The Occurrence Regularity Of Thick-Cu-rich Orebody In Jiama Copper Polymetallic Deposits,Tibet

Gandise metallogenic belt is one of the most essential porphyry metallogenic belt in China.As a super large scale porphyry-skarn deposit located in east of middle Gandisebelt,Jiama copper polymetallicdeposit,hosted a identified resource reserve of copper,molybdenum,lead,zinc,gold and silver in skarn-type ore to large-scale,which is magnificent for economy and research.Previous studies on the deposits have made great achievements,we have identified the regional geological background,the geological characteristics of the deposits,the zoning of mineralization elements,the alteration and zoning of skarn minerals,the diagenetic chronology,fluid evolution and so on.And the "four-in-one" mineralization model and exploration model have been proposed.However,some problems haven't been solved yet,for example,the predecessors have not yet studied systematically on the relationship between Tongshan-south pit copper-rich orebodies and its intrusion,for the lack of the studies about this area and the complex structure in Tongshan-south pit area,Therefore,this paper systematically summarizes the characteristics of Jima porphyry mineralization system on the basis of fully collecting the data of the mining area,and studies and analyzes the characteristics of copper rich orebodies and their relationship with intrusion,at the aim of finding out the control mechanism of copper rich orebodies.Five important mining areas have been discovered and evaluated in the Gangdise metallogenic belt including the Jama-Dulong-Bangpu mining areas.The copper-molybdenum ore bodies in the porphyry,the copper-molybdenum(gold and silver)ore bodies in the hornfel,the copper polymetallic ore bodies in the skarn,and the independent gold ore body in the periphery of mining area contribute to the Jia-Ma“four-in-one” ore deposit model,which is established by predecessor.The strata of the mining area are mainly the Mesozoic Upper Jurassic Duo Digou Formation(J3d),Lower Cretaceous Lin Buzong Formation(K1l)and Quaternary sediments.The main tectonic lines in the region are NWW direction,and the complex folds are developed,among which the Tongshan gliding nappe structure and the Jama-Kajun nappe structure are the most important.The magmatic rocks are mainly composed of basic-intermediate silicic intrusive rocks.Based on the latest survey data and research results of the deposit,we delineate the copper-rich ore-bodies according the mining industry recommended indexs Cu>1%,and systemically summarize and analysis the distribution characteristics and output status of the copper-rich ore-bodies in the plane and profile.The prospecting engineering study shows that there are three enriched centers for copper in the mining area: the north-west Niumatang area controlled by the 19-23-27 line profile,area near the middle concealed porphyry contract zone,controlled by the 0-4-8-12-16 line profile,and the Tongshan South pit area controlled by the 38-52-54-58 line profile.The ore minerals of the copper-rich orebody are mainly bornite + chalcopyrite + tetrahedrite ± galena + sphalerite assemblage,and gangue minerals are dominated by skarn minerals.The alterations associated with copper-rich ores are mainly silicification,carbonation,and degeneration of skarn.The results of electron probe analysis show that the concentration of Fe and Ag for copper-bearing minerals in the area near the porphyry contact zone is higher than that in Tongshan Nankeng copper-rich orebodies.and the former has lower concentration of Cu and Co than the latter.The research results indicates that the ore-controlling factors for Cu-rich orebody in Jima mining area are divided into three types: porphyry contact zone ore-controlling,anticline ore-controlling and gliding nappe ore-controlling.Compared with other manto deposits in the world,it is considered that the rich ore body in Tongshan gliding nappe is the manto type orebody outside the porphyry metallogenic system.At last,comprehensive analysis point out that potential areas for ore prospecting in the next step are deeply concealed porphyry contact zone,the southwest periphery of Tongshan-South Pit Manto type ore body,fold core occurred in carbonate formation.