The Matchless Amphibolite Belt (Damara Orogen, Namibia) hosts several volcanogenic-exhalative, sediment-hosted stratiform cupriferous pyrite deposits. These are thought to be related to submarine volcanism during the early evolutionary stages of a narrow Damaran ocean, the Matchless Trough. The mineralized bodies examined (Ongeama, Ongombo and Matchless West Extension) are deformed and metamorphosed to low-medium grade (greenschist-amphibolite facies). They are associated with metapelite and amphibolite country rocks, and crop out as prominent limonite-rich gossans. The elongated shape of the sulphide bodies suggests a structural control. The mineralization normally consists of a variably developed massive sulphide portion, either quartz-, talc- or amphibole-bearing, and a stratigraphically overlying, extensive horizon of sulphide- and baryte-bearing exhalite (magnetite quartzite and less common talc- and actinolite-bearing schists). Lateral and vertical mineralogical changes within the mineralization match with significant variations in the element distribution. A metamorphosed and deformed alteration pipe, indicating the position of the fluid conduit, can be recognized in association with some ore bodies. The formation of quartz-muscovite and chlorite alteration envelopes (Ongeama, Matchless West Extension) and the presence of subtle mineralogical changes (Ongombo) in the immediate wallrocks, accompanied by extensive redistribution, leaching and introduction of elements from outside, suggest the hydrothermal metasomatic origin of the alteration zones. Element zoning within the mineralized bodies can be related to the original position of the vent, possibly coinciding with the intersection of the axis of the alteration pipe with the sulphide body. Cu, Zn, Au (pro parte) and Mo are enriched proximal to the vent, whereas Pb, Ba, Mn, Ag, Au, Sn, Bi and W enrichment characterizes the distal facies of the mineralization. In spite of the obliterating and disrupting effects of the regional dynamo-metamorphism, the element distribution within the mineralization and alteration zones examined is comparable with the geochemical trends observed in present-day mineralizing systems in early- stage oceanic environments (e.g. Guaymas Basin). During exploration for blind volcanogenic mineralization, the detection of hydrothermally altered rocks is fundamental in indicating the proximity to the mineralization. The localization of the alteration zone is also important in the interpretation of the regional geology of the explored area: in deformed terrains the assessment of the stratigraphic position of the alteration zone, relative to the mineralization, helps in establishing the polarity of the sequence.

The late Proterozoic volcanic and sedimentary sequence in the Dordabis area SWA/Namibia has been named the Dordabis Formation and subdivided, on the basis of field, petrological and petrographic evidence, into the Opdam and Bitterwater Members. Relict phases including augite and minor plagioclase only occur in the Bitterwater metalavas, as recrystallisation is complete in the Opdam metal avas. The composition of the relict feldspars ranges from labradorite in the ophitic basalts to oligoclase in the blastoporphyritic metalavas. The feldspars in the Opdam member are albitic in composition (An content 0,0 to 1,7) . Epidote compositions are typical of those occurring in metabasic rocks. Samples with high-iron whole-rock compositions are accompanied by high concentrations of Fe3+ in concomitant epidotes. Sixty three samples were analysed using X-ray fluorescence spectrometry to determine concentrations of major and 16 trace elements. Although greenschist facies metamorphism, metasomatism and shearing have produced scatter in the more mobile element concentrations, variation trends in other elements closely resemble modelled low-pressure fractional crystallisation trends. The Dordabis metalavas are petrologically classified as sub-alkaline, tholeiitic continental basalts. Low K/Rb ratios and low ratios of less incompatible to more incompatible elements probably reflect a source that has either been metasomati ca lly enriched or that has undergone little previous partial melting. Overlapping whole-rock variation trends indicate that the generally more evolved Opdam and primitive tholeiitic Bittenwater lavas are cogenetic. A comparison of the Dordabis Formation with the Sinclair Sequence and the Koras Group shows that their ages, petrology, petrography, associ a ted sedimentary suites and depositional environments are similar. It is concluded that they may possibly be coeval equivalents.

A brief account of the location and physical aspects of the region is followed by descriptions of mapping and laboratory techniques employed. Recent ideas on regional stratigraphical correlation in South West Africa are critically reviewed. Strata lying southeast of the farm Losberg 105 have, on the basis of lithology and copper mineralisation, been correlated with the Tsumis Formation. The Hasib Formation, of predominantly marine character, has on structural grounds been excluded from the Damara System. The latter here has a greater thickness than elsewhere in South West Africa, unless isoclinal folding is much more prevalent than has been assumed. The occurrence on Eintracht 118 of a pebble conglomerate, tentatively equated with the Chuos Tillite, makes possible a subdivision of the Damara strata into the various series established in the literature. It has been found possible to differentiate between Kamtsas and Damara quartzites on petrological grounds. Further, it is concluded that the bulk of Hakos carbonate rocks originated as dolomites and have subsequently been dedolomitized to a greater or lesser extent. The area contains both ortho- and para-amphibolites, as well as one occurrence of intrusive granite. Evidence is given for at least three periods of deformation. It is oonsidered that, if the Hosib Formation was involved in a pre-Damara orogenic episode, later folding must have been co-axial with this. Sedimentation and metamorphism are treated in broad outline. There appears to have been a deepening of the basin of deposition from Hasib to Damara times. Cyclicity in sedimentation is evidenced by lithological associations in the Damara strata. The entire area falls into the greenschist facies of regional metamorphism. Superficial deposits include river gravel and, silt, quartzite- and vein quartz-rubble, calcrete and Kalahari sand. The economic geology is described with special reference to the widespread copper mineralisation.

M.Sc. (Geology) / The main objective of this study was to characterize the North Break Zone of the Otavi Mountain Land, Namibia in terms of stratigraphy and petrography and to investigate its relationship with the Tsumeb ore body and other mineralized prospects in the immediate vicinity of Tsumeb. The Late Proterozoic Otavi carbonate platform sequence is famous for its base metal deposits. The North Break Zone is a stratabound zone of sporadic mineralization, brecciation and silicification occurring in the lower part of Iithozone T6 of the Hoffenberg Formation (Tsumeb Subgroup). It intersects the pipe-like Tsumeb Cu-Pb-Zn-Ag ore body at a depth of about 900m below surface. Where the North Break Zone intersects the Tsumeb ore body large massive ore associated with calcitized dolomite, dolomite breccia as well as feldspathic sandstone lenses occur. These features extend along strike and dip outside the normal dimensions of the Tsumeb ore body. The genesis of the Tsumeb ore body is poorly understood. The conventional model is that meteoric fluids circulated through the so-called North Break Zone paleo-aquifer, dissolving carbonate and giving rise to solution collapse and eventually the creation of the Tsumeb karst pipe. However, no direct evidence is available to support this model. This study was devised to critically evaluate the relationship between the North Break Zone and formation of the Tsumeb ore body. The study entailed field mapping, detailed sampling of the stratigraphic sequence and ore bodies, white light, reflected light, UV/blue light and cathodoluminescence petrography. Cathodoluminescence proved to be the most effective petrographic tool for differentiating various carbonate phases. The North Break Zone is defined as a 10 to 14m thick chert free oolitic to intraclastic dolomitic grainstone, stromatolite and mudstone unit, in which discontinuous lenses of mineralized secondary quartz are present. It is interbedded with dark grey cherty micritic dolomite of Lithozone T6 of the HOffenberg Formation. Minor calcification, Cu-Pb-Zn mineralization and manganese and iron enrichment are associated with the quartz-rich bodies. The mineralized quartz bodies are only present up to 2.5km to the west and 2.6km to the east of the Tsumeb ore body. The petrographic study indicated that 1) the epigenetic sequence of carbonate alteration, precipitation of new carbonate phases and mineralization is virtually identical in all Cu-Pb-Zn occurrences and 2) that the mineralization is closely associated with Mn-bearing brightly luminescent (CL) carbonates. Earlier Cu-Pb-Zn sulphide mineralization is associated with Mn-bearing bright red luminescent sparry dolomite (dolomite IIIB). Late stage Cu-arsenate, oxide and silicate mineralization is associated with an episode of Mn-bearing bright yellow luminescent calcite (calcite II) which also causes dolomitization of the associated dolomites. A very simple paragenetic model of mineralization is proposed. The earliest is defined by pre-mineralization calcite (calcite I) vein formation with associated dolomitization. This phase is followed by deposition of kerogen luminescent Mn-bearing dolomite IIIB - quartz and Cu-Pb-Zn sulphides representing the main mineralization event. It is followed by a late mineralization event composed of Mn-bearing calcite (calcite II) with associated Cu-arsenates, oxides and silicates. Supergene alteration is represented by the precipitation of very late stage non-luminescent Mn and Fe-poor calcite (calcite III) and quartz without any associated Cu-Pb-Zn mineralization. The sequence of mineralization is explained by the evolution of a single hydrothermal fluid, from relatively cold to hot and then back to cold, during a major period of fluid migration through the carbonate platform sequence. The North Break Zone probably never acted as a paleo-aquifer for fluids that formed the Tsumeb ore body. Rather hydrothermal fluids moved from the Tsumeb ore body into the North Break Zone. Hydrothermal fluids may have been derived from the Damara orogen to the south of Tsumeb during a period of tectonic loading and thrust deformation.