Economic geology and photogeology of the Tsumeb area, South West Africa

Abstract

Abstract by author:

The base-metal deposits of the Otavi Mountains, South West Africa, occur as replacements, disseminated mineralization in pseudo-aplite, a rock of disputed origin, and in breccia pipes and zones of brecciation within the thick Precambrian carbonate sequence of the Otavi Series. The deposits are characterized by very local calcite and quartz alteration of the dolomite. Mineralized areas have a greater incidence of sinkholes as a result of the calcitic alteration, and the study of sinkhole distribution by airphoto analysis is a potentially useful exploration technique for the Otavi Mountain area

The two major base-metal deposits of the Otavi Mountains, Tsumeb and Kombat (Asis), are closely related to pseudoaplite bodies within dolomites and limestones of two stratigraphic zones of the Upper Tsumeb Substage. The spatial association of pseudoaplite with Tsumeb Zones 7 and 8 makes the areal distribution of these zones of exploration significance. The three zones of the Tsumeb Substage, Zones 6, 7, and 8, are the most easily distinguishable carbonate units of the Otavi Series during field or photogeologic mapping

Three major regional structures appear to control mineralization in the Otavi Mountains. These are the two deepest synclines, the Tsumeb and the Otavi Valley synclines, and a probable N. 50° E basement structure. Surface expression of the basement structure includes a series of roughly parallel dolerite dikes. Bedding-plane faults, zones of brecciation and breccia pipes form important ore loci within the Otavi Mountains. Structural settings most favorable for the formation of zones of intense fracturing are drag folding associated with the major east-west folds, intersections of regional folds and cross folds, and the peripheries of pseudoaplite bodies