Research On The Metallogenic Mechanism Of "Panzhihua" Vanadium-titanium Magnetite Deposit

Panzhihua and Baima mafic-ultramafic layered rocks containing super-large vanadium-titanomagnetite deposits are exposed in Panxi area.They are part of the?260Ma Emeishan large igneous province together with the widely developed high-Ti basalts,syenite and granite intrusions closely associated in time and space.The unique feature of these ore-bearing rocks is that the massive vanadium-titanium magnetite ore bodies are mainly located in the middle or lower part of the rock mass,which is different from other layered rocks hosting vanadium-titanium magnetite deposits in the world.Therefore,the enrichment mechanism of a large number of magnetite in bedded rock mass in Panxi area is a problem to be discussed.Taking Panzhihua and Baima intrusions as the main research objects,the enrichment mechanism of Panzhihua-type vanadium-titanium magnetite is discussed in this paper,and the following understandings are obtained:(1)The main rock-forming minerals of the Panzhihua type V-Ti magnetite deposit are olivine,Plagioclase,clinopyroxene and anphibole,and no clinopyroxene is found in the rock body.The grade of olivine Fo ranges from 64 to 75,suggesting that its parent magma is the product of evolutionary magma formed by primitive magma after a large degree of differential crystallization in the deep part.Plagioclase An is between 57 and 66 and belongs to elongated feldspar.As a whole,the Angrade shows a downward trend of rock mass.(2)Rock P2O5 shows a gradual upward trend from the bottom to the top of the rock mass,suggesting that the gravity crystallization differentiation process of rock mass is carried out from the bottom to the top,and the volatile components have the characteristics of the upper convergence.(3)The samples of Panzhihua and Baima intrusions show the right-leaning characteristics of REE and positive Eu anomalies of chondrite standardization curve,and the enrichment of light rare earth elements is obvious.However,there are slight differences between different lithofacies belts,and the fine-grained gabbro in the upper lithofacies belt has obviously higher total REE content.The normalized curves of trace elements in the original mantle show that Th,Zr and Hf are depleted while Rb,Sr,Eu,Nb and Ta are enriched.(4)The Sr-Nd isotope distribution of Panzhihua type vanadium-titanium magnetite deposit is relatively small,all of which fall within the boundaries of intraplate oceanic island basalt(OIB)and Emeishan high-titanium basalt.Sr-Nd isotope characteristics show that the Panzhihua type V-Ti magnetite deposit is less affected by continental contamination during diagenesis.(5)Compared with the original mantle,the Panzhihua and Baima intrusions have higher Nb/Th and lower Th/Yb,indicating that there is no strong continental contamination during the formation of the intrusions.In the Sm/Yb-La/Sm diagrams,most of the samples fall into the area of high-titanium basalts,indicating that the magma of the Panzhihua type vanadium-titanium magnetite deposit has the same magma source as that of the Emeishan high-titanium basalt.(6)The formation of Panzhihuatype V-Ti magnetite deposit is controlled by many factors,such as the composition of parent magma,oxygen fugacity and multi-stage magma recharge.Therefore,the metallogenic model of Panzhihua vanadium-titanium magnetite deposit has been established.