Ore-controls Of The Beichang Block At The Supergiant Jinding Pb-Zn Deposits In Western Yunnan,SW China

The Beichang Block is the most largest important block of the Jinding super-large Pb-Zn deposits in northern Lanping Basin,western Yunnan province,SW China.Its reserves of lead and zinc account for about 3/4 of the total mining area,and the deep parts still have great potential to increase the reserves of lead and zinc.The known lead-zinc orebodies are hosted in the salt-bearing carbonate breccia of the Member b of Cenozoic Yunlong Formation and Cretaceous Jingxing Formatioan sandstones,coresponding to two main mineralization types:limestone and breccia-type and sandstone-type,respectively.In addition to carbonate and breccia hosting ones,the large scale sandstone type lead-zinc orebody I is hosted in high porosity and permeability sandstones,which is a kind of atypical MVT type sandstone subtype deposit,its metallogenic significance is worth paying great attentions.However,the ore-controlling factors and metallogenic regularity are still not clear at present.Therefore,on the basis of the observation and cataloguing data of the surface geological sections,open-pit slopes,borehole cores and other contents in the field,and the assary geochemical data of borehole samples,combined with the regional geological background and geological characteristics from the Beichang Block of the Jinding lead-zinc deposits.On the basis of digital terrain model(DTM),stratigraphic model,structural model,block model of orebody,element contour line of typical exploration profiles and plane plan of levels,and statistical analysis of correlation between the main mineralization elements,the ore-controlling conditions of the Beichang Block in the Jinding lead-zinc deposit are recognized as follows.1.This time,a 3D geological model and an entity model of the main orebodies of the Beichang mining section have been established.Basic modeling data include:1)plane geological map of the Beichang Block,2)fifteen exploration line profiles and 3)two level plans,involving 263 exploration boreholes and statistics of Pb and Zn contents analysis data of 20736 samples.2.It is shown,by 3D geological modeling,that lead-zinc orebodies hosted in sandstone of Lower Cretaceous Jingxing Formation and carbonate breccia of the b members of Paleogene Yunlong Formation,and the sandstone-type Pb-Zn orbodies hosted in Jingxing Formation is an atypical subtype of MVT Pb-Zn deposit,and differ from the traditional carbonate-hosted MVT deposit.3.Based on the ore body entity model data of spatial analysis of ore-controlling conditions,the richment area of the Pb-Zn mineralization amomalies(orebodies)of the Beichang Block is mainly controlled by the known nearly WE-striking thrust faults F₂ and F₈,Jingxing Fm.(K₁j)sandstones,and the b member of Yunlong Fm.(Ey^b)limestone breccias and sandstones.Under the control of the main thrust faults and two groups of secondary strike-slip faults,the concentrated area of Pb and Zn mineralization anomaly shows a podform or bead-like intermittent arrangement trend near EW-striking distribution tendency.4.The correlation analysis results of main mineralization elements also showed that Pb and Ag,Zn and Cd were significantly correlated,and the correlation coefficients were0.539 and 0.703,respectively.This indicates that the relationship between the enrichment and production of Ag and Cd should be related to the spatial variability of Pb and Zn mineralization.5.Favorable ore-controlling conditions of the lead-zinc deposits(bodies)in the Beichang Block can be sumarized as follows.The formation system composed of the soluble metal-bearing rocks of the Paleocene Yunlong Formation and the carbonate rocks and high porosity and permeability sandstones of the Upper Triassic Sanhedong Formation constitutes well ore-bearing strata and storage space of the metals precipitation.The mudstone-siltstone assemblage of the Huakaizuo formation to Lower Cretaceous Jingxing Formation formed a good trap system overlying the ore-bearing hosting rock series.The near EW-extending thrust faults and their secondary fracture systems under regional compression sress field in the late Cenozoic are favorable structural style assemblages of hot brine and mineral materials in drainage and convergence basins.The coupling of these conditions is an important mechanism for the formation of large-scale lead-zinc deposits(bodies)in the Beichang Block.These results can be used as the basis for resource evaluation and prospecting in the deep edge and surounding areas of the this mining area and adjacent regions.