新疆萨日达拉金矿床成矿流体特征及地质意义

Characteristics of ore fluids of the Saridala gold deposit,Xinjiang,and its geological significance

新疆萨日达拉金矿位于西天山东段、中天山地轴北缘,是近年来望峰金矿带新发现的金矿床,规模达到中型。萨日达拉金矿床的直接赋矿围岩是前寒武纪绢云石英千糜岩和早古生代花岗岩类,矿床的形成明显受到胜利达坂韧性剪切带的控制,广泛发育黄铁矿化、绢云母化、硅化、钠长石化和碳酸盐化等蚀变。根据脉体穿切关系和矿物交代关系,可以将萨日达拉金矿分为早、中、晚三个成矿阶段。在萨日达拉金矿的石英中发育了CO2-H2O(C型)、纯CO2型(PC型)、H2O溶液型(W型)和含子矿物型(S型)四种类型流体包裹体。早期石英中原生的包裹体仅含有C型,均一温度为301.0～491.4℃;中阶段为主成矿阶段,该阶段石英中包含了所有四种类型的包裹体,其中C型包裹体占了大多数,成分为CO2+H2O±N2,盐度为0.43%～10.91%NaCleqv.,均一温度为255.8～475.0℃,由此计算主成矿阶段压力为115.1～307.5MPa,成矿深度为11km;晚阶段石英仅发育W型包裹体,盐度为1.32%～15.58%NaCleqv.,均一温度则为146.2～254.6℃。总体而言,萨日达拉金矿的初始流体具有中高温、富CO2、低盐度的变质流体特征,晚成矿阶段流体演化为低温、低盐度水溶液流体,流体的不混溶或减压沸腾作用导致了主成矿期的矿质的大量沉淀,萨日达拉金矿为中深成造山型矿床。

The Saridala gold deposit,Xinjiang Uygur Autonomous Region,is located in the east of West Tianshan,the north of the Middle Tianshan axis. It is a medium sized gold deposit in the Wangfeng gold belt and its host rocks are the Precambrian sericite quartz phyllonite and Early Paleozoic granitoid. The Saridala gold deposit is obviously controlled by the Shenlidaban ductile shear zone showing hydrothermal alteration of pyritization,sericitization,silicification,albitization and carbonation. The vein crosscutting relationships and mineral replacement suggest that the ore forming process includes the early,middle and late stages. In the quartz of Saridala gold deposit,four types of fluid inclusions (FIs) are identified as CO2-H2O (C-type),pure CO2 (PC-type),aqueous water (W-type) and daughter mineral-bearing (S-type). The early-stage quartz contains primary C-type FIs with homogenization temperatures of 301.0~491.4℃. The middle-stage quartz trapped all the four types of FIs,of them the C-type FIs account for the majority. The C-type FIs,composed of CO2+H2O±N2,have the salinity of 0.43%~10.91% NaCleqv. and homogenization temperatures of 255.8~475.0℃. Trapping pressure in middle stage estimated from the C-type FI ranges 115.1~307.5MPa,corresponding mineralization depth of about 11km. The late-stage quartz contains only the W-type FIs with the salinity of 1.32%~15.58% NaCleqv. and the homogenization temperatures of 146.2~254.6℃. Therefore,the ore fluids in the early and middle stages are characterized by meso-to hypothermal,CO2-rich and low salinity,which are considered as the nature of metamorphic fluids,whereas the late-stage fluids are low temperature,low salinity and CO2-poor. Depressurized fluid-boiling or phase separation caused gold precipitation in the middle-stage. The Saridala gold deposit is a meso-to hypozonal orogenic gold deposit.