The Geology, Geochemistry And Metallogenesis Of The Hongshiyan Pb-Zn-Cu Polymetallic Ore Deposit, Wenshan, Southeastern Yunnan Province

Hongshiyan orefield is located in Xichou county, Southeastern Yunnan Province, outcrops in a intersection between the NW-striking Wenshan-Malipo fault and the SN-striking Maguan strike-slip fault. It is a medium-sized deposit newly discovered in Laojunshan Sn-Cu-Pb-Zn polymetallic metallogenic province, Southeastern Yunnan. Many scholars have done a lot of research on the Dulong tin polymetallic deposit, Nan Yangtian large-scale Tungsten deposit and Other deposits in Laojunshan area. The regional mineralization is mainly affected by sedimentary exhalative processes, regional metamorphism and magmatic hydrothermalism, and due to the different influencing factors, the formation of deposit types are different. It has been a big controversy about the causes since the Hongshiyan deposit is found. So, this paper made research on the cause of the Hongshiyan polymetallic deposit through a detailed geological survey, drilling catalog combined with modern analytical testing methods and the comprehensive study of the geological background, geological features, rock geochemistry, isotope geochemistry, fluid geochemistry, then the following understanding is made.(1)Main ore-bearing rocks is greenschist facies metamorphic rocks from Cambrian Tianpeng group in Hongshiyan orefield. The paper made analysis to the protolith restoration and tectonic environment of metamorphic rocks by applying to the theory of petrogeochemistry and petrography. Results show that the original rock of greenschist is tholeiite; the protolith of Metamorphic clastic rocks is composed of argillaceous sedimentary rock and a few calcareous sedimentary. Classes flysch sedimentary formations is extensively developed in the Hongshiyan polymetallic deposit which is made up of carbonatite and clastic rocks, accompany with siliceous rock as a result of hot water depositional mineralization. Provenance of clastic sediments is of diversity, whose metallogenic environment is speculated to be back-arc, according to the regional geological setting and research from this paper. The geochemical characteristics of the main ore-bearing rock and the development of tholeiite show a higher consistency. co(Zn)/co(Pb+Zn) of the ore-forming elements is0.74, Much greater than0.9,which shows metallogenic material comes from the tholeiite and basement rocks.(2) Metallogenic fluid has the characteristics of the VMS deposit:the homogenization temperature of fluid is low, whose variation range is from130℃to220℃; salinity is0.35～ 9.21wt%NaCl, an average of5.64wt%NaCl, greater than normal seawater salinity (3.5wt%NaCl);fluid density,0.91g/cm3～0.99g/cm3,is low; pH is weakly acidic-neutral, ranging from5.8to6.2, and an average of6.0; logfo2=-14.81～-19.28,Eh=0.05-0.09,an average of0.08that shows the fluid is reducibility;mineralization depth, less than1000m,is shallower,and heated sea water by deep heat sources mixed with low temperature brine,and a small amount of magmatic water may be an important reason to cause this change.(3) δ34S=+4.85×10-3～+6.88×10-3,the sulfur source may come from deep of the deposit, influenced by shell source material contaminated seawater sulfate.(4) It is believed that the studied ore area is a massive sulfide polymetallic deposit mainly by volcano-jet deposition, which resulted from regional metamorphism movement of Caledonian-Indosinian and the Yanshanian magmatic hydrothermal superimposed on the volcanic cascade deposition.