3.2 Metallogenic potentialities of Neoproterozoic formations

The metallogenic potentialities of the Birrimian have represented for several ten years the unique pilot for all the prospections in West-Africa, preceding even the synthetic approach of Milesi et al. (1989) relative to gold. And it is now important to integrate observations collected from more recent formations especially those generated from the Birrimian, after alteration, dismantlement, transport, sedimentation and reworking.


The likely extension of a metallogenic potentiality to Neoproterozoic formations, results from the discovery of numerous and various supergene indexes. And that cancels the postulates according to which these formations were sterile.


In some ways, the abundance of ferruginous bodies, their composition, the variety of elements in high contents authorizes the comparison between North Burkina and Central Togo (table 21). The discovery of gossans in Togo has been determinant to create perspections as well for basic metals as for other elements (Blot et al., 1988 ; Blot and Magat, 1989), whereas these formations had always been considered as non-interesting for mining exploration (Bessoles and Trompette, 1980).


Neoproterozoic basins are collectors of all what has been removed from more ancient formations, metals included. The high contents of these metals are the result of a posterior history during which different processes of sedimentation diagenesis, metamorphism, magmatic and tectonic events interfere.


In this text, it was not taken in account that in the supergene zone, the result of endogeneous concentrations under the form of ferruginizations - among which gossans with brecciated facies – was first rather considered as a tectonic signal than a mineralization’s one.


A priori nothing can justify, as for metals and useful elements, that there are smaller perspectives in the Taoudeni basin of North Burkina Faso than in Atacora of Central Togo.


Table 21

Principal geochemical anomalies of the ferruginous outcrops of Pagala and Tin Akoff ; well-identified corresponding mineralizations or nearones.


The respective conclusions relative to ferruginizations of Central Togo and North Burkina are rather similar. The principal mineralization at Pagala was rapidly considered sedimentary and exhalative (Blot and Magat, 1990 ; Deschamps et al., 1991), displaying at least 4 mineralization varieties (Cortes et al., 2001). This Sedex type is considered in perspective as the probable form of the mineralizations of the Tin Akoff area (Castaing et al., 2003). In both regions, the ferruginizations display unquestionably the picture of associations of hydrothermal sulfides, principally low-temperature sulfides and complex sulfides.