It is well known that the release of long-lived radionuclides to the water path is probably the most relevant radiological risk originating from an underground repository. Transuranic elements (ie. all elements with an atomic number greater than 92 (U)) do not have any non-radioactive isotopes and are very rare in natural materials. The long term geochemical behaviour of these elements must thus be derived from chemical analogues such as the rare earth elements (REE), Th and U. Steenkampskraal monazite mine, situated 350 km north of Cape Town, has been found to be an excellent locality for the study of these elements, due to the high concentration of these elements in the ore as well as the ideal geology, which consists of low permeability rocks with groundwater flow governed by fractures. The ore body consists of a monazite [(REE, Th, U)P04], apatite [Ca₃P0₄)₂], chalcopyrite [CuFeS] and magnetite [FeP₄] veindeposit. Water was sampled from six boreholes in the vicinity of the mine and five wi.ndpumps on the surrounding farm Nabeep and Brandewynskraal. Surface water samples were taken from the slimes dam, an ephemeral stream on the western side of the mine, as well as from the surface of a road shortly after rain, below the tailings. Four water samples were taken from within the underground mine workings (Mainshaft, Main shaft extension, Sump on level 3 and Inclined shaft). Colloids were sampled from three of the boreholes and a precipitate was taken from the surface of the main shaft water. Soils were sampled along two transects away from the mine on the eastern and western side of the ore body. Due to the topography of the area, surface contamination could only occur on these two sides. Stable isotopes of oxygen (8 180) and hydrogen ((8 180) indicated the presence of two distinct groups of waters within the vicinity of the mine. One group is composed of unevaporated waters and includes all borehole sand the water sampled in the inclined shaft. The water moving through the inclined shaft is in contact with the ground water. A second group of highly evaporated waters was present in the slin1es dam samples as well as the underground water samples not directly in contact with groundwater. Groundwater contamination by REE-bearing phosphate minerals has resulted in measurable concentrations of U, Th and REE in all mine waters and boreholes in the near vicinity of the mine. The chondritenormalized REE patterns of the water samples are sin1ilar to those displayed by monazite, with a distinctive Eu depletion and an obvious enrichment in LREE with respect to HREE. Monazite-normalized REE patterns for the selected borehole waters show a marked fractionation between LREE and HREE, with the HREE strongly enriched in the aqueous phase. Heavy REE have been shown to have a greater tendency for complexatioi1 and a greater affinity for mineral surfaces. In the present study, the three boreholes in which colloids were found had high concentrations of U, Th and REE. It is likely that colloidal transport of these elements is the dominant mechanism of transport.

Includes abstract. / Includes bibliographical references (leaves 93-102). / This study demonstrates that diatom analysis of lake sediment can provide very detailed information on long and short term climate change, hampered only by inconsistent sediment accumulation at Groenvlei. Further work may provide insight to periods which were not covered in this study.

Bibliography: pages 106-110. / The Gannakouriep dyke swarm comprises a linear swarm of north to northeast striking mafic dykes emplaced during late Proterozoic rifting in the Gariep belt. The swarm has a strike length of over 300 km crossing terrane boundaries of the Gordonia sub-province, Richtersveld igneous sub-province and 8 ushmanland sub-province of the Namaqua Mobile Province. The main axis of dyke intrusion is centred within the 2.0 Ga Richtersveld igneous sub-province where the density of dyking increases westwards across strike towards the Gariep belt, prior to disappearing within the sediment/basement contact of the para-autochthonous Port Nolloth Assemblage. An internal Rb-Sr mineral isochron, together with pyroxene K-Ar plateau and whole rock model TCHUR ages, indicate that the dyke swarm was intruded around 720 Ma. The majority of the dykes comprise subophitic relict gabbros and dolerites of alkali affinities replaced by metamorphic minerals of both greenschist and amphibolite facies. The greenstones are encountered within the NE striking eastern sector of the dyke swarm which records the original tensile stress field, whilst amphibolites are encountered in the northerly striking western sector of the swarm which has been rotated 26° anticlockwise during Pan-African (500-550 Ma) deformation in the Gariep belt. The latter age of regional metamorphism and deformation is supported by available K-Ar age data on whole rock samples and amphibole mineral separates. Integrated field relationships, continuum mechanics modelling and geochemical studies suggest that the swarm was initiated as a series of low level crustal magma chambers which subsequently gave rise to a series of dyke complexes that comprise the Gannakouriep dyke swarm. The geochemical variability between individual dyke complexes across the entire swarm is negligible; only slight differences being recorded by their high-field-strength element concentrations. The latter suggests that all dykes are genetically linked to a single mantle diapir, with only slight source characteristic heterogeneities. All dykes are ferro-tholeiites with no primitive (picritic) member being present. Geochemical trends recorded by the swarm are easily reconcilable in terms of fractionation of the phenocryst assemblage olivine, plagioclase, clinopyroxene, (ilmenite and Ti-magnetite). However an earlier phase of fractionation of essentially olivine and plagioclase at the base of the crust is suggested since constraints on the degree of partial melting (3-6%) imposed by REE patterns would derive an alkali basalt parental melt. The geodynamic relationship between the Gannakouriep dyke swarm and rifting in the Gariep belt is accounted for by a lithospheric plate model containing non-coincidental crustal and mantle weaknesses represented by late Namaquan D4n extensional faults and a mantle weakness possibly resulting from crustal thickening within the Richtersveld igneous sub-province during Namaquan tectonics.

Atmospheric pollution on the South African high veld is perceived as a concern because of the combination of heavy industry and climatic features that prevail in the region. The frequent occurrence of surface inversions (80 - 90 % of days in the winter months), permits the accumulation of pollutants near ground level. Although industrial stacks, and those of power stations in particular, are generally able to emit gaseous and particulate pollutants above the boundary layer, looping and fumigation of plumes may occur under convective conditions. Under such circumstances, the concentration of pollutants at ground level may be high, especially within 4 km of the stack. Since considerable damage to European and North American ecosystems has occurred as a result of atmospheric pollution, concerns were first raised in a report by Tyson, Kruger and Louw in 1988, that similar effects may be taking place on the eastern highveld region of South Africa. The current study was prompted in direct response to these concerns. The first major objective was to establish long-term monitoring sites whereby changes in the pedosphere in response to atmospheric inputs could be detected. The second objective was to characterise the soil collection and to determine whether any impacts are detectable at this early stage. Arnot power station was selected as the focal point of the study as it is a base-load power station, is the most distant from the industrial centres of Witbank, Middelburg and Gauteng and has been in operation for over twenty years. Fifteen sampling sites located in an arc ranging ENE to SE downwind of the power station were selected. Both topsoil and subsoil were sampled at each site. Details of geographical co-ordinates and site features were noted to enable reproducible resampling. Sampling took place in August 1996, but three sites were visited again in October and resampled to test the reproducibility of sampling. Although not statistically comparable, the soils of each site showed similar results for key analyses, which included EC, pH, organic carbon and acid neutralising capacity.

Bibliography: pages 135-145. / Saldanha Bay is a natural deep-water harbour situated on the Cape West Coast, approximately 100 km north of Cape Town. The bay is not an estuary, since there are no rivers or streams entering the inlet. Saldanha Bay covers a total area of approximately 9.61 x 107 m2 and consists of three interconnected water bodies: Langebaan Lagoon, Big Bay and Small Bay. The latter two are separated from each other by a causeway and a series of jetties. At present, Small Bay is the most developed of the water bodies, supporting activities such as commercial and industrial fishing, the mariculture of mussels, and the exportation of iron ore and metal concentrates. Conflicting demands are being placed on the system, and the sediments are known to be contaminated with a range of trace metals. The handling of ore and metal concentrates in particular, have been identified as a threat to the survival of the mariculture industries. The overall objective of this study was to provide a geochemical characterisation of the sediments in Small Bay. It focused on identifying the factors which have the greatest influence on the mobilities of Cd, Cu, Pb and Zn in the sediments. This was achieved through a geochemical interpretation of the results obtained from analyses of sediment solid phase samples and pore water samples. Factors affecting the metal mobilities were identified by investigating the statistical relationships between calculated partition coefficients (Kp) and the characteristics of the sediment solid and aqueous phases.

Bibliography: p. 83-96. / Recently discovered base metal (Zn>Cu>>Pb) massive sulphide deposits in the Northern Cape district of Prieska occur at Kielder 12 kilometres north-west of a similar Zn-Cu deposit, the Copperton mine. Three massive sulphide bodies known as K3, Kl and K6 occur as stratabound massive sulphide lenses within granulite grade quartz-feldspar gneisses, basic granulites and amphibolites. Extensive exploratory core-drilling provided specimens of the massive sulphides, their disseminated pyritic haloes and the enclosing wall rocks in an area of poor outcrop with extensive calcrete and sand cover and, in places,in situ Karoo Super-group Owyka System varved shales.Geothermometry and geobarometry using garnet-biotite, garnetcordierite,garnet-hypersthene,and the FeS content of sphalerites showed a gradual metamorphic gradient from east to west, with the K3 area suffering P-T conditions of 695⁰ C and 6. 0 Kbars; the Kl area 686⁰ C and 5.8 Kbars and the K6 area 590⁰ C and 5.6 Kbars.

The objective of this study was to characterise the impact that a major industrial operation, situated at Somerset West and involved in the manufacturing of a diverse range of chemicals, has had on the sediments of the drainage system that drains the site on which these activities occur. Furthermore, the impact of these sediments on the geochemistry of a wetland, Wagenveldt vlei, situated downstream of the complex, has been investigated. Sediment cores and water samples were collected at a number of locations down the length of the drain . The water samples were analysed to determine which constituents were present in solution. The cores were separated into a top and bottom layer which were analysed separately to determine their geochemical composition. In some instances a lack of time resulted in some of the analyses being performed on only a select number of samples. An experiment was performed on the sediments collected from the bottom layer to determine what would happen if the sediments became oxic and the sulphides and organic matter in the sediments were oxidised.

Bibliography: pages 79-86. / Acid soils have long been associated with increased mobility of metals and the subsequent nutrient toxicity to plants, the cause of which is believed partly to be a reduction in cation exchange capacity (CEC). At the same time the reduction in CEC would result in a decline in the soil's ability to retain cations. The reduction in CEC is said to result from the development of positive charge at low pH in soils with variable charge which is enhanced by the amphoteric behaviour of Fe and AI oxides as well as the presence of organic matter. Aluminium tends to form stable complexes with organic matter and also competes with lower valency cations for exchange sites, in which way it interferes with the measurement of CEC in soils. Variation of charge with pH has important environmental implications, e.g. groundwater contamination with heavy metals as the soil becomes less capable of retaining them at low pH. Origin of variable charge in soil, factors affecting electric charge variation with pH and the methods employed in determining CEC appear to play an important role in understanding the concept of electric charge variation with pH as well as its environmental significance.

The Saltpeterkop Carbonatite Complex is a Late Cretaceous (≈76 Ma) volcanic and shallow intrusive magmatic feature located approximately 20 km southeast of Sutherland in the Northern Cape. It is unusual among southern African carbonatite complexes in that it has not been deeply eroded, and retains a significant vestige of its original volcanic features. The main geologic expression of the Complex is a ≈1.5 km diameter tuff ring, located on top of prominently updomed and fractured Beaufort Group (Karoo) sediments, that appears to have formed as the result of a major diatreme-type eruption. The volcaniclastic breccias making up the tuff ring have been heavily altered and silicified by hydrothermal activity, and thick (mm to tens of cm) Fe oxide-rich crusts, which appear to represent the alteration products of Fe-rich carbonatites, are common in this area. Outside of the central ring structure are numerous shallow intrusions (dykes, sills and irregular shapes), satellite breccia pipes and pipe-shaped intrusions that host fresh to only moderately altered igneous rocks. The main igneous rock types include (in decreasing order of abundance): carbonatite, potassic trachyte, olivine melilitite and ultramafic lamprophyre. This thesis provides the first detailed petrographic and geochemical description of these rocks (e.g., major and trace elements) and attempts to explain several aspects of their petrogenesis. The olivine melilitites and ultramafic lamprophyres are the most primitive igneous rocks in the complex and have experienced only minor to moderate extents of differentiation, respectively. They apppear to have been derived by low-degrees of partial melting of a carbonated, likely phlogopite-bearing mantle source. The lamprophyres appear to have been derived by melting at shallower depths than the melilitites based on REE constraints. The carbonatites range from relatively primitive to highly differentiated and they form a nearly continuous compositional range with the ultramafic lamprophyres and melilitites. This seems to argue against a major role for liquid immiscibility in their origin. Their REE content (up to 2 wt.% total REE oxides) correlates with their extent of differentiation. The potassic trachytes are plausibly linked to melts of mafic lower continental crust that has been metasomatised by hydrous potassium-rich carbonatitic melts and which have experienced significant fractional crystallization and assimilation of upper crustal sedimentary rocks during emplacement.

Bibliography: pages 200-204. / A low dilution fusion technique using a 2:1 flux:sample ratio has been developed for the accurate determination of major, minor and trace elements by x-ray fluorescence spectrometry (XRFS). This method has been used to analyze geological samples of widely varying and unusual composition such as lamproites and kimberlites. The results are shown to be of comparable if not better accuracy than other methods of sample preparation for XRFS. Analytical conditions, including corrections for spectral line interferences are reported for all the elements determined. For major element analysis three methods of calculating appropriate alpha coefficients were investigated, namely (1) multiple regression analysis, (2) Norrish and Hutton method and (3) a computer program, NBSGSC, involving fundamental parameters and the COLA equation. Methods (1) and (2) gave poor results for rock types of widely varying composition. The third method requires that the variation of alpha coefficients with varying weight fraction of the analyte element be taken into account when calculating alpha coefficients if accurate values for major and minor elements are to be obtained on low dilution fusion discs. For trace element analysis the average relative error was less than 5% and there was a decrease in sensitivity by about a factor of 2 compared with XRFS determinations on powder pellets. The elimination of particle size effects in the homogeneous glass fusion discs is a major advantage over the use of powder pellets, especially for the determination of elements such as Ba, Cr and the REEs. A loss on fusion technique has been employed to ensure complete loss of volatiles from the rock samples. Data presented highlight the problems encountered in the determination of the volatile content in geological samples. The oxidation and retention of sulphur in the discs was also investigated.