Abstract The Kalahari Copperbelt in northwestern Botswana is characterized by structurally controlled, stratabound, mineralogically zoned copper-silver deposits hosted along a major redox boundary within a late Mesoproterozoic rift succession. Copper-silver mineralized rocks occur on the limbs and in the hinge positions of regional-scale folds that characterize the Pan-African Ghanzi-Chobe zone fold-and-thrust belt. Regional facies changes along the base of the transgressive marine D’Kar Formation, the host to the majority of mineralized rocks, delineate a series of synsedimentary basin highs and lows. The facies changes were identified through both lithostratigraphic analysis of drill holes and along-strike variations in magnetic lithostratigraphy, a technique that correlates the magnetic fabrics of second vertical derivative aeromagnetic maps with changes in lithostratigraphy. Basin highs controlled the development and distribution of favorable lithostratigraphic and lithogeochemical trap sites for later sulfide precipitation. Major facies changes across the Ghanzi Ridge area straddle a significant crustal structure identified in gravity datasets that appears to have influenced extensional activity during basin development. During basin inversion, the basin highs, cored by rheologically stronger bimodal volcanic rocks, localized strain within mechanically weaker rock types of the Ghanzi Group metasedimentary rocks, leading to the development of locally significant permeability and the formation of structural trap sites for mineralization by hot (250°–300°C), oxidizing, metalliferous Na-Ca-Cl brines. Structural permeability was maintained within trap sites due to silicification and/or feldspar alteration during progressive deformation and associated hydrothermal mineralizing events.

Abstract The Okavango “Delta” is a large (25,000 km 2 ), low-gradient (1:3400) alluvial fan which has developed in a depression between two basement arch-horst systems which mark the tips of incipient rifts. Base flow in the Okavango River sustains about 4000 km 2 of permanent wetland in the Delta, while the seasonal flood can expand the area of inundation to more than 12,000 km 2 . The climate over the Delta is semiarid, and only 2% of combined inflow plus rainfall (ca. 15 km 3 /yr) leaves as surface flow, the remainder being lost to the atmosphere by evapotranspiration. Sedimentologically, the system is virtually closed, and about 600,000 tonne of sediment is deposited annually in the Delta, resulting in a very low average sedimentation rate. Two distinct types of sedimentation occur on the fan: clastic on the upper fan and chemical on the lower fan. In both, biotas play a key role. Although the region is tectonically active, there is little active faulting within the Delta itself, and apart form the rising arches associated with the propagating rifts, the major tectonic process in the Delta appears to be crustal sagging, induced by sediment accumulation. This has caused localized depression of the southeastern arch and associated faulting. Seismicity is localized to the area of the fan, and is also attributed to gravitational loading. Continued propagation of the rift is likely to result in diversion of the Okavango River into the Zambezi River.