The Genetic Significance of Pentlandite and Pyrrhotite and the Characteristics of Cobalt Occurrence in Xiarihamu Cobalt-Nickel Deposit of Eastern Kunlun

Jinchuan copper-nickel deposit being the world's third-largest deposit found in China, Xirihamu in Eastern Kunlun is another super large magmatic nickel-cobalt-sulfide deposit, and it is also the largest deposit in orogenic belts. Previous mineralogical research focused mainly on silicate minerals, studies on ore-forming materials (sulfide) is relatively less. Through systematic division of the output of pentlandite, based on the atomic ratio of Ni/Fe, the distribution of Co elements and the classification of pyrrhotite types, we infer that Xiarihamu deposit has experienced at least two stages of magmatism. At the first magmatic stage, some high-cobalt content sulfide crystallized at higher temperature; at the second magmatic stage, some sulfide with low-cobalt content crystallized at a relatively low temperature. Combined with the ratio change of metal atom to sulfur atom in pentlandite, we found that the sulfur fugacity increases gradually in the process of sulfide crystallization. This may be affected by such factors as the crystallization of sulfide and silicate minerals and the sulfur contamination. In the Xiarihamu deposit, cobalt exists mainly in pentlandite. In pyrrhotite, cobalt mainly exists in meteorite pyrite and hexagonal pyrrhotite. In arsenide, cobalt mainly exists in cobaltite. The arsenide contains more cobalt than the sulfides. These characteristics give scientific support to the extraction and synthetic use of cobalt.