胶西北焦家断裂带深部成矿流体包裹体特征

焦家断裂带是胶西北地区最重要的断裂带之一, 很多大中型金矿床沿此带分布。依托莱州市吴一村地区焦家断裂带深部的"中国岩金第一见矿深钻"钻孔岩心, 挑选了不同蚀变阶段及主断裂带上下盘不同深度的花岗岩、黄铁绢英岩和金矿石开展流体包裹体岩相学、显微测温及激光拉曼分析研究, 识别出3个成矿阶段、5个世代富含流体包裹体的石英和两大类型流体包裹体; 焦家断裂带深部金成矿流体性质为中-低盐度H2O-NaCl-CO2±CH4流体; 成矿流体来源为地幔富含成矿金属的流体与浅部下渗大气降水混合成因, 并可能有壳源变质流体的参与; 成矿流体中金主要以一价金的硫氢络合物(AuHSo)形式迁移。岩相学观察及显微测温结果表明, 主成矿阶段发生了H2O-CO2流体不混溶作用, 并导致金矿化, 发生流体不混溶的温度压力条件分别为210~260℃和150~210 MPa。中生代, 古太平洋板块向欧亚大陆的北西向俯冲, 引起胶东地区强烈的挤压变形和岩浆活动(形成玲珑花岗岩体)。随后, 在早白垩世, 构造体制从挤压向伸展转换, 导致郭家岭花岗岩的侵位、郯庐断裂带的左型走滑运动, 以及一系列NE—NNE向次级断裂形成, 为深部岩浆-热液流体的上升提供了通道。在岩浆-热液流体上升过程中与地壳中-上部循环的变质水和大气水发生混合, 最终形成金矿床。

The study of fluid inclusions in the deep part of the Jiaojia fault zone in the northwest of Jiaodong Peninsula

The Jiaojia fault zone, along which many large and medium-sized gold deposits are distributed, is one of the most important fault zones in the northwest of Jiaodong Peninsula.In this work, we have collected core samples from the "China's deepest drill-hole controlling gold orebody" to carry out a fluid inclusion study.This drill-hole conducted by Shandong Institute of Geological Sciences lies at Wuyicun village of Laizhou city and penetrates the deep part of the Jiaojia fault zone.The samples include fresh and altered granites, phyllic rocks with pyrite-sericite-silicic alteration and ores at different alteration stages and different depths on the hanging wall and footwall of the main fault zone.Through detailed field investigation and petrographic study of the samples we have identified three metallogenic stages, five generations of quartz and two types of fluid inclusions in the ores.Microthermometry and Laser Raman analysis were performed on the representative fluid inclusions.The results have suggested that the fluids responsible for gold mineralization in the deep part of the Jiaojia fault zone belong to the H2O-NaCl-CO2±CH4 fluids with medium to low salinity, which were generated by mixing of the mantle-origin metal-rich fluid and the shallow meteoric fluid with possible participation of the crustal metamorphic fluid.The gold in the ore-forming fluids occurs mainly as hydrosulphide complexes(AuHSo).Both fluid inclusion petrography and microthermometry have shown the phase separation(immiscibility)of H2O-NaCl-CO2±CH4 fluids took place during the main ore mineralization stage and caused gold deposition.The immiscibility occurred at the P-T conditions of 210 ~ 260 ℃ and 150~210 MPa, respectively.In the Mesozoic, the ancient Pacific plate initially subducted northwesterly towards the Eurasian continent that caused intense compresional deformation and magmatism(e.g.formation of the Linglong granite)in Jiaodong region.Later in Early Cretaceous, tectonic transition from transpression to trnastension in the region resulted in the Guojialing granite emplacement and strike-slip movement of the Tanlu fault as well as development of a series of subsidiary NE—NNE trending faults, which provided channels for the ascending of magmas and fluids from the deep.In this process the magmatic-hydrothermal fluids were mixed with metamorphic and meteoric fluids circulating in the middle and upper crust, and finally led to the formation of gold deposits in the Jiaodong region.