GOSSANS IN PAGALA, TOGO (WESTERN AFRICA) - CASE OF SUPERGENIC MINERALIZATION WITH SIDERITE PROTORE IN A DAHOMEY MOUNTAIN-RANGE

The study is carried out on 410 samples of gossan, siderite and countr y reeks of the Pagala area, on which 28 major, minor and trace element s and 6 rare earth element (La, Ce, Eu, Yb,Lu, Y) contents were determ ined. Using a multivariate statistical study, three geochemical phases were discovered. The first one corresponds to a quartz and mica phase of the residual country rocks (Si, Al, Na, K, Ti, Zr, Nb). The second one, corresponding to gossanous iron oxy-hydroxides (Fe, Mn, Zn, Co, LOI and HREE), is interpreted as resulting from hydrothermal enrichmen ts. The third one, shown as another gossanous phase and rarely underst ood mineralogically (P, Ca, Sr, Cu, Sc and LREE), is probably linked w ith the phosphatic formations of the area. The projection of the three facies in a system of orthogonal axes, F1 and F2 supports the assumpt ion that the massive siderite represents the protore of cascade gossan (Togbe et al., 1993). This can be applied to all gossans in the area.