Structure-Alteration-Mineralization Network Of Xincheng Gold Deposit, Jiaodong Peninsula

Xincheng gold deposit is one of the largest gold deposits, which is"Jiaojia Type"gold deposit in the Jiaojia gold field of Jiaodong Peninsula. Based on the detailed field geological survey, characteristics of ore-controlling structures, alteration belt as well as the mineralization network were studied in this paper.The Jiaojia fault and its secondary structures are the most important ore-controlling factors of Xincheng gold deposit, which directly controlled the formation and distribution of the deposit. Owing to long-term evolution of regional tectonic stress field, the Jiaojia main fault and its secondary structures experienced multistage structure-activity: ductile shearing activity before the ore-forming stage, compression-ductile-brittle shearing activity before the ore-forming stage, compression-shearing and stretching-shearing activity of ore-forming stage, stretching activity after ore-forming stage.Wall rock alteration of Xincheng gold deposit, controlled by fault, has a clear belt, which is not simply linear, however. From the footwall of major fracture planes to the external, altered rocks present a gradual change trend: from fault gouge, through beresitization belt, sericite-quartz alteration belt, granite of sericite-quartz belt and alteration silicified-potassic granitic belt, to fresh granite (biotite granite exists up -630 m while granodiorite exists below -630 m). By the method of mass balance calculation, the migration of the elements in the process of wall rock alteration, which means fresh granite altered to altered rocks, was studied. The result of study shows that the moving out elements are mainly Si, Na and Al, the immigration elements are mainly Fe, and both cases present in elements of Ca and K; trace elements of Ba, Pb, Zn, Sr are active, and secondly are Cu and Rb, of which, Ba and Sr always move out and Pb, Zn and Cu mostly move in.The beresitization mineralization of Xincheng gold deposit (No.I orebody) and Au-bearing quartz vein-type mineralization are the production of the same ore- forming fluids under the same tectonic activity but different structural site, which were caused by ore-controlling structure of different parts, level of sequence and property. Tectonic activity in the main slightly inclined fault with shear- compressional mechanical property, act intensively with strong fragment of rocks, and the ore-forming fluids characterized with infiltration metasomatism, with altered rock-type mineralization while in the secondary structure with the tenso-shear property which is the footwall of Jiaojia fault, far away from the main fault, the ore-forming fluids characterized with the ore-forming process of filling which was favorable for the precipitation for ore-forming mineral and forming sulfide quartz vein type ore bodies.The structure belt of Jiaojia faults coincide with the belt of alteration mineralization and the mineralization type presents as domimated horizontal belt. The alterated rocks changed from beresitization belt into potassic belt with compressional schistosity belt near the fault plane to the fissuring belt far from fault plane, and the mineralization types are changed from fractured altered rock type into Au-bearing quartz vein-type mineralization.