Temporal And Spatial Zoning And Genesis Of Hydrothermal Dolomite From The Hezhangliangyan Lead-zinc Deposit In Northwestern Guizhou

The Liangyan Pb-Zn deposit is a medium to large scale deposit in the northwestern Guizhou Pb-Zn metallogenic belt.Liangyan Pb-Zn deposit have widely hydrothermal dolomitization developed in the mining area.The Ore body occur in the middle Carboniferous Huanglong Formation(C2h)and lower Carboniferous(Cid)hydrothermal dolomite.This study carried in a large area of hydrothermal dolomitization zone,based on the systematic mapping,petrography with the mineral chemistry and C-O isotopic geochemistry method.Identifying the different types of hydrothermal dolomite genesis with spatial and temporal relations to establish its association with lead and zinc mineralization and favorable prospects.The main achievements of the study as following:(1)Three structural evolution process are identified,whereas,in the early stage an overturned anticline formed resulted from the nearly NNW-SSE trending compressional stress in the region,in the same time,the strata cut off by a thrust fault(Fi).In the second stage the dolomitizing fluid metasomatism of limestone within the old strata to form the early hydrothermal dolomite.In third stage,during the late metasomatism and early hydrothermal dolomitization,Lead-zinc ore body began to precipitate.(2)Liangyan lead-zinc deposit mainly formed within three types of hydrothermal dolomite,(a)The hollows-dolomite which as dolomitizing fluids moved preferentially through the hollows,(b)the crystalized-dolomite which are crystalized and having dark cores and limpid rims,(c)the zonal-dolomite which have more zonal structure.Different types of hydrothermal dolomite having close spatial and temporal relationship.The zonation in time from late to early have followed,crystalized-dolomite? hollows-dolomite?zonal-dolomite.The zonation in space from ore body center to the periphery have followed,zonal-dolomite?crystalized-dolomite? hollows-dolomite.(3)The C-O isotopic of dolomite revelation that the dolomite forming environment in the Liangyan lead-zinc deposit is middle-deep burial environment below the lagoon,with a high temperature.The medium salinity sea water of evaporating concentration containing Mg2+ in the upper is the source of the fluids.During the deep burial process,the fluids affected by the leaching of fresh water.(4)The dolomite which have more zonal structure can be directly used as mine prospecting signs,and we have combined with the relationship between lead and zinc mineralization and hydrothermal dolomitization with in the concealed ore body and favorable prospecting targets.