四川锦屏山地区金矿床的成矿机理和成因探讨

An approach to the metallogenic mechanisms and genesis of the gold deposits in the Jinpingshan area,Sichuan

在对研究区典型金矿床的矿化地质特征、围岩蚀变特征分析的基础上,讨论了四川锦屏山地区金矿床的成矿机理和矿床成因。锦屏山地区金矿床的含矿围岩以浅变质的三叠系粉砂质片岩为主,金矿床围岩中广泛发育碳酸岩化(早期)和硅化(后期),前者以铁白云石化为特征,后者以黄铁绢英岩化、绿泥石化和石英脉发育为特征。碳酸岩化主要发生在碳酸岩脉与泥质粉砂岩的接触带上的粉砂岩一侧,由碳酸岩脉侵入时的热液交代岩石中的泥质矿物而形成。金矿体的走向与碳酸岩化带的产状基本一致,金主要富集于硅化强烈、黄铁绢英岩化发育地段。碳酸岩化地层中具有较高的含金背景,指示成矿物质金来源于地幔,而矿化主要发生在黄铁绢英岩化和硅化带及石英硫化物脉中。结合矿床的同位素地球化学特征,认为研究区金矿的成矿作用主要是后期热液的改造作用中金元素发生再次富集的结果。金矿的形成经历了碳酸岩脉侵入、地层发生铁白云石化并初步富集形成矿源层(岩)阶段和以硫化物石英脉为代表的热液期的大规模富集成矿两个阶段,矿床的成因类型因属于改造型金矿床。

The metallogenic mechanisms and genesis of the gold deposits in the Jinpingshan area, Sichuan are treated on the basis of geology and wall-rock alteration of the representative gold deposits. The ore-beating wall rocks of the gold deposits in this area are mainly made up of epimetamorphosed Triassic silty schists, and subjected to widespread earbonatitization including ankeritization in the early stage and silicification characterized by beresitization, chloritization and quartz veins. The carbonatitization appears in the siltstones within the contact zone of carbonatite veins and muddy siltstones, and resulted from the muddy minerals in the hydrothermal metasomatic rocks during the emplacement of the earbonatite veins. The trends of the gold orebodies reconcile with the occurrence modes of the carbonatitization zones, and the gold is enriched in the highly silicified and beresitized zones. The higher background values of gold in the carhonatitized strata indicate a mantle source of gold. The gold mineralization tends to occur in the silieified and beresitized zones and sulfide quartz veins, and resulted from the re-enrichment of the element Au during the paulopost hydrothermal reworking in the study area. The gold deposits have gone through the early gold enrichment and the formation of the source rocks （beds） during the emplacement of the carbonatite veins and ankeritization, and large-scale gold enrichment during the hydrothermal processes represented by the sulfide quartz veins. It follws that the gold deposits in the study area are assigned to the hydrothermally reworked gold deposits.