Study On The Metallogenesis Of The Baima Ultra-Large V-Ti-Magnetite Deposit In The Emeishan Large Igneous Province, SW China

The Emeishan large igneous province?LIP?is located in the western margin of the Yangtze Block,which is related to the mantle plume in the late Permian.There are several Fe-Ti-V oxide deposits and Cu-Ni-?PGE?sulfide deposits in the area,among which the Baima ultra-large V-Ti-magnetite deposit in the Pan-Xi area?Panzhi-Xichang?is one of the representative deposits.In this paper,the major oxides,trace elements and Sr-Nd isotopes were measured on the Baima intrusion to reveal the origin,evolution,parent magma,source characteristics and metallogenic mechanism of the Baima ultra-large V-Ti-magnetite deposit.Several important conclusions can be made from this study.They are summarized below.1.The rocks of the Baima intrusion are derived from the same parent magma.The major oxides of troctolites and olivine gabbros indicate that the Baima rocks have the homologous origin.The compositions of the troctolites are controlled mainly by olivine,plagioclase and Fe-Ti oxides,and the compositions of olivine gabbros are mainly controlled by plagioclase,clinopyroxene,olivine,hornblende,and Fe-Ti oxides.The correlations of MgO contents with Cr,Ni,and P concentrations indicate that these rocks are genetically linked and are the product of the same parent magma after evolution and crystal accumulation.2.Primitive mantle-normalized trace elements and Chondrite-normalized rare earth elements patterns of the troctolites and olivine gabbros from the Baima intrusion in Emeishan LIP are similar to the coeval picrites and basalts in the nearby Ertan area.The samples show negative Zr and Hf anomalies,and positivie Sr,Eu,and Ti anomalies.There are positive and negative Nb and Ta anomalies among these samples.It is related to the accumulation of magnetite,clinopyroxene and plagioclase in the Baima intrusion.The olivine gabbro with high P₂O₅ content has the highest REE content and slight negative Sr and Eu anomalies.3.High?Nb/Th?_PMM and low?Th/Yb?_PMM ratios of the troctolites and olivine gabbros show that there was no obvious contamination by the upper crust and middle crust in the Baima intrusion.In the plot of La/Sm vs.Sm/Yb,most samples fall in the range of the high-Ti basalts in Emeishan LIP,and it indicates that the Baima intusion is originated from the same magma source with high-Ti basalts.4.The metallogenic magma of the Baima deposit derived from the mantle plume.The(⁸⁷Sr/⁸⁶Sr)_i ratios of the Baima intrusion range from 0.704232 to 0.704855 with the mean value of 0.704706.The?_Nd values of the intrusion vary between 1.40 and 3.94with the average value of 2.41.They all fall in the ranges of OIB and high Ti basalts in the Emeishan LIP.The mixing calculation displays that the Baima parent magm is less contaminated by the crustal material.By contrast,it had been contaminated by 10%-30%bulk assimilation of the siliceous marble country rocks.5.The correlations of the whole-rock MgO contents versus the compatible elements in the magnetite and ilmenite such as Cr and Ni concentrations show that the Baima intrusion went through a high degree of fractional crystallization,and the formation of the oxides layers,troctolites and olivine gabbros resulted from density difference and crystal differentiation of the troctolites and olivine gabbros.The formation of the Baima V-Ti-magnetite deposit is controlled by many factors such as the compositions of the parent magma,oxygen fugacity and magma recharge.