Recognition of high-T rhyolite melts in the Rosh Pinah - Skorpion Zn-Pb district, Southern Namibia

The base metal mining district of Rosh Pinah and Skorpion in Southern Namibia with its Zn-Pb(-Ag-Ba) and Zn-only deposits, has been interpreted mainly in terms of sediment-hosted metallogenesis. However, the presence of bimodal volcanic and subvolcanic rocks within the Late Proterozoic sequence has been increasingly acknowledged over the last few years. The succession includes dykes and sills, volcanic domes and flows, as well as hyaloclastic, pyroclastic and volcani-elastic rocks. The determination of zircon saturation temperatures for most of the metarhyolites from the vicinity of both deposits reveal anomalously high melt temperatures, ranging between 850 degrees C and 1000 degrees C. Such high-T rhyolite melts reflect anomalously high advective heat transfer into the volcano-sedimentary basin fill. This high heat flow likely caused the development of longlasting and highly efficient convection cells which resulted in the leaching of a mixed volcano-sedimentary source rocks and the formation of base metal sulphide deposits.