西藏冈底斯成矿带的斑岩-矽卡岩成矿系统:--来自斑岩矿床和矽卡岩型铜多金属矿床的Re-Os同位素年龄证据

笔者通过对冈底斯成矿带驱龙、厅宫斑岩铜矿区和甲马、知不拉等矽卡岩型铜多金属矿区的辉钼矿样品进行的Re-0s法同位素定年研究,获得驱龙、厅宫、甲马和知不拉等矿区的精确成矿年龄。4件驱龙斑岩铜矿区辉钼矿样品的Re-Os模式年龄介于(15.75±0.42)Ma～(16.23±0.90)Ma之间,等时线年龄为(15.99±0.32)Ma;7件厅宫斑岩铜矿矿区辉钼矿样品的Re-Os模式年龄介于(15.5±0.3)Ma～(16.3±0.3)Ma之间,等时线年龄为(15.49±0.36)Ma;在矽卡岩型铜多金属矿区中,7件甲马矿区辉钼矿样品的Re-Os模式年龄介于(15.4±0.2)Ma～(15.5±0.2)Ma之间,等时线年龄为(15.18±0.98)Ma;5件知不拉矿区辉钼矿样品的Re-Os模式年龄介于(16.88±0.28)Ma～(17.06±0.27)Ma之间,等时线年龄为(16.90±0.64)Ma。斑岩铜矿区和矽卡岩型铜多金属矿区所获得的年龄数据基本一致,其年龄明显晚于中生代弧间盆地和碰撞型花岗岩的发育时间,同时矽卡岩型铜多金属矿床在空间上亦分布于斑岩铜矿床的外围。因此笔者认为甲马和知不拉等铜铅锌矿床与冈底斯成矿带新生代晚期大规模成矿形成的斑岩铜钼矿床属于统一的斑岩-矽卡岩成矿系统,是由深源花岗质岩浆的岩浆-热液系统在不同的围岩介质条件成矿的产物。

THE PORPHYRY- SKARN ORE -FORMING SYSTEM IN GANGDESE METALLOGENIC BELT, SOUTHERN XIZANG: EVIDENCE FROM MOLYBDENITE RE- OS AGE OF PORPHYRY- TYPE COPPER DEPOSITS AND SKARN- TYPE COPPER POLYMETALLIC DEPOSITS

The relationship between porphyry copper deposit and skarn-type copper polymetallic deposit is an important issue in terms of study on mineralization in Gangdese metallogenic belt. In this paper, the highly precise Re-Os ages are acquired using molybdenite from Qulong, Tingong porphyry copper deposits and Jiama, Zhibula polymetallic copper deposits in the Gangdese metallogenic belt, respectively. The Re-Os model ages vary from ( 15.75±0.42) Ma to (16.23±0.90) Ma for 4 molybdenite samples from Qulong porphyry copper deposit, from (15.5±0.3) Ma to (16.3±0.3) Ma for 7 samples from Tingong porphyry copper deposit, from (15.4±0.2) Ma to (15.5±0.2) Ma for 7 samples from Jiama copper polymetallic deposit deposit, from (16.88±0.28) Ma to (17.06±0.27) Ma for 5 samples from Zhibula copper polymetallic deposit, yielding isochron ages of (15.99± 0.32) Ma, (15.49±0.36) Ma, (15.18±0.98) Ma and (16.90±0.64) Ma, respectively for all these samples. These ages of skarn-type polymetallic copper deposits are much younger than the ages of development of Gangdese inter-arc sedimentary basin and the ages of collisional granitic intrusive rocks in Gangdese block, but are obviously consistent with the mineralization ages of the porphyry copper deposits in the nearby regions, such as Qulong, Lakange in Jiama-Qulong ore-concentration area and Chongjiang, Tinggong porphyry copper deposits in Nyemo region in Gangdese metallogenic belt. The Re-Os ages thus derived suggest that the Jiama and Zhibula copper polymetallic deposits were formed in the same porphyry-skarn ore-forming system in a post-collisional extensional tectonic setting in Miocene epoch. The porphyry copper deposits and skarn type polymetallic copper deposits in Gangdese metallogenic belt are different results of mineralization processes of the same magmatic-hydrothermal system in different wall rock environments.