Study On The Geological Characteristics And Ore Genesis Of Sancha Cu-Ni-Au Deposit,Huangzhong County,Qinghai Province

Sancha Cu-Ni-Au deposit is situated on Shangxinzhuang town of Huangzhong county, Qinghai province, its geotectonic position belongs to Qilian Orogenic belts, and the concrete position is located in Danghenanshan-Lajishan Orogenic belts.The strata exposed in diggings are relatively simple, mainly includes Huangzhong Group, Liudaogou Formation and Quaternary. Magmatic rocks which are widely distributed in diggings include granodiorite, quartz diorite, diorite and so on, and in these intrusions enclaves is widely developed. This study obtains zircon U-Pb age of granodiorite and enclaves of 451±2Ma and 451±3Ma; vein rocks occurres basic to acid rock, and most of them along faults and fracture zone. Faults takes big folds as a main body, and develops north-north-west faults and north-north-east or south-north secondary faults.Metallization of Sancha deposit include magmatic mineralization and hydrothermal mineralization. The ore of magma period is hold in basic-ultrabasic rock, and it is strictly controlled by this rock. Hydrothermal period was mainly of transformation, although the wall rock alteration is wide-spread and intensive, the mineralization is poorer; sericitization-Au-polymetallic mineralization has little mineralization and Au is related to fuchsite. The morphology of orebody mainly is lenticular, secondly is stratiform-like, the orebody dips steeply and has a trend plunging northwest; thickness of orebody is unstable, the maximum thickness is 12m±, the average thickness is 7.25m. Gold orebody is hold in Cu-Ni deposit, its morphology also is lenticular, the Au is distributed in the enrichment of Cu and Ni, at the same tiame, the Au deposit extend along strike.The main ore minerals are pyrite,chalcopyrite,pyrrhotite, pentlandite, sphalerite, chalcocite, tetrahedrite, magnetite, linnaeite, skutterudite and so on; the secondly ore minerals are malachite, azurite, gothite, magnesite and so on. Gangue minerals mostly are quartz, sericite, carbonate and so on. Ore structure are dominated by stellate, bean structure, mass structure and disseminate, and secondly for banded structure and massive structure. The ore texture mainly is granular texture, metasomatic texture and sideronitic texture, and so on.The quartz fluid inclusion of hydrothermal period demonstrate that the scope of fluid salinity is 1.0%-17.0%wt%NaCl.eqv, density of 0.66～0.96g/cm3,and the fluid is a H2O-NaCl-CO2 system, The scope of ore-forming temperature is 160～387℃, pressure is 20-100Mpa, and the mineralization depth is2.0-8.3km.The sulfur isotope δ34S of magma period is 0.3‰-0.8‰, it shows that metallogenic material are coming from mantle. The sulfur isotope δ34S of hydrotherma period is-1.3‰～-0.8‰, it shows that metallogenic material are coming from magma; lead isotopic composition indicates that metallogenic material are coming from the deep crust; carbon and oxygen isotope composition indicate that host rock provide partial ore forming materials; study on isotope hydrogen and oxygen shows that ore-foming fluid was derived from magmatic, and some come from meteoric water.so the paper holds that metallogenic material are mainly from magma and orebody and stock of magma period.The SHRIMP U-Pb dating results of zircons from basic-ultrabasic rock is 489±3Ma, suggesting that the Cu-Ni deposit of magma period was formed in Late Cambrian; the Ar-Ar dating of sericite indicate Au-polymetallic deposit was formed in Late Ordovician-Early Silurian.According to all the research, it is subduction of plate that causes mantle material upwell and plutonic liquation is dominance during the magma period, then ore-bearing magma intruded upward along fault. The tectonic setting of Au- polymetallic deposit is extensional environment after collisional orogeny, magmatic hydrothermal fluid flow along fracture, at the same time, the ore -forming elements of magma period(eg. Cu,Co,Ni)were re-activated, transported and enriched, at last form forming the Cu-Ni-Au polymetallic deposit. So we can come to the conclusion that Sancha deposit is superimposed and mixed hydrothermal deposit.