The Xiarihamu Ni-Co deposit, located in the East Kunlun orogenic belt, northern Tibet plateau, is the secondary largest Ni deposit in China and contains ~157 million metric tons (Mt) sulfide ores with average grades of 0.65 wt % Ni, 0.14 wt % Cu, and 0.013 wt % Co. The intrusion consists of gabbroic and ultramafic portions, the main orebody being hosted in the ultramafic portion. The zircons separated from the gabbronorite and websterite yield SHRIMP U-Pb ages of 405.5 ± 2.7 and 406.1 ± 2.7 Ma, indicating a genetic linkage with the Early Devonian regional magmatism (400–410 Ma). The main orebody includes two large ore pods comprising a pod of disseminated sulfides in the western portion grading into multiple ore sublayers to the east. The ore sublayers consist of net-textured and disseminated sulfides. The distribution and shape of the ore pods and sublayers of the orebody are conformable with the undulating roof and bottom of the ultramafic portion. The unusually high Ni/Cu ratios (~4–18) and extremely low tenors of platinum-group elements (PGE; <4 ppb Ir, <85 ppb Pt, and <115 ppb Pd) of the disseminated sulfides indicate a genetic relationship with low degrees of partial melting of a pyroxenite mantle source. The slightly higher Ir and Ru tenors suggest that the disseminated sulfides in the western portion of the main orebody were segregated from less evolved magma under higher mass ratios of silicate melt/sulfide liquid than the sulfides of the middle and eastern portions.