CATHODOLUMINESCENCE AND ELECTRON MICROPROBE STUDIES ON CARBONATE-HOSTED CU-PB-ZN (-AG-GE) SULFIDE DEPOSITS FROM THE OTAVI MOUNTAIN LAND, NAMIBIA

The Otavi Mountain Land ore province is located in the northwestern part of the Pan-African Damara Belt, Namibia. Polymetallic (Cu-Pb-Zn) sulfide deposits are hosted by carbonate platform successions of the Proterozoic Otavi Group within a foreland fold- and thrust-belt setting. Cathodoluminescence (CL) and geochemical data are presented for core samples from the renowned Tsumeb deposit and the active mine at Khusib Springs. The CL data reveals a wide variety of alteration phenomena providing evidence for a complex hydrothermal alteration history. The participating processes in the carbonate host rocks at both locations are solution-generated vugs and cavity formation, vein development (in part polyphase), intense brecciation, neo-mineralizations in veins, vugs and cavities, replacement and alteration, and carbonate blastesis and recrystallization of the host rock matrix. Many of the microstructures resulting from these processes indicate episodic events of penetrative fluid flow with changing compositions. Chemically both Tsumeb and Khusib Springs exhibits unique trace-element signatures related to specific fluid-related events. At Tsumeb, complex rhythmically zoned calcite cavity fillings show concentrations of PbO up to 5.9 wt. % and FeO >2 wt. % in specific growth zonations. Coexisting with these Fe-/Pb-rich calcites are pure anhedral dolomites overgrown with euhedral (rhythmically zoned) Fe-/Zn-rich dolomites, hosting ZnO compositions up to 6.5 wt %. Relatively high Pb/Zn concentrations (3.5 & 3 wt. %) were analzyed in calcite veins with cyclical growth zonations above the main ore body at Khusib Springs, suggesting a possible proximity indicator. FeO concentrations of up to 5 wt. % occur at Khusib Springs in non-luminescent, idiomorphic zones within coarse-grained sparry luminescent dolomite veins. At both localities MnO concentrations are high in both calcite and dolomite, ranging up to 2.2 wt. %, and accounting for the high luminescence and CL intensity. This data will aid in discriminating the carbonate alteration events at Tsumeb and Khusib Springs and assign those events unique trace-element signatures.