拉拉铁氧化物铜金钼稀土矿床Re-Os同位素年龄及其地质意义

拉拉铁氧化物-铜-金-钼-稀土矿床的成矿年龄一直悬而未决.文章采用辉钼矿Re-Os同位素方法,首次对该矿床的形成年龄进行了直接测定.4个样品的测定结果为:928(±1)～1 005(±1) Ma.这一结果与矿床的地质事实相吻合,因此它代表了拉拉矿床的成矿时代.根据这一年龄数据与赋矿围岩河口群的变质年龄相一致等证据,初步提出拉拉矿床为变质热液成因.此外拉拉矿床的矿化时代与Rodinia泛大陆拼贴的时限相当,这表明Rodinia泛大陆拼贴事件对扬子地块的成矿作用产生了深刻的影响.

Re-Os DATING OF MOLYBDENITE FROM LALA Fe-Oxide-Cu-Au-Mo-REE DEPOSIT, SOUTHWEST CHINA: IMPLICATIONS FOR ORE GENESIS

The recentl works suggest that Lala deposit, located in Sichuan Province of China, is a typical Fe-Oxide-Cu-Au-Mo-REE deposit (Wang et al, 2002). Lala deposit is situated in the western margin of Yangtze block. The host rock of the deposit is named He Kou Group. He Kou Group is composed of quartz albitite, garnet-biotite schist, magnetite quartzite, quartz schist, hornblende schist and minor marble. The protolith of the quartz albitite, garnet-biotite schist, magnetite quartzite are spilite, keratophyre, and keratophyre volcaniclastic rock, with subsidiary co-genetic intrusive rocks.The Lala deposit appears to have the forms of lens and vein. The deposit strike east northeast and dip at approximatel 30° to south. The mineralization are also accompanied by high P concentrations, and anomalous, but erratic, F, U, Th, Nb and Ta. It was reported that the deposit was formed by the magmatic hydrothermal fluids secreted from a gabbro sill, at 800 Ma. In this paper, direct dating of molybdenite from the deposit using the Re-Os method has been done. Four Re-Os ages range between 928±1 Ma and 1005±1 Ma. These ages are interpreted as the age of Cu and Mo mineralization. This age is much older than the emplacement ages for the main intrusive suites. The age is consistent with the age of the metamorphism of He Kou Group, which is 969±52 Ma of the whole rock Rb-Sr dating of muscovite schist (Li et al.1988). We suggest that Cu and Mo mineralization is genetically linked to the metamorphic hydrothermal fluid processes at 1000 Ma thereby precluding the 800 Ma gabbro as the source for mineralizing fluids.