Origin of the Tudun Cu–Ni sulfide deposit in the eastern Tianshan, NW China: Constraints on the geochemistry of platinum group elements

Abstract

This study documents the geochemistry of sulfide ores of the Tudun Cu–Ni sulfide deposit, located at the western end of the Huangshan–Jing'erquan ore belt in the northern part of eastern Tianshan. The ores have been classified as (1) disseminated sulfide ores, (2) net-textured sulfide ores, and (3) massive sulfide ores.The geochemistry of barren rocks shows Ni and Cu contents ranged 889–1330ppm and 145–253ppm, respectively. The rocks generally contained ~0.10ppb Rh, Ir, Ru and Os, and ~1ppb Pt and Pd, as well as high Cu/Pd ratios (133–246). The contents of Cu, Ni and PGEs in sulfide ores were calculated on a 100% sulfide basis. Total PGEs on a 100% sulfide basis ranged from 13.2ppb to 443ppb (average=144ppb), which were lower than the values in the Huangshandong deposit (average=186ppb) in the eastern Tianshan ore belt, one order of magnitude lower than the Jinchuan deposit, and two orders of magnitude lower than the Noril'sk–Talnakh deposit. The R factor value ranged from 168 to 1810 in sulfide ores of the Tudun deposit, indicating Cu and Ni enrichment, although PGEs enrichment did not reach recoverable grades.In the Tudun deposit, the Pd/Ir ratio of sulfide ores was less than 100, showing weak hydrothermal fluid alteration. The massive sulfide ores exhibited less primitive mantle-normalized PGEs patterns, which are depleted in PPGEs and different from PPGEs-rich intrusions, as well as disseminated and net-textured sulfide ores. In addition, the massive sulfide ores exhibit a strong negative Pt anomaly. This may be due to fractionation of Pt–Fe alloys in the magma batches prior to its intrusion into the staging chamber. It could also be caused by selective Pt leaching from the sulfides by hydrothermal fluids during remobilization within the Tudun chamber.