四川丹巴燕子沟金矿床成矿流体不混溶的流体包裹体证据

Fluid inclusion evidence for the immiscibility during the formation of the Yanzigou gold deposit in Danba,Sichuan Province

四川丹巴燕子沟金矿床是产于泥盆系碳质板岩、千枚岩中的石英脉型金矿床,矿体形态呈脉状、似层状,明显受断裂构造和顺层韧性剪切带或层间破碎带控制。成矿过程可分为沉积期、热液期和表生期3个成矿期,其中热液成矿期为主要成矿期。该期石英脉中的流体包裹体分为H2O包裹体、CO2包裹体和CO2-H2O包裹体3大类,并以富含CO2-H2O包裹体为显著特征。加热时富H2O相CO2-H2O包裹体完全均一成H2O相,富CO2相CO2-H2O包裹体完全均一成CO2相,而且二者的完全均一温度和压力一致,说明它们是同期捕获的CO2-低盐水不混溶流体包裹体组合。当含CO2流体发生不混溶时,CO2的溶离使成矿流体中pH值升高、f（O2）降低,从而导致Au溶解度降低,这是形成本矿床的主要原因。成矿温度为393℃,成矿压力为148.5～179.0MPa,矿床属于高温高压的变质热液金矿床。

Yanzigou gold deposit is a quartz vein type of gold deposit, which is hosted by the carbonaceous slate and phyllite of the Devonian. The ore bodies taking the form of veins and quasi strata form are controlled by faults and interlayer fracture zone. Ore forming process can be divided into sedimentary period, hydrothermal period and supergene period. The fluid inclusions in quartz at the hydrothermal mineralization period are divided into three categories： Hz O inclusions, CO2 inclusions and CO2-Hz O inclusions, among which the CO2- H2 O inclusion is the main type. When heated, the H2O-rich CO2 H20 inclusions were homogenized into the H2O phase, and the CO2-rich CO2-H20 inclusions were homogenized into the CO2 phase. Moreover, they have the same homogenization temperature and pressure. This indicates that they were the CO2 and low-salt water immiscible fluid caught in the same period. When the immiscibility effect of the fluid occurred, a large amount of CO2 overflowed, the fugacity of O2 decreased, and pH increased. It led to the reduction of the solubility of gold in ore-forming hydrothermal fluid, to the rapid precipitation of gold, and to the formation of deposits. The ore-forming temperature was 393 ℃and the ore-forming pressure was in the range of 148. 5 - 179.0 MPa, which indicate that the Yanzigou gold deposit belongs to the high temperature and pressure metamorphogenic deposit.