岩地球化学研究。通过对胶东地区典型金矿床硫化物微区同位素分析，发现载金硫化物Pb同位素特征明显偏离变质基底趋势，显示了向古生代扬子板块俯冲交代的华北岩石圈地幔的演化趋势，早白垩世太平洋板块的俯冲作用是大规模金成矿的触发机制。通过对华北北缘不同金矿床硫化物Pb同位素研究表明，华北北缘东段金矿床均集中产出于下地壳遭受强烈改造的区域，载金硫化物Pb同位素组成与下地壳的组成变化一致，表明成矿过程中金在下地壳尺度发生过短暂的停留，并再次向浅表运移富集成矿。基于以上研究成果，提出了一个华北克拉通周缘金矿床从岩石圈地幔、下地壳，到地壳浅层次，连续的成矿演化富集过程。