Genesis Of Vohitasara Graphite Deposit On The East Coast Of Madagascar

The Vohitasara Deposit of Madagascar is located on the eastern side of the Vorokafotra giant ductile shear zone,which runs through the eastern part of Madagascar.It belongs to the edge of the crystalline basement type.The graphite flakes in the ores are relative ly large and linear,showing active belt type characteristics.They belong to medium pressure and temperature regiona l metamorphism mineralization.The main ore types include graphite containing slanted gneisses,graphite slanted gneisses and graphite inclined plagioclases.In the Neoproterozoic,the division of the Rodinia supercontinent caused the subduction of the ocean,resulting in many volcanic rocks with is land arc properties and the intrus ion of some calc alkaline magmatism,which was related to the metamorphic and deformationa l action of the same period.The geochemical analysis of ma jor,minor and rare earth elements in this paper can provide evidence.On the basis of the main element identification graphic of the genetic types of the igneous rocks,the cast points of the gabbro samples fall in the CAB region and fall into the OIA region in the tectonic setting of the gabbro,indicating that the sample rocks were formed in the tectonic environment of the active continental margin.The samples of the gabbro in the trace element original mantle normalized spider diagram showed the typical is land arc characteristics,such as the enrichment of large ion lithophile elements,low Yb and Y,and the loss of high fie ld intens ity elements.It is presumed that rocks formed in the continental margin environment of island arc type activities.The geochemical characteristics of the rare earth elements of metamorphic rocks are similar to the characteristics of the sandy sedimentary clastic rocks in the source from the magma arc,reflecting the depositional environment was the oceanic is land arc.Moreover,the metamorphic rocks are placed on the active continenta l margin and is land arc regions in the tectonic environmental discrimination graphic,which provides evidence for the above inference.From the geochemical test results and zircon U Pb age,the metallogenic process of the Archean and Proterozoic graphite deposits is roughly summed up as follows : the late Archean and early Proterozoic paleocontinent uplift and cracking,the formation of shallow sea areas and semi closed bays,resulting in the depos ition of the craton basin and the carbonate and argillaceous rocks in the rift valley.Accumulation and depos ition formed the protolith of the khondalite series.Later,the basin was closed due to land and land collis ion events before 2.0~1.9Ga,the origina l rock was involved in the lower crust,and the amphibolite facies heat flow metamorphism occurred in the middle pressure area,with the intrusion of ultrabasic magma and basic magma,and the sedimentary clastic rock formation in the relatively stable trough zone and the paleo Continental margin in the silicon aluminum shell metamorphosed.The formation of Vohitasara graphite ore is formed.Ore deposits exist in the metamorphic sedimentary rocks similar to khondalite series and belong to sedimentary metamorphic deposits.