Structural controls of auriferous quartz veins in the Karibib Area, southern central zone of the Pan-African Damara Belt, Namibia

[摘要] Detailed geological mapping and a structural analysis of auriferous quartz veins wereundertaken in the Karibib region of the Pan-African Damara belt in central Namibia. Thestudy focuses on the formation and controls of quartz-vein sets and associated lodegoldmineralization in heterogeneous, siliciclastic- and marble- dominated amphibolitefacieshost rocks around the Navachab gold mine and adjacent areas. Two main arraysof shallowly-dipping quartz veins can be distinguished that form a conjugate set. Steep,bedding-parallel and high-angle cross-cutting veins also occur, but play a subordinaterole for mineralization. The orientation of the main conjugate set and progressivedeformation of these quartz veins indicate that veining occurred during the late stagesof the main phase of NW-SE directed, subhorizontal shortening (D2) and associatedNW-verging folding and top-to-the-NW thrusting. Cross-cutting relationships withplutonic rocks indicate a timing of ca. 540 Ma for the mineralization.The quartz veins sets show a consistent orientation irrespective of their location withrespect to NE-trending, NW-verging first-order fold structures that were previouslyconsidered to be pertinent for the mineralization. The quartz vein sets also cross-cutdifferent lithologies at high angles. This suggests that the regional strain (D2) was thefirst-order control of quartz vein formation. More localized lithological and/orstructural controls played, however, an important factor for the formation of economicgrademineralization. Thick and closely spaced quartz veins in steeply dipping rocks ofthe Navachab open pit form a more than 150m thick economic-grade vein swarm. Inthis structural situation and during layer-normal subhorizontal shortening, the hostrocks experienced high extensional strains in a vertical direction, favouring theformation of subhorizontal extension fractures.

[发布机构] Stellenbosch University