PALAEOPROTEROZOIC GOLD MINERALIZATION OF THE ETEKE ARCHEAN GREENSTONE-BELT (GABON) - ITS RELATION TO THE EBURNEAN OROGENY

The gold deposits of the Eteke district (Gabon) are hosted by metasedi ments and intermediate tb ultramafic metavolcanites of the Eteke Archa ean unit (2940 +/- 6 Ma), a greenstone belt within the folded and meta morphosed Ogooue domain that was formed by the successive transport an d stacking of nappes during Palaeoproterozoic (Eburnean) D1-D2 collisi onal tectonism-this lithotectonic pile, in the east of the Eteke distr ict, rests on the Chaillu Archaean basement and Palaeoproterozoic Fran cevillian foreland basin deposits. The gold is contained in quartz +/- carbonate stockworks, 'hydrothermalite' lenses and mineralized quartz veins that indicate mineralization during a single D2 hydrothermal ev ent extending from an early-D2 stage (stockwork) to a late-D2 stage (v eins). The mineralization began during the early-D2 stage following a major phase of tangential tectonism (D1) when the Eteke unit, still in a shallow position (brittle deformation) in the outer (foreland) zone of the orogenic belt, would have received the repercussions of crusta l thickening taking place in the inner zone of the belt (Ogooue series s.s.). These repercussions are reflected by the development of stockw orks and 'hydrothermalite' lenses related to reverse faults that favou red the emplacement of tonalitic dykes and sills and channelled the fi rst hydrothermal fluids. At the peak-D2 stage the Eteke unit, which by this time formed part of the outer zone of the orogenic belt, was cau ght up in nappe tectonism that imparted a major S2 foliation, with mic rofolding and foliation of the early stockworks. The early-D2 reverse faults evolved to synmetamorphic thrusts (epi- to mesozonal conditions ) along which syntectonic granites and rare mineralized veinlets Were emplaced, reflecting a dormancy of the hydrothermal event. The nappe t ectonism ended with transport of the peak-D2 lithotectonic pile onto t he Chaillu Archaean terrain and nearby Francevillian foreland basins, accompanied by a late-D2 emplacement of gold-bearing quartz veins cutt ing the S2 foliation and marking the end of the mineralizing hydrother mal event.