Prospecting Prognosis And Geological Characteristics Of Tongchanggou Cu-Mo Deposit In Yunnan

The Tongchanggou Cu-Mo deposit located in zhongdian island arc of YiDun island arc belt's south which in the sanjiang metallogenic belt,is a large polymetallic deposit which give priority to porphyry molybdenum deposit.The Tongchanggou Cu-Mo deposit is one of the representative deposits of zhongdian island arc in late Yanshanian period,the study of it is a deeper exploration to the late Yanshan mineralization in Zhongdian island arc.In the paper,I made an in-depth study on the geological characteristics and prospecting prediction of the Tongchanggou Cu-Mo deposit and then had clear understanding of “structure—rock–control—mineralization” system and metallogenic model of two periods.In this process,I comprehensive used various means to prospect,which plays an exemplary role in the exploration of the combination of effective methods and techniques,and the promotion of the geological prospecting evaluation of the deposit.The strata and lithology of the mining area mainly include : basalt of Emeishan Basalt(P3e);carbonate rock of Beiya(T2b),is respectively limestone of T2b1,dolomitic limestone or calcite dolomite of T2b2 and angle limestone of T2b3;pyroclastic rock(K21)and sandy conglomerate strata(K22)of The Upper Cretaceous(K2),among them,P3 e and T2 b are ore bearing strata.The fold and fault structures are distributed in the mining area,the main tectonic line is NE-SW.Affected by regional tectonic activities,the two major faults :F1 and F2 in the mining area had two tectonic activities,which have caused the intrusion and mineralization of the intermediate acid magma along the structural fracture zone.Fault structure is the main ore controlling and hosting structure in mining area.Magmatic rocks include volcanic rocks(basalt)and intrusive rocks(sillite,granodiorite and granodioritic porphyry)and mainly distributed in the fault zone and carbonate rocks,configuration was NE-SW.Granodioritic porphyry was metallogenic rock of the deposit,mainly located near the fracture zone,fully embodied the structure-rock-controlling-mineralizationfeatures.The Tongchanggou Cu-Mo deposit is mainly composed of molybdenum,a small amount of copper reach the industrial grade,the ore types are mainly molybdenite and chalcopyrite.Molybdenite is closely related to granodiorite porphyry,copper mineralization is closely related to skarn.The mining area has 3 industrial orebodies: KT1,KT2,KT11.KT1 located in the F2 fault zone,both copper and molybdenum mineralization,the molybdenite was filling between the structural lens of copper skarn or skarn marble as vein which in the fracture zone,chalcopyrite was mainly hosted in the skarn or cracked skarn marble.KT2 is located in the footwall of KT1,mainly molybdenite,the molybdenite is densely disseminated in the granodiorite porphyry and interspersed in skarn,marble and limestone.KT11 is located in the slip zone between basalt and carbonate rocks near the F1 fault zone,mainly molybdenite,the molybdenite is densely disseminated in the granodiorite porphyry.the whole granodiorite porphyry is mineralized.Microscopic observation of pyrite,chalcopyrite and molybdenite shown that molybdenite interspersed in chalcopyrite and pyrite.Combined with the results of macroscopic investigation,chalcopyrite is formed by metallization in early tectonic activity,and molybdenite is late.The study of granodiorite porphyry's geochemical characteristics indicates that it had high contents of Si O2 and total alkali,is high-K calc-alkaline series magma;the light REE and the heavy REE different obviously,the heavy REE are depleted mightily,low contents of Y and Yb,relative enrichment of Sr,higher ratio Sr/Y and La/Yb,the ratio of Rb/Sr is between 0.09~0.37.Synthesize various features,the granodiorite porphyry of Tongchanggou is a medium acid magma formed by partial melting of the thickened lower crust with mantle material.The diagram of the structural environment is shown as the collision environment.I synthetically analyzed the metallogenic geological conditions of Tongchanggou Cu-Mo deposit and the regional tectonic setting of the Zhongdian island arc in the late Yanshan period,the deposit is formed in the extensional tectonic environment after collision.Restricted by regional tectonic background,the tectonic movements were frequent in the Tongchanggou area,and the ore bearing intermediate acid magma intruded and moved along the structural fracture,finally at least two mineralization occurred under the combined action of various geological conditions: In the first period of mineralization,the acidic magma intruded and formed the skarn deposit,the mineralization was mainly brass and pyrite mineralization,mainly existed in skarn;In the second period of mineralization,the ore bearing intermediate acid magma with crust-mantle mixed source intruded and formed hydrothermal vein type molybdenum deposit and porphyry type molybdenum deposit,the mineralization was molybdenite and pyrite mineralization,mainly existed in granodiorite porphyry and fracture zone,was the main metallogenic period.The alteration generally developed in the Tongchanggou mining area,the main alterations had skarnized,marbleization,chloritization,epidotization,silication,and so on,the main alteration minerals include calcite,kaolinite,epidote,actinolite,chlorite,montmorillonite and other minerals.I utilized near-infrared alteration mineral mapping technique to deep analyse the characteristics of altered mineral assemblages closely related to mineralization,and the result displayed that chlorite + montmorillonite was directly related to mineralized body and metallogenic porphyry body,calcite + kaolinite and epidote + actinolite were related to acidic rock.The characteristics of electrical parameters of rock(ore)in mining area were measured by AMT Profile measurement technique and the result displayed that the resistivity of ore related rocks,such as basalt,skarn marble and granodiorite porphyry which located in the vicinity of the fault structure,were medium-low resistivity.At the same time,it further confirmed that the fault structure in the mining area was the ore and rock controlling structure,and clearly reflected the distribution of the buried rock in the deep part.I integrated the altered mineral assemblages,the electrical properties of rocks,and stratigraphy,structure,magmatic rocks and geochemistry and other the prospecting indicators,and combined with previous research datum,Finally,established the prediction model of Tongchanggou mining area,based on this,delineated the prospecting target area in the periphery of the ore body.I delineated two prospecting target regions included Tongchang target region and Tongchangping target region,which were both good prospecting target for further prospecting breakthrough in synthetic judgement,the Tongchangping target region could be used as the first exploration target for deep engineering verification.