四川木里耳泽岩溶型金矿床形成条件和成矿机制

四川本里耳泽金-菱铁矿建造矿床,赋存于上二叠统海相碳酸盐岩层中,矿化受古岩溶的严格控制,组成矿石的基本矿物为菱铁矿,金不均匀地分布于菱铁矿矿体内。成矿溶液来自加热的循环地下水。成矿过程分为早阶段和中-晚阶段。成矿温度为156-210℃,成矿深度小于1km.成矿物质主要来自地层。成矿热液呈碱性和弱还原性,贫硫,含中等盐度。矿床形成时的地质构造环境较稳定。这是我国仅见的一种特殊金矿类型。

METALLOGENIC ENVIRONMENT AND GENETIC MODEL OF ERZE KARST-TYPE GOLD DEPOSIT OF MULI, SICHUAN PROVINCE

Erze karst-type gold deposit of Muli, Sichuan, discovered in the western margin of Sichuan-Yunnan metallogenic belt, is tectonically located in the transitional belt between Songpan-Gauze fold system and Yangtze paraplateform.The deposit occurs in the Upper Permian marine carbonate formation. The occurence of orebodies is strictly restricted within the Palaeokarst. The orebodies,which have complex morphology and sharp boundaries with enclosing rocks, are generally in sack-like, with rising and falling roof as well as bottom commonly developing “fibrous roots". Siderite is the dominant ore mineral, of which about 90percent of an orebody is composed, with minor quartz and pyrite. Native gold,and, secondly, electrum occur in the siderite bodies unevenly.It shows that the origin of the deposit is associated with a meteoric hydrothermal convection system. Two successive stages of ore-forming process are distinguished:the early one followed by the middle-late one. Temperatures range between 156 and 210℃, and depth is less than 1 km. It is suggested that the carbonate formation is the source bed.The solution is charaterized by alkli, weak in reduction, poor in sulfur, and medium salinity. It is interpreted that during the mineralization the tectonic environment is relatively stable, both gentle uplift and ground water convection are the necessary conditions for the karst development which created the best room for migrating solution and ore deposition; after the gold-siderite ore formation deposit formed. It was strongly suffered from weathering, leading to the widespread development of secondary oxide and the further enrichment of gold.It is a rather unusual and very important gold-deposit type, found only in our country so far. Obviously, it is necessary to study it more in detail.