Résumé
Oman Drilling Project Holes BA1B, BA3A and BA4A sampled over 1000 m of core from shallow mantle lithosphere rocks. Core logging, X-Ray diffraction, and petrographic examination of over 150 thin sections from these rocks were used as a basis for these preliminary observations of the opaque mineral paragenesis. The uppermost levels of Holes BA1B, BA3A and BA4A, extending a few 10s of metres into each hole, are characterized by red oxidized and carbonate-veined peridotites without visible sulfide phases. Below this, core is mostly black, black/grey and black/brown, hosts altered gabbroic and clinopyroxene-rich dykes, and is highly serpentinised. Opaque minerals observed include magnetite, heazlewoodite, pentlandite, chalcopyrite, pyrrhotite, bornite, cuprite, Fe-Ni alloy and native copper. The sulfide minerals occur mainly in the serpentine groundmass and/or in serpentine veins. Heazlewoodite, pentlandite and chalcopyrite are the most abundant sulfide minerals in all three holes. Bornite and cuprite are commonly observed as rims, sometimes colloform, on chalcopyrite. Tochilinite was identified by XRD in a vein, and details of this occurrence are presented in a separate poster (Tutolo et al., this session). In some highly serpentinized peridotites, sulfides are finely dispersed in the serpentine groundmass and the identity of the phase not be determined petrographically. Awaruite was tentatively identified only in peridotites from Holes BA1B and BA3A. Native copper was observed in Holes BA1B, BA3A, and in altered gabbros that cut peridotites in Hole BA4A. Chromite was altered to ferritchromite in the mesh texture and/or where serpentine veins intersect precursor chromite grains. Magnetite occurs in most samples from three boreholes as intergrowths with heazlewoodite and pentlandite, as overgrowths on altered chromite, and as fine-grained veins cutting the mesh texture.