The Rosebel concession lies within the Paleoproterozoic Guiana Shield. The Suriname portion of the shield is characterized by discrete corridors of low grade metamorphic rocks (greenstone belts), separated by large granite gneiss terranes.
The local greenstone belt stratigraphy comprises a basal mafic to felsic volcanic package (Paramaka Formation) and two overlying volcano-sedimentary sequences (Armina and Rosebel Formations). The Armina Formation includes intermediate to mafic volcanics and volcaniclastics, trubidite and minor conglomerate whereas the unconformably overlying Rosebel Formation is mainly comprised of coarser grained sandstone and conglomerate with subordinate mudstone. The entire sequence has been deformed by east-southeast to east-west striking folds and faults. A large tonalitic pluton occurs in the southern part of the property (Brinks Granite). Metamorphism is greenschist to lower amphibolites facies.
Primary gold mineralization occurs in several different styles on the property but is typically associated with multiple generations of quartz, quartz-carbonate and quartz-carbonate-tourmaline veining. Vein arrays are thought to have developed preferentially along pre-existing structural heterogeneities such as lithological contacts, fold closures and sub-vertical shear cooridors during major deformation phases. For example, gold mineralization at the Rosebel deposit is associated with north dipping quartz and quartz carbonate vein sets localised along shear corridors developed at contacts between sandstone and siltstone units of the Rosebel Formation. Low grade gold mineralization is widely dispersed in sericitic alteration halos surrounding these structures. Diamond drilling has intersected economic gold mineralization to a vertical depth of 200 metres below surface and the continuity of the mineralization can be traced for over two kilometres along strike. The deposit, like most others on the property, remains open on strike and at depth.
Gold mainly occurs in its native form as free grains, often precipitated close to vein selvages or as intergrowths in pyrite crystals within veins and adjacent country rocks. Mineralized quartz veins range from a few centimetres up to 4 metres in thickness and are typically associated with a wall-rock alteration assemblage comprising sericite, chlorite, carbonate, tourmaline, pyrite, pyrrhotite and plagioclase. Alteration halos range from 0.25 metres around individual veins to over 20 metres around major vein sets.