Geology and geochemistry of the Tulaergen conduit-style magmatic Ni-Cu sulfide deposit in the Central Asian Orogenic Belt, northwestern China

The Tulaergen magmatic Ni-Cu sulfide ore deposit is located along the southern margin of the Central Asian Orogenic Belt in northwestern China. This deposit is hosted by a small mafic–ultramafic complex composed of a Late Carboniferous (~ 301 Ma) gabbroic member at the margin and a younger ultramafic dyke in the center. Net-textured and semi-massive sulfides are mainly concentrated in the steeply dipping, widened parts of the dyke. Zircons from the ultramafic member yield a U–Pb age of 281 ± 2 Ma, ~ 20 myr younger than the gabbroic member. The average εHf(t) value of the zircons is ~ 16. The Tulaergen mafic–ultramafic rocks are characterized by light REE enrichments, pronounced negative Nb–Ta anomalies, (87Sr/86Sr)i ratios from 0.7034 to 0.7036, and εNd(t) values from 5.1 to 6.9. The isotope data indicate negligible bulk contamination with the crust. The δ34S values of sulfide ores are from − 0.3 to 1.5‰, similar to the values of the country rocks. The γOs values of the sulfide ores are from + 605 to + 954, much higher than typical mantle values. The Os-S isotope data together support the view that the addition of Os-bearing organic matter from the country rocks may have played a critical role in triggering sulfide saturation. In the sub-vertical segment of the deposit, the upper zone has lower PGE tenors coupled with lower and rather constant olivine Fo contents compared to the lower zone. Based on the geometry of the dyke and sulfide distribution, we conclude that the Tulaergen deposit formed in a dynamic magma conduit.