The Samapleu mafic-ultramafic intrusion and its Ni-Cu-PGE mineralization: an Eburnean (2.09 Ga) feeder dyke to the Yacouba layered complex (Man Archean craton, western Ivory Coast)

Abstract

International audienceThe Yacouba layered complex intrudes the Archean (3.5–2.7 Ga) Kenema-Man craton in the Samapleu-Yorodougou area, western Ivory Coast. In Samapleu area, the complex was recognized in drill holes at three locations: Samapleu Main (SM); Samapleu Extension 1 (E1) and Yorodougou (Yo). It comprises websterites, peridotites and gabbro-norites arranged symmetrically with mafic layers at the center and ultramafic layers at both margins. The complex is inclined at 70–80° to the SE. The thickness of individual layers varies from 2 to 60 m and the total thickness is 120 to 200 m. At the E1 site, the complex extends to depths > 500 m. Contacts with the country rock gneiss are characterized by a hybrid zone that is a few meters thick and composed of plagioclase-orthopyroxene bearing metabasites, and locally (E1 site) a metamorphic assemblage of sapphirine-cordierite-sillimanite-spinel ± rutile. This assemblage is attributed to contact metamorphism during intrusion of the complex in the lower crust at a depth of about 25 km. Zircons in country rock gneisses and granulites, as well as in the hybrid facies, yield Archean ages of ~ 2.78 Ga, similar to ages reported in the Man craton. Rutiles in the hybrid zone give a U-Pb age of 2.09 Ga, which is interpreted as the age of contact metamorphism and emplacement of the intrusion. The Samapleu Main and Samapleu Extension 1 sites contain Ni and Cu sulfide deposit with reserves estimated as more than 40 million tons grading 0.25% Ni and 0.22% Cu (Sama Nickel-CI, August 2013). The Ni-Cu mineralization is composed of pentlandite, chalcopyrite, pyrrhotite and rare pyrite, which is disseminated mainly in pyroxenite or occurs as subvertical and semi-massive to massive sulfide veins. The sulfide textures range from matrix ore, net-textured, droplets or breccia textures. Zones enriched in PGM, particularly Pd, are associated with the sulfides and several chromite bands are also present. These observations suggest that an immiscible sulfide liquid formed from a parental silicate liquid and percolated through the crystal pile. The parental melt composition, determined using the Chai and Naldrett [1992] method, has a SiO2-rich mafic composition with 53% SiO2 and 10% MgO. This result, the presence of the hybrid zone, and the trace-element signature determined using the Bedard [1994] method, suggest a mantle-derived basaltic parental magma that had assimilated abundant continental crust. These observations indicate that Samapleu intrusion corresponds to a magmatic conduit of the Yacouba complex as at Jinchuan (China), Voisey’s bay (Canada), Kabanga (Tanzania) or Nkomati (South Africa)

Source and deposition age of the Dialé-Daléma metasedimentary series (Kédougou-Kéniéba Inlier, Senegal) constrained by U–Pb geochronology on detrital zircon grains

“…In the Archean domain two orogenic cycles dated at c. 3.3-3.0 Ga (Leonian) and c. 2.9-2.7 Ga (Liberian) are distinguished (Kouamelan et al, 1997(Kouamelan et al, , 2014Rollinson, 2016). Pre-Leonian rocks dated at c. 3.6-3.4 Ga are preserved as relics of crustal segments within the Leonian, Liberian, Eburnean and Pan-African orogenic belts (Bruguier et al, 1994;Potrel et al, 1996;Kouamelan et al, 1997b;Kroner et al, 2001;Thieblemont et al, 2001;Gouedji et al, 2014). This Archean nucleus was locally reworked during the Eburnean tectono-metamorphic event coincident with deposition of the Paleoproterozoic Birimian (Rhyacian) formations (Kouamelan et al, 1997b;Thieblemont et al, 2004;Pitra et al, 2010;Eglinger et al, 2017).…”

Petrographic and Geochemical Characteristics of the Metabasites of the SASCA Domain (Yonaké, Mani- Béréby and Dehié Sectors), South-West Côte d'Ivoire

“…Paleoproterozoic domains lie adjacent to the Archean domain ( Figure 1) and are characterized by the typical Archean-like greenstone-granitoid assemblages that principally consist of volcanic, volcano-sedimentary, and sedimentary sequences separated either by extensive TTG and granite provinces or by slightly younger but still Paleoproterozoic sedimentary basins. The Archean and Paleoproterozoic domains were affected by multiple tectono-metamorphic and magmatic events, referred to as Leonian (3.2-3.0 Ga); Liberian (2.9-2.7 Ga) and Eburnean (2.15-2.07 Ga) orogenies, (Liégeois et al, 1991, Christian et al, 2004Thiéblemont, 2005;Gouédji et al, 2014;Kouamelan et al, 2015;Koffi et al, 2020). In particular, the whole complex of volcanic, volcano-sedimentary and sedimentary units has been intruded by several generations of granitoids (Thiéblemont, 2005…”

A review of the mineral potential of Liberia

“…A number of nickel-cobalt laterite deposits are known in the vicinity of Sipilou in western Côte d'Ivoire close to the border with Guinea and Liberia (Gouedji et al, 2014). Magmatic nickel-copper-cobalt-PGEbearing sulfide mineralisation has also been discovered nearby at Samapleu and Yepleu associated with the Palaoproterozoic Yakouba mafic-ultramafic complex which intrudes Archaean basement.…”

“…Magmatic nickel-copper-cobalt-PGEbearing sulfide mineralisation has also been discovered nearby at Samapleu and Yepleu associated with the Palaoproterozoic Yakouba mafic-ultramafic complex which intrudes Archaean basement. The sulfide mineralisation in the Yacouba complex has been compared with the major feeder-type magmatic sulfide deposits at Jinchuan in China, Voisey's Bay in Canada and Kabanga in Tanzania (Gouedji et al, 2014).…”