Apatite Geochemical Constraints On Petrogenesis And Metallogenesis Of Mafic-ultramafic Intrusions In The Emeishan Large Igneous Province

The formation of Emeishan large igneous province is related to the mantle plume in the Late Permian.There are several world-class super-magmatic Fe-Ti-V oxide deposits in the region.The genesis of mafic ultramafic intrusions containing ore in the area is still controversial.In this study,three representative mafic-ultramafic intrusions(Panzhihua,Hongge and Taihe)bearing Fe-Ti-V oxide deposits in the Emeishan large igneous province with different types of country rocks are taken as the main objects of this study.Apatite is a widespread accessory mineral in igneous rocks and has been used to study magmatic process.The in situ trace elements and Sr-Nd isotopes analyses were performed on apatite from the Panzhihua,Hongge and Taihe magmatic Fe-Ti-V oxide ore deposits in the Emeishan large igneous province in southwestern China to reveal the the divergence of the magma origin and evolution of the different intrusions,and then to discuss the differences of petrogenesis and metallogenesis among different intrusions.The chondrite-normalized REE patterns of most of the apatite grains from the Panzhihua,Hongge and Taihe samples exhibit right-inclined patterns,which can be attributed to fractional crystallization of clinopyroxene at the three intrusions.In the primitive mantle-normalized trace element patterns,the apatite samples show similar patterns,with notably negative Nb,Pb,Sr,Zr and Hf anomalies and positive Th and U anomalies.The obvious depletion of Nb,Zr,and Hf in apatites may be related to the early crystallization of Fe-Ti oxides.The relatively weak negative Eu anomaly with the lowest Ga contents in Panzhihua apatites and absence of negative Eu anomaly in the Taihe apatites indicates that they are crystallized from an oxidizing magma,whereas the negative Eu anomaly with the highest Ga contents in Hongge apatites should be caused by the less oxidizing oxygen fugacity.The Sr-Nd isotopes of the apatite separates have(⁸⁷Sr/⁸⁶Sr)_ivaring from 0.70441 to 0.70471 and?_Nd(t)from 2.1 to4.2 for the Panzhihua gabbro,(⁸⁷Sr/⁸⁶Sr)_ifrom 0.70488 to 0.70506 and?_Nd(t)from 1.9 to 4.1 for the Taihe gabbro,and(⁸⁷Sr/⁸⁶Sr)_ifrom 0.70565 to 0.70596 and?_Nd(t)from-1.2 to 1.8 for the Hongge clinopyroxenites.The negatively correlation of La/Yb and Sr/Y ratios with Sr contents,and the highest(⁸⁷Sr/⁸⁶Sr)_iand lowest?_Nd(t)in the Hongge apatite imply that the replenishment of new magma pulse with high Sr contents occur in this intrusion.The in situ trace elements and Sr-Nd isotope variations of apatite from the three intrusions are primarily indicated that contamination with Precambrian metamorphic rock and magma replenishment play an important role in the formation of the Hongge intrusion,and high oxygen fugacity in the Panzhihua and Taihe intrusion are attributed to marble assimilation.