江西武山和永平铜矿含矿花岗质岩体锆石SIMS U-Pb年代学

Zircon SIMS U-Pb Geochronology of Host Granitoids in Wushan and Yongping Copper Deposits, Jiangxi Province

江西武山和永平铜矿床是长江中下游金属成矿带中的两个重要矿床。对武山铜矿的花岗闪长斑岩和永平铜矿的花岗斑岩中锆石分别进行了离子探针(SIMS)U-Pb定年研究,发现两个矿区的锆石年龄可分作两期,武山铜矿含矿岩体锆石206Pb/238U年龄分别为145±3.9Ma和121±2.5Ma,永平铜矿含矿岩体锆石206Pb/238U年龄分别为160±2.3Ma和135±7.4Ma。这两期不同的年龄可能反映了锆石在岩浆侵位时的结晶年龄和后期热液蚀变作用的年龄。因此确定武山铜矿花岗质岩体的侵位年龄为145Ma,永平铜矿花岗质岩体的侵位年龄为160Ma。该年龄可能也反映了这两个矿床中与燕山期岩浆侵入有关的矽卡岩型矿床和斑岩型矿床的形成时代。

Wushan and Yongping deposits are two of the most important copper deposits in the Lower Yangtz Mineralization Belt. In this study, SIMS U-Pb dating was performed on zircons from host granitoids in both Wushan and Yongping deposits, Jiangxi province. Zircons from both Wushan and Yongping deposits yield two distinct age groups. In Wushan deposit the zircon ages are 145 ±4 Ma and 121 ±3 Ma. In Yongping deposit the zircon ages are 160 ±2 Ma and 135 ±7 Ma. The zircons of earlier stage were likely formed during emplacement of intrusion, and the later ones formed during the later magmatic evolution and/or hydrothermal alteration. We suggest that the granitic magma intrusion ages of Wushan and Yongping deposits are 145 ±4 Ma and 160 ±2 Ma, respectively. These ages also represent the ore forming age for both skaru and porphyry ores that related to the intrusions of Yanshanian magmatism in these two deposits.