The Ore-forming Geological Features And Metallogenic Pattern Of Bainiuchang Poly-metal Deposit In Mengzi County, Yunnan Province

Located in Mengzi county, Yunnan province, Bainiuchang deposit is a super-large poly-metal deposit with silver, lead, zinc, tin and copper. It is one of the three large deposits in tin-zinc-copper-silver-lead-tungsten poly- metal metallogenetic belt at east-south part of Yunnan province which is the west part of Nanling tungsten-tin metallogenetic zone.Based on the systematic collections to the former research and the data of prospecting and mining, the geological investigation to the ground and saps and the testing, the paper illustrated Bainiuchang deposit's ore-forming geological features and concluded its metallogenic pattern by the synthetical analysis to minerals and rocks , ore-forming tectonics-, geochemistry and isotope geochemistry.The detailed local geological investigation indicated that the main ore-body of Bainiuchang deposit is a low dip vein which submitted to strata in general and was controlled strictly by F₃ fault belt. Rich ore-bodies are often high dip veins and were controlled by side-crannies of F₃ and approximate north-south structures. The abundant pyrrhotine and marmatite in ore showed that the ore-forming temperature was higher than normal strata-bound lead and zinc deposit. The fact that there are some sedimentary tectonics in ore revealed that the syn-sediment was helpful to the forming of the deposit.The studies of geochemistry and isotope geochemistry indicated that the main ore-forming materials came from Tianpeng Group in the middle Cambrian and its under-strata and some from granite in Yanshan period; the ore-forming fluids which were driven by the heat of magma were the mixed solutions that contained the magmatic water and meteoric water and mainly meteoric water at late ore-forming stage.By the studies to the deposit's geological characteristics, mineralizing processes and ore-forming mechanisms, the paper built up its metallogenie pattern that Bainiuchang deposit was formed by the superposition of syn-sediment in Galedoniod period and the intrusion of granitic magma in Yanshan period. The intrusion not only provided heat source, part ore-forming fluids and elements, but also resulted in contact-belt tectonic systems and slide faults and caused the long convective circulation of heat water which took leached ore-forming elements into the appropriate spaces to form ore-bodies. In a word, Bainiuchang deposit was a polygenetic compound deposit.