THE CHARACTERISTICS,DISTRIBUTION AND PROSPECT OF EPITHERMAL GOLD DEPOSITS

The conception of epithermal deposits was firstly proposed by Lindgren in 1922.From then on, it has caught more and more attentions and set off an unprecedented "epithermal craze" all over the world,especially when a series of epithermal gold deposits of large and super large scale have been found in the circum Pacific mobile belt.With its own characteristics of lower temperatures (<300℃), lower pressures (10-50 MPa) and lower salinity(<5% NaCl),such type of gold deposits has a close relationship to continental volcanic rocks in mineralizing process.The ore forming backgrounds are complex.The deposits can be formed mainly in island arc surroundings of plate convergence,as well as in strike-slip fault belts,overlying volcanic basins and mid-plate rifts under plate pull-apart condition,the mineralization of epithermal gold deposits took place at the late stage of volcanic activity.The ore bodies were finally deposited within the scope of volcano-geothermal system,closely related to shallow-seated porphyry system in both space-time and genesis.The epithermal gold deposits are obviously characterized by concentrated distribution,mainly in the circum Pacific-belt,the Paleo Tethys belt and the Mid-Asian-Mongolian (paleo Asian) belt.The temporal range of the deposits is most importantly spanned in Tertiary,followed by Quaternary and then Mesozoic era. There is a great prospect for the epithermal deposits in China,because all the three worldwide epithermal ore-forming belts are going through China,where some deposits of the type have been discovered,such as the newly found large-scale Axi epithermal gold deposit in late Paleozoic Yili rift in West Tianshan Mountains.The discovery of Axi and its peripheral gold deposits indicates an important breakthrough in gold prospecting. The exploration area for epithermal gold deposits has spreaded into Paleozoic volcanic belt in Eurasian continent.After Axi gold deposit,many mineral occurrences have been found in Tianshan Mountains,Junggar basin,Beishan Moutains and Daxinganling Mountains,showing a great potential of epi-gold deposits in the Mid-Asian-Mongolia belt.The large East China Meso Cenozoic tectonomagmatic belt,belonging to the exobelt of the circum Pacific belt,is one of the important metallogenic belts in China.Many Au-Cu deposits,including Zijinshan gold deposit in Fujian,Jinshan and Yinshan gold deposits in Jiangxi,Tuanjiegou and Guliku gold deposits in Heilongjiang,Wufeng gold deposit in Jilin and Erdaogou gold deposit in Liaoning,have been found with a vast range of prospects for the epithermal gold deposits.