Late Proterozoic and Early Paleozoic Metasediment-hosted Tungsten Mineralization in Central Namibia: Recent Advances in Exploration and Research
Exploration & Mining Geology, Vol. 3, No. 4, 1994
N.M. STEVEN Department of Geological Sciences, University of Cape Town, South Africa. J.L. KUYPER, Johannesburg Consolidated Investment Company, South Africa
and J.M. MOORE, Geology Department, Rhodes University, South Africa
Mineral exploration and research has led to the identification of four types of tungsten mineralization in the NE-trending, largely ensialic, inland branch of the late Proterozoic/early Paleozoic Pan-African Damara Orogen. The mineralization (mainly scheelite) occurs in a terrane (the Central Zone) that is characterized by multiple deformation, greenschist/amphibolite-facies metamorphism and numerous peraluminous S-type granitic and pegmatitic intrusions. The four major types of scheelite mineralization are (in ascending stratigraphic order of host rock): (1) thin (5 cm to 2 meter) quartz + plagioclase + diopside ± scapolite calc-silicate granofels with finely disseminated scheelite (scheelite-bearing granofels; SBG) developed as discontinuous intercalations within the calc-silicate rocks of the Khan, Spes Bona, Oberwasser and Kuiseb Formations (Nosib and Swakop Groups);
(2) garnet + pyroxene ± vesuvianite+scheelite ± fluorite replacement skarns hosted by Okawayo, Karibib and lower Kuiseb Formation marbles in the aureoles of late tectonic, unmineralized leucogranites;
(3) metaturbidite-hosted scheelite- (and possibly wolframite-) bearing tourmalinites, both stratiform and crosscutting, in the Kuiseb Formation located in the 'cleavage fronts' of late tectonic granitoids;
(4) scheelite-bearing vesuvianite + quartz + garnet skarnoid rocks (several hundred meters in length) in the calcareous metaturbidites of the upper Kuiseb Formation. These scheelite occurrences were discovered by the follow-up of a large number of tungsten anomalies located during a regional stream sediment sampling program. Detailed mapping, ultra-violet surveys and rock sampling proved to be the most effective surface exploration techniques for locating mineralization; soil sampling and geophysics were of almost no use. The largest, continuous scheelite-bearing skam of economic interest, Otjua, has a drill-indicated reserve of 250 000 tonnes at 0.53 wt% WO3 and 8 wt% CaF2.