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Quartz fields contribute significantly to plant diversity in the Succulent Karoo biome. They are distinctly different from surrounding habitats and have high levels of plant endemism. Biological soil crusts are features of quartz field soils and fulfill a vital function in that they stabilize soils. It is important for managers of nature reserves and agricultural rangelands to know what factors influence quartz field soils and vegetation. Both stakeholders could benefit from new information that would allow for informed decision-making regarding land-use on quartz fields. The present study took place in the Namaqua National Park that contains a significant proportion of the Riethuis-Wallekraal quartz fields phytochorion. The first part of the study aimed to understand whether certain land-use activities potentially destabilize quartz field soils, which might have possible ramifications for associated biological soil crusts and vegetation. It was followed by relating variation in soil stability with species richness, cover and species composition of quartz field vegetation. Overall, positions assumed to be impacted by land-use activities had less stable soils compared to positions assumed not be impacted. Soil stability had a significant influence on species richness and cover but to a lesser degree on species composition. Quartz field vegetation was significantly influenced by soil physical and chemical properties as well as location in the quartz fields landscape. The second part of the study aimed at understanding how species richness of isolated quartz outcrops is related to their size compared to that of a mainland body of quartz outcrops. No clear species-area relationships emerged from the study. There were significant differences between isolated outcrops and mainland outcrops in substrate and vegetation composition. Findings are discussed in relation to Island Biogeography Theory.

Thesis (PhD (Soil Science))--Univ ersity of Stellenbosch, 2008. / The (semi-)arid Namaqualand region on the west coast of South Africa is wellknown for its spring flower displays. Due to the aridity of the region, soils research has lagged behind that of the more agriculturally productive parts of South Africa. However, rehabilitation efforts after the hundred or so years of mining, coupled with the increasing ecology and biodiversity research, have prompted a recent interest in Namaqualand soils as a substrate for plant growth. The area is also notable for the abundance of heuweltjies. Much of the previous heuweltjie-work focussed on biogenic aspects such as their spacing, origin and age, but although heuweltjies are in fact a soil feature, there have been few published studies on the soil forming processes within heuweltjies. However, the depositional history of the sediments on the Namaqualand coastal plain is well constrained, which is in stark contrast to the paucity of data on their subsequent pedogenesis. Given that the regolith has been subaerially exposed in some parts for much of the Neogene, the soil formation forms an important part of the sediments’ history. The primary aim of this thesis, therefore, was to examine the soil features of the Namaqualand coastal plain to further the understanding of pedogenesis in the region. The regolith of the northern Namaqualand coastal plain, often ten or more metres deep, comprises successive late Tertiary marine packages, each deposited during sea-level regression. The surface soil horizons formed from an aeolian parent material. The relatively low CaCO3 in the aeolian sands dictated the pedogenic pathway in these deposits. The non-calcareous pathway lead to clay-rich, redder apedal horizons that show a stronger structure with depth, and generally rest directly on marine sands via a subtle discontinuity that suggests pedogenesis continues into the underlying marine facies. The calcareous pathway lead to similar clay-rich, redder apedal B horizons, but which differ in that they are calcareous, and rest on a calcrete horizon often via a stoneline of rounded pebbles. Deeper in the profile, there is generally a regular alteration of sedimentary units, with the upper shoreface facies showing reddening, and the lower shoreface sands remaining pale. This seems to be a function of the grain size, since the upper shoreface materials are coarser, and the redder parts of the lower shoreface are also associated with slightly coarser sands. In some strata the oxidation of glauconite-rich sediments resulted in an orange colour. In an area with abundant heuweltjies, a strongly-cemented calcretized nest was present about 2 m deep within a silica cemented, locally calcareous dorbank profile. Vertical termite burrows are present up to 12 m deep, and appear to have been conduits for preferential vertical flow. Soil formation and termite activity is at least as old as the Last Interglacial. E horizons may have formed in a wetter Last Interglacial paleoclimate, but they are still active in the present day. The Namaqualand coastal plain, with its extensive areas of calcrete development, is almost a textbook setting for calcrete development by inorganic processes. However, these calcretes also show microscale biogenic features. These include M rods, MA rods, and fungal filaments. Abiotic alpha-fabric seems dominant in mature calcrete horizons, and beta-fabric in calcareous nodules in a calcic B horizon above calcrete. The apparent absence of Mg-calcite and dolomite, and abundance of sepiolite in the calcretes of coastal Namaqualand suggests that these Mg-rich clay minerals are the main Mg-bearing phase. Deformation (pseudo-anticlines) in the calcrete appear to result primarily from the displacive effect of calcite crystallization. Although evidence of shrink/swell behaviour is present in the form of accommodating planes, it does not appear to be as volumetrically significant as displacive calcite. Indurated light-coloured horizons that resembled calcrete but are non- to mildly calcareous, break with a conchoidal fracture, resist slaking in both acid and alkali, turn methyl-orange purple, and show a bulk-soil sepiolite XRD peak are similar to palygorskite-cemented material (‘palycrete’) from Spain and Portugal, and so were tentatively named ‘sepiocrete’. Sepiolite and palygorskite are often reported from arid region soils but there has been no recorded cementation of soils by sepiolite. The degree of induration in some of these horizons suggest that amorphous silica could play a role in cementation, and so this thesis compares the two silica-cemented horizons encountered in Namaqualand (silcrete and dorbank (petroduric)) to these ‘sepiocrete’ horizons. Both silica and sepiolite are present in the matrix, although the degree to which silica and sepiolite dominate seems to vary even within same horizon. It seems most probable that both contribute to the structural properties of the horizon. Sepiolitic horizons do not form a diagnostic horizon in the World Reference Base, Soil Taxonomy, or the South African system. To fit the existing soil classification schemes, the terms ‘sepiolitic’ and ‘petrosepiolitic’ (in the same sense as ‘calcic’ and ‘petrocalcic’) would be appropriate. The term ‘sepiolitic’ should be used for horizons which: contain sepiolite in amounts great enough for it to be detected by XRD in the bulk soil, peds (a fractured surface and not just the cutan) cling strongly to the wetted tongue, and methyl orange turns from orange to purple-pink over most of a fragmented surface. The term can be easily be applied as a adjective to other hardpans where sepiolite is significant but not necessarily cementing, such as ‘sepiolitic’ petrocalcic/petroduric. If the horizon is in addition to the above criteria cemented to such a degree that it will slake neither in acid (so cannot be classified as petrocalcic) nor in alkali (and so cannot be classified as petroduric) then the term ‘petrosepiolitic’ would be appropriate. The ‘sepiolitic’ criteria distinguish the ‘petrosepiolitic’ horizon from a ‘silcrete’, a silica-cemented horizon which does not fit the definition of petroduric. Sepiolite is more prominent than palygorskite in the XRD traces. The <0.08 μm fraction is the only size fraction where palygorskite could be detected before acetate treatment. It is unlikely that these fibrous clay minerals are inherited from either the marine or aeolian parent materials, they appear to be pedogenic in origin. Sepiolite and palygorskite are associated with the presence of calcite in the soil profile. Trends in MgO, Al2O3 and SiO2 show that the soil clay fractions lie on a mixing line between sepiolite and mica end-members, with a contribution from smectite, and is consistent with the XRD and TEM results. There is a good correlation between Fe2O3 and TiO2, which can be attributed to the ubiquitously presence of mica. There was no TEM evidence of fibrous mineral degradation to sheet silicates, nor for the evolution of mica laterally to a fibrous mineral. SEM analyses show that much of the sepiolite/palygorskite occurs as fringed sheets, but higher magnification often revealed these sheets to be composed of fibres. These are found coating (rather than evolving from) mica/illite particles, as free-standing mats, and are common on the grain-side of cutans. Some of these textures suggest illuviation of the fibrous clay minerals, but another explanation may be that sites such as that immediately adjacent to silicate grains have the highest concentration of silica for their formation. There was no conclusive evidence for or against the presence of kerolite in the clay fraction, although it does not appear to be a dominant phase in the <2 μm fraction. The hypothesis was that the permeable upper horizons in Namaqualand soils constitute a shallow ephemeral aquifer, which can be considered the pedogenic analogue of the saline lake environments in which sepiolite typically forms. The chemical evolution of the soil solution and clay mineral genesis could therefore be considered in the same terms as the geochemical evolution of closed-basin brines. The Namaqualand coastal plain, like other maritime areas, shows a trend of decreasing pH, increasing Ca and increasing Mg with increasing evaporation. This can be explained by their seawater-influenced initial ratios, and is consistent with the ‘chemical divides’ of the Hardie-Eugster model of brine evolution. Halite remains undersaturated at all concentrations in the saturated paste extracts. At higher concentrations, gypsum reaches saturation, and sulfate is removed from solution. H4SiO4 activity remains unchanged for all levels of evaporation and pH. Calcite remains close to saturation, and is only dependent on the HCO−3 activity and pH for the range of Cl− activity encountered. Most of the soils for which there is a positive sepiolite identification show a positive sepiolite saturation index. The sepiolite saturation index is independent of Mg2+ and H4SiO4 and only increases with increasing pH. Evidence of the pH control on sepiolite saturation is that sepiolite is commonly associated with calcareous horizons. Sepiolite precipitation is therefore more likely to be triggered when a solution encounters a pH barrier than by the concentration of ions by evaporation. The effect of a pH change on the sepiolite saturation index is much greater than that of the effect on calcite. The marine-influenced high Mg coupled with the Hardie- Eugster model of brine evolution offers an explanation for sepiolite-dominance at the coast, and palygorskite-dominance inland. Coastal areas, unlike continental areas, have Mg>HCO−3 initially, which results in an increasing Mg trend with evaporation during the precipitation of sepiolite according to the Hardie-Eugster scheme. The result is that after sepiolite precipitation is initiated by a geochemical pH-barrier, Mg levels will rise causing the increasing (Mg+Si)/Al ratio to continue to favour sepiolite precipitation. This suggests that once sepiolite has begun to precipitate, the subsequent salinity with its accompanying Mg increase makes substantial palygorskite formation unlikely to follow. The hardpan horizons in heuweltjies commonly grade from a ‘sepiolitic’ petrocalcic in the centre through ‘sepiolitic’/‘petrosepiolitic’ to the petroduric horizon on the edges. Noteworthy sepiolite-related pedofeatures in the calcrete include ‘ooids’ with successive sepiolite (hydrophilic and therefore a precipitational substrate) and micrite/acicular calcite layers in the coatings; and limpid yellow nodules with pseudo-negative uniaxial interference figures. They superficially resemble the spherulites in the fresh termite frass. Their fibrous nature and low birefringence, together with the low Ca, high Mg, Si composition, and molar Mg/Si ratios consistent with sepiolite. The pedogenesis of the hardpans in the heuweltjie is proposed to be as follows: enrichment of cations such as Ca and Mg in the heuweltjie centre caused by termite foraging results in calcite and clay authigenesis in the centre of the heuweltjie, leaving the precipitation of pure silica to occur on the periphery. The decaying organic matter concentrated in the centre of the mound by the termites is sufficient to supply the components for calcite precipitation in the centre of the heuweltjie. Following calcite precipitation, the pH is suitable for sepiolite precipitation. The movement of the Mg-Si enriched water downslope, coupled with the decrease in HCO−3 and increase in Mg2+ due to sepiolite precipitation, allows for the precipitation of the ‘sepiolitic’ zone on the outer side of the calcrete, and extend beyond the calcrete in some heuweltjies. The Namaqualand coastal plain is well positioned for further work on its regolith, particularly because of the mining excavations which provide excellent exposures of well-defined layers of the regolith down to bedrock. Soil formation and termite activity is at least as old as the Last Interglacial, and so more detailed work would further the understanding of the subaerial alteration history in southern Africa, as well as providing better-constrained information on the Namaqualand soils that can be used by land-use management and biosphere studies.

<p>Pastoralists in Africa have developed complex mechanisms by which they can alleviate the threat of drought. They practice mobility as one of the strategies to avoid the worst effects of natural stress and disperse grazing pressure. In the past in South Africa, the indigenous Nama people occupied large areas of land and moved around extensively to exploit seasonal differences in the availability of forage and water. With the settlement of the Europeans in the Cape the indigenous people lost most of their land to the colonists. The Nama people were, therefore, restricted to smaller rangelands and their patterns of rangeland use had to adapt to the spatial constraints. Descendants now herd livestock from semi-permanent stockposts that are scattered throughout the commons. Herders use a range of practices to manage their livestock. The aims of this study was to assess the agro-ecological knowledge of livestock keepers / assess the condition of the rangeland during drought / determine the herding strategies of herders during drought.</p>

The main aim of this study was to test rehabilitation interventions in a system altered by heavy grazing, and to develop methods of monitoring these interventions.

The main aim of this study was to test rehabilitation interventions in a system altered by heavy grazing, and to develop methods of monitoring these interventions.

<p>Pastoralists in Africa have developed complex mechanisms by which they can alleviate the threat of drought. They practice mobility as one of the strategies to avoid the worst effects of natural stress and disperse grazing pressure. In the past in South Africa, the indigenous Nama people occupied large areas of land and moved around extensively to exploit seasonal differences in the availability of forage and water. With the settlement of the Europeans in the Cape the indigenous people lost most of their land to the colonists. The Nama people were, therefore, restricted to smaller rangelands and their patterns of rangeland use had to adapt to the spatial constraints. Descendants now herd livestock from semi-permanent stockposts that are scattered throughout the commons. Herders use a range of practices to manage their livestock. The aims of this study was to assess the agro-ecological knowledge of livestock keepers / assess the condition of the rangeland during drought / determine the herding strategies of herders during drought.</p>

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / Natural resources play important roles in ecosystem service delivery, more especially in rural households where livelihoods depend heavily on natural resources for the delivery of ecosystem services. The various benefits derived from provisioning, supporting, regulating and cultural services of natural ecosystems such as food, medicines, carbon sequestration, spiritual fulfilment all support human life and sustain its well-being. Research on valuation of natural resources suggest that the values derived mainly from non-marketed natural resources are insignificant and thus, not reflected in national accounts. Economic valuations have traditionally been concerned with the quantification of direct use values of ecosystem services that are marketed to produce tangible benefits. The scope of natural resource valuations have, however been broadened by scientists in recent years to consider passive or non-use values to reflect the total economic values of natural resources and ecosystem services to societies. In this study, I valued the streams of ecosystem services derived from natural resources in Leliefontein communal rangeland; an area of 192 000 hectares in the semi-arid region of Namaqualand in South Africa. Rangeland forage for livestock, medicinal plants, fuelwood, and water resources from the Communal Area were valuated for one production year between January and December 2012. Valuation was done to incorporate both marketed and non-marketed natural resources which were used within the production year. The total economic value for the area was estimated at R20 156 672 per annum. Value of rangeland forage was estimated at R61.92 ha-1 yr-1, fuelwood’s value was estimated at R25.04 ha-1 yr-1, value of medicinal plants was R2.26 ha-1 yr-1 and water resources valued at R9.45 ha-1 yr-1. The non-use value was estimated by eliciting the willingness to pay for the conservation of the natural resources using a contingent valuation method. Economic value of natural resources in Leliefontein increased to R105 per hectare from R99 when non-use value was added to reflect the total economic value of ecosystem services in the area. Household income level positively correlated with individual’s willingness to pay for ecosystem services. I recommend that decision making should take into account the socio-economic conditions of a community when determining the total economic value of ecosystem services. Non-use value of the ecosystems should be considered especially in rural areas where people depend on the natural environment for livelihoods and socio-cultural well-being. Sustainable and equitable utilisation of natural resources for the purpose of maintaining a sustainable flow of critical ecosystem services should form the basis for formulating policies on land use and sustainable development.

The Mesoproterozoic Bushmanland Subprovince of northwestern South Africa forms the western continuation of the transcontinental Namaqua-Natal Metamorphic Province, a crustal domain affected by the 1020-1220 Ma Namaquan Orogeny. Cross-cut by several large faults, the Bushmanland Subprovince can be subdivided into a southern Garies Terrain and northern Aggeneys Terrain. The supracrustal rocks of the Aggeneys Terrain (i.e. Bushmanland Group), comprise a thin (<1 km thick) metavolcano-sedimentary succession composed of a very consistent, shallow marine duplex of sandstone-shale to chemogenic metasedimentary and metavolcanic rocks that have undergone multiple phases of deformation and metamorphism. Since the discovery of the Broken Hill-type (BHT) mineralization in the Aggeneys-Gamsberg district (~440 Mt, 5.2% Cu+Zn+Pb) in the early 1970’s, controversy has persisted regarding the stratigraphy of the Bushmanland Group, its lateral correlation throughout the Aggeneys Terrain, environment and age of deposition, as well as classification and origin of its base-metal sulfide ± barite deposits. For these reasons, the present study primarily focuses on two aims, namely: (1) regionally based comprehensive lithostratigraphic, geochemical and geochronologic analysis of the Bushmanland Group to be used in the construction of a basin model; and (2) petrographic and geochemical analyses of Fe-Mn-rich rocks and barites to determine if they are related to base-metal mineralization and if so, to what extent. New lithostratigraphic data for the Bushmanland Group indicate that it can be subdivided into two subgroups and thirteen formations that are directly correlatable throughout the terrain as well as similar supracrustal successions in neighboring portions of the Namaqua Metamorphic Province. The base of the Bushmanland Group (Wortel Subgroup) comprises a thin (250-350 m thick) sequence of interbedded upward-coarsening psammo-pelitic schists and mature quartzite (i.e. meta-orthoquartzites) of the Namies Schist Fm., Pella Quartzite Fm., Bloemhoek Fm. and laterally equivalent Kangnas Fm. In contrast, the metasedimentary rocks of the unconformably overlying Kouboom Subgroup can be separated into facies terrains divided by the Pofadder-Tantalite Valley Shear Zone (PTV Shear Zone). West of the PTV Shear Zone the Kouboom Subgroup is characterized by a thin (205-225 m thick) succession of interbedded mature quartzites and pelitic schists. East of PTV Shear Zone the Kouboom Subgroup encompasses a thick (~1250 m thick) succession of calc-silicate rocks hosted by biotite to calc-silicate-rich schists and metagreywackes. The Koeris Fm., a variably thick (0-650 m) succession of psammitic schists, metaconglomerates and ortho-amphibolites unconformably overlies the Kouboom Subgroup. Geochemical provenance and detrital zircon core populations of the Wortel Subgroup suggest the metasedimentary rocks were derived from the Paleoproterozoic continental island arc rocks of the Vioolsdrift Intrusive Suite and Gladkop Suite, as well as an unidentified sedimentary/metasedimentary succession. Deposition took place in a passive continental margin environment between 1140 to 1650 Ma. In contrast, the unconformably overlying Kouboom Subgroup is characterized by larger plutonic derived zircons of the basement rocks to the Orange River Group, suggesting deposition in a tectonically active environment marked by repeated periods of tectonic uplift. In addition, new age constraints reveal that deposition in the upper part of the Kouboom Subgroup (possibly upper part of the Gams Fm.) was synchronous with emplacement of the Little Namaqualand Suite (~1190 Ma) into the lower portions, i.e. Wortel Subgroup, of the Bushmanland Group. The geochemical attributes and detrital zircon populations of metagreywackes from the Driekop Fm. suggest they were eroded from the newly exposed, i.e. fresh to poorly weathered, intrusions of the Little Namaqualand Suite, indicating a renewed period of tectonic uplift. Lastly, unlike the other lithologic units of the Bushmanland Group, the Koeris Fm. exhibits four detrital zircon age populations at 1125-1325, 1605-1695, 1730-1910 and 1935-2075 Ma. The older sub-populations indicate sediment derivation from various units of the Richtersveld Subprovince and Steinkopf Domain, while the younger sub-populations suggest derivation from various units in the Rehoboth Inlier of Namibia and the Gordonia Terrain to the east. The provenance signature of the younger subpopulation implies that deposition of the Koeris Fm. occurred after continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. With regards to the base-metal deposits of the Aggeneys-Gamsberg district, petrographic and geochemical analysis of the Bushmanland Group Fe-Mn-rich rocks suggests that they can be subdivided into several types: (1) primary Fe-Mn-rich metasedimentary rocks; (2) magnetite-amphibole-rich Fe-Mn-rich rocks; (3) coticules; and (4) epigenetic Fe-Mn-rich rocks. Primary Fe-Mn-rich metasedimentary rocks occur throughout the western and central portions of the study area and appear to have been formed through the deposition of Fe-Mn-rich hydrogenous precipitates in areas of localized sediment starvation. However, as illustrated by the primary Fe-Mn-rich metasedimentary rocks of the Lemoenpoort prospect, a syn-diagenetic, hot (>250°C), metalliferous hydrothermal fluids infiltrated and altered these hydrogenous Fe-Mnrich metasedimentary rocks, resulting in the deposition of base-metal sulfides, formation of magnetite-amphibolite-rich Fe-Mn-rich rocks, as well as hydrothermal alteration of the siliciclastic wall rocks to form coticules. The spatial restriction of epigenetic Fe-Mn-rich rocks to shear zones, high Fe2O3 T (ca. 65 wt %), low ΣREE (ca. 13 ppm), presence of recrystallized quartz crystals, elevated concentration of Cu in some occurrences and general similarities with some hydrothermal iron/iron-oxide copper-gold (IOCG) deposits, suggests that the epigenetic Fe-Mn-rich rocks may have formed during prograde metamorphism. Low concentrations of SrO (0.5 ± 0.2 wt %), highly radiogenic Sr/ Sr ratios (0.7164 ± 0.0028), elevated δ S (27.3 ± 4.9 ‰) and δ O (7.7 ± 3.1 ‰) values in the barites, as compared to contemporaneous Mesoproterozoic seawater, suggests precipitation of stratiform and stratabound barite layers in the Bushmanland Group occurred through mixing of an evolved continental crustal source and contemporaneous seawater sulfate, 87 86 34 18 modified by bacterial sulfate reduction. Most importantly, δ O values suggest possible minimum temperatures of formation ranging from 18 <150°C for the Gamsberg deposit to >250°C for occurrences in the Aggeneys area. These obvious differences in temperature of formation are in good agreement with the Cu-rich, Ba-poor nature of the sulfide mineralization characteristic of the Aggeneys deposits versus the Cu-poor, Ba-rich character of the Gamsberg deposit. In conjunction with this, the isotopic and petrographic arguments favor a sub-seafloor replacement model for the stratabound barite occurrences of the Aggeneys deposits, while at Gamsberg, deposition at the sediment-water interface as a true sedimentary exhalite appears more acceptable. Data obtained in the present study, combined with the results of previous investigations can be used to develop a comprehensive model for the geological evolution of the Aggeneys Terrain and Namaqua Metamorphic Province. The tectono-sedimentary evolution of the Aggeneys Terrain and Namaqua Metamorphic Province is marked by two important tectonic events separated by an episode of tectonic quiescence. Extrusion and deposition of the metavolcano-sedimentary rocks of the Orange River Group at 1908 Ma marks the start of the Orange River Orogeny. vii Prior to emplacement of the Vioolsdrift Intrusive Suite, the Orange River Group appears to have undergone a period of folding and low-grade metamorphism [D1/M1] that was subsequently followed by emplacement of the Main Phase Vioolsdrift Intrusive Suite roughly dated at 1890 Ma. Rapidly following emplacement of these intrusions, the lower crustal rocks of the Richtersveld Subprovince underwent a second, higher, amphibolite-facies metamorphic event [M1B] from 1870-1840 Ma. This event may have resulted in lower crustal melting and emplacement of the Gladkop Suite into an unknown package of metasediments or metasedimentary rocks south of the present day Orange River at roughly 1820 Ma. The Gladkop Suite was subsequently subjected to high-grade metamorphism at 1800 Ma. The Orange River Orogeny was terminated by emplacement of the Late Phase Vioolsdrift Intrusive Suite at approximately 1765 Ma and later northward-directed thrusting. Following termination of the Orange River Orogeny, deposition of the Bushmanland Group began in a tectonically stable environment marked by punctuated periods of tectonic activity that lasted until emplacement of the Little Namaqualand Suite at 1190 Ma. The detrital zircon populations of the Pella Quartzite Fm. and Koeris Fm. support (a) regional correlation of these stratigraphic units throughout the study area, (b) confirms sediment derivation from various local source terrains and (c) suggests a maximum depositional age of 1650 Ma. Furthermore, new age constraints reveal initiation of the O’okiepian Episode (Namaquan Orogeny), characterized by regional-scale mid- to high-grade contact metamorphism, was synchronous with emplacement of the Little Namaqualand Suite and deposition of the upper Kouboom Subgroup. Furthermore, the detrital zircon populations for the Driekop Fm. (upper Kouboom Subgroup) contain a large population of 1190 Ma (i.e. O’okiepian-age) detrital cores, suggesting a renewed period of tectonic uplift. Analogously, age constraints for the Koeris Fm. indicate a maximum depositional age of 1130 Ma, as well as derivation from a number of local and exotic source terrains indicating that deposition of the Koeris Fm. must have occurred in response to continental collision between the Rehoboth Inlier-Kaapvaal Craton and the Namaqua Metamorphic Province. Furthermore, these new age constraints also constrain the timing of D2-D3 deformation to between 1130-1080 Ma and regional peak metamorphism to 1020- 1040 Ma. / Prof. N.J. Beukes Prof. J. Gutzmer

Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The Gamsberg Zn-Pb deposit is a metamorphosed and multiply deformed sediment-hosted base metal deposit in the central Namaqua Province of South Africa. The deposit is hosted by the Bushmanland Group, a late Palaeoproterozoic (2000-1600 Ma) supracrustal succession of quartzite, metapelitic schist and interbedded metavolcanic rocks. Mineralisation occurs within the central part of the Gams Formation, a heterogeneous sequence of metamorphosed metalliferous sediments and fine-grained organic-rich shales. The ore horizon is subdivided into a lower unit of metapelite-hosted ore, an intermediate layer of phosphorite-hosted ore, and an upper unit of banded garnet-apatite ore. The ore body is enveloped by unmineralised silicate-, carbonate- and oxide-facies metalliferous rocks, which originally represented mixtures of Fe-Mn-rich hydrothermal precipitates, authigenic carbonate, and variable concentrations of detrital material. Based on mineralogical and geochemical characteristics, the metalliferous host rocks are subdivided into iron formations, coticules, Fe-Mn silicates, impure marbles and barite/Ba-rich quartzite. Minerals of the Gams Formation mostly represent solid solution between the Fe and Mn end-members of garnet, pyroxene, pyroxenoid, amphibole, olivine, spinel and ilmenite. Calcium-rich rock types are a typical feature and characterized by the occurrence of manganoan calcite, clinopyroxene, andradite-rich garnet and titanite. A successive increase in the (Mn+Ca):Fe value of rocks and minerals is evident with increasing distance from the ore horizon. Amphibole is restricted to Fe-rich ore-bearing assemblages, whereas orthopyroxene, clinopyroxene, Fe-rich pyroxenoid and olivine are present in intermediate assemblages, and Mn-rich rhodonite and pyroxmangite in the most manganiferous assemblages. These variations are mimicked by an increase in the Mn:Fe value of coexisting garnet and ilmenite group minerals with increasing distance from ore. LA-ICP-MS analyses have been used to constrain the REE patterns of garnet and apatite. In the ore-body, these minerals display a positive Eu anomaly, which is interpreted to reflect a distinct hydrothermal signature. In contrast, garnet and apatite in unmineralised metalliferous rocks display nil or a negative Eu anomaly. Primary features of the Gams Formation, such as REE patterns, the banded nature of garnet-apatite ore, the presence of diagenetic apatite nodules, and the distribution of the redox-sensitive elements Ba and Mn have been used to constrain palaeo-environmental conditions. The results indicate that metapelitehosted ore has been deposited in a stratified ocean that was characterised by anoxic bottom waters and precipitation of Fe and Zn sulphides into organic matter-rich shales. These rocks were superceded by phosphorite-hosted ore, garnet-apatite ore and metalliferous host rocks that developed in a suboxic to oxic environment. The large size of the deposit, the internal lamination of the ores and the predominance of sphalerite and barite are consistent with a vent-distal setting and precipitation of the ore-forming constituents from dense and reduced hydrothermal fluids, which originated due to reactivation of dormant growth faults. Collectively, the geological evidence indicates that Gamsberg is bridging the gap betweenthe SEDEX and BHT classifications. The relationships demonstrate that differences between these two classes of sediment-hosted Zn-Pb deposits are predominantly related to environmental conditions within localised third order basins and not to fundamental differences in ore-forming processes. / AFRIKAANSE OPSOMMING: Die Gamsberg Zn-Pb afsetting is ‘n meerfasig vervormde en gemetamorfiseerde sedimentgesetelde onedel metaal afsetting in die sentrale Namakwa Provinsie van Suid Afrika. Die afsetting word geherberg deur die Boesmanland Groep, ‘n laat Paleoproterosoïse (2000 – 1600 Ma) bokors-opeenvolging van kwartsiet, metapelitiese skis en tussengelaagde metavulkaniese gesteente. Mineralisasie word gevind in the sentrale deel van die Gams Formasie. Die Gams Formasie is ‘n heterogene opeenvolging van gemetamorfiseerde metaalhoudende sediment en fynkorrelrige organiese skalie. Die erts horison word onderverdeel in ‘n onderste laag van metapeliet-gesetelde erts, n sentrale laag van fosforiet-gesetelde erts, en ‘n boonste laag van gebande granaat-apatiet erts. Die erts-liggaam word omhuls deur ongemineraliseerde silikaat-, karbonaat- en oksied-fasies metal-ryke rotse. Hierdie gesteentes word geinterpreteer as oorspronklike mengsels van Fe-Mn-ryke hidrotermale partikels, outigeniese karbonaat, en verskeie hoeveelhede detritale materiaal. Gebaseer op mineralogiese en geochemiese kenmerke word hierdie rotse onderverdeel in ysterformasies, „coticules“, Fe-Mn silikate, onsuiwer marmer en barite/Ba-ryke kwartsiet. Minerale van die Gams Formasie form meestal soliede oplossingsreekse tussen die Fe en Mn endlede van granaat, pirokseen, piroksenoid, amfibool, olivien, spinel en ilmeniet. Kalsium-ryke rots tipes is ‘n tipiese kenmerk van die Gams Formasie en word gekenmerk deur mangaan-ryke kalsiet, klinopirokseen, andradiet-ryke granaat en sfeen. Daar word ‘n stapsgewyse vergroting van die (Mn+Ca):Fe verhouding in gesteentes en minerale gevind met toeneemende afstand van die erts horison. Amfibool is beperk tot Fe-ryke ertsdraende gesteentes, ortopirokseen, klinopirokseen, Fe-ryke piroksenoid en olivien tot intermediêre gesteentes, en Mn-ryke rodoniet en piroksmangiet tot Mn-ryke gesteentes. Hierdie variasies gaan gepaard met vergroting van die Mn:Fe verhouding in granaat en ilmeniet-groep minerale met toeneemende afstand van die erts. LA-ICP-MS analises was gebruik om die skaars-aarde element patrone van granaat en apatiet te bepaal. In die erts-liggaam wys hierdie minerale ‘n positiewe Eu anomalie, wat geinterpreteerd word as ‘n hidrotermale kenmerk. In ongemineraliseerde gasheer gesteentes wys granaat en apatiet geen of ‘n negatiewe Eu anomalie. Primêre kenmerke van die Gams Formasie, soos skaars-aarde patrone, the gebande voorkoms van granaat-apatiet erts, die teenwoordigheid van diagenetiese apatiet knolle, en die verspreiding van die redox-sensitiewe elemente Ba en Mn, was gebruik om afleidings oor die paleo-omgewing te maak. Die resultate het gewys dat metapeliet-gesetelde erts afgeset was onder anoksiese bodem water deur presipitasie van Fe en Zn sulfiedes in organiese skalie. Hierdie erts gaan oor in fosforiet-gesetelde erts, granaat-apatiet erts en metaal-ryke gasheer gesteente wat in ‘n suboksiese tot oksiese omgewing ontstaan het. Die grootte van die afsetting, die interne gelaagdheid van die erts, asook die teenwoordigheid van sfaleriet en bariet dui op ‘n distale omgewing relatief tot die hidrotermale bron en presipitasie van die ertsuit digte en gereduseerde hidrotermale vloeistowwe, wat ontstaan het deur die heraktiveering van rustende groeiverskuiwings. Gesaamentlik bewys die geologiese kenmerke van Gamsberg dat gemetamorfiseerde SEDEX en Broken Hill-tipe mineralisasie binne die perke van ‘n enkele afsetting kan voorkom. Die geologiese verhoudings dui aan dat verskille tussen hierdie twee tipes van sedimentgesetelde afsettings meestal veroorsaak word deur omgewings-toestande binne in gelokaliseerde derde orde komme en nie deur fundamentele verskille in ertsvormende prosesse nie.