Geological Characteristics And Genesis Of The Ambatondrazaka V-Ti Magnetite Deposit In Madagascar

At present,there are many different interpretations for the formation mechanisms of coexisting vanadium-titanium magnetite deposits in mafic-ultramafic complexes.This open debated problem is very important to understand the mechanism of the large-scale aggregation of ore-forming minerals in mafic-ultramafic intrusions.The Ambatondrazaka rock mass in the Alaotra Lake area of the northeastern Madagascar is a typical mafic layered intrusion that hosts a very large vanadium-titanium magnetite deposit.The Shenyang center of China Geological Survey estimates prospective resource in the vanadium-titanium magnetite deposit to be 800 million tons of iron ore,60 million tons of titanium and 2.3 million tons of vanadium.This ore field provides a good example to study the formation mechanism of the vanadium-titanium magnetite deposit.In this paper,we study the geology,orebody geology,petrography,mineralogy and petrological geochemical characteristics of the Ambatondrazaka rock mass and our main conclusions are as follows:(1)The rhythmic layering is a typical mafic layered rock mass,whereas the pegmatite can develop into an independent invasive unit;(2)Orebodies mainly occur in the layered rock mass,and exist in three different types,i.e.,integrated type,unconformity type and pegmatite type;(3)Ore minerals and silicate minerals are thermodynamically unbalanced and coexist with dark-colored hydrous minerals,suggesting that the mineralization occurred in a volatiles-rich environment in the late stage of the magma evolution scenario;(4)The REE quadruple effect of the dense massive iron ore also indicates that the mineralization process was accompanied by fluid activities that brought much F,Cl and other chemical components.We propose here that the formation of vanadium-titanium magnetite deposit in the Ambatondrazaka rock mass was related to the tansmagmatic fluid.