Study On The Enrichment Regularities And The Ore Genetic Rules Of Nanhegou And Laobaotan Copper Deposits In Zhongtiao Mountains, Shanxi Province

Nanhegou and Laobaotan copper deposits are located in the southeast of Shanxi Province, and there is the Zhongtiao mountain range in the north, administrative regions are Yuanqu County,Yuncheng city, Shanxi Province. They are two important medium-rich copper deposits in the Zhongtiao Mt. copper ore area,fall into the Hu-Bi-type copper deposits.The area mainly expose the paleoproterozoic Zhongtiao Group,from top to bottom are the Jiepailiang Formation quartzite,the Longyu Formation slate,the Yuyuanxia Formation marble,the Bizigou Formation schist and Yujiashan Formation marble. Among them,the Yuyuanxia,the Bizigou and Yujiashan Formation are the principal ore-hosting Units. The mainly structures is the Hujiayu-Shangyupo"S"-shaped "short axis anticline".Nanhegou copper deposits lies in the Nanhegou-Xigou Secondary folds which in the south limb of the "short axis anticline". Laobaotan copper deposits located in the isoclinal fold which in the southeast limb of the "short axis anticline".The ore bodies of Nanhegou and Laobaotan copper deposits are stratiform,lenses or saddles,controlled by the stratum and the lithology,high grade,associated with the useful elements,such as Au,Ag,Co,etc, which can be comprehensively utilized. Nanhegou copper deposits lies in the Contact area of the Bizigou Formation and the Yujiashan Formation,the host rocks mainly include siliceous albite rock, impurity dolomite marble,secondly is blackschist;Laobaotan copper deposits mainly located in the Contact area of the Bizigou Formation and the Yuyuanxia Formation,the host rocks are the mud-carbon siliceous slate and impurity dolomite marble. Main metal mineral are chalcopyrite and pyrite,secondly is pyrrhotine,etc.; Major gangue mineral are quartz,dolomite,albite,sericite,biotite and chlorite and so on. Ore texture mainly is self-crystal and fractal granular blastic texture, charged texture, and metasomatic texture,etc., mineral ore structure are disseminated structure, banded structure, stockwork or veinlet- disseminated structure and brecciated structure,etc. The wall rock alterations of Nanhegou copper deposits are generally carbonatization, silicification ,albitizationand biotitization,etc.. The wall rock alterations of Laobaotan copper deposits are silicification, sericitization, carbonatization and chloritization.The siliceous albite rock, impurity dolomite marble etc. are widely developed in Nanhegou and Laobaotan copper deposits. Rock occurrence and structure characterized by sedimentary origin, but the major rock -forming minerals is fractal granular texture, enchased by each other, has no metasomatism, indicating abnormal detrital sediment; Rocks characterized by recrystallization which resulted in the particle size of the mineral increased. It show the rocks subsequently subjected to superposition of metamorphism reformation. Combined with geochemical characteristics, the siliceous albite rock, impurity dolomite marble etc. are thought to be hydrothermal sedimentary rocks., ore formation was dominated by exhalation-sedimentation, subsequently subjected to the regional metamorphism reformation.Both Nanhegou and Laobaotan copper deposits have two mineralization stage, namely inchoate hydrothermal deposition epoch(2060Ma) and terminal regional metamorphism and related deformation epoch(1900-1850Ma).Inchoate mineralization along the direction of stratification and schistosity, form disseminated and banded ore ; Terminal mineralization form along stratiform or through stratiform sulphide quartz-dolomite veins. After studying fluid inclusion, it is believed that early fluid was medium-low temperature, middle- high saldity, high-density hot brines. Flow inclusion measured range between 176.8 and 251.2 celsius degrees, average was 220.7 celsius degrees; Mean value of saldity and density were 33.11wt%NaCl, 1.14 g/cm3;channel phase fluid was complex, characterized by multiplesources, high saldity, high-density. In short,both Nanhegou and Laobaotan copper deposits were mainly formed by submarine exhalative-sedimentation and also enriched by late-stage superimposed mineralization.Nanhegou and Laobaotan copper deposits were formed under the background of the back-arc basin. Rift structure supplied the space and channels for seawater and atmospheric water percolates downward and mineralizing fluid transportation and invasion. Basic volcanics of Jiangxian group and mafic intrusive rock in Zhongtiao Group provided metallogenic materials; During the Zhongtiao orogeny stage, the extensional environment gave rise to detachments, including peel thrusts, but they occurred after the ore body,it's not important.Amoeboid fold of Zhongtiao movement made migration and deposition of copper in suitable place, ore bodies controled by the second order fold's hinge.