Geochronology And Geochemistry Of Diabase In The Liangshuigou Pb-Zn Deposit,Northwestern Guizhou,China

The Liangshuigou Pb-Zn deposit,located in the eastern part of the Sichuan-Yunnan-Guizhou Pb-Zn mineralization domain.It is a new Pb-Zn deposit discovered in the process of prospecting and exploration,in Northwest Guizhou ore concentration area.In this paper,the Liangshuigou le ad-zinc deposit and the diabase in the area are the main research objects.Based on the description of Liangshuigou Pb-Zn deposit geological characteristics,and the genesis of the deposit is determined.The main achievements of this paper are as follows :The Liangshuigou Pb-Zn deposit is located in the composite part of NW trending Jiangzishan-Maomaochang fold fault zone and NE trending Maomaochang-haozidong fold fault zone.The lead-zinc oxide ore bodies are mainly distributed in the northwest and southea st of the mining area.The overall strike of the ore bodies is NW and tends to SW or NE.The results show that there are two phases of pyrites in the Liangshuigou Pb-Zn deposit.Pyrite-I is sedimentary origin,and is obviously reworked by the superposition of late stage hydrothermal fluid.Pyrite-II is hydrothermal origin.Both kinds of pyrites are ric h in Pb,Zn,Co,Ni,As and Mo.The sphalerite is characterized with the enriched trace elements such as Cu,Cd,Pb,and Ga.Tr ace elements could occur in sulfides in forms of isomorphic replacement or their mineral inclusions.Based on the geological characteristics of the deposit and the regional metallogenic geological background,it is considered that the Liangshuigou Pb-Zn deposit were mainly formed in the metallogenic environment of low-medium temperatures,belongs to sedimentary-hydrothermal-reworked Pb-Zn deposit.The diabase of Liangshuigou deposit is named as High-K calc alkaline diabase,which is rich in Rb ? Th? Ba and other large ion lithophile eleme nts.The high field strength elements Nb ? Ta? Ti are slightly depleted.During the upwelling process of diabase in Liangshuigou deposit,weak fractional crystallization and assimilation of clinopyroxene and plagioclase occurred.Electron microprobe analysis of pyroxene shows that pyroxene is mainly augite,which is the product of gradual crystallization of mantle derived magma during its migration from deep to shallow.The age of diabase diagenesis of Liangshuigou deposit is 145±1.07 Ma,and the age of zircon captured by the two groups is 264 ± 0.54 Ma and 542.17 ± 3.62 Ma respectively.The zircon ages of 145 Ma and 264 Ma indicate that there are two stages of magmatism in Northwest Guizhou,corresponding to Yanshanian and Hercynian respectively;The 542.17 ± 3.62 Ma is the age of zircon in the captured Sinian surrounding rock.In this paper,it is considered that Liangshuigou diabase was formed in the background condition of transition from extensional rifting to subduction.It should belong to intracontinental r ift or passive continental margin rift.During the late Yanshanian Ningzhen movement at 145 Ma Ma,the basic magma emplacement occurred in Liangshuigou Pb-Zn deposit,forming diabase which is closely related to mineralization.It is speculated that diabase may provide thermal power and some ore-forming materials for Pb-Zn mineralization.