Summary:
The Sabodala-Massawa Project occurs in the West African (Birimian) Paleoproterozoic metallogenic province. The metallogenic district is associated with Paleoproterozoic epigenetic gold deposits which occur in 2.25 Ga to 1.90 Ga granite-greenstone belts of the Birimian and Tarkwaian cycles, which were deformed and metamorphosed during the Paleoproterozoic Eburnean orogeny adjacent to the Archean Sao Luis Craton in Guinea, Sierra Leone, and Liberia.
Gold deposits in the West African metallogenic district, including those on the Sabodala-Massawa Project and the company's adjacent exploration permits, show many characteristics consistent with their classification as orogenic (mesothermal) gold deposits and prospects.
Orogenic gold deposits exhibit a range of styles dependent on metamorphic grade, setting, fluid type, and fluid/confining pressure. They often include spatially associated quartz shear veins, extension vein arrays, shear zone and disseminated sulphide styles. Greenschist metamorphic grade, vein dominated styles such as those developed in the Sabodala district contain quartz-carbonate ± albite ± K-feldspar veins with up to 10% (pyrite ± arsenopyrite ± base metals) sulphides and associated Fe-carbonate albite, chlorite, scheelite, fuchsite and tourmaline as associated vein and hydrothermal alteration assemblages. Vein systems and shear zones are often semi-brittle in style, including both brittle veining styles (extension veins and fault hosted brecciated shear veins), which alternate with periods of ductile deformation, producing sequences of early folded and younger less strained vein systems during latter periods of regional deformation at peak to immediate post-peak metamorphic timing. Sigmoidal extension vein arrays are often present and are typical of the deposit style. This deposit type often also has great vertical extent providing potential for discovery of significant down dip and down plunge continuations of mineralized zones.
SABODALA
The Sabodala deposit comprises a network of mineralized shear zones and associated surrounding sets of quartz breccia veins and vein arrays that are discordant to, and cut across the hosting volcanic stratigraphy. Mineralization is most intensely focused in and west of where the shear zone network intersects, and crosscuts the mylonitic chert unit. The best-developed mineralization extends from the chert unit westward to the ultramafic-hosted Ayoub's Thrust, in the steeply west-northwest dipping host sequence comprising the volcaniclastic unit, mafic volcanic units and gabbro that lie between the chert and the shear zone. The deposit is developed over a strike length of at least 600 from the Sutuba deposit southwest of the current open pit, northward to several hundred metres north of the open pit, where it is open at depth.
Gold mineralization at the Sabodala deposit occurs in a combination of occurrences. Continuous grey quartz shear veins along shear zone surfaces in the Main Flat and Northwest shear zones, in sets of quartz-carbonate-albite-pyrite extension veins, in coalescing extension and shear vein domains forming zones of quartz-carbonate matrix breccia, and in areas of pervasive tan to pink coloured carbonatealbite-sericite-pyrite alteration which surrounds and links between veins, shear zones and breccia. Multiple generations of veins are evident, but the most voluminous veining and alteration forms the youngest generations.
MASSAWA
The Massawa stratigraphy is dominated by a western package of volcaniclastic rocks and an eastern package of greywackes, with bedding striking at 210° ± 10° and dipping steeply (75° to 80°) toward the west. Several igneous rocks including sills of gabbro, felsic intrusions, and feldspar (and/or quartzfeldspar) porphyries intrude this dominantly clastic sequence.
The volcaniclastic rocks have a bimodal mineralogy with both mafic and felsic variants. They consist of a package of agglomerates, lapilli tuffs, tuffs, ash-tuffs, and fine-grained carbonaceous ash-tuffs and include both purple and green variants. The purple colouration probably indicates deposition in an arid to semi-arid terrestrial environment. Laminated, fine-grained, volcaniclastic material is often green and could represent ash fall into standing water. The coarser volcaniclastic rocks are matrix supported and include elongated and sub-rounded felsic lithic clasts (up to 5 cm in size) with glassy textures and rounded mafic clasts (up to 10 cm in size).
Felsic and lithic wackes, which underlie the volcaniclastic rocks to the east, are composed of fine-grained layers at the top of the sequence with coarser units at the base. Graded bedding is common within these rocks and shows a downward younging direction implying that the steeply west dipping volcanosedimentary package is overturned, with the volcaniclastic rocks being older than the greywackes. At its northern end, the Massawa deposit is bounded by two prominent carbonaceous shale layers which act as the hanging wall and footwall of the mineralization. The carbonaceous shale is very fine grained, well laminated, and is inter-bedded with the coarser-grained greywackes. Layers are variable in thickness, on a millimetre scale, and form discontinuous lenses. Graphitic bands are common where the rock is more deformed and these units are referred to as graphitic schists. The greywacke and shale package displays soft sediment deformation fabrics typical of turbidite systems including load casts, slump and flame structures, and intra-sedimentary faults. Two main concordant gabbroic bodies are present at Massawa. The sills are up to 30 m in thickness; although towards the north they occur as narrow bands ranging from 0.5 m to 18 m in thickness. The gabbros predate shearing and host gold when intersected by the mineralized structures. Outside of the mineralized system, gabbro sills are massive and coarse grained. Quartz porphyry and fine-grained felsic sills, forming sheets 2 m to 60 m thick, occur throughout the deposit but are generally thicker and more abundant in the southern portion of the deposit. The porphyries are intrusive into the volcano-sedimentary sequence and show contacts against greywacke, volcaniclastic rock, and carbonaceous shale. The quartz-feldspar porphyry has a tonalitic mineralogy, comprising phenocrysts of oligoclase/andesine (altered to sericite) and quartz (50:50 ratio), and a groundmass composed of fine-grained plagioclase, albite, and small amounts of quartz. The earliest sills display a weak foliation and weak to strong alteration. Younger intrusive units are unaltered, undeformed and cross-cut the sheared rocks, and thus the emplacement of the porphyries spans the shearing event.
Massawa lies on a NE trending (030° to 035°) sinistral structure, likely a second order splay off the neighbouring MTZ. To the south and north of Massawa, the NE trending shears are dextrally offset by discordant north-south structures, resulting in dilation and mineralization. The mineralization is associated with anastomosing brittle-ductile shearing commonly localized at intrusive contacts.