摘要
普朗铜矿床是格咱岛弧产出的超大型斑岩型铜矿床,以往较多关注于含矿的石英二长斑岩,而对矿区出露的闪长岩、花岗闪长斑岩研究相对薄弱.对普朗矿区的闪长岩和花岗闪长斑岩开展了地球化学和锆石年代学分析,结果显示,闪长岩SiO_2含量为62.46%~62.25%,K_2O含量为5.53%~6.27%,MgO含量为3.58%~3.69%,(Na_2O+K_2O)总碱含量为7.93%~8.72%,K_2O/Na_2O>2,属中性超钾质碱性岩;花岗闪长斑岩SiO_2含量为66.00%~66.98%,K_2O含量为4.06%~4.19%,MgO含量为2.04%~2.17%,(Na_2O+K_2O)总碱含量为7.60%~7.81%,K_2O/Na_2O>1,属酸性钾质碱性岩.花岗闪长斑岩与中甸地区火山岩具有一致的Sr-Nd同位素特征,而闪长岩εNd(t)值变化范围大,二阶段模式年龄分散(369 Ma、913 Ma、1 138 Ma),指示有富集组分的混入.闪长岩LA-ICPMS锆石U-Pb年龄为227.0±2.9 Ma;花岗闪长斑岩LA-ICPMS锆石UPb年龄为211.5±3.7 Ma.结合岩石主量、微量元素、全岩Sr-Nd同位素及锆石U-Pb年龄,提出甘孜-理塘洋在长时期的西向俯冲(约25 Ma)过程中,普朗矿区(局部)可能发生过由挤压向伸展构造体制的转换,激发幔源的岩浆活动,导致钾质碱性小岩体侵位,该过程对该超大型斑岩铜多金属矿的形成具有重要意义.
The Pulang copper deposit is a super-large porphyry deposit located in Geza island arc in Yunnan Province.Previous studies were mostly concentrated on the ore-bearing quartz-monzonite porphyry,while the research on the diorite and granodiorite porphyry was relativelyweak.Inthispaper,we present geochemistry and zircon chronology analysis on the diorite and granodiorite porphyry in Pulang mine,northwest of Yunnan Province.The diorite is characterized by low SiO2（62.46%-62.65%）,high K2O（5.53%-6.27%）and total alkali（K2O＋Na2O=7.93%-8.72%）,K2O（5.53%-6.27%）,MgO（3.58%-3.69%）,and K2O/Na2O is bigger than 2.Likewise,the grano-diorite-porphyry is characterized by medium SiO2（66.00%-66.98%）and high total alkali（7.60%-7.81%）,with MgO（2.04%-2.17%）,and the K2O/Na2O is bigger than 1.They are enriched in large-ion lithophile and light earth elements,but depleted in high fieldstrength and heavy rare earth elements,and with weak to negative Eu anomalies.Furthermore,diorite yields lower（87 Sr/86 Sr）iratios（0.705 24-0.705 31）than granodiorite-porphyry（（87 Sr/86 Sr）i0.705 58-0.705 62）,and the granodiorite-porphyry yields negativeεNd（t）values from-3.34 to-1.01,while the diorite yields variableεNd（t）values from-1.65 to 7.78.New U-Pb dating of zircons of diorite and granodiorite-porphyry are 227.0±2.9 Ma and 211.5±3.7 Ma respectively.Comprehensively,we propose that a transformation from compression to extension process may have occurred in the Pulang area during the long period of westward subduction of Garze-litang ocean（about 25 Ma）,which has triggered the mantle source magmatic activity,and has resulted in the emplacement of deep source（ultra）potassium alkaline.And the transformation process is crucial to the formation of super-large porphyry deposit.
作者
石洪召
范文玉
胡志中
董涛
余海军
尹光侯
Shi Hongzhao;Fan Wenyu;Hu Zhizhong;Dong Tao;Yu Haijun;Yin Guanghou(Chengdu Center of China Geological Survey,Chengdu 610081,China;Key Laboratory for Sedimentary Basin and Oil and Gas Resource,MLR,Chengdu 610081,China;Yunnan Geological Survey,Kunming 650051,China;Yunnan Geological Survey Institute,Kunming 650051,China)
出处
《地球科学》
EI
CAS
CSCD
北大核心
2018年第8期2600-2613,共14页
Earth Science
基金
中国地质调查局项目(Nos.121201210000160017
121201210000160007)
