Includes bibliography. / Several physical characteristics, the carbon isotopic compositions, inclusion mineralogy, and distribution of the Dokolwayo diamonds were investigated. A representative suite of concentrate garnet megacrysts and macrocrysts were analyzed for their compositions. Concentrate macrocryst spinels and silicate inclusions recovered from these spinels were analyzed. The physical characteristics of the diamonds investigated were mass, size, morphology and colour. The relationship between mass and size in a population of diamonds recovered from a single hypabyssal intrusion and the general production as a whole, was found to be statistically the same. The most recognizable morphology is the dodecahedron. Octahedra decrease in significance with a decrease in size. Colourless stones predominate. Brown stones are more common than yellow stones, which is uncommon in primary southern Africa diamond populations. Diamonds characterized by "Tanganyika naats" have hitherto not been described from southern Africa. The relationship between the various physical characteristics investigated indicate that the general Dokolwayo diamond population consists of at least four sub-populations.

The blue amphibole asbestos, crocidolite, which occurs as interbedded seams in banded ironstones of the Lower Griquatown stage of the Transvaal System in the Northern Cape Province, is the finely fibrous form of the soda-amphibole riebeckite. Despite the widespread occurrence of the Precambrian type of banded ironstones, crocidolite is a mineral of rare occurrence and is only developed to a relatively minor extent in South Africa, Western Australia and Central China. The composition, structure and properties of riebeckite in general and of crocidolite in particular are discussed and four new chemical analyses are given. Particular attention is paid to the mode of occurrence of fibrous riebeckite and it is suggested that the name "crocidolite" be reserved for the asbestiform riebeckite which occurs interbedded with banded ironstones. The general geology, lithology and mineralogy of Precambrian banded ironstones are described and their distribution in space and time is discussed. It is found that no banded ironstones are known to be younger than 1000 million years. This fact is related to special conditions of atmosphere, surface temperature and biological development which existed during the so-called Primitive Period of the Precambrian, a period which lasted from approximately 3000 million years to 1000 million years ago. The banded ironstones of the Transvaal System are described in some detail and seven new chemical analyses as well as trace element data are given. The genesis of banded ironstones is discussed at some length and particular attention is paid to the authigenesis of riebeckite. It is concluded that banded ironstones were deposited in seasonally fluctuating, typically "non-aggressive", fresh to brackish water lakes which were fed by sluggish, mature rivers. The solutions of iron and silica, alkaline earths and clay colloids carried by these rivers were derived from basic igneous rocks by chemical weathering in a tropical, monsoon-type climate. Recognisable detrital material is virtually absent from the banded ironstones of the Transvaal System, but it is thought that the stilpnomelane layers are aeolian deposits and that their composition gives some indication of the material which remained behind as "lateritic" soils in the source area. It is suggested that both crocidolite and riebeckite were formed by the low temperature dehydration, in situ, of an ordered precursor which could have been a clay mineral similar in structure to attapulgite, but containing ferrous and ferric ions in the octahedral layer. This clay mineral acquired sodium by cation exchange during dry periods when the depositional lakes were enriched in sodium. It is found that the actual formation of crocidolite is completely unrelated to dynamic stress. It formed only where layers of proto-riebeckite were in close contact or traversed by magnetite layers. It grew by the diffusion of proto-riebeckite through the magnetite layers, its transformation to riebeckite during its passage, and final addition to fibre growth points in contact with the magnetite layer. This process was initiated by slight temperature gradients in the magnetite layers and was propagated by a type of thermal autocatalysis. The temperature gradients in the magnetite layers resulted from their superior heat conductivity combined with differences in depth of burial of the strata. Economic deposits of crocidolite formed where a sufficient number of layers of protoriebeckite were in contact with magnetite layers which maintained or repeatedly attained the requisite temperature levels. The superimposed economic deposits of the Kuruman area, which appear to be related to folding, are due to an early period of folding, possibly even slumping during deposition, which took place prior to the formation of crocidolite and caused the thickening of the protoriebeckite layers in the crests and troughs of folds by plastic flow from the flanks. Three appendices, giving details of chemical and spectrographic analyses and of chemical experiments carried out, are attached.

The purpose of this thesis is to describe the occurrence, nature, properties, and utilization of the refractory clays in South Africa with particular reference to the Transvaal deposits, focusing on those characteristics which may be of direct value in the future development of this important mineral resource. Principal attention has been devoted to producing areas and-generally confined to those materials used in the production of fire-clay refractories; however, in many cases these identical clays are employed in the manufacture of "golden brown" building brick, sewer pipe, earthenware, etc. A fundamental study of the constitution of the commercial refractory clays was carried out on selected samples obtained from operating workings. The differential thermal method of analysis was featured in these studies, supple mented by X-ray examination and other recognized determinative procedures. The basic data so obtained were correlated, where possible, with the ceramic properties of the clays in order to lead to a better understanding of the relationship between the refractory clays and the ware made from them.

Oceanic core complexes (OCCs) are the uplifted and rotated footwalls of detachment faults formed at areas of slow spreading on mid-ocean ridges. Detachment faults initiate close to the spreading axis, and because it is easier to continue slip along the existing fault rather than break a new fault, a cross section of lower crust and upper mantle material is eventually exhumed and rotated (Blackman et al. 1998; Tucholke et al. 1998; Schouten et al. 2010). Classic corrugated massifs, noncorrugated massifs, rafted blocks, and newly identified finely corrugated detachment surfaces at 16.5º N on the Mid-Atlantic Ridge have been observed using near-bottom bathymetry data, underwater Sentry surveys, and photographs from the WHOI Towcam (Smith et al. 2014). Active detachment faulting currently only occurs on the western flank of the ridge in the study area, which extends from 16°18'N to 16°55'N and encompasses two spreading segments. Since detachment faulting occurs on ridge segments where tectonic extension is greater than magmatic accretion, it is useful to examine the composition of melts from the underlying mantle to investigate potential mechanisms controlling the shift to a ridge being dominated by tectonic extension and detachment faulting rather than by magmatic accretion. Here, I discuss the results of major element, trace element, and isotopic analyses for MORB, and show that prolonged slip along detachment faults is the consequence of melting an extremely depleted, variably enriched mantle source which supplies little melt to the ridge. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2016. / April 18, 2016. / detachment fault, geochemistry, Mid-Atlantic Ridge, mid-ocean ridge, MORB, oceanic core complex / Includes bibliographical references. / Vincent J. M. Salters, Professor Directing Thesis; Munir Humayun, Committee Member; Roy Odom, Committee Member.

The study conducted U-Pb isotopic dating of the pitchblende mineralization of the Coles Hill uranium deposit in Pittsylvania County, VA. The ore body is found along the Chatham fault and within the Martinsville Igneous Complex. In attempt to constrain the time of uranium mineralization, samples were collected within the fractures to the west of the Chatham fault that separates the host rock from the Danville Basin. Fifteen samples were analyzed for uranium and lead concentrations, as well as their isotopic lead compositions. BSE imaging revealed that the milligram sized samples consisted of multiple phases mixed on a micron scale. Uranium and lead isotopic analyses revealed that some phase or phases contained highly radiogenic (206Pb/204Pb ratios between 2,000 and 3,000) while some phases or phases were dominated by common lead. Highly discordant Pb/U ages of the highly radiogenic samples seem to be due to recent loss of substantial amounts of uranium. Analyses of these on a Concordia plot seems to indicate that uranium loss was not in a single event but occurred over time and likely recently. Therefore it was not possible to directly determine the age of the uranium mineralization. The four samples dominated by lead lie closely at 1115 Ma Pb-Pb isochron. It is inferred from this that the common lead present was derived from Grenville age basement that underlies the Smith River Allochthon. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the Master of Science. / Spring Semester 2016. / April 7, 2016. / Cole Hill, lead, U-Pb dating, uranium deposit / Includes bibliographical references. / A. Leroy Odom, Professor Directing Thesis; James F. Tull, Committee Member; Stephen A. Kish, Committee Member.

Nain craton tonalites show overall similarities to Uivak gneisses of northern Labrador, but are K$\sb2$O-poor and have variable LIL element contents--ascribed to variable degrees of Late Archean migmatization. Orthogneisses from the southern part of the Nain Province and from the Rae Province in the area studied show the greatest signs of LIL element depletion. Few mafic igneous rocks of Archean or Early Proterozoic age in this area appear to represent primary liquids. Many of these rocks are compositionally alkali basalts, high-Mg tholeiites, basaltic komatiites, or contain appreciable cumulus olivine. Most have nearly chondritic elemental ratios, although a few are more akin to those in modern-day MORB. Fine-grained metasedimentary rocks have geochemical signatures appropriate for their being derived from the quartzofeldspathic orthogneisses. Nd, Sr and Pb isotopic data were obtained on samples of troctolites, norites, anorthosites and plagioclase megacrysts from across the entire central portion of the exposed NPS. Primitive initial Nd and Sr isotopic ratios are preserved in olivine-bearing plutons and in a plagioclase megacryst from the western side of the massif. Significant variation in initial $\varepsilon\sb{\rm Nd}$ occurs across the NPS, from about $-$4 to $-$7 for magmas emplaced into the Rae Province (west), decreasing to $-$8 to $-$15 for magmas intrusive into Nain craton (east) and underscores the role of pre-existing lithosphere in controlling massif anorthosite isotopic compositional variation. This is strongly supported by preliminary Pb isotopic data. Mixing models between an estimated parent magma derived from a depleted source and specific samples of crust from country rock contacts reproduce the observed data, but require 30-60% contamination. A uniform level of most primitive (least contaminated) isotopic anorthosites from the western section and troctolites implies a 'ceiling' of $\varepsilon\sb{\rm Nd} \sim-$3, $\varepsilon\sb{\rm Sr} \sim$ +5 at 1.3 Ga. A model is proposed involving enrichment of a previously depleted lithospheric source at a minimum of 2.0 Ga, which is then inherited by the parental magmas to the anorthosite suite at 1.3 Ga. Magmas then assimilate either Archean or Proterozoic lower crust (depending on location). Calculated assimilation proportions are thereby reduced by approximately 15%. (Abstract shortened by UMI.)

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Includes bibliographical references. / The precipitation of iron from aquifer water in boreholes is a problem in the Klein Karoo region of South Africa. The precipitation causes boreholes to clog and limits full use of well fields in the area. The iron is naturally occurring and this project sets out to identify the lithological source of the iron and in what form the iron is presented. The Table Mountain Group (TMG) aquifer is a fractured rock aquifer situated in the TMG and rock samples were taken from the various lithologies in the area.

Includes bibliographical references (leaves 99-105). / Trace elements have received increased attention since the mid-1900's. Although some studies have investigated trace element accumulation as a result of urban expansion in the Western Cape, South Africa, few have catalogued the accumulation and behavior of trace elements resulting from agricultural practices. This study investigates the distribution and behavior of trace elements for the Olifants and Berg river catchments by focusing on the sediments of the estuaries. The dominant industry in both catchments is agriculture and there exists relatively little urban sprawl. Two sediment samples taken from the offshore mud belt in the vicinity of the two river mouths were also analyzed. The sediments were analyzed for trace elements using inductively coupled plasma mass spectrometry (ICP-MS), major elements using X-ray fluorescent spectroscopy (XRF), total sulfur using XRF, total and organic carbon using a C:H:N analyzer, and grain size analysis was performed (>62 μm, 38-63 μm, 2-38 μm, <2μm). The mud belt cores were dated using 14C dating. Estuarine surface waters were analyzed for trace elements, pH, dissolved oxygen (DO), electrical conductivity (EC), and temperature. The trace elements arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) were focused on. The trace element concentrations in the sediments were compared with those of soils that occur in the study area, as well as their parent materials, to determine background concentrations. The concentration profiles of elements with respect to depth are compared with natural deposition rates to recognize signs of recent enrichment of individual trace elements. Inter-element comparisons are made in an attempt to determine speciation. Comparison between the estuarine and mud belt sediments were made to assess the estuaries ability to filter fluvial trace elements, as well as to determine the sediment contributions of the Olifants and Berg rivers to the mud belt. Statistical analysis was performed to"group sediment populations Trace element and organic matter concentrations showed strong positive correlations with fine-sized particles. The mud belt sediments displayed considerably more OC than the estuarine sediments. The trace elements appear to associate predominantly with clay minerals (alumino-silicates), Fe/Mn oxides, and organic matter. Trace element correlations with S and carbonate carbon were also observed. Comparison with estimates of natural deposition rates and compositions of soils occurring in the catchments did not suggest an anthropogenic pollution input. From the data available the estuarine and Mud Belt sediments appear enriched in Cd, Cu and Zn in comparison to the background soils. The estuaries seem to effectively trap Zn and Pb, but do not capture As well. Statistical analysis suggest that, of the rock types considered, the sediments of the Olifants and Berg river estuaries and those of the off shore mud belt are most similar to sediments derived from the Malmesbury and Ecca Groups. The Olifants and Berg rivers are important sources of water for the farming community, as well as for municipal use in the Western Cape. Based on this investigation of the estuarine waters and sediments the rivers appear to be in good health in regards to trace element concentrations.