A Dissertation Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in Fulfilment of the Requirements of the Degree of Doctor of Philosophy. / The Gariep Belt is an arcuate north-south trending tectonic unit extending ;along the western coast of southern Namibia and northwestern South Africa. It forms part of the Pan-African Damara Oragert, which consists of a north-south trending coastal branch (Kaoko and Gariep Belts) and an east-west trending inland branch. The Gariep Belt is subdivided into an eastern parautochthonous passive continental margin on the western edge of the Kalahari Craton, the Port Nolloth Zone, and a western allochthonous ophiolitic terrane, the Marmora Superterrane, thrusted on the Port Nolloth Zone. The sedimentary evolution of the Gariep Belt was initiated with the deposition of sediments of the Rosh Pinah Formation into fluvial, alluvial and lacustrine depositional systems, which are associated with bimodal volcanic activity and related Zn-Pb-Cu-Ag- (+Ba) sulphide mineralization. The overlying mixed continental/shallow marine deposits of the Gumchavib Formation are overlain by the carbonate dominated Pickelhaube Formation, which was deposited in shallow marine to pelagic depositional settings. The Rosh Pinah, Gumchavib and lower Pickelhaube Formations are intruded by basic volcanic sills of the "Gannakouriep dyke swarm", The conformably overlying Obib Peak Formation was deposited into a fluvial/alluvial palaeoenvlronrnent, The Numees Formation unconformably overlies the underlying stratigraphic units and consists predominantly of glaciomarine massive diamictites and occasionally interbedded iron formations, which are occasionally interbedded with interglacial sediments and volcanics. The regional structural pattern is characterized by three phases of deformation. The earliest deformational event, D1, comprises intrafolial small scale recumbent and isoclinal F1 folds, a penetratlve beddlnq-subparatel 81 cleavage and a preferred elongation of boulders, pebbles, grains and minerals (11). Associated with D1 are bedding-subparallel thrust faults. The D2 deformational phase is characterized by small to large scale, north to northwest trending F2 folds with a generally easterly vergence, which can change into a westerly direction due to backfolding. The F2 folds are associated with a penetrative axial planar S2 cleavage. Thrusting continued during the D2 deformational phase. The latest deformational event, D3, is characterized by small to large scale open F3 folds with southerly to south-westerly trending fold axes. The metamorphic evolution of the Gariep Belt during the Damara Orogeny was associated with barrovtan-type metamorphism with a geothermal gradient of about 20oC/km, reaching greenschist to lower amphibolite facies metamorphism. The sedimentological and structural features are explained in a tectono-sedimentery model, which started with rift initiation during the deposition of Rosh Plnah Formation lithologies along old tectonic weakness zones of Middle Proterozoic age at about 780Ma. Supercontinenta! breakup is documented by the initial transgression of Gumchavib Formation sediments and the continuous trensgression of the Pickelhaube Formation, which is related to thermal subsidence after the initiation of oceanic spreading of the Adamastor Ocean. Renewed rifting and/or glacial outwash heralding' the advance of the Numees glaciation and associated seale': :'changes may be responsible for the sudden break in marine sedimentation during the deposition of the Ohio Peak Formation. The Numees glaciation is probably contemporaneous with the 670Ma old Varangian glacial and the Rapitan glacial episodes and provides a minimum age for the deposition of Gariep Group lithologies. Rifting and spreading was followed by the closure of the Adamastor Ocean, associated with. a southeastward directed subduction. of oceanic crust under the Kalahari Craton and was accompanied by intense southeastward and subsequently eastward directed tectonic transport during 01 and D2. During D3, a late Sinistral movement developed along tre defined fault zones in the late stages of the Adamastor Orogeny.Metamorphic ages from the Nama and Vanrhynsdorp Groups indicate that that the tectonic evolution of the Gariep Belt only ceased at about 500Ma. / Andrew Chakane 2018

Thesis (MSc)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: The northeast-trending south Central Zone (sCZ) of the Pan-African Damara belt in central Namibia is structurally characterized by kilometer-scale, northeast-trending dome structures developed in Neoproterozoic rocks of the Damara Sequence. A number of different structural models have been proposed for the formation of these domes in the literature. This study describes the structural geology of the Usakos dome. The study discusses the structural evolution of the dome within the regional framework of the cSZ that represents the high-grade metamorphic axis of the Damara Belt, characterized by voluminous Pan-African granitoids. The northeastern part of the Usakos dome is developed as an upright- to northwestverging anticlinorium containing a steep southeasterly-dipping axial planar foliation. The northeast fold trend persists into the southwestern parts of the Usakos dome. However, this southwestern core of the dome is inundated by synkinematic granitic sheets. Distinct marker horizons of the Damara Sequence outcrop as screens within the granite, preserving a ghost stratigraphy. These screens illustrate the position and orientation of second-order folds. Significantly, most of the stratigraphy of the Damara Sequence is overturned in these folds. For example, some second-order anticlines developed in the northeastern parts of the Usakos dome can be followed along their axial traces into the southwestern hinge of the dome, where they appear as synformal anticlines, i.e. synformal structures cored by older strata, plunging towards the northeast. The inverted stratigraphy and northeasterly fold plunges suggest the northeast-trending folds are refolded by second-generation, northwest-trending folds, thus, forming kilometer-scale Type-2 interference folds. The resulting fold geometries are strongly non-cylindrical, approaching southwest-closing sheath folds indicating a top-to-the-southwest material transport. Lower-order folds in this overturned domain show radial fold plunges, plunging away from the centre of the dome core, as well as a shallowly-dipping schistosity. The close spatial and temporal relationship between granite intrusion and the formation of the southwest-vergent, sheath-type folds, radial distribution of fold plunges and the subhorizontal foliation confined to the southwestern hinge of the Usakos dome are interpreted to signify the rheological weakening and ensuing collapse of the developing first-order Usakos dome immediately above the synkinematic granite intrusions. Orogenparallel, southwest-vergent sheath folds and top-to-the southwest extrusion of the southwestern parts of the Usakos dome and northwest-vergent folding and thrusting characterizing the northeastern extent of the Usakos dome are both responses to the northwest-southeast- directed contractional tectonics recorded during the main collisional phase in the Damara belt. On a regional scale, the Usakos dome represents the link between the foreland-vergent northeastern part of the sCZ and the southwest-vergent, high-grade southwestern parts of the sCZ. The results of this study illustrate how dramatic variations in structural styles may be caused by the localized and transient rheological weakening of the crust during plutonic activity. / AFRIKAANSE OPSOMMING: Die noordoos-strekkende, suidelike Sentrale Sone (sSS) van die Pan-Afrikaanse Damara gordel in sentraal Namibië word karakteriseer deur kilometer-skaal, noordoosstrekkende koepel strukture, ontwikkel in die Neoproterozoïkum gesteentes van die Damara Opeenvolging. 'n Aantal verskillende struktuur modelle is voorgestel in die literatuur vir die vorming van hierdie koepels. Hierdie ondersoek beskryf die struktuur geologie van die Usakos koepel. Die ondersoek bespreek die strukturele ontwikkeling van die koepel in die regionale konteks van die sSS, wat die hoë graadse metamorfe magmatiese as van die Damara Gordel verteenwoordig, en karakteriseer word deur omvangryke Pan-Afrikaanse granitoïede. Die noordoostelike gedeelte van die Usakos koepel is ontwikkel as 'n antiklinorium met 'n vertikale- tot noordwestelike kantelrigting. wat 'n steil hellende, suidoostelike asvlak planêre foliasie bevat. Die noordoos-strekkende plooiing kom voor tot in die suidwestelike kern van die Usakos wat ingedring is deur sinkinematiese granitiese plate. Die posisie en oriëntasie van tweede-orde plooie is afgebeeld in die graniete deur 'n skimstratigrafie wat preserveer is deur duidelike merker horisonne van die Damara Opeenvolging. Die stratigrafie van die Damara Opeenvolging is opmerklik meestal omgekeer in hierdie plooie. Byvoorbeeld, tweede-orde antikliene ontwikkel in die noordoostelike gedeelte van die Usakos koepel kan gevolg word langs hul asvlakspore tot in die suidwestelike skarnier van die koepel, waar dit voorkom as sinforme antikliene, d.w.s. sinforme strukture met ouer strata in die kern wat na die noordooste duik. Die omgekeerde stratigrafie en noordoostelike plooi duiking impliseer dat die noordoosstrekkende plooie weer geplooi is deur tweede-generasie, noordwes-strekkende plooie, wat dus aanleiding gegee het tot die vorming van kilometer-skaal, tipe-2 interferensie plooie. Die gevolglike plooi geometrieë is uitdruklik nie-silindries, en toon 'n oorgang na skede plooie met 'n sluiting na die suidweste, wat dui op 'n bokant-na-die-suidweste materiaal vervoer. Laer-orde plooie in die omgekeerde domein vertoon radiale duiking van die plooie, weg van die middelpunt van die koepel kern, sowel as 'n vlak hellende skistositeit. Die noue ruimtelike en temporele verwantskap tussen graniet intrusie en die vorming van skede-tipe plooie met 'n kantelrigting na die suidweste, die radiale verspreiding van plooi duiking, en die subhorisontale foliasie wat beperk is tot die suidwestelike skarnier van die Usakos koepel, word interpreteer as 'n aanduiding van die reologiese verswakking en die gevolglike ineenstorting van die ontwikkelende eerste-orde Usakos koepel, onmiddellik aan die bokant van die sinkinematiese graniet intrusies. Die orogeenparalleie skede plooie met kantelrigting na die suidweste en bokant-na-die-suidweste ekstrusie van die suidwestelike gedeelte van die Usakos koepel, en plooiing met kantelrigting na die noordweste en stootverskuiwing wat kenmerkend is van die noordoostelike gedeelte van die Usakos koepel, is beide 'n reaksie op die noordwessuidoos- gerigte vernouings tektoniek opgeteken gedurende die hoof botsings fase in die Damara gordel. Op 'n regionale skaal verteenwoordig die Usakos koepel die verbinding tussen die noordoostelike gedeelte van die sSS met 'n voorland kantelrigting. en die hoë graad suidwestelike gedeelte van die sSS met 'n kantelrigting na die suidweste. Die resultate van hierdie ondersoek toon aan hoe dramatiese variasies in struktuur style veroorsaak kan word deur die gelokaliseerde en kortstondige reologiese verswakking van die kors gedurende plutoniese aktiwiteit.

The Elisenheim area is situated just north of Windhoek within the Windhoek Formation of the Swakop Subgroup and is underlain by monotonous succession of semi-pelitic schists with intercalations of amphibolite, talc schist, graphitic schist and marble. Petrographic studies on units of the Matchless amphibolite which outcrop in the south of the property, have resulted in the recognition of three different types of amphibolite, namely, epidote amphibolite, porphyroblastic amphibolite and chlorite-amphibole schist. Amphibole porphyroblasts generally display patchy and zonal intergrowths of hornblende and actinolite which are indicative of non-equilibration during prograde metamorphism. Talc schists have been mapped in the north of the property. All lithotypes have undergone three phases of deformation (Fl, FZ, F3) which terminated with the faulting which underlies the Klein Windhoek, Dobra, Tigenschlücht and Kuruma rivers. Medium grade regional metamorphism accompanied F 1, F Z and F 3 and outlasted the latter. Mineral assemblages throughout the area are those of the amphibolite facies and P, T conditions prevailing during metamorphism are estimated to have been at least 5 kb at ~ 550° C. Petrochemical evidence indicates that the Matchless amphibolites are igneous in origin and genetically related to the ultrabasic talc schists. They are similar in composition to oceanic tholeiites and are thought to have been extruded subaqueously.

The study area is situated in the Southern Central Zone of the intracontinental Pan-African Damara Orogen, approximately 20km NNE of Navachab Gold Mine in the Karibib district of Namibia. Mesothermal vein systems with Cu-Fe±Au mineralization are hosted by amphibolite facies calcitic and dolomitic marbles belonging to the Navachab Member of the Karibib Formation, and are best developed around the defunct Onguati Copper Mine, Brown Mountain and Western Workings areas. The Onguati study area is located in the saddle region of a moderately-to-gently inclined anticlinorium that experienced significant flattening during NNW-SSE-directed compression. The parallelogram arrangement of ENE- and NNE-trending thrusts and reverse faults that surround the Onguati study area may have developed when the direction of greatest principle subregional stress was oriented WSW-ESE. These structures define part of a Riedel shear system and later faults may have developed in the position of R and P shears respectively. Significant strain partitioning occurred between the ductile calcitic marbles which host the best developed, shear-related vein systems and the more competent dolomitic marbles. The thickness distributions of veins in the marbles of the Onguati Mine, Brown Mountain and Western Workings areas conform to a fractal or power-law distribution, The most intensely mineralized vein systems in the Onguati Mine and Western Workings calcitic marbles share similar low fractal dimensions (D-values) of 0.41 and 0.37 respectively. Veins In the calcitic and dolomitic marbles of the Brown Mountain area and in the dolomitic marbles of Western Workings have elevated D-values (>0.60) and are poorly mineralized. The low D-values «0.40) of the well mineralized vein systems reflect the higher degree of fracture connectivity. These vein systems were capable of efficiently draining and localizing large volumes of mineralizing fluids from crustal-scale structures. A metamorphic devolatization model is proposed where the entire Damaran metasedimentary and meta-volcanic package is seen as a large source area of very low concentrations of Cu, Au and other metals. Localization of deformation into crustal-scale faults and shear zones led to regional-scale hydrothermal fluid flow and focussing into the upstream fracture networks of the Onguati study area. Strong mineralization resulted when fluids encountered the reactive marble lithologies

The ENE trending Brandberg West - Goantagab Sn-W belt is located in the Southern Kaoko Zone of the northern coastal branch of the Damara Orogen. The lithologies in this area are turbiditic and consist of three schist units separated by two marble horizons, all of which are correlated with the Swakop Group. The formations are intensely folded by at least three episodes of which the first two are coaxial and resulted in prominent, approximately N-S trending, structures. Sn and Sn-W mineralization predominantly occurs as vein and replacement type mineralization. Vein type mineralization occurs as Brandberg West, Frans Prospect, Gamigab Prospect and the Goantagab Mining Area. The vein type mineralization is accompanied by intense alteration, consisting of greisenization, sericitization, hematitization and carbonatization. Replacement-type, hematite-cassiterite mineralization, occurs in the Goantagab Mining area in the marble close to, or at the schist marble contact. Intense ferruginous alteration of the marbles in this area, is associated with veins, which terminate against, or cross cut the marble. A regional metal zonation, ranging from Sn-W mineralization with minor sulphides at Brandberg West to Sn-sulphide mineralization at Goantagab can be detected. This metal zonation is attributed to the distance of the mineral locality from the source area, with Goantagab representing a distal and Brandberg West a proximal position relative to the source area. Structural, mineralogical and geological features of the mineralization in this area suggest that processes of ore genesis may be related to anorogenic magmatism of Karoo age.