Mineral compositional constraints on petrogenesis and oxide ore genesis of the late Permian Panzhihua layered gabbroic intrusion, SW China Kwan-Nang Pang a, ⁎, Chusi Li b , Mei-Fu Zhou a , Edward M. Ripley b a Department of Earth Sciences, The University of Hong Kong, Hong Kong, China b Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA abstract article info Article history: Received 26 September 2008 Accepted 13 January 2009 Available online 30 January 2009 Keywords: Mineral composition Fe–Ti oxide ore Layered intrusion Panzhihua A systematic study of mineral compositions has been carried out on stratigraphic sections through the Panzhihua intrusion, a layered gabbroic sill of late Permian age that hosts significant magmatic Fe–Ti–V oxide deposits in the Emeishan large igneous province, SW China. The intrusion, which is ∼ 19 km long and ∼ 2 km thick, is divided into a Marginal zone (MGZ), Lower zone (LZ), Middle zone (sub-zones MZa and MZb) and Upper zone (UZ) from the base upwards. Compositions of the most primitive cumulus olivine (Fo 81 ) and plagioclase (An 73 ) found in the intrusion suggest that the parental magma was similar to the Mg-rich end- member of the coeval high-Ti basalts in the region. Two reversals in terms of mineral compositions are found in the intrusion, one in the lower MZa and the other at the transition between the MZb and the UZ. The first reversal is marked by a gradual increase in the An content of plagioclase (∼ An 60 to ∼ An 70 ) over a ∼ 100 m vertical interval. The other is characterized by abrupt changes in the compositions of olivine (∼ Fo 28 to ∼ Fo 70 ), clinopyroxene (Mg#=∼ 51 to 75) and plagioclase (∼ An 24 to ∼ An 51 ) over a b 20 m vertical interval. These suggest that the Panzhihua intrusion opened at least twice for recharge of more primitive magmas. Strong depletion of incompatible trace elements, such as Zr, in the cumulate sequence without corresponding enrichment in any border series is suggested to be evidence for significant loss of residual liquid at a late- stage during solidification of the intrusion. Compared to other well-studied layered intrusions, the Panzhihua intrusion contains Fe–Ti oxides crystallized at a high temperature, consistent with evidence obtained in earlier studies. Early appearance of liquidus Fe–Ti oxides in the Panzhihua magma is most likely a combined effect of a rather high degree of initial oxidation and elevated volatile fugacity. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The ∼ 260 Ma Panzhihua intrusion is a layered gabbroic intrusion associated with the magmatism leading to the formation of the Emeishan large igneous province, SW China (Ma et al., 2001; Zhou et al., 2005). The intrusion hosts significant magmatic Fe–Ti–(V) oxide ores in its lower part. This stratigraphic relation, together with the discovery of abundant Fe–Ti oxide inclusions in rather Mg-rich cumulus olivine (∼ Fo 78–81 ), led Pang et al. (2008a) to propose that Fe–Ti oxides became cumulus at a relatively early stage and their accumulation from magma formed the world-class Fe–Ti oxide deposits. However, there has not been any attempt to study the petrogenesis of the Panzhihua intrusion using mineral compositions. For instance, whether the intrusion formed from a single differentiat- ing magma like the Skaergaard intrusion (McBirney, 1996) and the Kiglapait intrusion (Morse, 1979), or multiple pulses of magma like the Freetown Layered Complex (Chalokwu et al., 1995) and the Kap Edvard Holm Complex (Tegner et al., 1993), is not well-constrained. Systematic mineral chemical data for the Panzhihua intrusion not only can shed light on its magmatic history, but also allow refinement of previously-proposed ore-forming conditions and comparison with other layered intrusions. This study examines stratigraphic variations in olivine, clinopyroxene, plagioclase and apatite compositions in the intrusion. Our results corroborate previous arguments that Fe–Ti oxides in the Panzhihua intrusion crystallized at an earlier stage than usual, and further suggest that the intrusion experienced multiple magma injections and significant loss of residual liquid. 2. Geological background 2.1. Regional geology Southwest China comprises the Yangtze Block to the east and the Tibetan Plateau to the west (Fig. 1). The Yangtze Block consists of an Archean to Mesoproterozoic crystalline basement overlain by a thick Lithos 110 (2009) 199–214 ⁎ Corresponding author. Present address: Laboratoire de Géodynamique des Chaînes Alpines (LGCA), Université Joseph Fourier, 1381 rue de la Piscine, 38401 Grenoble, France. Tel.: +33 4 76 51 40 73; fax: +33 4 76 51 40 58. E-mail address: knpang@graduate.hku.hk (K.-N. Pang). 0024-4937/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2009.01.007 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos