小秦岭镰子沟金矿床辉钼矿Re-Os年龄和锆石U-Pb年龄及其地质意义

Zircon U-Pb age of intrusive rocks and molybdenite Re-Os age for Lianzigou Au deposit in Xiaoqinling area and its geological significance

镰子沟金矿床位于小秦岭金矿集区西部,矿体受断裂和石英脉体控制,围岩蚀变以钾化和硅化为主。矿床浅部以金矿为主,深部发现金钼(共)伴生矿体。为了确定镰子沟金矿床成岩、成矿时代,选择镰子沟金矿床正长斑岩和金钼矿石分别进行了LA-ICP-MS锆石U-Pb和辉钼矿Re-Os同位素研究。获得正长斑岩的207Pb/206Pb年龄加权平均值为1802.9±9.9Ma,此年龄明显早于小秦岭地区金矿床的形成时代;获得辉钼矿Re-Os等时线年龄为128.8±6.5Ma,指示矿床形成于早白垩世,晚于区域已知花岗岩形成时代。综合研究认为,镰子沟金矿床的形成与区域花岗岩无关,可能与深部流体或隐伏岩浆有关。

The Lianzigou gold deposit is located in the west of Xiaoqinling Au ore concentration area. The orebodies are hosted in the upper strata of Taihua Group and controlled by fault fracture zone or quartz veins. The wall rock alteration is dominated by potassium alteration and silicification. Au(Mo) orebodies have been discovered in the depth of the deposit. To constrain its petrogenic and metallgogenic ages, the authors carried out LA-ICP-MS zircon U-Pb dating on syenite porphyry and Re-Os dating on molybdenite, respectively. LA-ICP-MS zircon U-Pb dating of syenite porphyry gave a weighted average age of 1802.9±9.9 Ma,which is clearly older than the age of large-scale gold mineralization in the Xiaoqinling area. Re-Os dating on molybdenite from the Au orebodies gave an isochron age of 128.8±6.5 Ma, indicating that the Au and Mo mineralization occurred in Early Cretaceous. The Re-Os age is younger than the petrogenic ages of granites in the Xiaoqinling area, showing that there is no direct relationship between the known granitic magmatism and the mineralization of the Lianzigou Au deposit. Deep fluids or concealed magmatic intrusion probably played an important role in mineralization.