Geology, geochemistry and genesis of the Lashuixia Ni-Cu deposit in Hualong area, Qinghai Province

The Lashuixia Ni-Cu deposit is located in Hualong basic-ultrabasic belt, Qinghai Province. The Lashuixia rock body was altered intensely, mostly mineralized by Ni-Cu sulfides. The major metal minerals include pyrrhotite, chalcopyrite and pentlandite of the magmatic stage, violarite, pyrite and chalcopyrite of the hydrothermal stage, and nickel-bearing kaolinite, nickel-bearing chlorite and malachite of the oxidation stage. The LREE enrichment and negative Eu anomaly indicate that there probably existed fractional crystallization during the process of magmatic evolution. The average content of ∑PGE is 2460.46×10-9. The(Pd+Pt)/(Os+Ir+Ru) ratios (0.40~2.00) are closely related to the deep magma melting. However, because of the hydrothermal alteration, the ratios of Pt/Pd and Pd/Ir are from 0.01 to 2.62 and from 0.91 to 8.77 respectively. The average value of δ34S is 2.24‰, which indicates that S in sulfides was mainly derived from the mantle. On the whole, the ore-forming processes can be divided into magmatic, hydrothermal and oxidation stages.