The Geological Characters And Metallogenic Model Of The Lead-Zinc Deposits In Southeast Chongqing

Southeast Chongqing locates in the fold belt within the upper Yangtze Syneclise. The lead-zinc deposits are controlled by tectonic system and stratum,and occur in the Paleozoic carbonate rock. The ore bodies which occurrences are in conformity to wall rock's and are stratiform-like or stratiform occur in Cambrian carbonate rock(including Qingxudong formation, Gaotai formation,Pingjing formation, Gengjiadian formation), and they are roughly controlled by the infiltration of wall rock and formed during Caledonian,however,some vein- and lens-shaped ore bodies which occured in Cambrian carbonate rock were formed during Yanshanian.The lead-zinc deposits with small scale,which occur in Ordovician and Permian carbonate rock are almost vein type ores. They were formed during Yanshanian and dominated by cranny. The mineral association is relatively simple. The ore mineral usually includes sphalerite, galenite, cinnabar, pyrite, limonite, hemimorphite, anglesite,smithsonite,cerusite. Gangue mineral includes dolomite, quartz, calcite, barite, fluorite,et al. Disseminated, massive, brecciated, bedded,vein,banding, crustification,honeycomb,bone pattern structure are well developed. The texture mainly concludes metasomatic, autotype,subhedron, xenomorphic granular. The metallogenic period is roughly devided into two phases.Firstly, fine disseminated ores were formed.Secondly, brecciated,massive,vein, banding ores with relatively high grade were formed. The main wall rock alteration types includes dolomitization, silicification,pyritization,limonitization,calcitization baritization,fluoritization. Pb and Zn usually associate with Fe,Ag,Hg,Cd,Ge,Cu,Sb et al. Totally, The geological features above and some other features of Pb-Zn deposit in southeast Chongqing are similar with those of typical MVT Pb-Zn deposits.The basement was the main source of Pb and Zn contained in the Pb-Zn deposit in southeast Chongqing,and the host rock was the subsidiary source of them.Almost sulfur came from sulphate occurred in stratum. The ore-forming fluid which was composed of seawater, compaction driven flow and oilfield water may be hot brine with high salinity,and it was driven by gravitation and tectonic compression. The regional major faults were Ore-leading structure. The main mineralization was during Caledonian, and the deposits were reformed during Yanshanian.Therefore, the Pb-Zn deposits in southeast Chongqing which have been reformed by hydrotherm are considered as MVT Pb-Zn deposits,and they are temporarily named "southeast Chongqing type Pb-Zn deposits".