Summary:
The Kodiaran and Koulekoun deposits occur within both sedimentary and intrusive rocks. Intrusive units in the Tri-K project area are felsic to intermediate, predominantly porphyritic granodiorite and dacite. A spatial association exists between these intrusive rocks and gold mineralisation in both deposits.
The Koulékoun deposit is part of a NW-striking and steeply dipping porphyry hosted orogenic disseminated style mineralisation system. The dominant geological feature is massive, quartz feldspar porphyry, typically 20-80 metres wide. This has been drilled to a maximum vertical depth of 400 metres and is open along strike and at depth. An important feature is a younger, sub-horizontal dolerite dyke of Mesozoic age, which cuts the mineralised geology and controls the position of the water table and therefore restricts the depth of weathering at Koulékoun to 80 metres. Gold grades are higher in the intersection of the porphyry dyke complex and locally occurring NE striking structures.
The Kodiéran deposit is located in sediments close to the contact of a large diorite intrusive to the west. The bulk of Kodiéran is located in a deeply weathered saprolite profile where the ore is weathered to a depth of up to 100 metres. Mineralisation dips shallowly to the west and is 20–60 metres thick. Mineralisation has been tested over 2,500 metres along strike to date and remains open along strike and at depth.
Deposit Type
At Kodiaran, mineralisation is associated with north-northwest-striking silicified shear zones and dilational jogs. Quartz-carbonate vein halos developed along pre-existing heterogeneities, such as contacts between turbidites and granodiorite dykes, and along deeper incipient structures. Vein density is generally higher in more competent lithologies like granodiorite dykes and coarse volcanoclastic layers. Mineralisation is accompanied by silicification, sericitisation, and increased disseminated sulphides.
At Koulekoun, gold-bearing quartz-carbonate veins occur in quartz-feldspar porphyry (IQF) dykes and adjacent turbidites. As in Kodiaran, vein density is controlled by rock competency, but also by steep northeast-trending incipient structures in the sediments. Vein orientations are similar in both lithologies and match those observed at the Siguiri district (Lebrun et al., 2017), a major orogenic gold field in turbidites ~80 km north-northwest of Tri-K.
In summary, all gold occurrences on the Tri-K property are structurally controlled—whether in veins, shear zones, or via rheological contrasts affecting disseminated mineralisation—and are interpreted as orogenic in origin.
Geology and Mineralisation – Kodiaran
Kodiaran is hosted in fine-grained turbiditic sediments, occasional coarse volcanogenic sandstones, and at least two intrusive suites of dioritic and granodioritic composition. The intrusives form narrow, north-west to north-northwest-striking subvertical sills. In the northernmost part of the deposit, a large (500 m × 500 m) granodiorite batholith is present. Dioritic sills occur as sheet-like bodies interbedded, in some cases up to five, within granodioritic masses. The lateritic profile (laterite, saprolite, transition zone) generally exceeds 150 m in thickness, with the uppermost 2–5 m comprising laterite/cuirass/duricrust with pisolitic gravel, rock fragments, and soil. Fresh rock is not exposed at surface.
High-grade gold mineralisation is linked to large shear zones and quartz-carbonate-chlorite conjugate veins, coinciding with pyrite and/or chalcopyrite. Early silicification and brecciation, lithological contrasts, and vein density also influenced fracture development and localisation of mineralised veins.
Geology and Mineralisation – Koulekoun
Koulekoun is hosted in weakly metamorphosed fine-grained carbonaceous shale, siltstone, interbedded and locally graded greywacke, as well as quartz-feldspar porphyritic granodiorite dykes trending north-northwest and northeast and dipping steeply.
Weathering reaches depths of up to 80 m, consistent with the dolerite sill level, and is capped by a 2–5 m thick cuirass of pisolitic gravel, rock fragments, and soil. No fresh rock is exposed at surface.
Gold mineralisation is typically associated with quartz-carbonate veining and disseminated pyrite, arsenopyrite, and minor chalcopyrite. Higher gold grades correlate with zones of strong silicification and dense quartz-carbonate veining surrounded by halos of crystalline to amorphous arsenopyrite and pyrite. In sedimentary rocks, gold-bearing veins commonly have an orientation of about 70°/165° (dip/dip direction).