A metallogenic model for transmagmatic fluid of vanadium-titanium magnetite deposit:Evidence from Zhaka intrusion of Madagascar

At present, there are many different interpretations for the genesis of the vanadium-titanium magnetite deposits in the mafic-ultramafic complex, which has to a certain extent caused confusion to the resource exploration of these deposits. Therefore, it is very important to discuss the mechanism of large-scale aggregation of ore-forming minerals in mafic-ultramafic intrusion. The Zhaka rock mass in the Alaotra Lake area of the northeast of Madagascar is a typical mafic layered intrusion with a very large vanadium-titanium magnetite deposit. The Shenyang center of CGS has found the vanadic titianomagnetite deposit with 800 million tons of iron ore (including 333), associated with 60 million tons of Ti and 2.3 million tons of V. These results provide a good condition for clarifying the genesis of the vanadium and titanium magnetite deposit. This paper reports the geology, orebody geology, petrography, mineralogy and petrological geochemical characteristics of the Zhaka rock mass. The main conclusions are as follows:(1) The rhythmic layering is a typical mafic layered rock mass, whereas the pegmatite can form an independent invasive unit; (2) orebodies mainly occur in the layered rock mass, and can be divided into three different types, i.e., integrated type, unconformity type and pegmatite type; (3) gabbro has the crystallization sequence of olivine → plagioclase → clinopyroxene or olivine → plagioclase+clinopyroxene, suggesting that the Zacha rock mass is a shallow stratigraphic rock mass, with the emplacement depth of ~ 3 km; (4) ore mineral and silicate minerals are thermodynamically unbalanced and shared with water-dark mineral minerals, suggesting that mineralization occurred in the rich volatiles in the late magma evolution; (5) The REE quadruple effect of dense massive iron ore also indicates that the mineralization process was accompanied by fluid activities of F, Cl and other components. It is held that the formation of vanadium-titanium magnetite deposit in the Zacha rock mass was related to the process of the magmatic fluid.