大兴安岭下嘎来奥伊铅锌矿床钾长花岗岩的岩石成因及地质意义

Petrogenesis of Moyite from Xiagalaiaoyi Pb-Zn Deposit in Great Xing’an Range and Its Geological Significance

下嘎来奥伊铅锌矿床位于黑龙江省西北部,大地构造位于额尔古纳地块额木尔山隆起带南缘与大兴安岭火山岩带北缘接合部位的西段。研究区广泛分布大面积不同期次侵入岩,矿体产于中酸性浅成侵入岩及其与大理岩接触带——矽卡岩带中。LA-ICP-MS锆石U-Pb定年结果表明,下嘎来奥伊钾长花岗岩成岩年龄为(168.9±2.1)、(165.9±2.1)Ma,认为其成矿时代为中侏罗世。元素地球化学测试结果显示,下嘎来奥伊钾长花岗岩属于准铝质-弱过铝质碱性系列;岩石具有高Si、K、碱和贫Al质量分数的特征;A/CNK值为0.97~1.02;锆石饱和温度介于760~851℃之间,平均温度为811℃,具A型花岗岩特征;稀土元素特征表现为轻稀土富集、重稀土相对亏损,富集大离子亲石元素(Rb、K)和高场强元素(Th、U、Zr、Hf),亏损高场强元素(P、Ti、Nb、Ta),具Eu负异常(δEu值为0.01~0.27)。下嘎来奥伊钾长花岗岩w(Sr)=(13.20~62.80)×10^-6,平均值为38.95×10^-6,w(Yb)=(2.44~7.81)×10^-6,平均值为4.50×10^-6,属于低Sr高Yb质量分数型花岗岩。结合区域大地构造背景及相关研究认为,矿区钾长花岗岩的形成与中侏罗世蒙古—鄂霍茨克洋闭合所形成的伸展环境密切相关。

Xiagalaiaoyi Pb-Zn deposit is located in the west section of the intersection line between the south edge of the Erguna block Ermul Mountain uplift and the north margin of the Great Xing’an Range volcanic belt,northwest of Heilongjiang Province.Non-contemporaneous intrusive rocks are widely distributed in Xiagalaiaoyi district,and the ore bodies occur in the intermediate-acrid hypabyssal intrusive rocks and their contact zone with marble.LA-ICP-MS zircon U-Pb dating results show that the diagenetic age of moyite is(168.9±2.1)Ma-(165.9±2.1)Ma,suggesting that the metallogenic age of Xiagalaiaoyi Pb-Zn deposit is Middle Jurassic.Based on the geochemical data,the moyite belongs to quasialuminous to weakly per-aluminous alkaline A-type granite,which is characterized by high Si,K and alkali,poor Al,A/CNK value of 0.97-1.02,and the saturation temperature of zircons ranges from 760to 851℃(average 811℃).The granite exhibits weakly negative Eu anomalies(δEu=0.01-0.27),enrichment of LREE,large ion lithophile elements(such as Rb and K),high-field strength elements(such as Th,U,Zr and Hf),and depletion of HREE and high-field strength elements(such as P,Ti,Nb and Ta).The rocks belong to low-Sr and high-Yb type granites with Sr(13.20-62.80)×10-6(average 38.95×10-6)and Yb(2.44-7.81)×10-6(average 4.50×10-6).Combined with the relevant regional tectonic evolution research,we conclude that the moyite formation is closely related to the extensional environment after the closure of the Mongolia Okhotsk Ocean during Middle Jurassic.