Discussion On Geological Characteristics And Metallogenic Genesis Of Pianyanzi Gold Deposit In Kangding, Sichuan Province

Pianyanzi gold deposit located 4km away from the north of Kangding, Sichuan province. Which situated at the compounding position of the Sichun-Yunnan meridional structural system, the Qinghai-Tibet-Burma-Indonedian eta structural system and the Longmenshan-quasi-Cathaysian structural system. In the srudied area, the Presinian Kangding Group ?AnZkd?, Upper Sinian Dengying Formation ?Zbdn?, Upper Triassic Hanfengya Formation ?T3h?, etc. Vocanic activities have been frequent in the area, which provided auriferous matters for the gold mineralization.The orebodies generally occur as irregular beins along the beddings. Altogether, 4 gold orebodies ?numbered as M1, M8, M10 and M13? have been discovered within the range of the Pianyanzi gold deposit, occurring as a almost SN belt along the fault zone. Those that dip steeply ?at an angle ranging from 56 to 86? are generally from 45m to 72m in length, froml.5m to 8m in thickness and from 40m to 80m in buried depth. The average grade:Au,6.80 g/t to 18.28 g/t. The primary metallic minerals include mainly pyrite, galena and kilbrickenite, and subordinately chalcopyrite, teteahedrite, tennantite, etc., while the nonmetallic minerals mainly including quartz, sellaite, dolomite etc. The ores can be distinguished into 3 types:the pyrite-quartz type, the polymetallic sulfide ?sulfate?-sellaite-quartz type and mineralized host rock type.According to the fluid inclusion and thermodynamics, this paper deals with the physicochemical conditions of mineralization and the transportation and deposition of Au in bydrothermal ore-forming fluid of the deposit.The conclusion shows that gold mineralization mainly occurs under the conditions of medium temperature ?158?-340??, medium salinity ?8.6%-23.6%?, medium-deep and near surface ?1.0km-2.3km?, weak alkali ?PH=7.21?,weak reduction ?Eh=-0.334V?. The media for mineralization were essentially the circulating ground termal water at depth and some magmatic water,which formed mixed orebearing thermal solution. AuF₂- AuF₄ AuCl₂?AuCl₄?AuS-?Au?HS?₂-?Au?HS?₂S₂- is a main existing form of Au in a medium temperature, weak alkalie hydrothermal solution.The deposition of Au is closely related to reaetion of the ore solution with the dolomite.