西藏甲玛超大型铜矿石榴子石特征及成因意义

Features of Garnet in the Jiama Super-Large Cu Polymetallic Deposit and Its Genetic Significance

石榴子石是西藏甲玛超大型铜多金属矿床的主要矽卡岩矿物,分布广、颜色变化大,且石榴子石矽卡岩中矿化好,是开展甲玛矽卡岩成因研究的一个重要切入点。通过对甲玛矿区大量岩矿芯的地质编录,归纳石榴子石的颜色、晶形、矿物组合、矿化等地质现象,总结石榴子石在甲玛矿床的空间分布、矿化特征等,结合显微镜下鉴定,分析石榴子石的矿物学特征,并通过电子探针分析其化学成分。甲玛石榴子石集中于矽卡岩中,少量分布于角岩、大理岩和斑岩中。石榴子石为钙铁-钙铝榴石系列,以钙铁榴石为主,发育颜色与成分环带,光性异常致部分非均质。深色环带的SiO2、Al2O3含量较浅色环带高,而TFeO含量相反。石榴子石形成于矽卡岩早期,为晚期Cu、Mo、Pb、Zn、Au、Ag等多金属硫化物沉淀富集提供了有利空间。甲玛石榴子石的矿物学特征、化学成分组成、REE特征、流体包裹体、H-O同位素特征等显示其属于接触交代成因,认为甲玛是典型的岩浆热液接触交代矽卡岩型铜多金属矿床。

Garnet as one of the most typical and important skarn minerals in the Jiama super-large copper polymetallic deposit, Tibet is a key point for study of skarn due to its wide distribution, various colors and strong mineralization. Through the numerous geological logging of rock/ore core, this study summarized physical features such as color, crystal shape, mineral assemblage~ and geological features such as mineralization and spatial distribution. Combining with microscopic observation, author analyzed mineralogical features and chemical compositions using electron probe. The Jiama garnet is concentrated in skarn, with minor in hornfels, marble and porphyry. The contents of SiO2 and A12 03 in the dark zones are higher than those in the light zones, whereas the TFeO content is opposite. Garnet formed at the early stage of skarnization and provided a favorable space for precipitation of sulfides of Cu, Mo, Pb, Zn, Au and Ag mineralization at the late stage. The mineralogical features, chemical compositions, REE components, fluid inclusion and H-O isotope of garnet indicate its contact metasomatism genesis. Therefore, it is concluded that the Jiama ore deposit is a typical magma-derived hydrothermal contact metasomatism skarn type copper Dolymetallic deposit.