青海省牛苦头铅锌矿床成矿时代研究:来自成矿岩体年代学和黄铁矿Re-Os地球化学证据

Mineralization Age and Ore forming-Source of Niukutou Pb-Zn Deposit,Qinghai:Evidence from Geochronology of Ore-forming Rock Bodies and Re-Os Geochemistry of Pyrite

东昆仑造山带祁漫塔格地区是青海重要的矽卡岩多金属成矿带,牛苦头矽卡岩型矿床位于该地区中西段,为祁漫塔格地区探明的中-大型矽卡岩型铅锌多金属矿床之一。鉴于矿区成岩成矿时代以及金属成矿物质来源存在争议,笔者通过LA-ICP-MS及热表面电离质谱Re-Os同位素测试技术对锆石及黄铁矿年代学进行了研究。结果表明,牛苦头矿区M1矿段10线钻孔底部成矿花岗岩体年龄分别为(362.2±2.7)Ma、(361.8±3.4)Ma,与主成矿阶段闪锌矿密切共生的黄铁矿Re-Os等时线年龄为(359.2±6.3)Ma。牛苦头矿区矽卡岩铅锌多金属矿床成岩与成矿时代耦合于(362.2±2.7)~(359.2±6.3)Ma,表明该矽卡型铅锌多金属矿床形成于华力西期晚泥盆世。黄铁矿初始187OS/188Os值为0.13±0.24,表明牛苦头铅锌矿床金属成矿物质为壳幔混合来源,形成于晚泥盆世早古生代—晚古生代早期构造-岩浆旋回中碰撞-后碰撞的拉伸背景之下。

The Qimantagh area of East Kunlun orogeninc belt is an important skarn-type polymetallic mineralization belt in Qinghai,and the Niukutou deposit is located in the central-western part of this area,which is one of the middle-large Pb-Zn skarn deposits in Qimantagh area.In view of the controversy about the diagenetic and metallogenic age and the source of the metal ore-forming materials of Niukutou ore district,the zircon and pyrite chronology has been studied by LA-ICP-MS and thermal surface ionization mass spectrometry Re-Os isotope testing technology in this paper.The results show that the ages of the ore-forming granite bodies at the bottom of the 10 line drill hole in the M1 ore block of Niukutou ore district are(362.2±2.7)Ma and(361.8±3.4)Ma respectively,and the Re-Os isochron age of the pyrite closely associated with the sphalerite in the main mineralization stage is(359.2±6.3)Ma.This shows that the diagenesis and mineralization age of the skarn Pb-Zn polymetallic deposit in Niukutou ore district are coupled at(362.2±2.7)~(359.2±6.3)Ma,which further indicates that the skarn Pb-Zn polymetallic deposit was formed in the late Devonian of Variscan.The initial 187OS/188Os of pyrite is 0.13±0.24,which indicates that the metal ore-forming materials of Niukutou Pb-Zn deposit are of crust mantle mixed source,and formed under the extensional background of collision-post collision in the tectonic magmatic cycle from Early Paleozoic to early Late Paleozoic at Late Devonian.