The geology of the western Otavi mountain land, South West Africa

Abstract

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Scattered malachite-chalcocite blebs were found in a few localities. Two areas of possible economic interest are recommended for further investigation. The view is expressed that copper in the Middle Tsumeb dolomite is syngenetic but was concentrated in favourable sites by lateral secretion or by fluids accompanying tectonic movements. Silicification is of too general occurrence to act as indicator to mineralization. A more direct clue is provided by calcitisation which seems to accompany tectonic deformation. The banded ironstone of the Upper Nosib forms a low grade iron deposit of large tonnage

On the unexposed Basement lies the Proterozoic arenaceous and rudaceous Nosib (Hundskopf) Formation overlain unconformably by the Damara System which consists of the Otavi Series (mainly dolomite and limestone) at the bottom and the Mulden Series (mainly quartzite) at the top. Sediments of glacial origin at the base of the Tsumeb Stage of the Otavi Series transgress the Abenab Stage and older formations in some areas. In the southernmost part of the area and farther south two major changes set in (a) a facies change whereby argillaceous interbeds in the limestones and dolomites become more prominent (b) metamorphism of these equivalents to schist-and phyllite, and to marble, respectively. Correlation with the type area at Tsumeb is possible, despite much local variation as described in detail

Only one period of deformation with stresses operating persistently in a north - south direction affected the area. Folding was mainly open and symmetrical, except along a zone where overfolding culminated in a thrust fault with strike of at least 36 kilometres and displacement of the order of thousands of metres in some areas. A flexure with strike almost parallel to the later deformational stresses developed at the time of sedimentation. During deformation the flexure acted as an immobile block and had a pronounced effect on folding in its vicinity. Relief of pressure caused the development of normal transverse faults