Two Types Of Magmatic Deposits Mineralization In Pobei Complex,Northeast Tarim Plate

The Pobei complex is of the largest mafic-ultramafic layered intrusion rocks in China,with an area of about 180km2.The complex has two kinds of layered layered rock series,which contain two types of magmatic deposits. The magmatic Cu-Ni sulfide deposits occurs in the small layered ultramafic intrusions which intrusive in the late.At present,ore bodies have been found in Poyi and Poshi intrusions. The main body of the Pobei complex is based on mafic layered intrusion,which has magnetite ore integrated with cumulate bedding. There are many previous studies about the Cu-Ni sulfide deposit of the Poyi and Poshi intrusion,But there are few studies about geological characteristics and mineralization of magnetite ore in the mafic layered intrusion which is the main body of Pobei complex.The comparison and discussion of the two types of magmatic deposits are basically blank. Therefore, this paper chooses the Poyi 、Poshi intrusion and mafic layered intrusion as the research objects.The paper focusing on petrography, mineral petrography, mineral crystallochemistry, geochemistry, isotope geochemistry, compare with the copper-nickel sulfide deposits and magnetite ore.The following questions are discussed in detail:(1) whether the intrusion has underwent crustal contamination or not,the type of hybrids and the degree of crustal contamination,the relationship between crustal contamination and mineralization;(2) fractional crystallization,magma evolution;(3) the nature of magma source and the composition of primary magma;(4) mineralization.The following are the main results:(1)The of magmatic differentiation of the Poyi and Poshi intrusions are fully.Almost all rock types are formed under this condition.The highest basic-levels is dunite,the lowest basic-levels is quartz diorite.But mafic layered intrusion that has layered magnetite ore.Its rocks type is single.The main rocks is gabbro, pyroxenolite is local.(2)The magma of Poyi and Poshi intrusions contaminated by country rock or crust when the magma riding and emplacing, the degree of contamination about 5%~10%. The magma of mafic layered intrusion is contaminated by country rock or crust when the magma riding and emplacing, the degree of contamination about 5%~20%.(3)Comprehensive study shows that the Poyi、Poshi mafic-ultramafic layered intrusion is the result of the partial melting of the mantle plume, and the mafic layered intrusion is the result of partial melting of the ithosphere mantle which induced by mantle plume.In the northeast of Tarim Permian mantle source magmatite is a product of mantle and lithosphere interaction.In the northeast of Tarim Permian mantle source magmatite is a product of mantle and lithosphere interaction.(4)The melting of copper and nickel sulfide in the Poyi 、Poshi intrusion is the result of interaction between assimilation and magma evolution. When the magma is in the course of rising it should be happen sulfide segregation in the deep. The layered magnetite ore of the mafic layered intrusion was due to the local magma gradually separated crystallization assimilation and increased contamination.The increasing of oxygen fugacity is very likely the main factor to induce immiscibility of oxide melt.However, its primary magma is not the iron rich magma which is the basic reason for the formation of large magnetite deposit.(5)Poyi、Poshi intrusions formed Cu-Ni sulfide deposit, mafic layered intrusion formed magnetite ore(Although not much),The fundamental reason is that the magma is different in nature.Poyi、Poshi intrusion’s primary magma is picritic magma which formed by high degree partial melting of mantle.,the magma source region is a depleted mantle.The primary magma of mafic intrusion is basaltic magma formed by low degree partial melting of the lithospheric mantle,the source area is the lithospheric mantle.