Integrated Lithostructural Mapping of the Rössing Area, Namibia using High Resolution Aeromagnetic, Radiometric, Landsat Data and Aerial Photographs

Abstract

This paper presents results of an integrated appraisal of recent high-resolution aeromagnetic, radiometric and remote sensing data over the Rossing mine area and lower Khan Gorge region of Namibia. The interpretation used stereoscopic aerial photographs to establish structure around the Rossing mine and high-pass filtered aeromagnetic data for the regional structure, followed by analysis of spectral Landsat TM data, total field magnetic intensity data and imaged airborne gamma-ray spectrometer data to delineate lithology. Resulting interpretation maps clearly show an hierarchy of polyphase folding, which had been described by earlier field mapping, and a hithertounrecognised system of late (post-F3) sinistral strike-slip faulting and thrusting. Early Palaeozoic alaskitic intrusions of the type which host the world-class Rossing uranium deposit appear to be largely related to late sinistral transtensional ladder veins associated with the northnortheast trending post-F3 sinistral strike-slip faults.

The Rössing Uranium Deposit: a product of late-kinematic localization of uraniferous granites in the Central Zone of the Damara Orogen, Namibia

“…Multiple, parallel to sub-parallel, NNE-trending (''Welwitschia Trend''), left-lateral shears occur in the vicinity of the R€ ossing Dome (see Fig. 2), a feature documented by Anderson and Nash (1997) and Lord et al (1996). Corner (2000) observed that mafic dykes, possibly of Karoo-age, have utilized this trend, as is shown in the Landsat interpretation of Fig.…”

“…1; Corner, 2000). Although there are no published ages for the initiation of this late-kinematic lineament, its crosscutting relationship with respect to the products of earlier deformation events (specifically those of ''D 3 ''--see later), pre-existing lineaments and lithological trends is evident from regional and local aeromagnetics (Corner, 1982(Corner, , 1983(Corner, , 2000Eberle et al, 1995;Anderson and Nash, 1997). Late-kinematic, left-lateral, strike-slip movement along the Welwitschia Lineament is also suggested by its truncation of the N-trending Okahandja Lineament ( Fig.…”

“…S 1 and S 2 migmatitic banding, particularly evident in the areas to the west of the R€ ossing Dome, are preserved within the Khan and Etusis formations, while S 1 and S 2 occur as laminar flow which are delineated as shears due to their offset of banding/foliation (q.v. Anderson and Nash, 1997). The inset shows a Rose diagram of the trends of NNE to NE-trending (probably late-Cretaceous; Lord et al, 1996) dykes (N ¼ 236) in the area between R€ ossing and Goanikontes.…”

“…Stratigraphy of the R€ ossing area Nash (1971), Henry (1992), Lehtonen et al (1996) and Anderson and Nash (1997) have described the basal Swakop and Nosib Groups, that rest unconformably on the Abbabis Metamorphic Complex/Basement, to the SE of the Omaruru lineament in the vicinity of R€ ossing (Table 1). The highly metamorphosed pre-Damara Abbabis Complex, consisting of augen, migmatitic, biotite, sillimanite and granitic gneiss, biotite schist and amphibolite, is exposed in domes in the Swakop and Khan River areas (e.g.…”

“…5. Regional structural evolution Smith (1965), Sawyer (1978), Martin (1983), Coward (1980), Buhn and Stannistreet (1992), Anderson and Nash (1997) and Nex et al (2001a,b) provide overviews of regional deformation events in the southern Central Zone, which includes the R€ ossing, Khan River, Goanikontes and Swakop River areas (Table 2). Original sedimentary layering (S 0 ) is preserved in the form of bedding and cross-bedding within the Khan and Etusis formations in the Goanikontes area.…”