西藏邦铺钼(铜)矿床含矿二长花岗斑岩LA-ICP-MS锆石U-Pb定年及地质意义

摘要

邦铺斑岩型钼(铜)矿床位于甲玛铜多金属矿床北东约30 km处,与钼(铜)成矿有关的岩体主要为二长花岗斑岩,次为花岗闪长斑岩及闪长(玢)岩.通过对二长花岗斑岩体进行LA-ICP-MS锆石U-Pb年龄测试,获得了含矿母岩的年龄,二长花岗斑岩的26颗锆石206Pb/238U加权平均年龄为(16.23±0.19)Ma(MSWD＝2.0,n＝26),系冈底斯带中新世花岗质岩浆侵位的时间.前人所测的辉钼矿Re-Os同位素等时线年龄为(15.32±0.79)Ma,晚于所测的成岩年龄约1 Ma.邦铺斑岩型钼(铜)矿床与甲玛、驱龙等斑岩-矽卡岩型矿床的成岩成矿时代具有统一性,区域成矿规律的研究表明,该矿床与甲玛、驱龙斑岩型矿床应具有一致的构造、岩浆地球化学动力学背景,系印-亚大陆碰撞过程中伸展背景下的成矿大爆发的产物.%The Bangpu porphyry Mo (Cu) deposit is located about 30 km northeast of the Jiama copper polymetallic deposit. The rocks related to molybdenum mineralization in this ore deposit are mainly monzogrante porphyry,with minor granodiorite porphyry and diorite (porphyrite). The age of the ore-forming rock was obtained through LA-ICP-MS precise determination of the zircon U-Ph age for the molybdenite-bearing monzogranite porphyry. 26 zircons from the monzogranite porphyry yielded the weighted average 206pb/238U age of ( 16.23 ±0.19) Ma (MSWD= 2.0, n = 26), suggesting Miocene granitic magma emplacement in the Gangdese belt.The previous dating of the molybdenite from this ore deposit had yielded a Re-Os isochron age of (15.32 ± 0.79)Ma, which is about 1 Ma later than the time of rock cooling. Thus the authors' work has improved the constraint of mineralization in time. Regional minerogenetic regularity shows that the Bangpu porphyry Mo (Cu)polymetallic deposit has an uniformity with the regional porphyry-skarn deposits (such as Jiama, Qulong and other ore deposit in this region) in the age of petrogenesis and mineralization, which shows that this ore deposit has the same tectonic and magrnic geochemical dynamic background as other ore deposits in this region, and that this ore deposit was a product of mineralization explosion during the extension phase after India-Asia continental collision.