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Boreholes carried out in 1995 by Guyanor Ressources SA in the Dac hine reg io n (Transa mazon ian Inini Gree nstone Belt, So uth French Guia na) have cut through ta lcschists rich in microd iamonds. T he most commo n mineral assemblage of these rocks is: "talc + chlorite ± trcm olite ± carbonate" . Th ese minera ls can be ofte n acc ompan ied by albite, se rpen tine. su lpnomclanc or phlogopite. T he volca noc lastic texture o f the pro tolith is preserved despite metamorphism and deformation. Eve n scoria frag ments arc preserved in places. Diamonds. acco mpanied by cc logitic and man tle ind icators. arc present as xenoc rysts . They arc of cc logi tic ty pe, the timcspan o f their resid ence in mant le condi tions is < 200,000 ye ars and they were transported ill a magma charac terised by a high H 2 0 /C0 2 ratio. The diamond s form ed therefore only a shor t time before the kom atiitic magm as. Th e mobile cleme nt compositio n o f the talcschists is var iable. T hey were firs t slightly mod ified during gree nschis t facies meta morp hism . Later, they we re locally hydrothermally altered in the surroundi ngs of lateto post-orogen ic intrusions. Final ly. they were subjec t, to var ious degre es. to tropica l alteration. On the other hand , the imm ob ile c lement co mposition is co ns tant and allow s an unequ ivoca l identifi cat ion of the protolith. This chemical compos ition co incides with that of Ti-rich Al-dc plcrcd koma tiircs (Ka rasjok-typc ). Th e AIdepleted character imp lies an origi n of thc primary magmas by part ia l melt ing of a garnet-bearing man tle source ..it de pths > 250 km and unde r anhyd rous co nditions. Thesc komat iites are co mmo n in the Inini Greenstone Bel t.

PRIMARY DIAMOND SOURCES IN FRENCH GUIANA: IMPLICATIONS FOR TRANSAMAZONIAN GEODYNAMICS AND DIAMOND EXPLORATION