青海东昆仑西藏大沟金矿床花岗闪长斑岩锆石U-Pb年龄、地球化学及其成矿意义

摘要

The Xizangdagou gold deposit lies in the Bayan Har tectonic belt of East Kunlun.LA-ICP-MS zircon U-Pb dating shows that the weighted mean age of granodiorite porphyry, which is closely related with the mineralization of the Xizangdagou gold deposit, is(225.0 ±1.2)Ma, in the Late Triassic. This suite of rocks are enriched in LILE(such as Rb,Sr,Ba,K),LREE and Pb,relatively depleting in HFSE(such as Nb,Ta,P,Ti),with rich LREE and low HREE.Based on the study of evolutionary characteristics of regional structures and chronologic data of gold deposits in East Kunlun, the authors suggest that the granodiorite porphyry in the Xizangdagou gold deposit was formed under a conversion tectonic setting from compressional to extensional,and the Xizangdagou gold deposit formed at 225.0~218.6 Ma,in the Late Triassic.%利用LA-ICP-MS锆石U-Pb定年,对位于东昆仑地区巴颜喀拉成矿带的西藏大沟金矿床进行研究,首次获得与成矿有密切关系的花岗闪长斑岩加权平均年龄为(225.0 ±1.2)Ma,厘定为晚三叠世;岩石明显富集大离子亲石元素(Rb、Sr、Ba、K)、轻稀土元素和Pb,明显亏损高场强元素(如Nb、Ta、P、Ti),显示轻稀土元素强烈富集的右倾式稀土配分型式.结合东昆仑地区区域构造演化及金矿成矿年代学资料分析认为,西藏大沟金矿床花岗闪长斑岩形成于挤压向伸展转换阶段,西藏大沟金矿床成矿时间应介于225.0~218.6 Ma,属晚三叠世.