Geology
Semna shares many characteristics of a classic orogenic or lode-style gold deposit. Mineralisation is mostly hosted in steep southerly-dipping shear zones which themselves host gold-bearing quartz veins. These E-W mineralised structures appear to be constrained between two NNE striking major boundary faults.
Mineralised structures are hosted within a granodioritic intrusion, which is intruded into a regional mafic to intermediate metavolcanic package.
Underground rib pillar on the MVZ, consisting of a mineralised and sheared quartz vein
Auriferous quartz veins strike, with some exceptions, approximately east-west with variable dip and notably pinch and swell. The area hosts multiple, parallel mineralised zones, though the Main Vein zone (MVZ) is the largest and most significant. Historically, 200m of its strike length was worked from underground, however the 2023 phase 1 RC drill programme indicated that the MVZ extends at least a further 200m to the east, where it is blind and sub-crops beneath alluvial wadi sediments. The RC drilling indicated that the MVZ mineralisation is open along strike, and at depth along the entire strike length drilled to date. Mapping and drilling have indicated that mineralised zones are offset by a series of NNE strike-slip fault structures.
The highest-grade mineralisation occurs on the margins of white, opaque quartz veins. These margins are often associated with blebs of fresh pyrite (and less often chalcopyrite), though often these margins are oxidised and gossanous.
The metal endowment at Semna is primarily only gold, although copper and silver grades are locally elevated. Screen fire assay results have indicated that the gold is often coarse, and preliminary metallurgical testwork has indicated excellent gold recoveries of >97%.
Oblique view of the Semna gold mine prospect, looking southwest (from 2010 Google Earth image, prior to recent artisanal mining activity)