Marc Gasparotto HBSc thesis abstract
The Otjikoto project in Namibia is an orogenic gold deposit situated in the province of Otjozondjupa, approximately 300 km north of the capital city of Windhoek. Research for this thesis was carried out through the microstructural analysis of thin sections (obtained from Auryx Gold) that were collected from drill core. The microstructures produced by deformation exhibited in the minerals of this deposit provide information about the relative timing of metamorphism, deformation, quartz veins and gold mineralization of the Otjikoto project.
The metapelitic Okonguarri Formation, host to the Otjikoto gold mineralization, contains evidence for peak metamorphism at the temperatures and pressures of the sillimanite zone of the amphibolite facies. Grain-size reduction of feldspar indicates that mylonitization also occurred at amphibolite facies temperatures. The formation also exhibits heterogeneous ductile deformation, specifically associated with the competent amphibole and garnet porphyroblasts, which occurred during synchronous metamorphism and ductile deformation. The mineralized quartz veins are synorogenic as evidenced by both brittle and ductile deformation under at least greenschist facies metamorphism. In particular, boudins of coarse-grained quartz (interpreted to be boundinaged quartz veins) indicate the mutual overprinting of brittle and ductile deformation which is characteristic of a shear-zone-hosted gold deposit.
Based on evidence for the synchronous metamorphism, brittle deformation and ductile deformation, and the synorogenic mineralized quartz veins, a shear-zone-hosted gold deposit model should be considered for the Otjikoto project.