The Genesis Of Thick Layer Fe-Ti-(V) Oxide Ore Deposit In Emeishan Large Igneous Province

There are many Fe-Ti-?V?oxide deposits in the large-super large mafic-ultramafic layered intrusions distributed in the central part of Emeishan Large Igneous Province.As one of typical mafic intrusion,Baima layered intrusion can be divided into the Lower and Upper Zones from the bottom up,which the ilmenite oxide ore are mainly hosted in the Lower Zone.The hornblende,plagioclase and phlogopite,associated with Fe-Ti oxide are typical constrained minerals for physical and chemical conditions of the ilmenite oxide ore.The mineral interpenetration relationship indicates that the formation of ilmenite oxide is earlier than that of hornblende and phlogopite,both of which can constrain the Temperature and pressure of the ferrotitanium oxide.In addition,the iron content of plagioclase can be used as a indicator of the change of the iron content in the melt.The results show that the the crystallization temperature,pressure and the oxygen fugacity of hornblende in Baima intrusion is between 1020-1100?,220-450MPa,NNO-0.4 and NNO+0.4respectively which consistent with the order of mineral formation.Then,we can drive the conclusion that the crystallization of ilmenite oxide ore in Baima intrusion is>1100?,the oxygen fugacity is>NNO+0.4,and the depth of emplacement is<14km.The EPMA results of plagioclase,combined with the partition coefficient of iron between the plagioclase and melt ??? showed that the corresponding melt TFeO content of the plagioclase core and the rim crystallization is TFeO<17.8wt.%and TFeO<13.9wt.%,respectively,indicating that there is no high Fe-rich?TFeO>20wt.%?melt.Appeared,is a typical basaltic melt.From the bottom up of two layers of ilmenite oxide ore in the Lower Zone of the intrusion,The SiO₂,TFeO,TiO₂ and An values and the TFeO content in plagioclase show three cycle variations with depth,which indicate there are three stages of magma replenishment.The positive correlation between An values and TFeO content of plagioclase indicate that there is no Fe enrichment in each magma replenishment process,moreover,ferrotitanium oxide as the primary crystal phase and separation from the melt,trend residual melt evolves toward the iron depletion,in other words,the recharge magma is highly Fe-rich magma.The appearance of the hornblende gabbro in the upper zone of Lower Zone of the Baima intrusion is a indicator of water-rich.Combined with the changes of composition in the magma system,it is considered that the last stage of magma replenishment is water-rich than the first two periods.Therefore,we believe that the formation of two layers of ilmenite oxide ore and the formation of cunulate rock in the Lower Zone of the Baima intrusion have experienced three periods of magma replenishment.The continuous replenishment of this multi-stage iron-rich magma leads to the formation of ilmenite oxide ore layer in the Baima intrusin.