冈底斯东段羌堆铜钼矿床年代学、矽卡岩石榴石成分及其意义

Zircon U-Pb Geochronology and Garnet Composition of the Qiangdui Cu-Mo Deposit in the Eastern Section of Gangdese and Their Significances

羌堆铜钼矿床是在冈底斯成矿带东段新发现的一处斑岩-矽卡岩型矿床。二长花岗斑岩是该矿床的主要成矿斑岩体,本文用精确的LA-ICP-MS锆石U-Pb定年获得其年龄为16.7±0.9Ma,确定该矿床为中新世成矿,与冈底斯成矿带上驱龙、甲马矿床为同一期成矿事件。对该矿床矽卡岩中石榴石系统研究表明,早期矽卡岩主要以钙铝榴石为主,晚期以钙铁榴石为主;并暗示相应的成矿流体温度和盐度逐渐降低,而氧逸度和pH逐渐升高。另外,部分石榴石含有高含量的F,暗示成矿流体可能富含一定的F。同时,矽卡岩中发育石英-黄铜矿-辉钼矿等脉系,暗示有类似于斑岩型的后期热液活动叠加,以及钻孔中发现岩枝状产出的成矿二长花岗斑岩,综合显示下部有斑岩型矿床找矿前景。

The Qiangdui Cu-Mo deposit is a newly discovered porphyry-skarn type deposit in the eastern section of the Gangdese metallogenetic belt.Argillic monzogranite porphyry is the major ore-forming rock.In this study,ore-forming monzogranite porphyry yields the precise LA-ICP-MS zircon U-Pb age of 16.7±0.9Ma,confirming this deposit formed in the Miocene.This age indicates that the Qiangdui Cu-Mo deposit belongs to the same metallogenetic event as the Qulong and Tinggong Cu-Mo deposits,Jiama Cu-Pb-Zn deposit in the central Gangdese belt.Additionally,the systematic researches of garnets in the skarn indicate the early-stage skarn is dominated by grossular,and the late-stage skarn is dominated by andradite.This observation also suggests that the salinity and temperature of ore-forming fluid gradually decrease,while oxygen fugacity and pH gradually increase.Besides,partial garnets show high content of F,possibly suggesting the ore-forming fluids have a certain amount of F.It is worth noting that the quartz-chalcopyrite-molybdenite veinlets occur in the skarn,implying they may be superposed by the later hydrothermal activity similar to the porphyry type deposit.Ore-forming monzogranite porphyry apophyses appear in the drill holes.These observations may indicate that there is a prospecting potential of the porphyry type mineralization in the deep subsurface.