ALBITIZATION IN THE PALEOPROTEROZOIC OF E ASTERN SENEGAL - RELATION TO THE IRON ORE BEDS ALONG THE LEFT BANK OF FALEME

The Dalema Supergroup (Paleoproterozoic of Eastern Senegal) is charact erised by a sedimentation in a shalow but unstable environment showing many limestone beds, which is rather uncommon in the West African Pal eoproterozoic. A significant calcalkaline volcanic episode started aro und 2070 Ma. Later on, the Dalema Supergroup was intruded by the Bobot i pyroxene granite and by the Saraya granite (around 2000 Ma) at the e nd of the Eburnean episode. The Dalema Supergroup hosts Fe, Au and U m ineralisations, all are linked to hydrothermal exhalations yielding ex tensive tourmalinisation, carbonatation, chloritisation and albitisati on. Iron; ore mineralisation amounts to several hundred million metric tons. Although the pyrometasomatic features seem quite obvious, the o rigin of the ore stock pile is not clear. Very often the ore bodies ha ve spatial connections to the albitisation process. Considering the Ch inese studies on the same type of deposits (Ordovician and Triassic ag e, Hebei Province) one can envisage that the Fe ore and albitised hori zons result from the action of hydrothermal fluids with a significant NaCl ratio. (C) 1997 Elsevier Science Limited.