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A PRELIMINARY APPRAISAL OF THE SEDIMENTARY, VOLCANIC, AND TECTONIC SETTING OF THE SKORPION NON-SULPHIDE ZN-DEPOSIT, SOUTHERN NAMIBIA
The volcano-sedimentary sequence features rapid facies changes, partly controlled by pronounced local basement highs. The siliciclastics have been deposited in both high energy (olistostromes, conglomerates) and lower energy (metaarenites) environments. The debris originated from external (metaarenite) and internal sources (olistostromes of reworked basin sediments). Carbonates within the region are of detrital as well as of microbialitic origin, including small LLH-type stromatolites.
The bi-modal metavolcanics of this region consist of individual rhyolitic domes and thin basaltic flows and tuffites and interfinger with the metasediments. The felsites comprise porphyries, ignimbrites, welded tuffs and tuffites, whereas the basalts feature locally vesicular pillows. The metavolcanic units are locally associated with siliceous, carbonatic, ferruginous, and rarely sulphidic exhalative rocks, including Fe-, Cu-, Zn-, (Pb) sulphides and barite. However, similar exhalative units, hosted entirely by metasediments, have also been found away from the metavolcanics, related to (synsedimentary?) faults in the region. The exhalites formed vertically and laterally both proximal and distal to the volcanics, and within sediment-starved subbasins and local depo-centres with a high-sediment-influx.
The geological setting represents an initial rift phase with crustal extension, strong vertical tectonics, associated with subaqueous, mixed siliciclastic-carbonate sedimentation. The area featured typical bi-modal rift magmatism, an elevated heat flow, and hydrothermal/exhalative fluid systems. The Skorpion Zn-silicate-carbonate ore body occurs in a thick locally altered metaarenite unit, flanked by marble to the east and by biotite-chlorite-amphibole-(titano)magnetite-quartz- bearing schists at depth to the west.