党河南山乌里沟中酸性岩体锆石U-Pb年龄、地球化学特征及与金矿成矿关系

通过对南祁连山党河南山东段乌里沟金矿区中酸性侵入岩锆石U-Pb年龄测定及岩石地球化学分析,探讨了岩体形成的构造环境及其与金矿成矿的关系。矿区角闪石闪长岩体侵位年龄为457±6.3 Ma,岩石中各组分的质量分数:SiO2为48.98%~59.16%,Al2O3为14.51%~16.77%,K2O+Na2O为8.24%~9.47%,属准铝质、碱性-过碱性岩系列;DI为58~79,属I型花岗岩类;岩石Cr和Mg#值较低,Na2O和K2O含量接近,表明源岩含有较多的壳源成分;稀土总量中等,轻稀土富集,具弱Eu负异常;相对富集大离子亲石元素Rb、Ba、Th、K、U,亏损Nb、Ta、P、Ti。矿区二长花岗岩属碱性岩系列,比角闪石闪长岩稀土总量低、更加亏损Nb、Ta等,与角闪石闪长岩属同一岩浆源,分异程度比角闪石闪长岩高。两种岩石均具岛弧岩浆岩特征,是中晚奥陶世南祁连俯冲到较浅部位熔融形成。岩体金含量高,目前探明的矿体产于岩体内部及接触带,围岩蚀变强烈,显示岩体为金矿成矿提供物质来源和成矿热液。

Zircon U-Pb geochronology and geochemical characteristics of neutral-acidic intrusions of Wuligou in South Qilian Mountains:their implications on forming gold deposit

This paper reports the zircon U-Pb dating and the lithogeochemistry of the small-scale neutral-acidic intrusions in the Wuligou gold deposit in the east of Danghenanshan,South Qilian Mt., and interprets their tectonic settings and the linkage to gold mineralization.Our data show that the emplacement age of the amphibole diorite is 457 ±6.3 Ma.The mass fraction of SiO2 is 48.98% ~59.16%,that of A1 2 O3 is 14.51%~16.77%,that of (K2 O+Na2 O)is 8.24%~9.47% and that of DI is 58 ~ 79,indicating that the amphibole diorite belongs to the ultra-alkaline to alkaline,sub-aluminous rock series and I-type granitoid rocks.The amphibole diorite is poor in Cr and has low value of Mg# ,suggesting that its source rock has many crust materials.The total REE is moderate and LREE is rich,with slightly negative Eu abnormity.The large ion lithophile elements of Rb,Ba, Th,K,U are relatively rich and Nb,Ta,P,Ti are poor.The monzonitic granite belongs to the alkaline rock series,and its total REE is lower than that of the amphibole diorite and its Nb and Ta are more poor. These two types of rocks are originated from the same magma source. The differentiation of the monzonitic granite is higher than that of the amphibole diorite.They have geochemical characteristics of the island arc magmatic rock,and formed in the island arc when the north margin of Qaidam subducted beneath South Qilian during middle-late Ordovician.The Wuligou gold deposit is temporally and genetically related to the intrusions,because the alternation and the mineralization occur in the intrusion’s contact zones,and the Au content is extremely higher than that in the crust.All these show that the intrusions provide both the metallogenic materials and the thermal fluids for the formation of the gold deposit.