A New Type of Large Ultramafic Intrusion-Hosted Fe-Ti-V Deposit in the West-African Archean Craton: The N’Guérédonké Complex, Guinea
Résumé
A new type of large ultramafic intrusion-hosted Fe-Ti-V deposit has been discovered by BRGM in the West-African Archean craton. The N’Guérédonké intrusive complex (7 x 0.9 km) is composed of a dunite core surrounded by rims of wehrlites and pyroxenites. This syntectonic complex is emplaced within a crustalscale shear zone. The disseminated mineralisation made of ilmenite and magnetite is mainly hosted by pyroxenite units along the northern and southern contacts. Surface and drilling exploration work (47 drill holes totalling 10124 m) demonstrate polyphased injection of successive ultramafic melts from core to rims and also crosscutting of dunite core by a network of successive pyroxenite generations. A 3D modeling constrained by drilling and joined inversion of magnetic and gravity data ascribe the thickness of the intrusion up to 1000 m. A first very conservative titanium resource assessment on a small part of the intrusion (1000 x 100 x 250 m) lead to definition of 141.38 Mt ore @ 10.52 % TiO2. The lack of typical features of Ural-Alaskan type intrusions and strong differences with classical Gabbro-Anorthositehosted Fe-Ti-V deposits demonstrate a new type of large low grade high tonnage Fe-Ti-V deposit occurring in Archean craton