1: Dipartimento di Geoscienze, Università degli Studi di Padova, Via G. Gradenigo 6, I-35131, Padova, Italy 9 2: Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, V6T 1Z4 Vancouver, Canada 10 3: Institute of Precambrian Geology and Geochronology RAS, 199034, St. Petersburg, Russia 11 4: Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Botticelli 23, I-20133 Milano, Italy 12 5: Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada T6G 2E9 13 6: Department of Earth Sciences, University College London, Gower St, London WC1E 6BT, UK 14 7: Department of Earth and Environmental Sciences, University of Pavia, Via Ferrata 1, I-27100 Pavia, Italy 15 8: CNR-Istituto di Geoscienze e Georisorse – Sezione di Padova, Via G. Gradenigo 6, I-35131, Padova, Italy 16 9: University of Cape Town, Cape Town, South Africa, john.gurney@msgroup.net 17 10: Rhodes University, Grahamstown, South Africa, andy.moore.bots@googlemail.com 18 11: Petra Diamonds, Bryanston, South Africa, jim@petradiamonds.com 19 20 21

Laboratory experiments and seismology data have created a clear theoretical picture of the most abundant minerals that comprise the deeper parts of the Earth's mantle. Discoveries of some of these minerals in 'super-deep' diamonds-formed between two hundred and about one thousand kilometres into the lower mantle-have confirmed part of this picture. A notable exception is the high-pressure perovskite-structured polymorph of calcium silicate (CaSiO3). This mineral-expected to be the fourth most abundant in the Earth-has not previously been found in nature. Being the dominant host for calcium and, owing to its accommodating crystal structure, the major sink for heat-producing elements (potassium, uranium and thorium) in the transition zone and lower mantle, it is critical to establish its presence. Here we report the discovery of the perovskite-structured polymorph of CaSiO3 in a diamond from South African Cullinan kimberlite. The mineral is intergrown with about six per cent calcium titanate (CaTiO3). The titanium-rich composition of this inclusion indicates a bulk composition consistent with derivation from basaltic oceanic crust subducted to pressures equivalent to those present at the depths of the uppermost lower mantle. The relatively 'heavy' carbon isotopic composition of the surrounding diamond, together with the pristine high-pressure CaSiO3 structure, provides evidence for the recycling of oceanic crust and surficial carbon to lower-mantle depths.

Africa’s modern Zambezi is proposed as an example of a major extant river system, which archives the tectonic events that assembled and then fragmented a supercontinent. The Zambezi and an earlier Karoo river system, (here designated the ProtoZambezi River system), have a recorded geological history spanning approximately 280 million years. Its original headwaters were formed when the End-Neoproterozoic to Ordovician amalgamation of the Gondwana Supercontinent created a central Himalayanscale mountain belt, now called the Trans-Gondwana Mountain Range (at the core of the East Africa-Antarctica-Orogenic Belt). Eroded remnants of these mountains were the source of west-directed Dwyka glacial sediments and Ecca and Upper Karoo, PermoTriassic, rift-controlled lakes and rivers across West Gondwana. The reversed drainage of the Zambezi River started to flow eastwards through the same rift valleys in the Middle Jurassic (at about 165 Ma), as Africa started to separate from the eastern part of West Gondwana, with the resultant development of an eastern seaboard. This second stage in the evolution of the Zambezi River mirrored sequential openings of the Indian and Atlantic Oceans, in the post-Gondwana interplay between epeirogeny and rifting. Protracted longevity of the Zambezi River and its ancient precursor shows that major drainage systems can survive plate break-up, albeit with changed flow directions and continuously evolving catchments. SOUTH AFRICAN JOURNAL OF GEOLOGY. 2015. VOLUME 118.4 PAGE 425-438 doi:10.2113/gssajg.118.4.425 y _ j g

Africa's modern Zambezi is proposed as an example of a major extant river system, which archives the tectonic events that assembled and then fragmented a supercontinent. The Zambezi and an earlier Karoo river system, (here designated the Proto-Zambezi River system), have a recorded geological history spanning approximately 280 million years. Its original headwaters were formed when the End-Neoproterozoic to Ordovician amalgamation of the Gondwana Supercontinent created a central Himalayan-scale mountain belt, now called the Trans-Gondwana Mountain Range (at the core of the East Africa-Antarctica-Orogenic Belt). Eroded remnants of these mountains were the source of west-directed Dwyka glacial sediments and Ecca and Upper Karoo, Permo-Triassic, rift-controlled lakes and rivers across West Gondwana. The reversed drainage of the Zambezi River started to flow eastwards through the same rift valleys in the Middle Jurassic (at about 165 Ma), as Africa started to separate from the eastern part of West Gondwana, with the resultant development of an eastern seaboard. This second stage in the evolution of the Zambezi River mirrored sequential openings of the Indian and Atlantic Oceans, in the post-Gondwana interplay between epeirogeny and rifting. Protracted longevity of the Zambezi River and its ancient precursor shows that major drainage systems can survive plate break-up, albeit with changed flow directions and continuously evolving catchments.

Type II (N-poor) diamonds do not constitute a single genetic population with a common paragenesis. Rather, several distinct populations (P-, E-, W- and sub-lithospheric) can be recognized, which formed in contrasting geological environments, with very different factors controlling the N-deficient character of these stones. Mantle-derived silicate and oxide inclusions are absent or extremely rare in large, Irregular Type II stones, which are often of exceptional gem quality. Such characteristics set these diamonds apart from N-poor (Type II) stones with “superdeep” inclusions, as well as the peridotitic and eclogitic suites, both of which include stones with non-detectable N. This in turn points to crystallization of the Irregular Type II stones in an environment markedly different from those in which the other three associations formed. Carbon isotopic signatures and syngenetic inclusions link both framesite and Irregular Type II diamonds to the websterite paragenesis. The latter in turn shows strong chemical affinities to the megacryst suite. From a purely petrographic perspective, the large Irregular Type II stones would be classified as megacrysts on the basis of their size (often >10 mm). The megacryst suite formed as pegmatitic veins from small volumes of kimberlitic liquids, injected into fractures within the thermal aureole surrounding the pooled kimberlite magma in the mantle prior to eruption. Crystallization of Irregular Type II diamonds was initiated when small volumes of evolved, residual megacryst magmas became buffered by highly reduced mantle wall rocks. Visually identified graphite inclusions, often rounded and thus inferred to be protogenetic, are relatively common in these diamonds. This observation is consistent with the inferred P-T conditions of crystallization of megacrysts across the graphite-diamond inversion curve, and thus within the lithosphere. Rapid crystallization of framesites from reduced megacryst magmas was probably triggered by stresses in the mantle immediately prior to kimberlite eruption. The websterite diamond suite is thus directly linked to megacryst crystallization, broadly coeval with the kimberlite magmatic event in the mantle. Experimental studies on the crystallization of granite pegmatites, complemented by processes specific to formation of the megacryst suite, provide a framework to account for the absence or extreme rarity of inclusions of other megacryst phases in the Irregular Type II stones. The elevated boron contents of blue Type IIb diamonds are consistent with the model for crystallization from highly fractionated pegmatitic megacryst magmas. Reduction of boron to the metallic state is ascribed to buffering of the megacryst magma by extremely refractory and highly reduced wallrock harzburgites, such as those found at Premier, which is one of the world’s major kimberlite sources of blue diamonds. Formation of fibrous cubic diamonds and the Premier eclogitic diamonds, which are both broadly coeval with eruption of the host kimberlite, can also be linked to the kimberlite magmatic event in the mantle.

Kimberlite and lamproite exploration programmes have traditionally been underpinned by systematic sampling programmes, aimed at identifying anomalous concentrations of kimberlite indicator minerals (KIMs) proximal to the host rocks. These “pathfinders”, which typically include one or more of the phases ilmenite, eclogitic and peridotitic garnets, chromite, Cr-rich diopside, occasionally olivine, and sometimes diamond, tend to concentrate as a lag halo around the source rocks because of their relatively high densities compared to more abundant crustal minerals such as quartz and feldspar.. Dispersion of the KIMs away from the parent rocks by processes such as fluvial and glacial transport, and longshore currents in lacustrine or marine environments, typically results in decreasing concentrations away from the source. However, distal re-concentration of pathfinder minerals may occur in geomorphic settings which act as traps or sinks for relatively dense phases. It is important to distinguish between proximal and distal pathfinder concentrations at an early stage, not only because of the time and cost associated with sampling programmes, but also with the view to planning ongoing exploration to locate the ultimate source rocks. This study highlights some of the typical characteristics of distal KIM anomalies within the Kalahari environment with reference to a major kimberlitic garnet anomaly located in the southwestern Makgadikgadi basin in northern Botswana.

The Makgadikgadi Pans in northern Botswana are the desiccated relicts of a former major inland lake system, with fossil shorelines preserved at five distinct elevations (similar to 995 m, 945 m, 936 m, 920 m and 912 m). These lakes persisted in the Makgadikgadi Basin, which evolved in the Okavango-Makgadikgadi Rift Zone: the south-western extension of the East African Rift System (EARS) into northern Botswana. This paper synthesizes cross-disciplinary evidence, which reveals that the antiquity of this lake complex has been widely underestimated. It presents a Regional Drainage Evolution Model that invokes tectonically initiated drainage reorganizations as the underlying control over lake evolution. Lake formation was initiated by rift-flank uplift along the Chobe Fault, across the course of the Zambezi River, which diverted the regional drainage net into the Makgadikgadi Basin. Filling of the basin initiated a major climatic feedback mechanism that locally increased rainfall and lowered evaporation rates. This progressively enhanced water input to the basin, and most likely led to overtopping of the Chobe Horst barrier during the three highest lake stands, with outflow into the Zambezi River. During this period, the hydrology of the basin would have been closely analogous to modern, shallow Lake Victoria. Fragmentation of the regional drainage network by successive river captures resulted in sequential contractions of the lake to lower elevation shorelines. In turn, resultant decreases in areas of these successive lakes modulated the magnitude of the feedback mechanism. Thus, loss of the Upper Chambeshi catchment caused the lake to drop from the 990 to the 945 m level. Severance of the former link between the Kafue and Zambezi resulted in a further drop to the 936 m shoreline. Inflow declined further after the impoundment of a major lake (Palaeo-Lake Bulozi) on the Upper Zambezi River, causing contraction to the 920 m shoreline. Continued incision of the Zambezi channel into the Chobe horst barrier ultimately terminated input from this river to the Makgadikgadi depression, causing contraction of the lake below 920 m, sustained by the Cuando and Okavango prior to final desiccation. This Regional Drainage Evolution Model contradicts previous proposals that have invoked Late Pleistocene climatic forcing to explain inferred fluctuations in lake levels. The timeframe developed for the drainage reorganizations requires that the lake was initiated by similar to 1.40 to 0.51 Ma at the most recent (Early - Mid-Pleistocene), while archaeological evidence shows that it had contracted below the 936 m shoreline before 500 ka. This contrasts with C-14 and quartz luminescence dates (generally <100 ka), which require that the 945 m lake stage was extant during much of the Upper Pleistocene. The calcareous radiocarbon dates reflect multiple episodes of calcrete formation, while the young luminescence dates are ascribed to the extensive bioturbation of older Kalahari landforms.

Prospecting carried out to the south of the Zambezi-Limpopo drainage divide in the vicinity of Bulawayo, Zimbabwe, led to the recovery of a suite of ilmenites with a chemical “fingerprint” that can be closely matched with the population found in the early Palaeozoic Colossus kimberlite, which is located to the north of the modern watershed. The ilmenite geochemistry eliminates other Zimbabwe Kimberlites as potential sources of these pathfinder minerals. Geophysical modelling has been used to ascribe the elevation of southern Africa to dynamic topography sustained by a mantle plume; however, the evolution of the modern divide between the Zambezi and Limpopo drainage basins is not readily explained in terms of this model. Rather, it can be interpreted to represent a late Palaeogene continental flexure, which formed in response to crustal shortening, linked to intra-plate transmission of stresses associated with an episode of spreading reorganization at the ocean ridges surrounding southern Africa. It is proposed that the formation of the flexure was a dynamic process, with the initial locus of flexure located to the north of the Colossus, resulting in the dispersal of ilmenites to the south of this kimberlite. Subsequently, the axis of flexure migrated to its present position, to the south of Colossus.

Type II diamonds from Premier are characterised by light carbon isotope-enriched compositions, markedly different from the signatures of the associated Eclogitic (E-type) and Peridotitic (P-type) diamonds at the same locality. This provides strong evidence that these Type II stones represent a third and hitherto unrecognised diamond paragenesis. Their isotopic signature is closely similar to that of rare Orapa diamonds with websterite inclusions, arguing for a common paragenesis. The Orapa websterite garnet inclusions are Ti- and Cr-rich relative to those from other kimberlites, and overlap the compositional field for Orapa garnet megacrysts. These chemical characteristics, coupled with the large size and irregular shape of Type II diamonds links them to the megacryst suite. This conclusion is supported by evidence which shows that at the low temperature range of megacryst crystallisation, the associated residual liquids, if buffered by mantle wall rocks, at oxygen fugacities between the WM and IW, would be in the diamond P-T-f(O2) stability field. The low N concentrations and light cabon isotopic-enriched fingerprint of the Type II stones are consistent with their crystallisation from such evolved magmas. It is demonstrated that in addition to the irregular and often large (megacryst) Type II stones, there are two further suites of N-poor diamonds which can be assigned to either an eclogitic or peridotitic paragenesis on the basis of their inclusions, physical properties and carbon isotopic signatures.Diamonds with complex growth zones and deformation textures can be explained in terms of dynamic mantle processes, linked to formation of the sheared peridotites, within the thermal aureole surrounding the kimberlite magma in which the megacrtst suite crystallised. Framesites, fibrous cubic diamonds, and eclogitic diamonds which formed just prior to kimberlite eruption, can also be linked to the processes responsible for crystallisation of the megacryst suite, which is considered to be cognate to the host kimberlite magma.

Evidence is presented to model drainage evolution across Zimbabwe since the Permian. This provides the framework to Understand the marked difference in character of the rivers to the north and South of the modern central Zimbabwe watershed, which separates the Zambezi and Limpopo drainage basins. North-flowing tributaries of the Zambezi rising Off this river divide have low gradients and senile characteristics. The northwest orientation of the upper sections of many of these rivers is unusual for tributaries of a major east-flowing drainage, but is in accord with the west-orientated fluvial system that deposited the Triassic sediments of the Karoo Supergroup in the Cabora Bassa basin of the Zambezi Valley. The modern drainage system to the north of the central Zimbabwe watershed is thus largely controlled by a surface that has existed since pre-Karoo times. Headwaters of the Zambezi tributaries were originally located well to the south of the modern divide, with high ground extending to the present-day Chimanimani and Nyanga mountainland in eastern Zimbabwe. This drainage system, persisted until the late Triassic, when rifting, linked to the early disruption of Gondwana, initiated the formation of the modern Save and Zambezi river systems. The central Zimbabwe watershed represents a late Palaeogene (similar to 43 to 33 Ma) asymmetric epeirogenic flexure, part of the Axis, which beheaded the headwaters of the early Zambezi tributaries. The resultant steeper gradients to the south of the watershed initiated the modern youthful south-flowing, drainage system. A further disruption to the Zambezi drainage system occurred during Plio-Pleistocene arid episodes, when major dunes developed across dry river systems such as the Shangani, in the northwest of the country. Renewed flow in these rivers during subsequent wetter pluvial episodes resulted in them exploiting the inter-dune streets to develop new courses. Some, like the Shangani, incised their courses through the Kalahari sand cover to become superimposed drainages.The landscape of much of Zimbabwe reflects the imprint of two major cycles of erosion (African and post-African) since the disruption of Gondwana. The African erosion cycle commenced with the disruption of Gondwana, while the ensuing post-African cycle of erosion was initiated by the late Palaeogene uplift along the line of the modern central watershed. This rejuvenated the river network, leading to removal of the carapace of deeply weathered saprolite that developed under the humid mid-Cretaceous climate of the earlier African cycle. The post-African surface is thus an etch surface, with the characteristic plain and inselberg topography marking the weathering base of the African erosion event. A very subordinate Plio-Pleistocene cycle is reflected by terraces immediately marginal to the major river systems. The confinement of the Save and Zambezi drainages to graben structures resulted in their evolution largely independently of the two major erosion cycles that moulded the landscape of the rest of the country.The palaeo-drainage reconstruction has important implications for the dispersion of diamonds and associated pathfinder minerals front primary kimberlite sources. The Sese-Murowa kimberlites are inferred to be the primary source of hitherto unexplained alluvial diamonds in basal gravels of the Somabula Karoo outlier, located on the central Zimbabwe watershed, some 120 km to the northwest. The drainage evolution model also provides a framework to infer likely distal kimberlite sources for a number of major unexplained kimberlitic pathfinder mineral anomalies associated with the southern margin of the Kalahari Formation.

Shaving the axilla is a regular part of the personal care regime for many women in Europe, North and South America. To assess the impact of shaving on underarm skin, a series of investigations were carried out, in which the thickness of the axillary vault and fossa were measured using optical coherence tomography (OCT), and underarm shaving debris was collected for study. The response of the axilla to histamine iontophoresis was also investigated. Additionally, a study was carried out to investigate the impact of a novel anti-perspirant roll-on formulation on irritation and self-perceived sensory properties of the axilla. The results clearly demonstrate that shaving the underarm consistently removes skin (stratum corneum) as well as axillary hair (with a mean value of 36.1% of the debris being skin). OCT measurements demonstrated that in shaved areas of the axilla, epidermal thickness is higher than in unshaved areas. In response to histamine, wheal and flare were both found to be greater in the shaved axilla, when compared with an unshaved control, but flare in the fossa was greater than that in the vault. On the basis of these results, we propose that the axillary vault has adapted to frequent shaving, notably by the development of a thickened epidermis. However, this adaptation is often not sufficient to fully protect the axilla from damage and irritation resulting from hair removal (shaving). In these instances, we have demonstrated that use of a novel anti-perspirant roll-on formulation containing glycerol and sunflower seed oil was able to reduce the impact of shaving-induced irritation and improve self-assessment of axillary condition.

The axillary skin is cosmetically important with millions of consumers daily applying antiperspirant/deodorant products. Despite this, we know virtually nothing about axillary skin or how antiperspirant use impacts upon it. To characterize axillary stratum corneum and determine whether this is a unique skin type, we have evaluated a range of skin parameters, comparing these with the volar forearm. Trans‐epidermal water loss and corneosurfametry revealed a reduced barrier function in the axilla. However, application of antiperspirant had no effect upon these barrier properties. High performance thin layer chromatography analysis of stratum corneum lipids demonstrated statistically elevated levels of fatty acids, ceramide and particularly cholesterol in the axilla. This modification of barrier lipid ratios appeared to result in a more ordered lipid lamellae phase behaviour, as determined by attenuated total reflectance Fourier transform infrared spectroscopy, with transition phase changes occurring at higher temperatures. Morphological differences were also seen in the cells of the axillary stratum corneum. Microscopic evaluation of axillary‐cornified envelopes revealed them to be smaller, indicative of a shorter stratum corneum turnover. However, there appeared to be no significant difference corneocyte maturation. ‘Skin dryness’ squamometry measurements indicated that the axillary stratum corneum retained desquamated material on its surface more than on the forearm. This correlated with decreased levels of the desquamatory stratum corneum chymotryptic enzyme in the surface layers of the skin. These results indicate that the axilla has a distinct phenotype. Paper presented at the 22nd IFSCC Congress 2002, Edinburgh, Scotland

The dramatic escarpment bounding the Drakensberg-Maluti mountainland has long been regarded as a classic example of a topographic feature formed by scarp retreat processes. However, this view has recently been challenged on the basis of apatite fission track (AFT) and cosmogenic isotope data, which are argued to be inconsistent with a uniform rate of scarp retreat from the original position of continental break-up. It was suggested rather, that the evolution and present position of the escarpment was controlled primarily by a pre-existing inland drainage divide. Numeric surface process models have been used to support this interpretation, although these rely on a large number of unconstrained variables, and thus do not provide unique solutions.However, several lines of direct geological field evidence support the scarp retreat model for the evolution of the Drakensberg escarpment. The Drakensberg-Maluti Mountains in southern Africa are formed by a similar to 1000 m thick sequence of Karoo basalts, capping Karoo sediments. This mountainland has an approximately rectangular shape, surrounded by orthogonal escarpments, except in the southwest, where it is dissected by the deeply incised Orange River. In detail, these marginal scarps are everywhere double topographic features, reflecting two resistant layers that form prominent cliffs: the thick upper basalt flows, and the Clarens Formation sandstone at the base to the lava sequence. Moreover, in the Drakensberg-Maluti example, the presence of inland-facing escarpments reveals that escarpment formation is not exclusively related to processes that occur at or adjacent to the site of continental break-up. These direct geomorphological and geological observations demonstrate that resistant units are the dominant influence in escarpment formation. Headward retreat of large waterfalls on major rivers over considerable distances (10-100 km) provides clear field evidence that scarps formed by resistant lithologies will not invariably degrade as a result of the existence of an inland drainage divide, as has been argued on the basis of surface process modelling.Several complementary factors provide a ready explanantion for apparent inconsistencies in the scarp retreat model that were identified from the AFT and cosmogenic isotope studies. The Drakensberg-Maluti mountains are surrounded by a dense network of dolerite dykes that were contemporary with, and supplied, the Karoo basalts. The massive lava flows capping the modern escarpment therefore probably originally extended at least to the edge of the dyke network. The advance inland of an erosion front, initiated by continental break-up, would have slowed dramatically where such massive lava flows were encountered. Tectonic processes climate changes, and possibly plant evolution may have compounded this decrease in erosion rates. Although these latter factors are not readily quantified, they were probably subordinate to the dominant lithological control that we invoke. Escarpments may thus form and persist over long periods, extending from the time of continental break-up to the present, independently of inland drainage divides. These field observations must be taken into consideration when assigning values to the numerous uncontrained variables used in surface process models.

Karoo-age diamond-bearing conglomerates, located to the southwest of Gweru in central Zimbabwe, have long presented an enigma in terms of their mode of deposition, and the primary source of the diamonds. Although conglomerate units occur throughout the Somabula Karoo succession, the diamonds and associated varied heavy mineral suite are concentrated in a discontinuous basal unit, with large subangular to subrounded clasts, supported by a clay-rich or arkosic matrix, which fills irregularities in the palaeo-floor. The concentration of diamonds and heavy minerals in this extremely immature basal deposit is not readily explained in terms of simple single-stage fluvial processes. Further, the occurrence in the gravels of well formed crystals of soft Pt-group minerals, as well as a small proportion of idiomorphic crystals of staurolite (the dominant heavy mineral phase, with a distal provenance), is difficult to reconcile with fluvial transport over any significant distance. It is therefore suggested that the basal conglomerate clasts and associated heavy mineral suite, including diamonds, represent the winnowed and concentrated lag products of a former Permian till, with a distal provenance. This implies a major erosional break between the deposition of the basal till and overlying Triassic (upper Karoo) sediments. The latter are dominated by immature arkoses with subordinate rudaceous and argillaceous units, interpreted to reflect deposition in a braided river system. The initial pulse of upper Karoo sedimentation swamped the residual clast/heavy mineral lag left by winnowing of the former Permian till, with only minor reworking of this material. The result was an assemblage of clasts and heavy minerals in marked hydraulic disequilibrium with the supporting matrix.

The source area of Dwyka Group glacial sedimentary rocks in southern Africa contains a province of pre-Karoo diamondiferous kimberlites. Ice-flow vectors and facies variations indicate that diamonds and kimberlitic indicator minerals, acquired in this source region during the Dwyka glaciation, were transported to and deposited in areas adjacent to the modern Atlantic coast of southern Africa. Diamonds and kimberlite garnets, recovered from the Koa River gravel deposits on the Bushmanland Plateau, were probably derived by weathering of these Dwyka Group rocks. Along the west coast of South Africa and Namibia, marine and fluvial diamond concentrations of Cretaceous, Miocene and Plio-Pleistocene ages were also partly derived from Dwyka sources in both the Karoo and Kalahari Basins, as well as from other secondary sources such as glacial and fluvial sedimentary rocks of the Gariep Complex, Nama Group and Table Mountain Group. On the coastal plain, Cretaceous fluvial deposits formed during scarp retreat under podzolic weathering conditions. Miocene and younger fluvial and marine deposits formed by weathering processes that involved stripping of back-escarpment Karoo cover. Due to the presence of oversized diamictite-clast trapsites, concentrations of diamonds accumulated on exposed pre-Karoo surfaces during extended periods of crustal stability. Brief episodes of increased precipitation and uplift during the Miocene and Pliocene caused the flushing of these concentrations, in discrete events, via a few major drainages, into marine and near-coastal fluvial and aeolian settings.The majority of inland alluvial diamond deposits are located in a broad belt to the north and west of the Cretaceous diamondiferous kimberlite clusters in central South Africa. This distribution is probably the result of north-westward-flowing fluvial systems, inland of the Great Escarpment, which eroded significant thicknesses (up to 1.5 km) of Karoo cover rocks and drained into the palaeo-Molopo (Kalahari) River across the buried Cargonian Highlands. Lag concentrations of diamonds ultimately formed on the African Surface in traps such as karstic depressions and fluvial channels. Post-African weathering exposed south-westward-draining pre-Karoo glacial valleys along the margins of the Cargonian Highlands and established the Vaal-Harts-upper Orange River system, which reworked the older African-Surface regolith into secondary Miocene and younger colluvial and alluvial gravel deposits. Additional diamond contributions came from limited post-African weathering of primary kimberlite and secondary Dwyka sources. These gravel deposits extend as far as Prieska on the upper Orange River and may not have contributed large quantities of diamonds to the west-coast diamond resource. The inland alluvial deposits, therefore, have a significant primary Cretaceous kimberlite source, whereas those on the west coast were derived from multiple sources that include a substantial primary pre-Karoo kimberlite component via secondary Dwyka Group glacial redistribution. (C) 2003 Elsevier Ltd. All rights reserved.

Removal of underarm hair is an intrinsic part of the care regimen for the majority of female consumers, with most using a wet shave with a disposable razor. However, little is known of the impact of shaving on axillary skin, and it is a particularly neglected area of research. To investigate this, we have studied the acute and chronic effects of shaving ultrastructurally, biochemically and functionally. A forearm patch test protocol was devised for antiperspirant (AP) product screening, which involved a pre-shave of the test site with a dry razor just prior to patching. Comparison of the irritation caused by a series of AP products confirmed that shaving leads to increased irritation consistent with enhanced sensitivity. The effect of regular shaving in the axilla was assessed in a 4-week in-use study with shaving either once a week or once a day, both combined with the application of an AP. Expert visual assessment of skin condition showed that more frequent shaving promoted a higher level of visible irritation. However, indirect measurement using corneosurfametry indicated no significant changes to the lipid barrier over the study period irrespective of shaving frequency. Nevertheless, digital images of the axillary skin after dry shaving show distinct opaque lines because of uplifting skin flakes with a corresponding increase in scaliness parameter. Moreover, histamine iontophoresis to assess skin sensitivity demonstrated a significant enhancement of histamine-induced itch and neurogenic flare.