新疆喀喇昆仑喀拉果如木铜矿成矿岩体地球化学和锆石年代学

Geochemistry and geochronology of the Kalaguorumu porphyry Cu-mineralized intrusions, Karakorum Mountains, Xinjiang

喀拉果如木铜矿是近年在新疆喀喇昆仑地区发现的铜多金属矿。铜矿化赋存在二长花岗斑岩中,矿石呈细脉浸染状、斑点状。矿石矿物主要为黄铜矿,少量黄铁矿、斑铜矿和毒砂。围岩蚀变有硅化、绢云母化和青磐岩化,具有与斑岩铜矿类似的蚀变组合。二长花岗斑岩主要由斜长石、钾长石、石英、黑云母及蚀变的暗色矿物组成。二长花岗斑岩的SiO2(67.28%～73.08%)、Al2O3(13.38%～15.53%)、K2O(2.92%～6.15%)和Na2O(2.78%～4.89%)含量较高,CaO和TiO2含量较低,属于高钾钙碱性系列;富集大离子亲石元素(LILE),亏损高场强元素(HFSE)和重稀土元素,Nb和Ta负异常,显示准铝质-弱过铝质过渡的特点,岩浆结晶分异作用明显,具有陆缘弧花岗岩的地球化学亲缘性,微量元素显示其为同碰撞-后碰撞花岗岩。成矿岩体锆石LA-ICP-MS测年结果为189.3±2.8Ma,成岩成矿作用发生在早侏罗世。结合区域地质演化,本文认为喀拉果如木铜矿形成于南昆仑地体与喀喇昆仑-甜水海地体之间的古特提斯洋消减闭合之后的后碰撞伸展背景,喀喇昆仑在晚三叠世-早侏罗世进入后碰撞造山时期。

The Kalaguorumu polymetallic porphyry copper deposit is newly-discovered in the Karakorum area. The copper mineralization occurs in the monzonitic granite-porphyry, characterized by veinlet, disseminated and spotted ore types. The major ore minerals are chalcopyrite, with a small amount of pyrite, bornite and arsenopyrite. The wall rock alteration includes silicification, phyllic and propylitic alterations, which are similar to those of the porphyry Cu deposits. The monzonitic granite porphyry is mainly composed of plagioclase, potash feldspar, quartz, biotite and altered mafic minerals. Geochemical analyses indicate that the rocks contain high contents of SiO2, Al2O3, K2O and Na2O, low contents of CaO and TiO2, belonging to the high-K calc-alkaline series. These rocks are relatively enriched in large ion lithophile elements （LILE）, depleted in high field strength elements （HFSE） and heavy rare earth elements （HREE）. They commonly have Nb and Ta negative anomalies and show metaluminous to weakly peraluminous features. Geochemical signatures of strong magmatic crystallization differentiation have also been identified, supported by trace elements with syn- to post-collision granites features. Zircon U-Pb （LA-ICP-MS） dating of the granite yields the weighted average 206Pb/238U age of 189.3±2.8Ma, indicating that the mineralization and its causative magmatism occurred in the Early Jurassic. Combining with regional geology, this study considers that the Kalaguorumu porphyry Cu deposit was formed in the post-collisional extension setting after Paleo-Tethys closure between the Karakorum-Tianshuihai and southern Kunlun terranes during the period of Late Triassic to Early Jurassic.