Yunnan Jinding Deposit Provenance Characteristics And Metallogenic Age Of Discussion

Jinding deposit is a famous giant lead-zinc deposit,located in Lanping,Yunnan province.There are also large scale gypsum and celestite deposit,middle scale sulfur iron ore within 10 km².,besides lead-zinc deposit.Some basic geological problems are still ambiguous,and ore deposit genesis are controversial.With systemic field and indoor work,some conclusions are acquired about division of the strata,distribution and shape of ore bodies,genesis of limestone breccias,derivation of the ore deposit, lead-zinc metallogenic age,and so on.With contrast rock assemblage sequence between the ore district and region,and research on spore-pollen combination and trace element,limestone breccias do not belong to Yunlong formation(E₁y),but upper Trias,which underwent structural deformation and salt dissolution.Gypsum also belongs to Trias according to their sediment characteristics and contrast to the relative stratum layer in the region,The 3-dimensional model of lead-zinc orebodies in Jinding district is established with Surpec for the first time.The model display a mushroom shape of the lead-zinc and Salt ore bodies.Ore bodies of limestone breccias type and sandstone type are conjoint.Ore bodies of sandstone type are on the upside,and vast distributing,with stratoid structure.Ore bodies of limestone type are on the downside,which like the root of the mushroom with finite distribution.Salt ore bodies,such as gypsum and celestite,located between them,which are on the middle and lower part of the mushroom,showing that the distribution of the ore bodies relate well to the salt dome of the diapir structure.There are two kinds of breccias in Jinding deposit:structure-salt dissolution breccias and diapar structure-emplacement breccias.Structure-salt dissolution breccias,accompanied by the limestone in Sanhedong formation,overlay on the Yunlong formation with isolated islands along the occurrence of the regional thrust sheet.The breccias generated due to structure and salt dissolution,which being simplex composition,composed of bituminous limestone and crystalline limestone, intermixing by big and small breccias(n mm～nX10m),no separation.They are characterize by irregular and subangular with sandy filling or no filling,and some of them are jointable.Diapar structure-replacement breccias are discovered for the first time.This type is accompanied by the structure-salt dissolution breccias,being vein or flamboyancy in cross section while some of them shot through the lead and zinc ore. In fact,the breccias were lead and zinc orebodies themselves.Some spore-pollen assemblages of late Trias and the youngest zircon of 225Ma were also obtained in this type.Deriveration of the ore is from the upper crust according to the features of trace elements,zircorn U-Pb age and initial value of ⁸⁷Sr/⁸⁶Sr.It has not any charateristics of the mantle.Deriveration of main host rock is mostly felsic sediments,little basic and medium-acidic magma and old crust material.Geological setting of diagenism mostly belongs to passive continental margin,few to continental arc.Plaeoproterozoic zircons in Jingxing Formation(K₁j) are discovered first.The isotopic ages,such as Pb-Pb model age of galena,Rb-Sr isochrone age of sphalerite and pyrite,indicate that there exist mineralization concentration in Jinding deposit at middle-late Trias(230Ma±),which must be the era of ore sources. Therefore,the present dominated genetic models about Jinding deposit have to be considered again.