Processes of magmatic sulfide mineralization of the Huangshan-Jingerquan Ni-Cu metallogenic belt, NW China: Insights from reviews of chalcophile elements

The Ni-Cu sulfide deposits along the Huangshan-Jingerquan metallogenic belt in the southernmost Central Asian Orogenic Belt contain ∼1.0 million tonnes Ni metal with average grades of 0.4–0.5 wt%. Published data on siderophile and chalcophile elements of sulfide ores and sulfide-poor rocks of the deposit hosting complexes are integrated to address the processes affecting compositions of the sulfide ores, such as sulfide segregation, differentiation and mixing. The sulfide-poor rocks are low in platinum-group elements (PGE), e.g. Ir <0.23 ppb and Pd <2.3 ppb, even containing minute amount of sulfides. These data indicated that the basaltic magmas were primarily depleted in PGE due to sulfide retention in the mantle sources or in the lower crust. Abundances and variation of PGE of the sulfide-poor rocks indicate that fractional crystallization of olivine, pyroxene and chromite lead to fractionation of Ir and Ru from Pt and Pd in the basaltic magmas ascending in the crust. The disseminated sulfide ores with S < 3.0 wt% from the deposits have restricted PGE tenors (0.5–45 ppb Ir, 10–900 ppb Pt and 10–780 ppb Pd) and Pd/Ir values (3.0–250), whereas the net-textured/massive ores have relatively large variations in PGE tenors (0.05–55 ppb Ir, 0.4–2900 ppb Pt and 4.0–2560 ppb Pd) and Pd/Ir values (0.3–4000). Large compositional variations of the net-textured/massive ores demonstrate differentiation and mixing of the sulfide liquids carried by different batches of magma along the magma plumbing system. The sulfides settled down in widen parts of magma conduits forming sulfide mineralized mafic–ultramafic dykes. Downward percolation of differentiated sulfide liquids could form Fe-rich and Cu-rich massive ore veins adjacent to dyke-like orebody. More sulfides were deposited in shallow large complexes along the magma plumbing system.