The Geochemical Characteristics And Genesis Of Xinqiao Cu-S-Fe Deposit, Tongling, Anhui Province

Xinqiao Cu-S-Fe deposit is important deposit in Tongling concentrated mineralization zone in middle and lower Yangtze River copper-polymetallic metallogenic province, which is located in the middle of Guichi-Maanshan Zone of Bruchfalten, Zone of Bruchfalten Along the Yangtze River Arch(Ⅲ22), Lower Yangtze Geotectogene(Ⅲ2), Yangtze Paraplatform(III). Based on the analysis of the ore-forming geological setting, geology characteristics, geochemical characteristics and ore-forming geological conditions of the deposit, the source of ore-forming materials, the ore-controlling factors, the genesis of deposit and etc are studied. The main achievements are obtained as follows:1. By studying the characteristics of petrology and the geochemical characteristics of constant elements, trace elements, rare earth elements and isotope, it’s known that Jitou Rock Strains are weak silicate saturated, vice-metaluminous and calc-alkaline(WsiO2==56.59～61.83%, σ=2.56～2.88, A/CNK=0.81-0.94), that the LREE/HREE is from9.84to13.00, which means light rare earth elements are enriched strongly, and that δEu and δCe is from0.90to0.98,0.78to0.82respectively without obvious anomalous. Through the analysis of magma source, formation environment and formation process, it’s pointed out that Jitou Stock originated in the mantle of alkaline basaltic magma, formed in the environment of orpgenic belt, and suffered from contamination of matter from the Silicon aluminium crust during diagenetic evolution process.2. By measurement of EPMA, Fe/S, S/Se and Zn/(Pb+Zn) of colloidal pyrite is from0.803to1.058,1.651×103to8.712×103and0.027to0.460, respectively. And colloidal pyrite is located in hydrothermal causes areas. So colloidal pyrite formed because of hydrothermal. The content of siderite is mainly from1.500%to2.500%, which means that siderite formed because of sedimentation.3. Through the analysis of the ore-forming geological background and characteristics of deposit geology, orebody, ore and wall-rock alteration, the ore-forming process of Xinqiao Cu-S-Fe deposit is divided into three stages and six phases, based on the relationship of mineral association combination, namely:sedimentation stage(siderite); skarn stage(early skarn phase:garnet, diopside; terminal skarn phase: epidote; oxide phase:magnetite, hematite and etc); sulfide stage(early sulfide phase:colloidal pyrite, pyrrhotite and a small amount of siderite; terminal sulfide phase:chalcopyrite, crystalline pyrite and pyrrhotite; carbonate phase:carbonate minerals).4. By discussing the relation between stratum, structure, magmatic rock and mineralization, it’s thought that the stratum supplys not only the ore-forming materials but also favorable conditions which are "silicon-calcium-silicon" structure of lithology and the fracture zone between layers, that the structure is the necessary factor because it made magma and orebody in place, and that Jitou Rock Strains is the first factor because not only magmatic hydrothermal supplys main ore-forming materials, ore-forming fluid and energy but also it controls mineral zonation of Orebody No.1.5. Based on the the analysis of characteristics of geology and geochemistry, ore-forming geological conditions, source of ore-forming materials, ore-controlling factors and mineralization, Xinqiao Cu-S-Fe deposit is suggested as skarn-type Cu-S-Fe deposit, and the mineralization is mainly contact metasomatism for intermediate-acid magmatic hydrothermal.