Geology within the Santa Rosa Gold Project is dominated by hornblende-biotite diorite and quartz diorite of the Antioquia batholith. The batholith is a calc-alkaline, plutonic intrusive complex belonging to an early- to mid-Cretaceous magmatic arc. Basement geology is a complex elongated mosaic of Palaeozoic and younger autochthonous and allochthonous terranes that were accreted to the South American continent and subjected to transpressional tectonics and episodic subduction-related magmatism. Mineralisation is contained within numerous mesothermal veins and stockworks structurally related to east-west and north-north-west corridors.
Hypogene gold mineralization within the Santa Rosa Gold Project is generally associated with the shear zones developed in homogeneous diorite country rock, with higher grades occurring in the associated sulfide-mineralized quartz veins or as steep high-grade quartz-sulfide veins. East-west-trending structures, including the San Ramon Gold Mine deposit shear zone, appear to be related to northwest-trending regional structures. Sinistral movement along these structures may have created eastwest dilation zones, up to 60 m wide in the case of the San Ramon Gold Mine deposit shear zone, into which quartz and quartz-carbonate veins and veinlets were emplaced. Most of the quartz veins and contained sulfides have been brecciated by post-mineralization deformation, which suggests that the mineralization is syndeformational.
Gold mineralization in the Santa Rosa Gold Project has characteristics in common with mesothermal or orogenic and intrusion-hosted gold veins. Mineralization of these types consists commonly of quartz and quartz-carbonate veins located in moderately to steeply dipping, brittle-ductile shear zones and locally in shallow-dipping extension fractures. Veins commonly extend along strike and down dip over very significant distances and occur alone or, typically, in complex vein networks and shear zones. Vein minerals are mostly quartz and carbonates with minor native gold, pyrite, and base metals sulfides. Veins are usually massive or ribbon-textured, but vein breccias and drusy, crystalline quartz can also occur. Wall-rock alteration is zoned and consists of carbonate (often ankerite), sericite, and pyrite. Gold at the Santa Rosa Gold Project was historically extracted from saprolite (and alluvial gravels). Potential exists for discovery of new deposits in the area and additional mineralization down-dip of the known San Ramon Gold Mine deposit mineralization.