0361-0128/12/4020/481-26 481 Introduction MAJOR MAGMATIC Ni-Cu-(PGE) sulfide deposits may have formed when sulfides entrained and transported by ascending silicate magmas were concentrated in the widened parts of the conduits or near their exits into larger chambers because of a decrease of the flow velocity (Naldrett et al., 1996; Li and Naldrett, 1999; Barnes and Lightfoot, 2005; Maier, 2005). Thus, magma conduits and lava channels with complex geometries are considered as favorable sites for S-saturated magmas to form magmatic sulfide deposits such that offer op- portunity for the concentration and accumulation of mag- matic sulfides at the base or margin of mafic-ultramafic in- trusions or lava flows. The Kalatongke Cu-Ni sulfide deposit in the Altay orogenic belt, NW China, is a major magmatic sulfide deposit formed in a postcollisional environment (Zhou et al., 2002; Zhang et al., 2008; Song and Li, 2009). The Kalatongke deposit con- tains 33 million metric tons (Mt) of sulfide ores at a grade of 0.8 wt % Ni and 1.3 wt % Cu (Liu et al., 2005). The ore-bear- ing intrusion at Kalatongke does not have ultramafic compo- nents. The occurrence of a major massive sulfide orebody within the intrusion raises a question about the mechanism of sulfide concentration. The Kalatongke deposit is PGE de- pleted relative to Ni and Cu (Wang et al., 1991; Jiang et al., 2009; Song and Li, 2009). The depletion of PGE and enrich- ment of Cu in this deposit has not been adequately addressed in the previous studies but is important in understanding the compositional diversity of magmatic sulfide deposits. In this study, we describe the geology of the Kalatongke in- trusion and report on the compositional diversity of Cu-rich ores that were not well known previously. Our field and pet- rographic observations demonstrate that the Kalatongke Cu- Ni sulfide deposit formed from two magma pulses. Chemical compositions of minerals and bulk-rock compositions are used to constrain the nature of the parental magmas and their differentiation histories. Utilizing the chalcophile elements, PGE, Cu, and Ni, we examine the processes that led to the enrichment of Cu and the depletion of PGE at Kalatongke, Origin of PGE-Poor and Cu-Rich Magmatic Sulfides from the Kalatongke Deposit, Xinjiang, Northwest China JIAN-FENG GAO, 1 MEI-FU ZHOU, 1,2,† PETER C. LIGHTFOOT , 3 CHRISTINA YAN WANG, 4 AND LIANG QI 2 1 Department of Earth Sciences, University of Hong Kong, Hong Kong, China 2 State Key Lab of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China 3 Vale, Highway 17 West, Sudbury, Ontario, Canada P0M 1N0 4 Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China Abstract The Kalatongke Cu-Ni sulfide deposit in the Paleozoic Altay orogenic belt, NW China, is hosted in a Per- mian mafic intrusion consisting of norite, troctolite, gabbro, and diorite. Disseminated Ni-Cu, massive Ni-Cu, and massive Cu-rich sulfide ores are mainly hosted in norite and gabbro. Some massive Ni-Cu ores also occur in the Carboniferous sedimentary rocks. The geologic and compositional relationships between various sulfide ores and the rocks of Kalatongke offer a new interpretation of the sequence of emplacement of the magmas, which underpins an understanding of the compositions of the ores and the formation of the Kalatongke deposit. Olivine grains from disseminated Ni-Cu ores have Fo values ranging from 71.6 to 78.0 mol % and Ni con- tents from 1,000 to 2,200 ppm. Typically, Ni decreases from the cores to the rims from 2,000 to 1,000 ppm at constant Fo content, indicating the reaction of early-formed olivine with later-segregated sulfide melt. Cr spinels at Kalatongke are highly enriched in Fe 3+ and Fe 2+ , with relatively low Cr, Al, and Ti, reflecting reac- tion with evolved trapped intercumulus melt. Norites are depleted in Nb, Ta, Zr, Hf, and Th and enriched in Sr and Ba, whereas disseminated Ni-Cu sul- fide ores have considerable depletion of Rb and enrichment of Sr and Ba and lack depletion of Nb, Ta, Zr, and Hf, indicating their different origins. Disseminated Ni-Cu sulfide ores have bulk compositions with variable Cu and Ni contents which are much lower than those of massive Cu-rich and Ni-Cu ores, but disseminated and massive Ni-Cu ores have similar PGE contents with relatively low Pd/Ir ratios. Massive Cu-rich ores have much higher Pd and Pt with very high Pd/Ir ratios. The Kalatongke Cu-Ni sulfide deposit appears to have formed from two different pulses of PGE-poor and Cu-rich basaltic magmas that underwent different degrees of assimilation and fractional crystallization. The first magma pulse gained sulfide saturation because of minor crustal contamination and fractionated a small amount of sulfide (<0.03%); the evolved melt then intruded and assimilated crustal materials to attain sulfide saturation again. Sulfide liquid segregated from the magma to form the massive sulfide melts and residual magma formed the noritic rocks in the shallow magma chamber. The segregated massive sulfide melts then un- derwent further fractionation to form massive Ni-Cu and massive Cu-rich ores. The second pulse of magma after removal of sulfides (<0.02%) experienced more crustal contamination and re attained S saturation. This new S-saturated and phenocryst-laden magma intruded the earlier formed massive sulfide ores and norites and formed the disseminated sulfide ores. † Corresponding author: e-mail, mfzhou@hkucc.hku.hk ©2012 Society of Economic Geologists, Inc. Economic Geology, v. 107, pp. 481–506 Submitted: January 30, 2011 Accepted: October 6, 2011