西藏甲玛铜多金属矿床石英脉特征

Characteristics of quartz in stock work veins from Jiama copper polymetallic deposit,Tibet

西藏甲玛铜多金属矿床位于冈底斯火山岩浆弧的东段,是冈底斯成矿带的重要组成部分,也是最具代表性的产于后碰撞伸展环境中的超大型斑岩-矽卡岩-浅成低温热液铜多金属矿床。文章以该矿区斑岩体中各类脉体的矿物特征,尤其是脉体石英显微结构以及微量元素特征为切入点,初步划分出3大类5个阶段的岩浆-热液流体。金属硫化物主要沉淀于第2、第4和第5阶段。脉体石英中Al、Fe、K含量的变化指示了流体pH值的变化以及与钾化有关的蚀变。流体的温度范围跨度极大,从602℃到130℃,即从斑岩型高温岩浆流体演化为浅成低温热液型流体。岩浆热液生命周期至少持续3 Ma,具有多期多阶段性,开始于岩浆房中岩浆-热液流体的出溶,一直演化至成矿作用结束,贯穿整个岩浆-热液成矿系统。含矿流体中金属元素沉淀得益于岩浆流体pH值的改变。

The Jiama polymetallic copper deposit is located in eastern Gangdise volcano-magmatic arc,which is an important component part of the Gangdise metallogenic belt.The Jiama deposit is a typical superlarge porphyry-skarn-epithermal polymetallic copper deposit related to post-collision.The combination of scanning electron microscope-cathodoluminescence（CL） and LA-ICP-MS microanalysis of Al,Ti,K and Fe in veined quartz has yielded results permitting a greater understanding of the complex mineralization of the Jiama porphyry-style deposit.The data obtained demonstrate the relationship between quartz precipitation,dissolution and ore deposition with the variation of ore-forming fluid through time.Five major quartz generations were identified.Ti-in-quartz geothermometer and fluid inclusion analysis show that the crystallization temperature from JMi to JMⅴ varies between 602°C and 130°C.The CL and trace element signatures from JMi to JMⅴ stages of the porphyries show features similar to those observed in porphyry-style deposits of other areas.This suggests that a common sequence of quartz crystallization occurred during the formation of early veins in many porphyry copper systems.