In order to investigate how Fe was enriched from parental high-Ti basaltic magma to form the stratigraphically thick Fe-Ti oxide ore at the bottom layers, we present a systematic study for Fe isotopic compositions of whole rocks and mineral separates (clinopyroxene, magnetite, and ilmenite) throughout the Panzhihua intrusion. Whole rock δ 56 Fe ranges from 0 ± 0.02‰ to 0.15 ± 0.04‰, consistent with the range of clinopyroxene (0.01 ± 0.02‰ to 0.16 ± 0.05‰). On the contrary, magnetite (Mt) separates have δ 56 Fe ranging from 0.17 ± 0.05‰ to 0.62 ± 0.02‰, showing a strikingly complementary trend with coexisting ilmenite (Ilm) separates (À0.52 ± 0.03‰ to À0.09 ± 0.02‰) along the profile. The calculated bulk δ 56 Fe of Fe-Ti oxides (Mt + Ilm), however, has a small range from 0.01‰ to 0.16‰, identical to those for clinopyroxene separates and whole rocks. The uniform δ 56 Fe of clinopyroxene may have resulted from the small Fe isotope fractionation between clinopyroxene and parental magma in early-stage magma differentiation before substantial crystallization of Fe-Ti oxides. The complementary trends of δ 56 Fe for Mt and Ilm along the profile and the uniform bulk δ 56 Fe of Fe-Ti oxides are better interpreted as in situ crystallization of Fe-Ti oxides from the interstitial liquid. Our Fe isotopic data and petrographic observations indicate that the thick Fe-Ti oxide ore layers in the lower zone of the Panzhihua intrusion may be attributed to in situ crystallization of Mt and Ilm from the interstitial, immiscible Fe-rich melt in the lower part of the magma chamber.Fe-Ti oxide ores and host rocks in the layered intrusions are generally composed of olivine, plagioclase, clinopyroxene, magnetite, and ilmenite in different proportions. In theory, heavy Fe isotopes are preferentially partitioned into phases with smaller coordination number (CN) or higher Fe 3+ /∑Fe than those with higher CN or lower Fe 3+ /∑Fe (Young et al., 2015). This explains why olivine, clinopyroxene, and ilmenite have similar or slightly lighter Fe isotopic compositions than the coexisting melt and why magnetite is isotopically heavier CAO ET AL.358

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