Department of Geosciences

Permanent URI for this community

http://hdl.handle.net/11070/3533

Browse

Now showing 1 - 20 of 28

Tektonik und Metamorphose im Grenzbereich Damara-Prädamara, südwestlich Windhoek (Südwestafrika)
(1973) Groote-Bidlingmaier, Michael
Petrography and geochemistry of the Gross Spitzkoppe Igneous Complex Central-Western Namibia
(1997) Frindt, Stephen
Late Quaternary southwestern African terrestrial-climate signals in the marine record of Walvis ridge
(2001) Stuut, Jan-Berend W.
Abstract taken from website http://www. library.uu.nl/digiarchief/dip/diss/2002-0503-091238/inhoud.htm
A taxonomic revision of the genus pentatrichia (asteraceae)
(2007) Klaassen, Esmerialda S.
Abstract provided by author
The Lithological and structural controls on mineralisation at Kombat mines, Otavi mountainland, Northern Namibia
(2009) Changara, Leonard; ;
Copper
(2009) Nujoma, Sam
Copper is the oldest industrial metal known to man and has contributed to the development of many civilizations in the world, including pre-colonial African communities in southern and central Africa, where copper metal was produced and traded on a wide scale centuries before the arrival of Europeans. Despite having produced 10.6 of world copper metal valued at 193 billion US dollars in the past 100 years, Namibia, Zambia and the Democratic Republic of Congo have functioned mainly as exporters of copper metal rather than as manufacturers of finished copper products. As a consequence, copper mining has not made a significant impact to the economic development of these countries despite the fact that copper has many varied industrial uses. Industrial plants that add value to the copper metal are required in order to enable Namibia, Zambia and the Democratic Republic of Congo to manufacture secondary and tertiary copper products, including cable wire for power transmission and generation, construction and telecommunication as well as electrical and electronic equipment
The source of uranium and vanadium at the Langer Heinrich and Klein Trekkopje uranium deposits-genesis and controlling factors for uranium mineralization, Western Namibia.
(2012) Iilende, Abraham
The Langer Heinrich and Klein Trekkopje U deposits are located within the Namib Desert in Central Namibia. Both deposits are hosted by calcretes developed within palaeo-channel systems of Tertiary age. The sources of both U and V in the two deposits and the reasons why the two deposits differ in terms grade and tonnage have remained unclear to many researchers. The study aimed to resolve these uncertainties. During the study, the geology of the area was reviewed and a number of research methods were employed. U and V concentrations and the mineralogy of various rocks in the catchment area were analyzed by ICP-MS, XRF and thin sections. Leachability of various rocks was studied through the analysis of mineralogy, texture, structures, etc. This study found that the Bloedkoppie granite, which is located in the catchment area for Langer Heinrich, contains about 5 – 15 ppm U and 5 – 20 ppm V. The Tinkas schist, which forms most of the bedrock in the catchment area for the Langer Heinrich deposit, contains 3 – 6 ppm U and 120 – 160 ppm V. The Bloedkoppie granite is considered to represent the source of U for the Langer Heinrich deposit. It is deeply weathered due to its relatively high proportion of ferromagnesian minerals, compared to average granites. The fluid which mobilized U and V from the Bloedkoppie granite also mobilized V from the Tinkas schist. In the case of Klein Trekkopje, the main source of U was the Klein Spitzkoppe granite, Gross Spitzkoppe granite and some Damaran leucogranites. V is considered to be derived from the Kuiseb schist, which contains about 100 – 160 ppm V. The Klein Spitzkoppe granite contains about 10 - 20 ppm U and about 1-3 ppm V whereas the Gross Spitzkoppe granite contains about 15 – 25 ppm U and 3 – 5 ppm V. The catchment area for Langer Heinrich had more V than that of Klein Trekkopje, and V was found to be a key factor in the precipitation of carnotite. The geomorphology around the Langer Heinrich deposit (Etusis and Schieferberge mountains) is more favourable for constriction and ponding of subsurface water unlike that of Klein Trekkopje, which lacks resistant rocks which would restrict the fluids. Oxidizing conditions were fully achieved at Langer Heinrich because there were less saline marine fogs and the subsurface water spent longer periods of time in ponds, resulting in lengthy interaction with air and seasonal rains. By contrast, at Klein Trekkopje, oxidizing conditions were regularly offset by the inflow of highly saline marine fogs and by the fact that poor constriction and ponding resulted in subsurface water moving faster downstream and having less time to interact with oxidizing atmospheric air and rain waters. As a result V4+ could not be effectively oxidized to V5+, which is a pre-requisite for the precipitation of carnotite. Controlling factors for U precipitation in calcretes are redefined in the context of Langer Heinrich and Klein Trekkopje U deposits. Multiple sources of V are proposed. Exploration for calcrete – hosted U deposits could therefore start with investigations of the catchment, by gaging the availability of U and V as well as the suitability of the geomorphology and palaeo-climate.
Hydrogeological investigation of the Naukluft mountains, southwest Namibia
(2014) Kambinda, Winnie N.
The Naukluft Mountains area is also referred to as the Naukluft Nappe Complex (NNC), that consist of northwest dipping carbonates and sandstones aged 750 Ma and form part of the Damara Super Group that has been thrust over the younger sedimentary rocks of the Nama Group, aged 550 Ma. In this study, three aquifers are characterized within the study area. First, is the Naukluft Karst Aquifer which is fractured and karstified, and partly underlies the surface run-off catchments of the Tsauchab and Tsondab ephemeral rivers; second is the Nama Aquifer, largely stratified aquifer with limited fractures to the east of the Naukluft Karst Aquifer and third, is the Namib Aquifer, which is a porous phreatic aquifer to the west and south of the Naukluft Karst Aquifer, confined to the alluvial formations of the Tsondab and Tsauchab ephemeral rivers. The Naukluft Karst Aquifer is a high rainfall and discharge area in terms of rainfall; however, in terms of recharge the volume of water available for groundwater recharge is low, due to high surface water discharge from the mountains. National average annual rainfall is 200 mm/a while the study area average is 170.36 mm/a based on the rainfall data collected from farmers during this study. Using the Chloride Mass Balance Method rainfall available for recharge is estimated to range from of 0.41 to 24.43 mm/a translating to 0.24 to 14.24% of received rainfall for the season of 2008/2009 calculated considering only wet deposition values for chloride. Places in the Naukluft Karst Aquifer area receive more rainfall and slightly higher recharge than calculated. Reconnaissance pumping tests were conducted in a well and boreholes at Leybank, Naukluft Park office, Zais and Solitaire to estimate transmissivity. Results indicate that transmissivity ranges from 4.1 to 23.1 m2/d. storage coefficient was not estimated due to lack of piezometers during test pumping. The main groundwater flow is oriented along surface water drainages to the northwest and southwest, with minor flow to the northeast. Flow is controlled by elevation above sea level and structural geology of the Naukluft Karst Aquifer. A west-east trending groundwater divide is identified separating two distinct groundwater flows.
Detektion eines mesozoischen Gangschwarmes in NW Namibia und rekonstruktion regionaler spannungszustände während der Südatlantiköffnung; XXX
(2014) Hahne, Kai
Gangschwärme nehmen eine bedeutende Stellung im Verständnis zur kontinentalen Fragmentierung ein. Einerseits markieren sie das Paläo-Spannungsfeld und helfen bei der Rekonstruktion der strukturellen Entwicklung der gedehnten Lithosphäre, andererseits gibt ihre petrologische Beschaffenheit Aufschlußüber die Entstehung des Magmas, Aufstieg und Platznahme und schließlich erlaubt ihre Altersbestimmung die Rekonstruktion einer chronologischen Reihenfolge magmatischer und struktureller Ereignisse. Das Arbeitsgebiet im namibianischen Henties Bay-Outjo Dike swarm (HOD) war zur Zeit der Unterkreide einem Rifting mit intensiver Platznahme von überwiegend mafischen Gängen unterworfen. Geochemische Signaturen weisen die Gänge als erodierte Förderkanäle der Etendeka Plateaubasalte aus.Durch den Einsatz von hochauflösenden Aeromagnetik- und Satellitendaten war es möglich, die Geometrie des Gangschwarmes erstmals detailliert synoptisch zu erfassen. V! iele zu den Schichten des Grundgebirges foliationsparallel verlaufende magnetische Anomalien können unaufgeschlossenen kretazischen Intrusionen zugeordnet werden. Bei der nach Norden propagierenden Südatlantiköffnung spielte die unterschiedliche strukturelle Vorzeichnung durch die neoproterozoischen Faltengürtel sowie Lithologie und Spannungsfeld des Angola Kratons eine bedeutende Rolle. Im küstennahen zentralen Bereich war dank der Vorzeichnung des Nordost streichenden Damara-Faltengürtels ein Rifting in Nordwest-Südost-Richtung dominierend, bis das Angola Kraton ein weiteres Fortscheiten nach Nordosten hemmte und die Vorzeichnung des Nordwest streichenden Kaoko-Faltengürtels an der Westgrenze den weiteren Riftverlauf und die letztendlich erfolgreiche Öffnung des Südatlantiks bestimmte. Aus diesem Grund kann das Gebiet des HOD als ein failed rift betrachtet werden. Die Entwicklung des Spannungsfeldes im HOD kann folgendermaß! en skizziert werden: 1. Platznahme von Gän! gen bei gleichzeitig hoher Dehnungsrate und hohem Magmenfluß. 2. Platznahme von Zentralvulkanen entlang reaktivierter paläozoischer Lineamente bei Abnahme der Dehnungsrate und fortbestehendem hohen Magmenfluß. 3. Abnahme/Versiegen des Magmenflusses und neotektonische Bewegungen führen zur Bildung von Halbgräben. Dike swarms play a fundamental role in understanding continental breakup. On the one hand they represent strain markers of the paleo-deformation field and help to reconstruct the structural evolution of the rifted lithosphere. On the other hand their magmatic infill contains information about the conditions of magma generation, ascent and emplacement. Finally, dating of dikes allows reconstructing a chronological order of magmatic and structural events. The study area of the Namibian Henties Bay-Outjo Dike swarm (HOD) underwent tectonic extension in the Lower Cretaceous associated with the widespread emplacement of predominantly mafic dikes and intrusive ring complexes representing the remnants of volcanic centres. Geochemical signatures of the dikes prove them to be the feeder structures of the Etendeka Plateau Basalts.The application of recent high resolution aeromagnetic surveys and satellite imaging revealed the dike swarm's extent and geometry for the first time.! The distribution and geometry of the dikes shown in the aeromagnetics reflect the propagation of the South Atlantic opening from south to north by their relative-ages. Northwest-southeast-directed rifting was dominant in the central coastal area, due to the structural control of the northeast striking basement structures until further propagation was hampered by the Angola Craton. Subsequently the structural control of the coast-parallel Kaoko Belt became dominant and determined the successful opening of the South Atlantic. Hence, the area of the HOD can be considered as a failed rift. The stress field evolution within the HOD can be outlined as follows: 1. Intrusion of dikes when extension rates as well as magma supply were high. 2. Intrusion of volcanic ring complexes along reactivated Panafrican lineaments when extension rates decreased and magma supply remained high. 3. Neotectonic movements create half-grabens after the termination of magmatism
Estimation of hydraulic parameters of the shallow, perched Ohangwena aquifer (KOH-0) and determination of its interaction with the deeper regional Ohangwena aquifer (KOH-1), Ohangwena region, Namibia
(University of Namibia, 2015) Ananias, Asteria L.
The Ohangwena Multi-Layered Aquifer (KOH) is one of the six Aquifer Systems found in the Cuvelai-Etosha Basin, Namibia. The aquifer system is multi layered, consisting of a shallow perched Ohangwena 0 aquifer (KOH-0), semi-confined Ohangwena I aquifer (KOH-1), and confined Ohangwena II aquifer (KOH-2). Currently, a large portion of the population in the study area rely on water from KOH-0 by means of hand-dug wells. The occurrence and potential of this perched aquifer is not fully understood. This fact motivates the characterization of the aquifer properties, to enable more thoughtful management of the resource. The study evaluates the hydraulic properties of KOH-0 and determine its connection to KOH-1. The methods used in this study included soil sampling, analysis for grain size distribution and review of existing borehole lithology logs. Examination of existing borehole lithology logs indicate that the perched KOH-0 is contained in the Kalahari sand layer from the surface up to 30 m depths, underlain by a multi-layered semi-confining layer with alternating silty sands, clays and calcrete. Based on the documented textures and standard hydraulic conductivity tables, KOH-0 has hydraulic conductivities from 1.20E-04 to 2.83E-04 m/sec and the multi-layered aquitard below, from 3.17E-9 to 1.90E-4 m/sec. Grain size analyses of the aquifer material show that the material consist of fine to course grained sand indicating a hydraulic conductivity that spans between 10-6 and 10-4 m/sec, a porosity between 0.49 and 16.25% and a coefficient of uniformity between 0.369 and 25. Potentially an amount between 2.01E-03 and 5.02E-03 m3/day, may flow from the perched KOH-0 into the unconfined KOH-1 per square meter of aquitard. The estimated amount of horizontal flow through KOH-1 is much higher than this, ranging relatively between 690 m3/day (at minimum hydraulic gradient) and 6700 m3/day (maximum hydraulic gradient). The results have shown that KOH-0 is hydraulically connected to KOH-1, especially in the northern part of the study area with higher hydraulic gradients where most hand dug wells occur and groundwater is younger. This will aid future groundwater development and utilization in the study area.
Characterization of quartz in some potential high purity quartz deposits in the Damara orogenic belt
(University of Namibia, 2016) Siseho, Kamwi R.
This research project was aimed at characterizing quartz from selected potential High Purity Quartz (HPQ) deposits in terms of trace element associations, associated trace element concentrations, and growth zones. Six quartz rock samples were collected from three different localities, with two samples collected from each locality. Concentrations of Na, K, Li, Al, Ca, Fe, Ti, B and P were analysed in situ by LA-ICP-MS. This analysis was aimed at finding out whether the total concentrations of these trace elements do not exceed 50 μg g-1 as required by the HPQ definition. The Lowest total concentrations obtained from analysed samples were found to be much higher than the required minimum of less than 50 μg g-1and are given as follows: sample DB2 from the farm Doornboom 316 yielded 2,144.6 μg g-1, sample ALT2 from the farm Alt-Seeis 133 yielded 726.3 μg g-1 and sample MA1 from SP14 pegmatite intrusion in the Cape cross – Uis Pegmatite belt yielded 1,753.5 μg g-1. Analytical results obtained from LA-ICP-MS showed very low Fe concentrations in all three deposits with all samples giving an average of <2μg g-1 and is the only trace element that met HPQ definition requirement of <3 μg g-1 Fe content. All three deposits showed very high average calcium concentration values varying between 450 and 750 μg g-1 and these high concentrations are likely to be associated with the chemistry of the fluids from which the hydrothermal quartz crystallized. Aluminium and alkali metals (Li, Na and K) concentrations were relatively high in all the deposits with fewer exceptions. Average values of lithium were noted as being between 170 and 230 μg g-1, those of sodium as being between 70 and 1600 μg g-1, and those of potassium as being between 65 and 120 μg g-1, while aluminium average values were found to be between 150 and 660 μg g-1. Exceptions were exhibited by sample ALT 2 from the hydrothermal vein deposit at the farm Alt Seeis 133, in which all the alkali metals and aluminium average values were found to be less than 63 μg g-1. Titanium content in all samples was found to be relatively low (averaging between 20 and 31 μg g-1). All the samples from deposits under this study do not meet the requirements of the HPQ definition and are thus not HPQ deposits. However a beneficiation study on these deposits is recommended to establish possible industrial applications that may be feasible. Scanning Electron Microscopy - Cathodoluminescence (SEM-CL) images of quartz grains were obtained from polished carbon coated samples. SEM-CL imaging was aimed at revealing replacements, fluid driven overprints and different quartz generations. The transformation of primary to secondary quartz through replacement was very limited in some samples and absent in others. This implies that metamorphic conditions did not have a major impact if any at all on the chemistry of trace elements in quartz. Statistical interpretation of analytical results from SP14 pegmatite intrusions and those from Doornboom indicate significant compositional similarities.
The geology, petrography, geochemistry and uranium ore mineralogy of the Namibplaas sheeted leucogranites, Damaran orogen, Namibia
(University of Namibia, 2017) Shilongo, Emmanuel
This research study focused on the previously unknown uranium mineralisation hosted in garnet and magnetite bearing sheeted leucogranites (SLG's) I alaskites at Namibplaas. The various SLG's were distinguished and characterised by means of field, petrographic and geochemical studies into B, C and D-types based on the classification scheme ofNex and Kinnaird (1995) in the Goanikontes area. In addition, the stratigraphic positions of the SLG' s were established. The research techniques applied in the study included review of historical data, ground mapping, diamond drill core logging and sample preparation, thin section preparation, geochemical analyses and uranium ore mineralogical investigation. At Namibplaas, the Damaran sequence is most complete; the B-types are least abundant and are localised to the Kuiseb Formation, the C-types are most abundant and intrude the whole stratigraphic sequence. The D-types are emplaced within the Karibib, Chuos, Rossing and Khan Formations and at the Khan-Rossing-Chuos-Karibib Formation boundaries. The B and C- types are post D1- D2 but pre D3 deformation and are barren in uranium. D-types are post D1- D2- D3 deformation, these are uranium enriched and cross-cut the B and C-types making them the youngest of the intrusives. The sheeted leucogranites at both Goanik:ontes and at N arnibplaas have undergone similar structural events. But there is however a difference in accessory mineralogy and U & Th geochemistry. The D-types at Namibplaas bear garnet and magnetite. The occurrence of these accessory minerals can be explained as a result of host stratigraphic - assimilation. Individual sheeted leucogranite types are discemable from each other by a number of major, trace and rare earth element discrimination plots. Uranium and thorium and U/Th ratio distinguishes and characterises the Namibplaas sheeted leucogranites very well. The D-type contain the highest concentrations of uranium (22.5ppm to 1020ppm) with a U/Th ratio > 1. The C-type sheeted leucogranites show the highest thorium concentrations (10ppm to 301ppm) with a U/Th ratio < 1. The B-type sheeted leucogranites have lower concentrations of uranium (3ppm to 9ppm) and thorium (Sppm to 17.5ppm) The late- to post- orogenic conformable and transgressive sheeted leucogranitic bodies range in composition from tonalite to syenogranite. The Namibplaas leucogranites are peraluminous to metaluminous indicating a highly evolved crustal source most probably the Abbabis basement gneisses. Partial melting of the Abbabis basement gneisses which was induced by M2 resulted in the B and C-type leucogranites. Continued partial melting of the Abbabis basement gneisses during M3 resulted into the more uranium enriched D-type leucogranites. QEMSCAN investigation shows that uranium phases present in the D-type sheeted leucogranites are U-oxides as uraninite, U-Ti-oxides as betafite and Th(U)-silicates as uranothorite. The Namibplaas uranium propect is typically a low grade high tonnage deposit with a resource in the measured category; 25 Mt at an average grade of 206 ppm U30s at a cut-off grade of 160 ppm. The project may not be economically viable under the current global uranium price; however, the project may become viable if the global uranium price doubles in the near future. Further work which can be carried out at Namibplaas may include age dating of the leucogranites in order to establish the sequence of formation of the various leucogranites as well as fluid inclusion studies to determine the pressure and temperature regime, types and compositions of the ore forming fluids, as well as more detailed structural studies to better constrain the various deformation phases of the Damaran Orogen in relation to uranium mineralisation.
The impact of small-scale mining activities on the environment: Examples from Uis, Xoboxobos, Neu Schwaben and Otjinene
(University of Namibia, 2017) Chirchir, Isabella
This study explored the impact of small-scale mining activities on the environment in two regions in Namibia: Erongo (examples: Uis, Neu Schwaben, Xoboxobos) and Omaheke (example: Otjinene). Limited research is done on the activities of small-scale mining in Namibia which results in unavailability of data. Although recent studies reveal that about 5 000 to 10 000 Namibians work as small-scale miners, information about mining activities in Namibia remain a rare commodity. Small-scale miners mostly concentrate on commodities that are easily accessible and do not use mechanised equipment, i.e. tin, tantalum, calcrete and semi-precious stones (tourmaline, aquamarine, topaz, amethyst, garnet, rose and smoky quartz). This study was done through field observations, groundwater analysis and interviews/ questionnaires in order to determine the impact of small-scale mining activities on the environment. Groundwater was analysed for pH, oxidation-reduction-potential and conductivity to evaluate the quality of water. In addition, the study determined the possible environmental impact of small-scale mining activities on the lithosphere, hydrosphere and atmosphere. Data from GROWAS Database was used to supplement the primary data. On the atmosphere, the dust generated by small-scale mining activities was found to be very minimal and thus, only affecting the miners through dust inhalation. This study did not find any evidence of identified impact on the hydrosphere (groundwater) close to the mining sites. The groundwater quality in Neu Schwaben and Uis were excellent based on the analysis done in the field on two boreholes close to the mining sites. The groundwater quality in Neu Schwaben and Otjinene were excellent, but unacceptable for Uis area based on the results from GROWAS database. No boreholes were found in Xoboxobos area. The impact of small scale mining activities at the four sites with regard to the lithosphere was land degradation. Neu Schwaben was the most affected amongst all the four sites observed. Small-scale miners indicated that SSM activities have a positive socio-economic impact through poverty alleviation and employment creation. Although the activities of small-scale miners have a positive impact on the lives of the miners and their families, the same have a negative impact on the environment. The study recommends the government to take an active role in providing mining equipment, training on mining safety, education of small-scale miners on the environment and land rehabilitation. The study further recommends awareness campaigns for small-scale miners in order to ensure that the impact on the environment remains minimal.
A study of isotopic composition of xylem water of woody vegetation and groundwater along a precipitation gradient in Namibia
(University of Namibia, 2017) Kanyama, Cristofina M.
An understanding of the water used by vegetation in water limited environment is critical to fully understand water relations of natural areas with vegetation. Such information can be integrated in water management plans to estimate the influence of groundwater abstraction on the vegetation. Trees and shrubs are able to access water from: the upper unsaturated soil profile, the capillary zone of a groundwater store, from nearby streams and rivers. Previous studies have proven that uptake of water by roots is not associated with isotope fractionation. Stable isotope ratios of oxygen and hydrogen were analyzed in groundwater, surface water and plant xylem water. Groundwater samples from the north east part of the country (Enyana and Fair constantia) were most depleted, while samples from the southern part (Guruchas) were enriched. A very weak negative correlation (R2=0.07), statistically insignificant (P>0.05) relationship has been noted between δ18O values of precipitation and altitude. The estimated depletion rate was 1.3‰ δ18O per km. The correlation between distance from the coast and δ18O composition of precipitation was negatively weak (R2=0.29) and statistically significant (P<0.05) with an estimated depletion rate of 0.31 ‰ per 100 km inland. The correlation between longitude and δ18O composition of precipitation was very weak (R2=0.016) and statistically insignificant (P>0.05) at roughly 0.09‰ δ18O depletion per degree. A strong negative correlation (R2=0.64) existed between δ18O of precipitation and latitude and it was statistically insignificant (P>0.005). The observed high variability in δ18O and δ2H values of groundwater at different sampling sites was attributed mainly to continental, elevation and amount effect. Both groundwater and xylem water samples plotted below the GMWL, however plant xylem were more depleted in comparison to groundwater. Throughout all the sampling sites there was a considerable variation in average isotope ratio of xylem water of different species examined, but there were still noticeable patterns regarding their main water source. The results displayed that P. juliflora, A. hebeclada and V. erioloba relied mainly on soil water for transpiration. S. mellifera mostly utilized a mixture of groundwater and soil water while B. albitrunca, C. mopane, C. imberbe and T. sericea and R. trichotomum predominantly utilized groundwater. The water uptake pattern is highly attributed to the rooting morphology. These vegetation uptake groundwater and soil water in a hierarchical manner at different depths to avoid competition between species.
Groundwater recharge of perched aquifers in the Cuvelai-Etosha basin, Namibia
(University of Namibia, 2018) Hamutoko, Josefina Tulimevava
The United Nation predicted that by 2025, 1.8 billion people will be living in countries with absolute water scarcity and two-thirds of the world population could be under stress condition. In semi-arid regions, most communities depend on groundwater as the source of drinking water and thus with changes in global climatic conditions and increase in population, groundwater resources are facing challenges of both over-exploitation and contamination. Therefore, there is an urgent need to improve the understanding of existing groundwater resources in terms of aquifer distributions and interactions and process that control the groundwater dynamics, recharge and chemistry groundwater for an effective strategy to reduce the pressure on the hydrologic system. The main aim of this PhD is to contribute to knowledge about shallow groundwater in semi-arid environments by estimating groundwater recharge of perched aquifers in the Cuvelai-Etosha Basin (CEB). Four specific objectives were examined in this study; first, the study characterizes the groundwater chemistry and isotopic composition of oxygen (δ18O) and hydrogen (δ2H) in order to understand mechanisms of groundwater dynamics and quality of groundwater in perched aquifers, secondly, it analyses and understand the spatial and temporal variations of hydrochemical data and isotopic compositions of hand-dug wells in the CEB, with particular focus on water origin and recharge processes, thirdly, the study evaluates the relationship between the shallow (perched) aquifer and the deeper seated aquifers and finally develops a conceptual model for the perched aquifers. Methods employed in this research are based on isotopic and hydrochemical data to understand groundwater recharge mechanisms. Integrated isotopic and hydrochemical tracers along with standard hydrological data are used to understand complex dry land hydrological processes on different spatial and temporal scales. Different spatial and temporal scales are particularly important for arid environments due to high heterogeneity that are associated with these environments. Therefore in this study, water samples were collected from rain collectors, hand-dug wells and boreholes and analysed for major ions and stable isotopes (18O and 2H) for three years (2014-2017) in a total of 12 sampling campaigns. Chemical analyses were performed at the Analytical Laboratory Services in Windhoek, Namibia and at the hydrochemistry laboratory of BGR in Hanover, Germany using Titration, Ion Chromatography and ICP-OES. The reliability of the analyses was checked by an ion charge balance error on all samples. Stable isotopes were measured at the University of Namibia (UNAM) and BGR laboratories using an off-axis integrated cavity output spectroscope (OA-ICOS, Los Gatos DLT-100) and a cavity ring down spectrometer (CRDS, model L2120-i, Picarro Inc.) respectively. Results show that groundwater chemistry of perched aquifers is controlled mainly by strong evaporation, dissolution of carbonate minerals (calcite and dolomite) and evaporitic minerals (gypsum and halite) and silicate weathering and cation exchange. Stable isotope composition suggests that deep groundwater is recharged by high intensity/large rainfall events, whereas the shallow wells can be recharged by less intense/small rainfall events. Water in deep wells reflect mixture of water influenced by evaporation during or before infiltration and water that infiltrated through fast preferential pathways whereas shallow wells are strongly influenced by evaporation. The mean parent isotopic composition for shallow wells in the ephemeral river is -7.8 for δ18O and -51.8 for δ2H, for deep wells in the pans and depressions is -8.7 and -58.2 for δ18O and δ2H as well as - 8.6 and -57.5 for δ18O and δ2H for wells in Omusati region. Hydrochemical and isotopic data reflect spatial variability between samples from Omusati and Ohangwena regions. The spatial heterogeneity as shown by TDS can be attributed to lithological, climatic and anthropogenic factors. Furthermore, temporal variations indicate the timing of the groundwater recharge. Results also imply interaction between perched aquifer and regional aquifer in the pans and depressions while in the ephemeral river no relation could be established. High recharge rates are estimated for the pans and depressions (7.3 % to 25.5%) in comparison to the ephemeral river (7.9% to 17.8%). Therefore, it is recommended that groundwater management practices should be designed taking into account differences in perched aquifer characteristics. For example designing abstraction infrastructures which include treatment for natural contaminants i.e. fluoride and TDS. On the other hand contaminants from anthropogenic sources in the wells can be reduced or prevented by introducing protection zones. Education on basic water usage and protection will also be of an advantage. Furthermore, it could be shown that it is indeed essential to unravel the hydrogeological complexities of heterogeneous perched aquifers using isotopic and hydrochemical tracers at different spatial and temporal scales and thus more research is needed in this regard.
Well log petrophysics and re-interpretation of the exploration target intervals in the southern Walvis basin
(University of Namibia, 2018) Domingos, Keron Mwatungange
The Walvis Basin is situated in the eastern Atlantic margin south of the Walvis Ridge offshore Namibia. The Basin is underexplored with only 8 exploration wells drilled in the basin to date. The basin and the entire offshore Namibia at large are extensively covered by 2D and 3D surveys, and despite these comprehensive activities, no commercial discovery of hydrocarbons has been made to date. Some of the reasons the wells failed discovering economic quantities of recoverable hydrocarbons include lack of one or two petroleum system elements and/or processes; with the absence of reservoir or charge being the more common reasons of failure. This project included the analysis of three well log data (Wingat-1, Murombe-1 and 2213/06-1 well) with focus on reservoir unit’s prognoses from seismic profile and comparing them to those of volcanics. Characterization and differentiation of turbidite reservoir units from volcanic intervals involved observing actual petrophysical characteristics and relating those characteristic to seismic reflection amplitudes. Interpretation and preconditioning of well data was performed in Interactive Petrophysics (IP) using standard petrophysical property equations. These properties include neutron-density, resistivity, γ-ray and sonic logs. Thereafter, acoustic impedances were calculated of those volcanic and sandstone unit that have been penetrated by the respective wells at the predicted reservoir depths. The results indicate that volcanic units of the Murombe-1 prospect depicted petrophysical properties similar to those of turbidites sandstones (e.g. the Murombe-1 Baobab sandstones and the Wingat-1 Cenomanian sandstones). In addition, integration of well log with seismic profiles revealed that the volcanics are lava flows with intercalated sediments. The lava flows deposited as a stratified sequence onlappping against an eastern high and herewith their seismic expression is similar to that of a sedimentary succession. Despite the challenges, the basin at large is deemed to be prospective for hydrocarbons with both, mature source rocks and good reservoirs being present.
The geochemistry and geochronology of the barby formation in the sinclair area, Southern Namibia
(University of Namibia, 2018) Malobela, Theresia R.
Volcanic and sedimentary rocks of the Sinclair Supergroup occur in the Konkiep Terrane of Southern Namibia. Three volcanic and sedimentary cycles are recognised. The Barby Formation belongs to the second cycle which consists of the Kunjas. Formation, Barby Formation and the Guperas Formation. In this work, the volcanic rocks of the Barby Formation, a key unit in the Sinclair area are described and dated. The coeval Spes Bona Syenite and the Tiras Granite are also described and dated. The rock types in the Barby Formation are rhyolites, basaltic trachyandesites, trachybasalts and trachydacites as well as volcanoclastic rocks. The rocks are largely undeformed and partly altered by deuteric processes and also mildly metamorphosed. Based on geochemistry of the rock samples and previous work, the bulk of rock types are calcalkaline although some alkaline rocks are present. U-Pb dating and Lu-Hf isotopic microbeam analyses were made on zircon and baddeleyite grains from four samples using cathodoluminescent images. A Barby rhomb porphyry sample gives an U-Pb baddeleyite age of 1217 ±2 Ma and a Barby felsic tuff has an 207Pb/206Pb zircon age of 1214 ±5 Ma. The Spes Bona Syenite which intrudes the Barby formation has a U-Pb baddeleyite age of 1217 ±3 Ma and an indistinguishable Rb-Sr biotite isochron age of 1238 ±20 Ma, showing that there was no regional metamorphic event. Subduction zone assemblages are generally made of high potassium basalts or calc-alkaline association. The Barby Formation records such assemblages. The Barby Formation reflects a subduction event which took place during the assembly of the Rodinia supercontinent. It is slightly younger at 1204 ±9 Ma and reflects the end of subduction-related volcanism due to the collision of Namaqua terranes with the Konkiep Terrane. The Spes Bona syenite and the Barby units have Lu-Hf crustal residence ages between 1682 and 1873 Ma suggesting the two units probably formed from a mixture of juvenile and older crustal material.
The influence of groundwater management strategies on groundwater levels of Namibian savannah aquifers
(University of Namibia, 2019) Nuunyango, Ester Mwadhina Ndahafa.
Namibia has been known as water scarce, attributing mostly to its geographic location and primarily because of the limited surface water as well as the high potential evaporation rates beyond 2000 mm/year. Groundwater therefore quickly becomes crucial, most of which is located in aquifers in the savannah biome which covers a large part of the country. This is also where most industrialization as well as most farming is practiced. It is however unknown how these savannah aquifers are managed on a local scale and how the management strategies influence the long term groundwater levels of the aquifers. To understand these strategies, three research sites along a rainfall gradient, namely Tsumeb area, Waterberg and Kuzikus area were studied. Through means of a self-developed questionnaire tailored for the government officials and farmers, five (5) interviews were conducted with government officials at DWAF. Across all three research sites a total of seventeen (17) farmers were interviewed. For the scientific groundwater management strategy, the sustainable yield was calculated using the catchment area and the recharge of the area. The short-term volume available was calculated for each research site using the formula Volbal = G*Sy (ϕave - ϕmin). The quantitative data from these four strategies were modeled using the Processing MODFLOW modelling software. The results show that the government strategy employed makes use of the Water Act no 54 of 1956. In comparison with the regulatory guidelines such as carrying capacity, many farmers abstract greater volumes per Small and Large livestock unit per hectare. However they have a similar influence on the groundwater levels over time when compared to the government policy guided strategy. The influence on groundwater levels by the farmer and policy guided strategies are well within the scientific sustainable yield strategy.
Age dating of groundwater in perched aquifers Okongo area, Ohangwena region
(University of Namibia, 2019) Masule, Nicco Libuku
Knowledge of groundwater age / residence time in Okongo perched aquifer is important in understanding key issues in the evolution of groundwater, recharge rates, recharge mechanisms, resource renewability, flow rate and distribution of recharge areas. The build-up in the atmosphere of trace gases such as sulfur hexafluoride (SF6) and tritium (3H) from over a centenary ago offers a convenient way of dating groundwater up to the age of 60 years. These gases are well mixed in the atmosphere; therefore, their input functions help to provide information about groundwater age, distribution and recharge patterns. In this study, sulfur hexafluoride and tritium were used as an age dating tracer for shallow groundwater. The focus of the study was to understand how age dating of groundwater in a perched aquifer system can help to determine recharge dynamics, e.g. recharge rates, processes, and vulnerability of these aquifers to pollution. The study consequently contributes to the knowledge on shallow groundwater in respect to the effectiveness of age dating methods to determine age / residence time of groundwater in perched aquifers. The study’s objective was to determine the residence time, investigate the distribution of recharge and examine the origins of recharge to the perched aquifer using sulfur hexafluoride, tritium and hydrochemistry, stable isotopes (2H and 18O) methods. A total number of 26 groundwater samples were collected during two separate sampling seasons / campaigns namely in October 2016 (for tritium and stable isotopes testing) and April 2017 (sulfur hexafluoride, hydro-chemistry and stable isotope). Samples were then grouped into sub-sets of six samples (18O and 2H) and five sample sets (SF6, 3H) by method of analysis and by the six (6) sampling sites namely Omboloka 1 and 2, Ohameva, Okamanya, Oshanashiwa and Epumbalondjaba. The results on concentration of SF6 in the groundwater samples indicate that recharge to the perched aquifer happened in 2000 for Omboloka 2, with a groundwater age of 17 years; Ohameva in 2010 with an age of 7 years; Okamanya in 2012 with an age of 5 years; and Omboloka 1 and Oshanashiwa in 2016 with an age of 1 year. Epumbalondjaba borehole was not sampled during the sampling campaign due to the site being flooded. Applying a conservative mixing ratio model, the samples were observed to have a higher proportion of young water compared to old water. This proves that the groundwater in the perched aquifer is young with a short residence time. Furthermore, the tritium method used to calculate theoretic/hypothetic activities suggests that groundwaterat Ohameva, Okamanya, Omboloka 1 and Oshanashiwa, is sub-modern. While results for Epumbalondjaba and Omboloka 2 portray a mix of both sub-modern and modern water. The ionic composition of groundwater in the perched aquifer presents three groups of water types characterised by mixed zone water, Na+-K+-HCO3 and Ca2+-Mg2+-HCO3. The perched aquifer system is dominated by the Ca2+-Mg2+-HCO3 water type which is a result of the dissolution of calcrete and the formation of carbonate-rich rocks derived from recent recharge with short residence times. Stable isotopes show that groundwater in perched aquifer systems is enriched in heavy isotopes and has been subjected to evaporation, which is caused by the prevailing climatic and hydrological conditions in the area. This shows that groundwater recharge to the perched aquifer originate from the local catchment systems. Therefore, it is recommended that thetrace gases (sulfur hexafluoride and tritium) methods should be applied to a wide range of groundwater in the perched aquifers of the Okongo area in order to understand recharge areas better. It is necessary to further investigate the groundwater chemistry and isotopic composition of perched groundwater aquifer in more detail. It is further recommended that a long-term monitoring programme consisting of sampling stations for water levels, water quality and stable isotopes is established.
Geological mapping, petrological characterisation and geochemistry of rocks in the Aus area, Southern Namibia: Implications for potential Copper mineralization
(University of Namibia, 2020) Mutongolume, Claudia
The study area is located in the southern part of Namibia within the Aus Domain which forms part of the Mesoproterozoic Namaqua Sector of the Namaqua-Natal Metamorphic Province. The sector hosts some significant base metal sulphide deposits that have been mined for the past century. In this study, detailed field mapping, petrography, geochemistry and U-Pb zircon dating were conducted to evaluate the chemical characteristics and tectonic setting of the area with the intent to assess the feasibility and potential of known copper occurrences around Aus area. The Garub Group represents the oldest rocks in the area and comprises marble, calc-silicates, metapelites, garnet biotite quartz gneisses, amphibolites, mafic granulites and serpentinites, which have been intruded by several, variably deformed granites. The Aus, Tsirub and Kubub orthogneisses are the main intrusives in the area. However, field mapping identified a highly fractured and metasomatized K-feldspar plagioclase epidote rock which requires further investigation. Petrographic studies confirm the compositional and deformational variability observed in the field. Geochemistry reveals that all granitoids within the study area are acidic, strongly peraluminous and products of shoshonitic and high-K calcalkaline magma derived from an A-type source. The A-type granites formed as a result of crustal contamination during the continental extensional phase and have been subjected to compressional deformation. Chondrite-normalised spider diagrams show negative Ta, Nb, P and Ti anomalies, with enrichments in Th and LREE, which suggest that the rocks are derived from an arc environment. Plots of K2O vs SiO2 show a considerably greater degree of scatter, which may be attributed to the effects of crustal contamination. Three geotectonic settings are established, i. e. the syn-collisional-Granite (syn-COLG), Volcanic Arc Granites (VAG) and Within Plate Granites (WPG). These inconsistent plots of samples may be attributed to hydrothermal alteration and/or sharing of varying degrees of fractionation within multiple flows, and support a collision of crustal fragments model. Granitoid plutonism for Tsirub augen gneiss and Aus granite gneiss occurred at 1110 ± 7 Ma and 1085 ± 36 Ma respectively. Several granites, which could be responsible for hydrothermal activity, quartz veins, fault structures and occurrence of malachite may bear evidence for copper mineralization in the study area.

Browse

Browsing Department of Geosciences by Issue Date

Results Per Page

Sort Options