In-situ LA-ICP-MS trace elemental analyses of magnetite: Fe–Ti–(V) oxide-bearing mafic–ultramafic layered intrusions of the Emeishan Large Igneous Province, SW China

摘要: Abstract The Taihe, Baima, Hongge, Panzhihua and Anyi intrusions of the Emeishan Large Igneous Province (ELIP), SW China, contain large magmatic Fe–Ti–(V) oxide ore deposits. Magnetites from these have extensive trellis or sandwich exsolution lamellae ilmenite spinel. Regular electron microprobe analyses are insufficient to obtain primary compositions such magnetites. Instead, laser ablation ICP-MS uses spot sizes (~ 40 μm) can produce reliable data for magnetites with lamellae. Although deposits variable trace element contents, they similar multi-element variation patterns. Primary controls variations magnetite in include crystallography terms affinity ionic radius overall charge balance, oxygen fugacity, magma composition coexisting minerals. Early deposition chromite Cr-magnetite greatly deplete magmas Cr thus Cr-poor crystallized magmas. Co-crystallizing minerals, olivine, pyroxenes, plagioclase apatite, little influence on contents because elements compatible incompatible silicate phosphate Low bi-modal distribution highly as V Fe–Ti ores ELIP suggest that may not form fractional crystallization, but relatively homogeneous Fe-rich melts. QUILF equilibrium modeling further indicates parental Baima had high fugacities massive and/or net-textured at bottom intrusive bodies. Magnetite Hongge intrusions, other hand, under low and, therefore, formed disseminated oxides after a lengthy period fractionation. Plots Ge vs. Ga + Co be used discrimination diagram differentiate oxide-bearing layered massif anorthosites Cu–Ni sulfide Variable amounts Fe–Ti–(P) Damiao anorthosite (North China) Sudbury (Canada) Huangshandong (northwest demonstrate control major magnetite.