GEOLOGY AND GENESIS OF ZHULAZHAGA GOLD DEPOSIT, INNER MONGOLIA, CHINA

Zhulazhaga gold deposit, located in Inner Mongolia Autonomous Region, is the first large-scale deposit found in the Middle-Upper Proterozoic strata along the western part of the north margin of North China Platform. The wall rocks of the ore bodies are a series of epimetamorphic rocks, which are mainly composed of metacalcareous sandstone, siltstone and slate with minor thin-bedded carbonate rocks. The authors discover the widespread acidic volcanic rocks within the strata. The occrrence of the main ore body is similar to that of the wall rocks. The intensive hydrothermal alteration in the deposit is closely related to the ore-forming process. Five ore types are identified, which are SEDEX type, altered volcanic rock type, altered sandstone type, metasomatic rock type and quartz vein type. Most gold minerals appear as native gold and electrum. Based on the detailed research, it is supposed that the mineralizing process may experience two epoches. In the earlier epoch, the SEDEX type of mineralized beds was formed during the Middle Proterozoic volcanic activity. During the latter epoch, different types of ore and orebodies were formed in the gold-bearing thermal fluid, when the fluid was evolved from the granitic magma which intruded during the late Hercynian movement, and replaced the wall rocks intensively. The apperance of the quartz vein type of orebodies demostrates the end of the endogenetic ore forming.