内蒙古二道河子铅锌银多金属矿床流体包裹体红外显微测温研究

Infrared Microthermometry of Fluid Inclusions in the Erdaohezi Pb-Zn-Ag Polymetallic Deposit, Inner Mongolia

二道河子铅锌银多金属矿床是得耳布干成矿带具有代表性的铅锌矿床之一。闪锌矿作为主要矿石矿物,可分为早期黑色-中期红棕色或棕色-晚期黄褐色或浅黄色三个世代。采用红外显微镜技术和激光拉曼技术对不同世代闪锌矿及共生石英中的流体包裹体进行显微测温和成分测试,初步认为三个世代闪锌矿基本与石英内的三次流体活动相对应,推测它们形成于同一物理化学条件,捕获同一成矿流体,但闪锌矿流体包裹体能更直观而细致地勾勒出成矿流体的演化过程。从成矿早期至晚期,随着流体演化,流体包裹体的均一温度、盐度及CO2含量均明显下降,流体从中温、中低盐度、CO2-H2O-NaCl体系向低温、低盐度、H2O-NaCl体系演化。此外,在整个主成矿过程中,影响成矿物质沉淀富集的机制也随时间变化有所差异:早期流体沸腾是黑色闪锌矿等硫化物形成的重要因素;中期以流体自然冷却作用为主,形成了红棕色闪锌矿等硫化物;至晚期,随着大气水的混入,流体混合作用是形成晚期闪锌矿等硫化物的重要原因。二道河子矿床为与火山-次火山有关的浅成中低温热液矿床。

The Erdaohezi Pb-Zn-Ag polymetallic deposit, one of the largest and representative deposits in the Derbugan metallogenic belt, is mainly hosted in the volcanic rocks of the middle Jurassic Tamulangou Formation along NW and NWW-trending fault zones. Sphalerite, which is one of the main ore minerals in the deposit, has been classified into three generations according to their corresponding ore-forming stages. Black sphalerite formed at the earliest stage, followed by reddish brown to brown sphalerite, and tawny or pale yellow sphalerite in the latest stage. Fluid inclusions in sphalerite of different ore-forming stages and its coexisting quartz have been studied using infrared microscopy. It is believed that the sphalerite-hosted fluid inclusions may provide direct and detailed information regarding the ore-forming fluids. Out results show that the fluid inclusions in sphalerite and its coexisting quartz generally have similar morphological characteristics, salinities, densities and homogenization temperatures, which is consistent with the fact that sphalerite is intergrowth with quartz. Microthermometric and laser Raman spectroscopic data indicate the ore-forming fluid evolved from a moderate-temperature, low to moderate-salinity and CO2-rich aqueous fluid in the earliest ore-forming stage to a low to moderate-temperature, low to moderate salinity and CO2-depleted aqueous fluid in the middle stage, and a low-temperature, low-salinity and aqueous fluid in the last ore-forming stage. Boiling, natural cooling and mixing with meteoric water took place at three different ore-forming stages respectively and caused deposition of sphalerite. The Erdaohezi deposit is, therefore, a post-magmatic mesothermal-epithermal Pb-Zn-Ag polymetallic deposit related to volcanic-subvolcanic magmatism.