北祁连甘肃毛藏寺铜-钼矿床花岗质岩石锆石U-Pb年龄、地球化学特征及其地质意义  

Zircon U-Pb age,geochemical characteristics and geological significance of granitoids in the Maozangsi deposit,Northern Qilian Mountain

作　　者：赵辛敏 郭周平[1] 王育习[1] 高永伟[1] 张乐[2] 白赟 杨生飞[1] ZHAO Xinmin;GUO Zhouping;WANG Yuxi;GAO Yongwei;ZHANG Le;BAI Yun;YANG Shengfei(Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits/MLR, Xi’an Center of China Geological Survey, Xi＇an710054, Shaanxi, China;School of Earth Science and Resources/Chang＇an University, Xi＇an 710054, Shaanxi, China;Tibet Geological Research Institute of Nuclear Industry, Chengdu 610052, Sichuan, China)

机构地区：[1]国土资源部岩浆作用成矿与找矿重点实验室/中国地质调查局西安地质调查中心,陕西西安710054 [2]长安大学地球科学与资源学院,陕西西安710054 [3]核工业西藏地质调查院,四川成都610052

出　　处：《地质通报》2018年第4期669-681,共13页Geological Bulletin of China

基　　金：中国地质调查局项目<祁连成矿带肃南-大柴旦地区地质矿产调查>(编号:DD20160012)

摘　　要：甘肃毛藏寺铜钼矿是与花岗质岩石有关的斑岩型矿床,矿区内花岗质岩石类型主要为似斑状二长花岗岩和花岗闪长岩。对矿区岩体进行年龄、地球化学研究,以约束其形成时代,并探讨岩石成因及其与成矿的关系。LA-ICP-MS锆石UPb测年分别获得似斑状二长花岗岩与花岗闪长岩谐和年龄为455.8±3.1Ma和425.0±2.8Ma,属于晚奥陶世和晚志留世岩浆活动的产物。地球化学数据显示,似斑状二长花岗岩属于过铝质钙碱性岩浆系列,花岗闪长岩属于准铝质高钾钙碱性岩浆系列,二者均富集大离子亲石元素,亏损高场强元素,稀土元素配分曲线呈右倾型,轻、重稀土元素分馏明显。似斑状二长花岗岩具有弱正Eu异常(δEu=1.18～1.24),显示埃达克岩的地球化学特征,形成于北祁连洋俯冲消减阶段,由俯冲洋壳(含海洋沉积物)部分熔融形成,源区主要残留物为石榴子石。花岗闪长岩显示弱负Eu异常,形成于碰撞后伸展环境,是洋壳板片断离后软流圈上涌诱发的下地壳玄武质岩石部分熔融的产物。似斑状二长花岗岩符合成矿期埃达克岩特征,具有较好的成矿条件。结合前人资料,在北祁连东段寻找和勘查与埃达克岩有关的铜-钼-金矿可能是一个新的方向。The Maozangsi Cu-Mo deposit in Gansu is a porphyry type deposit related to granitoids. Maozangsi granitoids are com？posed of porphyritoid monzogranite and granodiorite. In this paper, zircon U- Pb dating and geochemical study of the Maozangsigranitoids were conducted to constrain its geochronology and discuss petrogenesis and its relationship with mineralization. ZirconLA-ICP-MS dating yielded concordant ages of 455.8±3.1Ma and 425.0±2.8Ma respectively, indicating that the two plutons wereformed in Late Ordovician and late Silurian respectively. Geochemical data show that porphyritoid monzogranite is a peraluminousgranite and belongs to the calc-alkaline series, whereas granodiorite is a aluminous granite and belongs to the high-K calc-alkalineseries. They are characterized by enrichment of LILEs and depletion of HFSEs, with REE patterns exhibiting the right- deviation type and strong fractionation with LREE enrichment. The porphyritoid monzogranite show weak positive Eu anomalies （δ Eu=1.18~1.24） and geochemical affinity to adakite, probably resulting from the slab melting （including marine sediments） of the subduction ofNorth Qilian Ocean with the residual minerals of garnet in the source. The granodiorite shows weak negative Eu anomalies and wasgenerated in a post-collisional extension setting and derived from partial melting of basaltic rocks in the lower crust induced by asthe.nosphere after the breakup of previously subducted North Qilian oceanic slab. The features of porphyritoid monzogranite are in ac.cordance with the characteristics of ore-forming period adakitic rocks and thus suggest good mineralization conditions. In combina.tion with data obtained from previous studies, the authors hold that it is possible to find Cu-Mo-Au deposits related to adakites inthe eastern section of the Northern Qilian Mountain.

关 键 词：花岗质岩石 地球化学 LA-ICP-MS锆石U-PB年龄 毛藏寺铜钼矿 北祁连 

分 类 号：P597.3[天文地球—地球化学] P618.41[天文地球—地质学]