PGE- and Au-Distribution in Rift-related Volcanics, Sediments and Stratabound Cu/Ag Ores of Middle Proterozoic Age in Central SWA/Namibia

摘要: A failed continental rift system, consisting of several partly discontinuous grabens, developed during Middle Proterozoic times in SWA/Namibia and Botswana, possibly response to a mantle plume. The basins contain thick successions bimodal volcanics, marine sediments. High-potassium acid volcanics as result partial melting mainly sedimentary crust. basal are enriched PGE Au which might have been supplied by derived fluids, released the initial phase crustal fracturing lithosphere. After this anomalous volcanism, ‘more normal’ were extruded. Mantle tholeiitic basalts, extruded along deep reaching fractures, show typically magmatic distribution patterns. Overlying coarse red beds, from denudation older basement reworking uplifted blockfaulted generally barren Au. Laterally extensive, sediment-hosted, stratabound Cu/Ag mineralization at base dark pyritic shale unit is slightly Pt (0·04–0·12 g/t), (0·04–0·06 Th Ni. Generally, display typical chondrite normalised Altered volcanic rocks, well ore samples, patterns may indicate hydrothermal reworking. authors suggest model wherein derived, plume triggered development system. Selective remobilisation leached Cu, Zn Co basalts beds. metals precipitated redox-cline between sediments whereas overlying sediments, also pyritic, remained unmineralised.