The Geological Characteristics And Mineralization Enrichment Regularity Of Yinaocao Copper Polymetallic Deposit, Qinghai Province

Yinaocao copper polymetallic deposit tectonic units belong to the Qinlin-Qilian-Kunlun orogenic system, the North Qilian arc basin system, the North Qilian ophiolite melange belt, located in the middle of Au-Cu polymetallic Tuolai mountain metallogenic belt.The exposed strata in the mining area mainly is Yingou group volcanic rock formation of Lower Ordovician, Quaternary strata locally appears. The mining area is controled by the North Qilian deep fracture and the Tuolai Mountain north slope deep faults, developing series of structural fracture altered zone with NWW-SEE. Exposed in the north of mining area, the late Caledonian period gabbros is the main intrusive rocks with little scale forming dyke. Locally find neutral-acidic veins invasion.The orebody of Yinaocao copper polymetallic deposit is mainly hosted in structural alteration zone, mineralization is found both in the marble and basalt. According to the distribution of the ore bodies and the grade, the deposit is divided into 13 orebody, among them the No. Ⅰ、Ⅴ、Ⅺ orebodies have the biggest scale. The ore trending is iniform with the structural alteration zone, distributing almost in EW trend at 55-65° angle, the lateral trending is in NWW trend at about 30°. Pyrite, chalcopyrite, galena and sphalerite are the main minerals in the orebodies. Ore textures are mainly idiomorphic or hypidiomorphic granular structure, xenomorphic granular textures, and metasomatic texture,secondly are harbor dissolution textures, crushing textures. Ore structures are mainly disseminated structure, veinlet structure, and network structure, secondly are block and stratified structure. The wall-rock alteration mainly is silicification, carbonation. sericitization, chloritization, epidotization and highly kaolinitization.The exhalative hydrothermal sedimentation stage do exist, but not yet ore-forming, just has some Cu and Zn minealization. According to orebody cross the basalts and marbles at the same time and existing dipping regularity, we consider that there is hydrothermal stage. The matollogenic temperature of exhalative hydrothermal sedimentation stage is 385.1℃～398.7℃. The fluid salinity is in the rang of 2.06～ 3.53%NaCl, fluid density is 0.529～0.563 g/cm3.The depth of ancient seawater is 2.2～ 2.8km. The ore-forming fluids are of low salinity and low density H2O-NaCl system. The matollogenic temperature is 240℃～280℃. The matollogenic pressure is about 50～ 80MPa, using Sun Fengyue (2000) the depth calculation method, it is concluded that the matollogenic depth of the copper polymetallic deposit is 5.6～7.29 km.Based on the hydrogen oxygen isotopes, during the hydrothermal mineralization stage, the ore-forming hydrothermal solution is probably provided jointly by magmatic hydrothermal fluids and meteoric water. Carbon is mainly derived from marine carbonate. Sulfur isotopes are mainly derived from the granite, a small amount of basalt and metamorphic rocks. Lead isotopes show the characteristics of mixing of crustal materials with mantle components, with the model age between 158～634Ma.The lateral trend of ore bodies is in NWW trend at about 30° the side, which is according with the section enrichment and the horizontal correspondence regularity of the hydrothermal ore deposit. Finally, the author holds that Yinaocao copper polymetallic deposit is superimposed type deposit, namely hydrothermal exhalative mineralization and hydrothermal mineralization superimposed, and later hydrothermal mineralization is mainly mineralization stage.