Guangxi Beishan MVT Type Lead-zinc Deposit Geology And Geochemistry Study

The Beishan Pb-Zn deposit is located in the western tip of Nanling metallogenic belt most in Guangxi.It is a typical Zn-Pb polymetallic deposits that have no immediate connection with magmatism,the proved reserves of Zn(103 million tons),Ge(215 tons)and pyrite(2065 million tons)being large-scale.After years of exploitation,the reserve resources are becoming more and more insufficient.It changes into a severe crisis mine.It is necessary to put in the further research on metallogenic regularity.Based on studying and analyzing the previous results material,through a great deal of field work and laboratory study,guided by the theory of regional metallogeny,ore mineralogy and ore deposit geochemistry,the main line of the typical ore deposit study.It carries out the integrated research of the relation between characteristic and evolution of strata-structure-fluid and mineralization.Finally,the author discussed the metallogenetic mechanism and preliminarily established the metallogenic model of the Beishan Pb-Zn deposits.The tectonic position of the Beishan Pb-Zn deposits is the outside of the southern margin,Yangtze Para-platform,the southern margin of Jiangnan terrain,the northern margin of the Guizhong depression.The outcropped strata of the mine district are Devonian limestone,dolomite and Carboniferous sandstone and shale.The pyrite orebody mainly occurs in the top of the Donggangling Formation and macrocrystalline and medium-crystalline dolomite between reef limestone and argillite,marl cover at the bottom of the Guilin Formation.The mining area structure was developed and dominated by fold structure.Pb-Zn was controlled by Shangchao-Chuanshan anticline and Beishan deposit is located in the east wing main anticline.Mining area fault is very developed and its strike is mainly NNE.The orebodies are distributed in hanging wall and footwall of both faults,but the main are situated in fault footwall.The mining area and its periphery have no the outcropped magmatic rocks.Sulfur and lead isotope research reveals that sulfur isotope in the ore minerals of Beishan Pb-Zn deposit has a wider distribution range,showing the characteristic of light and heavy sulfur rich enrichment simultaneously,indicating that sulfur source not only derives from reduction of marine sulfates,but also may be from formation.Lead isotope composition has little change and is radiogenetic lead mainly.Through the judgment of isotope composition characteristics and its parameters,the analysis of Zartman Pb tectonic setting evolution graphical,we can confirm that lead primarily comes from the upper crust.The study of fluid geochemical characteristics indicated that the fluid property of the Beishan Pb-Zn deposit significantly different from other magmatic hydrothermal type lead-zinc deposits in Nanling.The characteristics of carbon and oxygen isotope indicated that ore-forming fluid that interacted with the carbonate in mineralization process may be part from deep basin,in the Beishan Pb-Zn deposit.Carbon may be primarily from dissolution of marine carbonate rocks.The study of fluid inclusion indicated that the ore-bearing fluid have the characteristics of low temperature and high salinity(generally greater than 15wt%NaCl),it is Na-Ca-Cl type brines that rich in organic matter and contain a little CO2 and H2 S.Fluid inclusion homogenization temperature vary in 75~150?.The Cl/F ratio of fluid inclusion is relatively large,distinguished from the magma source deposit obviously.By this research,we concluded that Beishan Pb-Zn deposit is a typical MVT type Pb-Zn deposit.Through the analysis and discussion of the ore-forming materials,migration and evolution of ore-forming fluids,lead and zinc precipitation mechanisms.Eventually,metallogenic model of area where Beishan and the deposit are established.