U-Pb ages were determined on single grains of monazite and xenotime as well as small populations of rutile from amphibolite to granulite facies metasediments of the Quebec Gneiss Segment of the Grenville Province in an area extending 45 to 135 km south of the Grenville Front in La Verendrye Park, Quebec. Recent geochronological studies include Pb-isotope ratios of metamorphic minerals corresponding to ages of 2.5 to 2.65 Ga and U-Pb monazite ages to 2649 to 2655 Ma, which define a lower discordia intercept of approximately 1.01 Ga. Recent thermobarometric studies indicate the presence of two metamorphic episodes in the region. / Monazite and xenotime grains obtained from high grade metasediments at five locations between 45 and 70 km southeast of the Grenville Front yielded $ sp{207}$Pb/$ sp{206}$Pb ages of 999 $ pm$ 5 Ma to 1021 $ pm$ 2 Ma. Monazite from the norther part of this terrane also defined an upper intercept age of 2596 $ pm$ 3 Ma. / The southernmost sample location, 135 km south of the Grenville Front, yielded both monazite and rutile. Monazite gave an age of 1072 $ pm$ 2 Ma. Small populations of rutile yielded an age of 916 $ pm$ 2 Ma. (Abstract shortened by UMI.)

No abstract available.

An assessment of uranium trial mining on four mining sites in the Karoo Uranium Province, South Africa revealed localised above-background values for U, Mo, Pb, Cu, As and Fe in surface - and ground water, soils, sediment and crops. Inadequate remedial action on cessation of mining activities in 1980 led to the presence of uranium ore in stockpiles, open pits, mining shafts, mining equipment and waste dumps within featured areas. Heavy metal contamination is suppressed by the lack of runâoff and the dry climate experienced within the mining areas. However, the heavy metal content in surface water and sediment within the open pits on Rietkuil and Mooifontein is especially high. These values pose a risk for human ingestion and may cause cancer in the long term or renal damage over the short term. These pits are easily accessed, lack a fence and are used for a drinking medium by fauna and as a growth medium for flora. The easily accessed Cameron Shaft on Ryst Kuil is a matter of concern due to the possible presence of the radioactive inert gas, radon. Farm owners were unaware of the possible toxic effects of uranium and coherent heavy metals. This led to previous usage of mine water for crop irrigation, the moving and feeding of livestock as well as wildlife amongst uranium ore stockpiles, swimming in water-filled open pits and using crushed uranium ore for gravel road maintenance and construction. The presence of uranium ore in stockpiles and the coherent effects on the water, soils, sediment, fauna and flora and possibly man, prioritises the remediation and rehabilitation of the of uranium trial mining sites within the Karoo Uranium Province.

The ultimate objective of all exploration within the Witwatersrand Basin is to locate concentrations of gold which can be exploited economically. Gold in the B placer has high variance. The gold present in the B placer consists of small heavy detrital particles which are contained in the sedimentary host rock. In order to interpret the variable distribution of the gold within the B placer, cognisance must be taken of the sedimentological framework. The aim of this study was to employ a different approach to acquire an insight into the nature of the B placer and to shed more light on the depositional environments that played a major role during the formation of the B placer. Pebbles of the B placer conglomerates were investigated macroscopically in order to determine localities of possible gravel bar formation within the B placer. It was established that the B placer represented a braided river system with three different depositional environments, namely a fluvial environment, braid plain and a braid delta environment. The Upper Shale Marker at Masimong 5 Shaft played a major role in the development of these different depositional environments. The B placer remained river dominant and neither tide nor wave-related processes had an overwhelming influence on the system. The extreme fluvial dominance of the B placer improved the sorting of the braided delta system. The degree of reworking of the gravel bars in the braid delta by waves and current action resulted in the formation of thicker and better sorted conglomerates which, in turn, led to the formation of the B1 facies. Reworking and re-sedimentation of the B1 conglomerate occurred in the subaqueous setting. The B3 facies present at Masimong 5 Shaft were deposited in a purely fluvial braided environment. The improved perceptive of the B placer made it possible to identify four potential scenarios for the development of gravel bars within the braided river system, namely channel junctions, point bars, side bars or lateral bars; midchannel bars and barrier bars.

The study forms part of the COALTECH 2020 research program, a collaborative study which aims to ensure the continued viability of the South African Coal Mining Industry well beyond the year 2020. It participates in the Geology and Geophysics Technology Area of the COALTECH 2020 Technology Wheel. The mission statement of this Working Group is to facilitate applied research to identify, quantify and qualify the remaining Coal Resources, starting with the Witbank-Highveld Coalfield, to enable informed decisions when defining and extracting Coal Reserves. The structural investigation of dolerites in the south-eastern part of the Witbank Coalfield contributes to Task 1.1.1; Sedimentological and Structural Model of the Witbank-Highveld Coalfield. The Witbank Coalfield in the Mpumalanga Province of South Africa is situated on the northern sector of the main Karoo basin. The main Karoo basin is described as an asymmetric depository with a stable, passive cratonic platform (Kaapvaal Craton) in the northwest and a foredeep to the south with the Cape Fold Belt on its southern margin. The study area is situated south of the prominent ï± 15m thick Ogies Dyke, which strikes from Ogies in the west to Optimum Colliery in the east. The east-west trending pre-Karoo Smithfield Ridge, consisting of Rooiberg Felsites, bounds the study area to the south and also separates the Witbank Coalfield from the adjacent Highveld Coalfield to the south. The study was conducted on four collieries, namely Bank, Goedehoop, Koornfontein and Optimum Collieries in the south-eastern part of the Witbank Coalfield. The objective of the study is to investigate the intrusion mechanism of the dolerites and the metamorphic effect the dolerite intrusions had on the coal in order to quantify the impact on mining and coal utilisation in the south-eastern part of the Witbank Coalfield. The most important effects of dolerites on mining with a decreasing order of importance are: 1. Decrease in the safety conditions and an increase in the risk of roof failures, pillar and floor stability. 2. Increase in the overall production and mining costs with a decrease in the potential profit. 3. Decrease in saleable tonnages with a decrease in the profit margin. 4. Increase in waste product generation and an increase in the environmental risk. From the objective two separate studies were identified: the first study (A) focuses on the relationship between geological structures and dolerite intrusions and the second study (B) determines the metamorphic effect the dolerite intrusions had on the coal. The structural investigation of the relationships between geological structures and the dolerites is contained in this document. Regional scale information was acquired by using various remote-sensing techniques. The CSIR Miningtek through the COALTECH 2020 Research Program provided this state of the art information. In conclusion to the regional scale study probable relationships between certain Karoo-age dyke, sill and lineament trends that are associated with the northern main Karoo basin and surroundings could possibly provide insight into better understanding of the intrusion mechanism of dolerites in the south-eastern Witbank Coalfield. It is therefore probable that some of the Karoo-age intrusives in the south-eastern Witbank Coalfield followed older basement structures inherited by the Karoo strata and/or syn-tectonic structures related to Gondwana fragmentation which was synchronous with dolerite intrusion (Encarnación et al., 1996). The EW striking Ogies Dyke, which is the main structure in the Witbank Coalfield, most probably pre-dates its associated smaller scale dykes and sills. Conclusions for this relative age difference are summarised as being the following: Its association with EW basement Pre-Karoo diabase, which probably acted as a plane of weakness and might have triggered its earlier intrusion. Difference in geochemical and mineralogical characteristics. Absence of sills immediately to its north. Should the NS striking dykes north and south of the Ogies Dyke be favoured by cooling joints which developed as a result of its earlier intrusion, the age difference is evident. Comparing the physical appearance of the ± 20m sill (main sill) in the Witbank Coalfield with the B8 sill in the Secunda Coalfield, the two sills have a number of properties in common. However, these physical property comparisons are not precise and it is therefore suggested a detailed geochemical analysis be undertaken focussing on the mineralogy, major and trace elements. The sedimentary sequence is reconstructed by removing the main sill from the stratigraphy. The reconstruction is aimed at determining if a spatial relationship exists between the coal seams, the intra-seam strata and the main sill prior to the intrusion event. Borehole information on the elevation of the pre-Karoo basement is sparse as borehole penetration was terminated at the bottom of the coal seam of interest. The removal of the dolerite convincingly reveals the pre-Karoo basement topography, palaeo-floor and -roof morphology, as well as the width distribution of the sedimentary units. The following reconstructed sedimentary units were examined individually: No. 2 Coal Seam; Facies between the No. 2 Coal Seam and No. 4L Coal Seam; No. 4L Coal Seam; Facies between No.4L and No. 5 Coal Seam; No. 5 Coal Seam. The examination process of the data of each unit starts with the statistical analyses thereof which includes histogram and probability plots of the palaeo floor, width and palaeo roof. The investigation resulted in nearly direct linear correlation curves which disclose the existing relationships between the palaeo floor elevations of the No.2, No.4L and No.5 Coal Seams. Considering the range of correlation coefficient values of 0.81 to 0.99 for the palaeo floor elevations it convincingly reveals the co-existing relationship in the geometry of elevations throughout the entire stratigraphy of the sedimentary sequences. Several sedimentological factors contributed to the present day geometries and widths of coal and associated clastical sedimentary rocks of sequence of succession. The evidence in the relationship of the geometries of the palaeo floor and roof elevations concludes that irrespective of variable intra-seam strata and coal seam widths the pre-Karoo topography is reflected throughout the entire stratrigraphic sequence. Prior to sediment burial, plant growth took place most probably on similar structural relief of gentle attitudes. To conclude, a four-stage model is proposing how burial could have influenced widths and aerial distribution of peat and intra-seam clastic sedimentary rocks of sequence of succession. At the time of peat formation, the unconsolidated sediments had not yet undergone a great deal of lithification in that the floor structure of the peat might have been without undulations. In conclusion, a reasonable inverse relationship between the net width of the stratigraphic sequence from the palaeo floor of the No. 2 Coal Seam to the palaeo roof of the No.5 Coal Seam and the floor elevation of the main sill exists. A Quantile-Quantile-plot and the regression slope analysis of the data sets convincingly conclude the inverse relationship that exists between the floor elevation of the main sill and the net width of the almost entire sediment sequence. In this context the reasonable negative correlation coefficient of -0.57 is good. This negative correlation implies that where the main sill is present in the lower stratigraphic levels it underlies thicker sedimentary sequences and conversely where the sill had stepped up to higher stratigraphic levels it underlies the thinner sedimentary sequences. In conclusion the differential compaction of the sedimentary strata was in the main controlled by the the Pre-Karoo basement topography. This in turn resulted in the fracturing and jointing of the sedimentary rocks over the flanks of the pre-Karoo basement topography which to a large extent controlled the propagation path of the main sill. Evidence established in this study suggests the effect of basin tectonics to be the overriding controlling factor of the stratigraphic position of the main sill in the Vryheid Formation sedimentary rocks of sequence of succession of the south-eastern Witbank Coalfield. Other factors i.e. the influence of the Ogies Dyke and syn-tectonic related regional scale structures seem to have had some control in the propagation paths of the associated offshoots of the main sill.

This study presents petrological, mineralogical and geochemical data from the country rocks surrounding the basic to ultrabasic Uitkomst Complex in the Mpumalanga Province, South Africa. The investigations resulted in a isograde map based on the determination of critical mineral reactions for different lithotypes, i.e. the Timeball Hill Shale, Bevets Conglomerate and the Malmani Dolomite. Several minerals occurring in the metamorphic aureole, for example almandine in the Timeball Hill Shales, allow to determine temperatures and to a lesser degree pressure prevailing in the country rocks during the emplacement of the Complex. Geochemical profiles perpendicular to the contact into the country rocks indicate moderate enrichment of Mg, Fe, Cr and Ni close to the contact, levelling out to threshold values within 50 m distance from the contact. Additionally to the thermometric aspects of this thesis, an appraisal of the possible applications of corundum is given. The Uitkomst corundum shows, in parts, gem quality. Sapphire has been found in the Timeball Hill Shales south of the Complex. The corundum-bearing hornfelses are found in a distance of approximately 240 â 270 m from the contact in north-easterly and south-westerly direction. The rocks in this zone are characterized by a under-saturation of SiO2 and an elevated Al2O3-activity; the required temperature of corundum formation lies above 400 °C on average.

A study was firstly conducted on the mineralogy and geochemistry of the dolerites, secondly on sedimentological controls (syngenetic) on coal deposition and diagenesis to gain a better understanding of the environment of the coal deposition and thirdly, the metamorphic influence of dolerite intrusions (epigenetic) on coal. The Ogies Dyke is the only intrusion found in the study area at Optimum Colliery. The absence of dolerite sill intrusions in this area made it possible to study coal deposition and diagenesis. It was to investigate the behaviour of a 20m thick bifurcating dolerite sill (the Witbank sill) and its associated metamorphic influence which occurs in the other Koornfontein, Bank and Goedehoop Collieries. The most prominent structure, the Ogies Dyke, forms the northern limit of the study area and forms a very important part of the geochemical and mineralogical study. Thin section investigations revealed the involvement of plagioclase in both the Witbank and Sasolburg dolerite fractionation assemblages indicates that the fractionation processes must have occurred within the crust although within different depths. The absence of pyroxene phenocrysts in the B5 sill (Sasolburg) indicates that the fractionation took place at a pressure significantly higher than that at which the plagioclase and olivine microphenocrysts have formed. The high percentage olivine in the B4 sill (Sasolburg) indicates that these two sills originated from different magma sources. Plagioclase microphenocrysts in the B5 sill as oppose to the macrophenocrysts of the B4 sill concludes that the fractionation processes of the B5 sill must have happened deeper within the crust. This study engage with dolerites that crystallised rapidly, intermediately and slowly as the crystal sizes are directly related to magma cooling. Fine crystalline dolerites like the chilled margins and bifurcations tend to be more susceptible for alteration as opposed to the medium and coarse crystalline dolerites. The 40m thick, fine crystalline B4 sill has undergone the most alteration comparing to the B5 sill, Witbank sill and the Ogies Dyke. The differences identified during this study distinguish the Sasolburg dolerites from the Witbank sill and the Ogies Dyke. X-ray fluorescence techniques were used to analyse the dolerite samples from the study area. All the dolerites are falling in the âbasicâ group. The B4 â Sasol dolerite sill is a high-MgO (picritic) basalt while the rest are basalts. The chilled margins of the bifurcations have an arithmetic mean of 4.89% MgO and the Ogies Dyke has 4.9% MgO and can be classified as evolved basalts. Lower MgO and Ni values in the Witbank bifurcations comparing to the Witbank sill indicate that the bifurcations are more evolved. The basaltic and evolved basalts can further be divided into low and intermediate K2O concentrations. A higher K2O concentration is placing the Ogies Dyke in the intermediate-K2O group whilst the Witbank sill (interior and chilled margins), and the Witbank bifurcations (interior and the chilled margins) are all falling in the low-K2O group. Two of the Witbank bifurcations (interior) having intermediate-K2O concentrations and are associated with the Ogies Dyke. The picritic B4 sill (Sasol) is also classified as a low- K2O dolerite. Considering K2O and MgO element concentrations the samples are falling in three categories, from evolved to picritic with the majority in the basaltic field. Borehole information was used to conduct isopach and isopleth maps of the pre-Karoo topography, floor elevation and thickness distribution, coal parameters and statistical data of various coal seams to underpin the sedimentological controls (syngenetic) on coal deposition and diagenesis The undulated platform onto which the No. 2 Upper Coal Seam formed at the Optimum study area had a major influence on coal grade. Thicker coals were deposited in the lower lying areas while they were thinning towards palaeohigh areas. Significant values indicate that the thinner coals are higher in ash (air-dry), lower in VM (daf), lower in CV MJ/kg (air-dry) and higher in relative density comparing to the coals deposited in the lower lying areas of the palaeovalley. Lithological descriptions from boreholes and structural interpretations in geological crosssections revealed the presence of a green 20m thick, bifurcating dolerite sill that intruded into the Vryheid formation of the Karoo Supergroup. It is associated with ±20m displacement and metamorphism on coal which is putting major constraints on coal mining in general. The metamorphic influence of the coal is largely restricted to the width of the contact aureole. The nature of the aureole depends on the geometry, variation in thickness and bifurcation of the sill. It is also found that the metamorphic contact aureole is much more extensive in the displaced and uplifted coal seams comparing to those beneath the sill. Moisture (ash-free) of the proximate analyses, volatile matter (daf), CV (daf) and approximated ash yield (AD) isopleth maps show that the dolerite sill caused a localised increase in rank. Areas of high moisture (proximate analyses moisture content) correspond to devolatilised areas, which are higher in ash and therefore having lower CVâs and are adjacent to known intrusions.

The Florisbad Quaternary Research Station and archaeozoological site is located 45 km north-west of Bloemfontein, Free State Province, South Africa (28° 46` 05.4âS, 26° 04` 10.7âE), and is sited around a series of highly saline, warm water spring vents. The site is partially covered by a large sand dune. The site is significant for three important reasons. Firstly, the discovery of the Florisbad skull (Homo helmei) in 1932 by Prof. T. Dreyer, secondly, a collection of faunal fossil remains representing at least 31 taxa, including extinct and extant species, and referred to as the Old Collection and, thirdly, a Middle Stone Age (MSA) human occupation horizon representing a temporary butchering site with evidence of a hearth, butchering tools, and faunal fossil remains. Spring- and excavation pit water samples were taken and analysed in 1988 during a high rainfall period, and in 1999 during an average rainfall period. In relation to the spring water, the results show that the total dissolved solids (TDS) of the excavation pit water were, in relation to the spring water, higher during the high rainfall period and lower during the average rainfall period. This was contrary to the norm, where it is expected that high rainfall periods should produce a decrease in TDS due to a dilution effect. The TDS of the spring-water remained stable throughout both high and average rainfall periods. Further analysis showed considerable TDS increases between the excavation pit waters, and between the pit waters and the spring-water. It is concluded that the pit waters were not directly related to the spring water and that the two water bodies were separate entities with the pit water being recognized as groundwater. An analysis of rainfall in relation to the TDS of the spring- and groundwater indicated that short-term rainfall affected the quality of the groundwater, but not the quality of the spring-water, while long-term rainfall had little effect on the quality of the spring-water. The question arose as to why the TDS of the groundwater was so much higher than that of the spring-water, and what factors were causing these differences? Organic-clay (peat) samples from the walls of the excavation pits as well as the walls of the open excavation area were analysed. The results of the analyses, and an examination of the stratigraphy, strongly suggested that minerals had accumulated in the organic-clay layers due to organic matter having a similar colloidal organization to that of clay, with the ability to adsorb large quantities of minerals on their outer surfaces. A comparison of the groundwater and organic-clay analyses results showed that the TDS of the decomposed Peat II organic-clay layer was considerably higher than that of the groundwater, with the same being true for the far less decomposed Peat IV organic-clay layer. By analysing and combing the water and organic-clay layer results with the many factors, mechanisms, and processes involved, it is concluded that the salinization of the organic-clay layers, and the flushing of ions from the organic-clay layers by percolating water during rainfall periods, is responsible for the increased mineralization of the groundwater. Other factors, mechanisms, and processes, such as rainfall, aeolian deposition, evaporation, capillarity, wind, temperature, matrix-suction, pH, Eh, PCO2, PO2, DOC, and biomineralization, all of which support the accumulation of free salts in a semi-arid environment such as Florisbad, were also investigated. Of primary importance was the question as to whether the spring-water was actually responsible for fossilization of the faunal remains, and could fossilization have taken place within the environs of the spring vents, or in the spring vents themselves? Previous research has suggested that the spring-water was calcium-carbonate rich, with evidence of calcium-carbonate deposition further suggesting that faunal remains of the Old Collection must have been in contact with the spring-water in spring vents for some time. An analysis of the spring-water analysed over the past 84 years indicated that there had never been sufficient Ca (under-saturation) in the spring-water for fossilization to occur, and this is confirmed by the current analyses. The contemporary lack of Ca in the springwater, combined with other environmental factors within the environs of spring vents, such as the lack of organic matter and clay, combined with a high Eh environment, also strongly indicated that, historically, fossilization could not have taken place within the environs of the springs. Contrary to earlier hypotheses, it is concluded that the spring water and spring flow would directly assist in the de-mineralization of faunal remains. A detailed investigation of the site, along with an analysis of the stratigraphy and sedimentation, revealed that previous theories on the formation of the site did not sufficiently accommodate the current stratigraphy in the context of the organic-clay layers, the salinization process, and fossilization. From this deduction all the existing and pre-existing evidence was revisited in an attempt to provide a hypothesis which would accommodate the existing morphology of the site, sedimentation, and fossilization. It is hypothesised that the spring site formed around a large drainage-impeded pan which was largely covered by a sand dune that had migrated from the area of the extensive salt pan to the north and north-west (Soutpan). The arms of the dune eventually came to rest up against the windward slope of a dune belt located just south of the spring site, and a dam began to form. High rainfall periods produced organic-clay layers, while sandy layers were produced during drier windy periods. This led to the formation of alternating horizontal layers of organic-clay and sand, eventually building up to almost the top of the sand dune on the leeward face. When the water level in the dam reached the top of the arms of the sand dune, it broke through the eastern arm. The dam water and sediments then evacuated the dam in a flash flood. This flash flood eroded the area to the east of the site to such an extent that the drainage was diverted, and a wide flat-bottomed vlei was formed where much of the dam sediments were deposited. This hypothesis provides an alternative for the formation of the spring site, accommodating all aspects of sedimentation, salinization, and fossilization. The dating of the Florisbad deposits and fossils has been subject to an ongoing debate since the first 14C dating was carried out in 1954. The ages and depths of recently published profiles did not appear to correspond to the assumption of greater compaction with depth and time. In an attempt to resolve this issue, linear, exponential, and logarithmic mathematical trend lines were then experimentally applied to the published profiles of electron spin resonance (ESR) and optical stimulated luminescence (OSL) dates in order to test the theory of compaction, and to validate the results. The hypothetical effect of manipulating ages on trend lines was also tested. A discussion on some possible shortfalls regarding the dating methods used is undertaken. A best logarithmic fit to data was obtained by holding the ESR Middle Stone Age Human Occupation Horizon (MSA) age at 127 ka, and advancing the lower deposit age from 250 ka to 420 ka. The next best fit to data occurred by regressing the ESR MSA age from 127 ka to 78 ka, and holding the lower deposit age at 250 ka. The application of exponential and linear trend lines produced poor fits to data. A suggested compaction trend line was also introduced which produced an ESR MSA age of 75 ka and a lower deposit age of 384 ka. In the final analysis, trend line results suggested an MSA age of 92 ±12 kyr and a basal deposit age of 400 ±20 ka. The logarithmic and suggested compaction trend line ages for the lower deposits both produced ages similar to the suggested Florisain â Cornelian faunal boundary of c. 400 ka. The exercise confirmed that the ages in the published profiles were disjunct and that this disjunction may be related to a number of different physical forces.

Numerous dykes traverse the Witwatersrand Supergroup rocks in the Carletonville Goldfield. The aim of this study was to investigate a classification system for the dykes. Samples were obtained from Tau Tona and Mponeng mines as well as from AngloGold Ashantiâs field office. The mineralogical investigation revealed that most dykes, with the exception of the Brazil dyke, are altered. The most abundant minerals are chlorite, actinolite, epidote, quartz and albitised and/or saussuritised feldspar, corresponding to a greenschist metamorphic facies mineral composition. Veins are commonly filled with quartz, calcite, epidote and chlorite, with sulphides and Fe oxides occurring occasionally. However, mineralogical heterogeneity as a result of different degrees of alteration, were found between samples from the same dyke. This heterogeneity may be an important consideration where rock engineering is concerned as it could cause different sections of the same dyke to have different physical properties Geochemical separation of the dykes into different groups was achieved by means of Bowenâs (1984) TiO2 v Zr and Zr/P v P/Ti plots as well as Lintonâs (1992) discriminant plot. These same plots were employed in order to classify the dykes according to geochemical data taken from literature for four igneous events, namely, the Ventersdorp Supergroup, Transvaal Supergroup, Bushveld Igneous Complex and Karoo Supergroup, as well as geochemical data for dykes from the East Rand Proprietary Mine. Rare Earth Element patterns from the dykes were compared to literature data for the above-named igneous events in order to obtain a better classification.

The Vioolsdrif Suite and Orange River Group represent genetically related calcalkaline plutonic and volcano-sedimentary assemblages of Palaeoproterozoic age formed during the Orange River orogeny. Together they occupy the largest part of the Richtersveld Subprovince â a unique tectono-stratigraphic terrane. Radiometric data indicate the period of formation roughly between 2.0-1.73 Ga. The subprovince has been vastly eroded and isolated from its original tectonic environment by subsequent tectonic processes, leaving a relatively small portion of its original extent for investigation. Previous studies have dealt with limited parts of the subprovince and although informal subdivisions of the Orange River Group and Vioolsdrif Suite are generally in use, some correlations and further subdivisions remained controversial. This study has two main aims, viz., to propose formal subdivisions of the two units and to investigate the magmatic processes and original tectonic environment of their formation. Geochemical evidence is presented here to support the proposed subdivisions, which were previously based entirely on field evidence. The subdivisions largely follow that of previous studies. The Orange River Group is subdivided into the Haib and De Hoop Subgroups. Geochemical evidence show that these two subgroups differ in the magmatic processes that led to their formation. The Haib Subgroup shows a genetic gradational relationship with the Vuurdood Subsuite, which is regarded as remnants of the primary magmas. The De Hoop Subgroup does not display this relationship with the Vuurdood Subsuite. The Vioolsdrif Suite is subdivided into the Vuurdood, Goodhouse and Ramansdrif Subsuites. Mafic-ultramafic bodies of the Vuurdood Subsuite are regarded as remnants of the primary magmas. This is based on multi-element variation diagram patterns and comparison to source magmas in modern island arcs (MORB). Previous studies have also shown that initial isotope ratios for the Vuurdood Subsuite are similar to those of the Goodhouse Subsuite and Orange River Group, relating them to a similar source. Dark mineral cumulate material are contained in the mafic-ultramafic bodies. The Goodhouse Subsuite is subdivided into the Khoromus Tonalite, Blockwerf Migmatite, Xaminxaip River Granodiorite, Gaarseep Granodiorite and Hoogoor Granite. The Khoromus Tonalite is identified as the oldest unit within the subsuite based on contact relationships as well as radiometric data, which continuously render older ages for the Khoromus Tonalite compared to the other units within the subsuite. Certain field and petrological observations in this unit may be interpreted as products of magma mixing processes. The Blockwerf Migmatite is distinguished from the other units by its migmatitic character and anomalous La/Yb ratios. The unit is identified as a possible remnant volcanic centre. The Xaminxaip River Granodiorite is interpreted as a subvolcanic unit and is characterised by the development of migmatite in places. This migmatite is attributed to metamorphic conditions which locally reached high grade in an orogenic geothermal regime. The Gaarseep Granodiorite represents the main phase of the Vioolsdrif Suite. Its compositional range includes all those represented by the other units individually from gabbro through diorite, tonalite and granodiorite to granite. Its development spans almost the entire evolutionary history of the Richtersveld Subprovince as a whole. The Hoogoor Granite is included in the Goodhouse Subsuite based on the geochemical variation patterns and available radiometric evidence. The Ramansdrif Subsuite is subdivided into the Ghaams and Sout Granites based on grain size variation and petrological evidence. The subsuite could have been formed by partial melting of the older plutonic phases of the Vioolsdrif Suite. The deformation associated with this partial melting event has not been identified. Previous studies have related the evolution of the Richtersveld Subprovince to modern subduction zone magmatism similar to that of the Andean volcanic arc. This is largely supported by the current study, however, a change in magmatic processes and the tectonic environment can be observed in the geochemical variation patterns. Multielement diagrams show patterns typical of subduction zone magmatism for both the Orange River Group and Vioolsdrif Suite. During the initial stages, primary magmas, now represented by the Vuurdood Subsuite, were derived from a depleted mantle reservoir. The first volcanic eruptions â those of the Haib Subgroup â represent fractional crystallization products off the primary magmas. With progressive development of the arc, newly formed crust was continuously recycled back into the mantle and crustal partial melting led to a change in magmatic processes with magma mixing and contamination becoming increasingly important. Tectonic discrimination diagrams suggest that the initial stages of the batholith development may be compared to a primitive continental arc, while the later stages may be be compared to a typical continental arc.