青海祁漫塔格海西期成矿初探——以牛苦头M1铅锌矿床为例

The preliminary discussion of the Hercynian metallogenic period in Qimantag area——with the example of Niukutou lead and zinc deposit

牛苦头矿床位于祁漫塔格成矿带中西部,目前已探明铅锌资源储量逾100万t,是近年来祁漫塔格地区最具找矿潜力的矿区之一。大多数学者认为,祁漫塔格地区多金属矿床主要是三叠纪构造-岩浆作用的产物。然而,随着牛苦头矿区矿产勘查和科研工作的不断深入,发现牛苦头矿区与铅锌成矿有关的成矿岩体年龄为海西期。文章通过LA-ICP-MS锆石U-Pb年龄测得牛苦头沟西侧与M1、M4矿区(磁异常区)空间关系密切的岩体年龄为394Ma,此年龄与M1、M4底部岩体成矿岩体年龄一致,说明祁漫塔格地区中泥盆世可能发生了大规模的岩浆作用和与之有关的成矿作用。结合区域地质资料可知,青海祁漫塔格地区早、中泥盆世处于后碰撞的构造背景,暗示着早、中泥盆世可能是青海祁漫塔格地区另外一个重要的铅锌矽卡岩成矿期。

The Niukutou deposit is situated in the middle-west of Qimantag metallogenic belt.At present,1 million tons of lead and zinc reserves have been ascertained in this deposit,it is one of most potential deposits in this metallogenic belt.Most scholars believe that the Qimantag polymetallic deposits is the product of the Triassic tectonic-magmatic activity.However,with the profound study of the Niukutou deposit,it has been proved that the metallogenic epoch should be Hercynian.In this paper,we present new LA-ICPMS zircon U-Pb age of the Niukutou pluton,which show that the emplacement age of the Niukutou pluton is 393.7±4.9 Ma.This age is consistent with the bottom granitoids of M1 and M4 deposit,the latter is considered as the ore-forming rock bodies of Niukutou lead and zinc deposit.In combined with the regional geological data,the Niukutou pluton should be in the post-collisional tectonic setting,and also indicating that the early-middle Devonian may be the other metallogenic period of lead and zinc skarn deposit in the Qimantag area.