ORIGINAL PAPER Xie-Yan Song Æ Mei-Fu Zhou Æ Reid R. Keays Zhi-Min Cao Æ Min Sun Æ Liang Qi Geochemistry of the Emeishan flood basalts at Yangliuping, Sichuan, SW China: implications for sulfide segregation Received: 5 December 2005 / Accepted: 21 March 2006 / Published online: 3 June 2006 Ó Springer-Verlag 2006 Abstract A well-developed, 1,000 m thick basaltic se- quence in the Yangliuping region, northern part of the Emeishan basalt province, includes the Lower and Middle Units of tholeiitic basalts and an Upper Unit of both tholeiites and subalkalic basalts. The basalts contain 42–55 wt% SiO 2 and 4.1–8.3 wt% MgO. Most of these lavas have Gd/Yb > 2.0, Zr/Nb < 12, and e Nd(260 Ma) values from +2.5 to +4.7. The platinum- group elements (PGE) are very mildly depleted in most of the basalts which contain 8–19 ppb Pt and 7–27 ppb Pd. However, a significant proportion of the Middle Unit basalts are strongly depleted in PGE with some samples having concentrations lower than detection limits. They have extremely high Zr/Nb ratios (up to 14.5) and low e Nd(260 Ma) values (+3.21 to +0.65), features of extensive lower crustal contamination. Some samples in this unit have high Ni/Pd (3,965–61,198) and low Pd/Cr (410,000–3,930,000) ratios, indicating sulfide segregation and PGE depletion prior to erup- tion. The primary magmas were S-undersaturated and derived from partial melting at variable depths in the upper mantle. The early and late stage magmas, as represented by the Lower and Upper Units, underwent AFC processes which induced mild S-saturation and PGE depletion in some of the basalts, whereas the magmas represented by the Middle Unit experienced more extensive crustal contamination resulting in stronger S-saturation and in most cases significant PGE depletion. Introduction The Emeishan Large Igneous Province (ELIP) cover large areas in SW China and Northern Vietnam and include the Emeishan continental flood basalts (ECFB) (Song et al. 2001) and mafic–ultramafic intrusions that have been dated at 260 Ma (Zhou et al. 2002a, 2006; Guo et al. 2004). Numerous magmatic Ni–Cu–(PGE) (platinum-group elements) sulfide deposits, such as the Yangliuping, Limahe, and Jinbaoshan deposits, are hosted in conformable mafic–ultramafic sills or discon- formable bodies (e.g., Zhou et al. 2002b; Song et al. 2003, 2004a) (Fig. 1). Some layered intrusions in the ELIP host V–Ti magnetite deposits, such as the Hongge and Panzhihua intrusions (Fig. 1) (Zhong et al. 2002; Zhou et al. 2005). The magnetite deposits and most of the magmatic sulfide deposits are distributed in the central part of the ELIP (Song et al. 2005a, b). However, the temporal evolution of the basaltic magmas and a potential genetic link with the formation of Ni–Cu– (PGE) sulfide deposits has not been well addressed. In the Yangliuping area, some differentiated mafic– ultramafic sills contain Ni–Cu–(PGE) sulfide ores and are spatially associated with the Permian ECFB (Zhou et al. 2002b; Song et al. 2003) (Fig. 2). Petrographic and geochemical data of rocks from the differentiated sills in Communicated by J. Hoefs X.-Y. Song (&) State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, 64th Guanshui Road, Guiyang 550002, People’s Republic of China E-mail: songxieyan@vip.gyig.ac.cn Tel.: +86-851-5895538 Fax: +86-851-5895538 M.-F. Zhou Æ M. Sun Æ L. Qi Æ X.-Y. Song Department of Earth Sciences, The University of Hong Kong, Hong Kong, People’s Republic of China R. R. Keays School of Geosciences, Monash University, PO Box 28E, Monash, VIC 3800, Australia R. R. Keays Mineral Exploration Research Center, Laurentian University, Sudbury, ON, Canada P3E 2C6 Z.-M. Cao College of Earth Sciences, Ocean University of China, Qingdao 266003, People’s Republic of China Contrib Mineral Petrol (2006) 152: 53–74 DOI 10.1007/s00410-006-0094-3