四川若尔盖阿西金矿岩石学及岩石地球化学特征

Petrology and petrogeochemistry of the A'gyi gold deposit, Zoige, Sichuan

关键词:  岩石学  岩石地球化学  阿西金矿

Key words:  petrology  petrogeochemistry  A'gyi gold deposit

摘要:

阿西金矿地处川甘陕"金三角"成矿集中区,中三叠统为本区内最重要的金矿源层和赋矿层。阿西金矿田的形成经历了一个从沉积-成岩-富集成矿的漫长复杂的由量的积累到质的飞跃过程,是多阶段、多层次、多因素作用有机结合的产物。赋矿岩系特征表明,阿西金矿田的主要成矿环境为半深海斜坡环境。区内岩石类型极为复杂,三大岩类均有产出。主要有细砂岩、杂砂岩、沉凝灰岩、碳酸盐岩、硅质岩;变粒岩、石英岩、角岩、大理岩、夕卡岩、角砾岩;岩浆岩类主要为英安斑岩(玢岩)、闪长岩等。其中最重要的赋矿岩石为石英岩,其主要特征为具块状、不规则条带状构造,呈褐黄色/浅灰色变余层状构造。由石英(75%~80%)、高岭石(10%~15%)、绢云母(2%~3%)、钛铁质(3%~4%)、玉髓(2%~3%)及少量碳质组成。其岩石化学成分与典型硅质岩相比,SiO₂偏低,Al₂O₃总体偏高,出现较强的高岭土化。通过研究认为,该区主要赋矿岩石石英岩的原岩应属正常碎屑沉积岩。

Abstract:

The A'gyi gold deposit in Zoige, Sichuan is located in the "golden triangle" as metallogenic clusters at the juncture of Sichuan, Gansu and Shaanxi Provinces, where the Middle Triassic strata are considered to be the most important source rocks and host rocks. The gold deposit resulted from polyphase geological processes and has polyphyletic origins, and thus recorded the complex evolution from deposition through diagenesis to enrichment and finally to mineralization. The study of the host rocks indicates that the gold deposit was formed in the bathyal-slope environment. The rocks cropped out in the region include the sedimentary and metamorphic rocks composed of fine-grainded sandstones, graywacke, sedimentary tuff, carbonate rocks, siliceous rocks, leptynite, quartzite, hornfels, marble, skarns and breccias. The magmatic rocks consist dominantly of dacite porphyry (porphyrite) and diorites. The quartzites as the most important host rocks exhibit massive and irregular banded structures, brownish yellow/light gray blastobedded structures, and consist of quartz (75%-80%), kaolinite (10%-15%), sericite (2%-3%), ilmenite (3%-4%), chalcedony (2%-3%), and a small amount of carbonaceous components. Petrochemically, the quartzites can be distinguished from the representative siliceous rocks by lower SiO₂, higher Al₂O₃ and highly kaolinization. The quartzites are interpreted to be a kind of altered products and their primitive rocks should be normal clastic sedimentary rocks.