Ph.D. Project Topic
Factors, parameters, distribution dynamics, and genesis
of the Issia columbite-tantalite deposits, Central-Western
In the Issia area, Central-Western Ivory coast, it has been discoverd many columbite-tantalite detrital deposits at the contact between a non oriented muscovite granite and a chlorite and sericite schist.
In this contact zone and in the intrusive granite, it has been noted the presence of several types of pegmatites in which it was never found columbite-tantalite in place. Moreover, this granite is between two other granites which differ from it in texture, structure and composition. Therefore, it arises a problem on the origin and the genesis of the columbite-tantalite mineralization.
The field observations indicate a pegmatitic origin. But, even if this assumption is allowed, it has not been specified yet the nature of mineralized pegmatite (structure, mineralogy and chemistry). The presence of several types of granites in the area also leads us to question on the source of the mineralizing fluid because either of the granites can have played an important role in the genesis of this fluid.
It is also noted that there has not yet done any scientific approach to indicate the genetic relations between mineralized pegmatites and these surrounding granites.
Besides the problem of the primary mineralization, there is also the problem of the secondary mineralisation. The base of this last question is the fact that the Issia columbite-tantalite deposits are of alluvial and eluvial/colluvial type and , nowhere in the area, columbite-tantalite minerals have been seen in the pegmatite veins supposed to be theire parental rocks. It is thus necessary to search for the mechanism of the secondary concentration in order to specify the predilection zones of the economnic deposits.
Comparative studies carried out on Central Africa (democratic Republic of Congo, Rwanda, Chad, Central African Republic), Nigeria and Ivory Coast indicate that the tendencies in the succession and in the spatial distribution of pegmatites in and around granites remain the same. In spite of this similarity in the geological contexts, it returns that the importance of exploitable mineralizations such as those of tin, niobium, tantalum and beryllium is however quite less in Ivory Coast. It is thus necessary to prove the existence of not yet discovered more important deposits or, failing this, to show why pegmatites are richer elsewhere and less rich in our study area.
The aim of our study is finally to conceive and propose a geodynamic model of the concentration of the primary and secondary columbite-tantalite mineralizations and other economic minerals associated in the Issia columbite-tantalite district, in order to place at the disposal of the mining prospector and the scientific people some effective guides for the research of this kind of mineralization.