Zircon U-Pb Geochronology and Petrogenesis of Taipinggou Copper (Gold)-related Granites, South Qinling
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摘要: 太平沟铜（金）矿床位处秦岭造山带南秦岭印支期褶皱带与老牛山-胭脂坝燕山期北东向构造岩浆岩带交汇的构造结合部位，与矿化相关的蚀变岩体呈似椭圆状，地表出露面积为0.12 km2；蚀变岩体以石英闪长岩、细粒花岗岩为主，局部可见有斑状花岗岩，其中石英闪长岩、细粒花岗岩与铜（金）矿化具有密切的成生关系。锆石的LA-ICP-MS U-Pb年代学研究表明，太平沟矿化石英闪长岩成岩年龄为（223.2±2.9）Ma，表明其侵位于晚三叠世，指示本地区铜（金）矿化成矿时代为印支晚期。岩石地球化学分析表明，石英闪长岩具有富钾（Na2O/K2O=1.21～1.75）和富碱（Na2O＋K2O=7.31%～9.67%）的特点，属高钾钙碱性系列准铝质岩石；岩石的稀土元素总量较高，具明显负Eu异常，稀土配分模式呈明显右倾型；微量元素以Ba、U、K等大离子亲石元素富集，Nb、P、Ti等高场强元素亏损为特点，属于I型花岗岩。综合分析认为，太平沟铜（金）矿床为印支晚期岩浆活动的产物，暗示南秦岭宁陕—镇安地区存在重要的印支晚期岩浆成矿事件。Abstract: Taipinggou copper (gold) deposit is located in Qinling orogenic belt, at the junction of the Indosinian fold belt of south Qinling and the northeastern structural magmatic belt of the Laoniushan-Yanzhiba period. The altered rock mass relating to mineralization appears to be an ellipse, with a exposed surface area of 0.12 km2. The altered rock mass is mainly composed of quartz diorite and fine-grained granite, which were closely related to copper (gold) mineralization, with porphyry granite scattered. The LA-ICP-MS zircon U-Pb shows that the age of Taipinggou quartz diorite mineralization is 223.2±2.9ma, indicating that it was emplaced in late Triassic of the late Indosinian. The geochemical analysis shows that the quartz diorite is potassium-rich (Na2O/K2O=1.21-1.75) and alkali-rich (Na2O+K2O=7.31%-9.67%) and belongs to high-potassium calc-alkaline series of quasi aluminous rocks. The total amount of rare earth elements in the rocks is high, with obvious negative Eu anomaly, and the REE distribution pattern is obviously right dipping. The trace elements are characterized by the enrichment of big ion lithophile elements such as Ba, u, K, and the depletion of high field strength elements of Nb, P, Ti, belonging to type-I granite. Based on the comprehensive analysis, the authors hold that Taipinggou copper (gold) deposit is the magmatic activity of late Indosinian, suggesting some important magmatic mineralization events in late Indosinian in Ningshan-Zhen'an area of South Qinling.
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Key words:
- granite /
- copper (gold) ore /
- chronology /
- petrogenesis /
- Taipinggou /
- south Qinling
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