博茨瓦纳卡拉哈里含煤盆地及开发前景

通过广泛收集资料以及野外考察,博茨瓦纳的主要含煤盆地是卡拉哈里盆地和图利盆地。卡拉哈里盆地形成于石炭纪—二叠纪,面积约43×104km2,可进一步分为7个次级盆地。主要次级盆地为东南中部卡拉哈里次盆和南带中卡拉哈里次盆。主要含煤地层是卡鲁超群的爱卡群。煤层一般受断裂控制,沿一定构造部位分布。主要煤田为莫鲁普莱煤田及姆马马布拉煤田。已查明这些盆地的煤储量约为170亿吨,博茨瓦纳煤炭的销路主要从南非出口,运往欧洲和印度,或供给本土发电,具有较好的勘探开发前景。     

Lithostratigraphy of the Kalahari Group in northeastern Namibia

The Kalahari Group in northeastern Namibia consists of terrestrial sediments deposited in a tectonically active basin that was formed by flexural uplift of the African continental margin and independent structures related to rifting. The thickness of the sequence varies from a few meters to around 400 m. Greatest thicknesses occur where the NW–SE trending Kalahari basin axis conjugates with NE–SW trending grabens.Repeated phases of flooding and desiccation dominate the depositional environments of the Kalahari Group in northeastern Namibia. Associations of lithofacies allow recognition of distinct depositional settings such as proximal debris flows, braided streams and sand fans, and pans and sandflats.The northeastern Namibian Kalahari Group rests unconformable on the pre-Kalahari surface which showed a relatively pronounced relief in the Epukiro area. The succession starts with conglomerates, breccias and pebbly sandstones, followed by carbonates, sandstones of various maturities, and silcretes. Ferruginous sandstones and ferricretes occur locally. The onset of Kalahari Group deposition was likely a basin-wide event and therefore the basal lithostratigraphic units can be correlated with confidence. Conversely, the correlation of the succeeding lithostratigraphic units remains fairly speculative.     

博茨瓦纳境内卡拉哈瑞铜-金成矿带找矿前景

卡拉哈瑞(K alah ari)成矿带上有世界著名的铜、金、镍矿产,其中纳米比亚辛克莱特大型铜矿和赞比亚特大型铜矿,已探明储量占世界的10%.该成矿带经纳米比亚~博茨瓦纳~赞比亚,长1500km ,宽15 km .博茨瓦纳位于该成矿带的中段,境内长约500 km 、宽10 km .1982年西方一家公司在乔贝(C hobe)地区的古哈山钻探验证航磁异常,寻找成矿潜力区.在深部见多层铜、金矿体.1995年 A stra E xploration and M ining C om pany(Pty)Ltd 公司在卡拉哈瑞成矿带乔贝(C hobe)地区完成了航磁调查和重力异常调查     

Identity building and social transformation: the cases of Namibia and Botswana compared

Namibia and Botswana differ from other sub-Saharan nations in their record of stable political performance. However, both countries have to face increasing social problems. In the case of Namibia these are still mainly related to the process of post-apartheid national reconciliation and identity building, in the case of Botswana they refer to issues of growing tribal tensions and of a gradual interior restructuring of society. This paper analyzes the various patterns of social transformation in the two countries and examines in what ways state-society relations are different from other African nations. This revised version was published online in July 2006 with corrections to the Cover Date.     

香港区域地层划分

本文在研究前人大量工作的基础上,以香港地区的地质演变历史为主要线索,重新拟定了泥盆纪以来香港的地层层序;对各主要地层单位,尤其是近年来新建的地层单位进行了讨论;将香港的地层与广东和中国南方进行了对比,并对香港今后进一步地层工作的方向提出了一些建议。本文的目的是建立一个简要的、索引式的有关香港地层的回顾,以便使读者能迅速掌握香港地层划分和对比的概况以及基本的地质演化历史。     

Impact of recharge variations on water quality as indicated by excess air in groundwater of the Kalahari, Botswana

Groundwater is an important and often exclusive water resource in arid and semi-arid regions. The aim of the present paper was to gain insight into the processes and conditions that control the deterioration of groundwater quality in the semi-arid Kalahari of Botswana. Measurements of ³He, ⁴He, ²⁰Ne, ²²Ne, and of ¹⁴C of dissolved inorganic carbon (DIC) were combined with existing isotopic and hydrochemical data to investigate groundwater from the Ntane Sandstone Aquifer, which is affected by high nitrate concentrations of non-anthropogenic origin. All groundwater samples revealed neon concentrations in excess to air-saturated water, which we attributed to the addition of excess air during recharge. Neon concentrations ranged from values close to air saturation for ¹⁴C DIC rich samples (up to 80.5%MC) up to values of 90% in excess to air-saturated water for lower ¹⁴C DIC contents (2.6-61.3%MC). A strong linear correlation of excess Ne with nitrate concentrations suggests an intimate connection between groundwater quality and the processes and conditions during groundwater recharge. Low groundwater recharge rates under present-day semi-arid conditions are associated with low amounts of excess Ne and elevated nitrate concentrations. In contrast to this, higher excess Ne values in groundwater of lower ¹⁴C DIC and nitrate contents indicate that the high quality groundwater end-member presumably is related to higher groundwater table fluctuations during wetter climatic conditions in the past. We attribute the decline in groundwater quality with respect to nitrate to a decreasing rate and temporal variability of groundwater recharge, and to concurrent changes in biogeochemical activities following a transition to a drier climate during the Holocene. Under such conditions, a much stronger decrease in groundwater recharge compared to the release of nitrate from soil organic matter may result in elevated nitrate concentrations in the vadose zone and groundwater. This implies a strong impact of climate change on the transport of solutes like nitrate through the vadose zone which needs to be considered in predictions of future groundwater quality.     

Hydrochemical models of the sulphidic tailings dumps at Matchless (Namibia) and Selebi-Phikwe (Botswana)

The sulphidic tailings dumps at Matchless (Namibia) and Selebi-Phikwe (Botswana) are located in a similar semiarid environment but have a contrasting mineralogical composition. The Matchless tailings are pyrite-rich, whereas the Selebi-Phikwe tailings are dominated by pyrrhotite. Hydrochemical models are established with computer codes for water-balance, sulphide oxidation rate and hydrochemical equilibrium calculations. The data input is based on detailed mineralogical, chemical and kinetic investigations carried out on the core of boreholes drilled in 2000 and 2003. The oxidation of pyrrhotite proceeds at a much faster rate than the oxidation of pyrite. The PYROX code, which is used for kinetic calculations, can take these differences into account by applying different oxide-coating diffusion coefficients (D₂) for pyrrhotite and pyrite. Humidity-cell testing is widely used to predict the post-mining composition of drainage water in humid climates. However, the semiarid conditions at Matchless and Selebi-Phikwe only allow a minimal water flux within the dump. Under such conditions, humidity-cell testing is likely to overestimate the seepage-water pH. This is suggested by the hydrochemical equilibrium calculations for the post-mining period at Selebi-Phikwe, which predict a seepage-water pH about one unit lower than the pH at the end of the 26-weeks humidity-cell testing period. The acidity of the seepage water can be reduced by about half a pH unit, if an oxygen barrier below the evaporation zone is installed. A clay layer 0.5 m thick covered by >1.5 m tailings represents the optimal design for a wet barrier. All three computer codes used for water-balance calculations (HELP3, UNSAT-H and HYDRUS-1D), predict >85% average water saturation for such a layer, which diminishes the diffusion of oxygen into the pile and production of SO₄⁻² and H⁺. The alternative design for a dry barrier consists of a vegetated silt layer 1 m thick on top of the tailings. This barrier does not significantly influence the diffusion of oxygen although it reduces the net infiltration to ≤11 mm/year.     

Depositional ages and provenance of the Neoproterozoic Damara Supergroup (northwest Namibia): Implications for the Angola-Congo and Kalahari cratons connection

The Damara Orogen is composed of the Damara, Kaoko and Gariep belts developed during the Neoproterozoic Pan-African Orogeny. The Damara Belt contains Neoproterozoic siliciclastic and carbonate successions of the Damara Supergroup that record rift to proto-ocean depositional phases during the Rodinia supercontinent break up. There are two conflicting interpretations of the geotectonic framework of the Damara Supergroup basin: i) as one major basin, composed of the Outjo and Khomas basins, related to rifting in the Angola-Congo-Kalahari paleocontinent or, ii) as two independent passive margin basins, one related to the Angola-Congo and the other to the Kalahari proto-cratons. Detrital zircon provenance studies linked to field geology were used to solve this controversy. U-Pb zircon age data were analyzed in order to characterize depositional ages and provenance of the sediments and evolution of the succession in the northern part of the Outjo Basin. The basal Nabis Formation (Nosib Group) and the base of the Chuos Formation were deposited between ca. 870 Ma and 760 Ma. The upper Chuos, Berg Aukas, Gauss, Auros and lower Brak River formations formed between ca. 760 Ma and 635 Ma. It also includes the time span recorded by the unconformity between the Auros and lower Brak River formations. The Ghaub, upper Brak River, Karibib and Kuiseb formations were deposited between 663 Ma and 590 Ma. The geochronological data indicate that the main source areas are related to: i) the Angola-Congo Craton, ii) rift-related intrabasinal igneous rocks of the Naauwpoort Formation, iii) an intrabasinal basement structural high (Abbabis High), and iv) the Coastal Terrane of the Kaoko Belt. The Kalahari Craton units apparently did not constitute a main source area for the studied succession. This is possibly due to the position of the succession in the northern part of the Outjo Basin, at the southern margin of the Congo Craton. Comparison of the obtained geochronological data with those from the literature shows that the Abbabis High forms part of the Kalahari proto-craton and that Angola-Congo and Kalahari cratons were part of the same paleocontinent in Rodinia times.     

Origins of strandline duricrusts around the Makgadikgadi Pans (Botswana Kalahari) as deduced from their chemical and isotope composition

Trace elements together with some O and C isotope analysis were undertaken on duricrust strandline deposits in the palaeo-Makgadikgadi sub-basin (PMSB) to provide insight into palaeo-climatic conditions through the interpretation of calcrete, silcrete–calcrete intergrade and silcrete deposits. Trace element content and relative abundance suggest that the duricrust origins are associated with the long-term weathering of the Karoo Large Igneous Province which underlies the PMSB. This work shows that duricrust origins are related to Ca²⁺ and Si (and associated trace elements) being transported mainly through the groundwater and then subsequently precipitated at different strandline elevations over time. Local groundwater feeding in towards the pan margin and accumulating in near-neutral pan-marginal pools, appears to facilitate Si concentration and permeation of pre-existing calcretes. The silica precipitates as the pH drops when renewed freshwater enters the pools. Hence the inferred palaeo-climatic regime for silcretisation may be similar to that occurring in Botswana at present being dry semi-arid with low seasonal rainfall. In contrast the extensive calcrete precipitation in the strandlines results from abundant Ca²⁺ in adjacent waters which appear to be derived from both local and regional sources. The arrival of Ca²⁺ from regional sources (shown by trace element evidence) infers heavy rainfall in the upper catchment suggesting a major humid event followed by regional drying. Palaeo-climatic inferences suggest the juxtaposition of major humid events interspersed with more normal semi-arid palaeo-climates with an exception obtained from isotope data, of drier and cooler conditions than usual for the region around 80–90 000 years ago. Whereas trace element data can greatly assist in the interpretation of complex deposits such as duricrusts, care should be taken over the use of particular ratios (such as Yb/Gd ratio) which may produce spurious results.     

Gender sensitisation in the Zambian Copperbelt

This paper examines gender sensitisation in Kitwe, Zambia. My evidence, derived from a year’s ethnographic research, suggests that gender sensitisation is most effective when participants are also exposed to flexibility of gender divisions of labour. Seeing a critical mass of women performing socially valued roles appears to be interpreted as validation of abstract messages of equality. Such synergy is most commonly enabled when gender sensitisation is participatory. By sharing experiences of flexibility in gender divisions of labour, group discussants often come to publicly question widely-shared assumptions about men and women’s differing competence and status. Hearing others express support for gender equality also shifts presumptions about cultural expectations.     

Linear dune accumulation chronologies from the southwest Kalahari, Namibia: challenges of reconstructing late Quaternary palaeoenvironments from aeolian landforms

The linear dunes of the southern Kalahari dunefield constitute one of the major palaeoenvironmental proxies in the region. The application of optically stimulated luminescence (OSL) dating since the1990s and advancements in the depth of sampling using augering equipment over the past few years have permitted the reconstruction of linear dune accumulation chronostratigraphies for entire dune profiles from base to crest. These methods are applied to four dunes in the Mariental–Stampriet region of the southern Kalahari dunefield, sampled at predominantly 0.5 m intervals. Individual dunes record multiple phases of dune construction, but with only a few phases recorded consistently between two or more of the dunes. Results from the 48 OSL ages produced here extend the aeolian accumulation record for the southern Kalahari dunefield through the last three glacial–interglacial cycles with two ages from the early part of MIS6. A synthesis of all existing luminescence ages for the southern Kalahari reveals that the dunefield has been partially active throughout much of the past 120 ka. There are no clear clusters of ages within OSL age errors. This is in contrast to previous syntheses of ages for this region. In addition, these new data from Mariental–Stampriet dunes show that clusters in grouped dune OSL ages can be spuriously produced as a function of reducing the sampling frequency with depth within the dunes, from 0.5 to 1 mintervals. This has significant implications for previous conclusions regarding discrete phases of aeolian accumulation based on sampling at 1 m intervals and less vertically intensive sampling techniques. The total luminescence data set of 136 ages for the southern Kalahari implies that this dunefield has been close to the threshold of reactivation throughout much of the late Quaternary.     

Radiocarbon ages for coatings on cupules ground in quartzite bedrock at Rhino Cave in the Kalahari Desert of Botswana,and their paleoclimatic significance

Geophysical techniques have been widely employed for the noninvasive location of burial sites in archaeological and forensic investigations. This approach has met with varying degrees of success, depending on factors such as equipment choice, survey methodology, burial type, and geological setting. This paper reports the results of a multitechnique geophysical survey carried out immediately prior to the salvage excavation of two Indigenous burials from an eolian dune in coastal South Australia. Ground‐penetrating radar was not successful in defining the location of the burials owing to the disturbed nature of the local stratigraphy. Magnetic field intensity and apparent magnetic susceptibility surveys identified discrete anomalies that coincided with the location of skeletal material revealed during excavation, which we hypothesize to be due to burning or ochre use during funerary practices. Despite the spatial association of these features, subsequent laboratory analyses of the mineralogy and magnetic properties of sediments collected from the site failed to find a definite cause of the anomalies. Nevertheless, the association between them and the primary interment locations has implications for archaeological surveys carried out in the Australian coastal zone, as it highlights the potential of magnetic field intensity and apparent magnetic susceptibility geophysical techniques undertaken with a more refined survey methodology to afford a noninvasive, culturally appropriate means through which to detect Indigenous burials. This approach may prove particularly useful in areas with disturbed stratigraphy where ground‐penetrating radar is less effective. © 2010 Wiley Periodicals, Inc.     

Regional compilation and analysis of aeromagnetic anomalies for the Transantarctic Mountains–Ross Sea sector of the Antarctic

Magnetic observations over the area of the Transantarctic Mountains (TAM) and the Ross Sea have been compiled into a digital database that furnishes a new regional scale view of the magnetic anomaly crustal field in this key sector of the Antarctic continent. This compilation is a component of the ongoing IAGA/SCAR Antarctic Digital Magnetic Anomaly Project (ADMAP). The aeromagnetic surveys total 115 000 line km, and are distributed across the Victoria Land sector of the TAM, the Ross Sea, and Marie Byrd Land. The magnetic campaigns were performed within the framework of the national and international Italian–German–US Antarctic research programs and conducted with differing specifications during nine field seasons from 1971 until 1997. Generally flight line spacing was less than 5 km while survey altitude varied from about 610 to 4000 m above sea level for barometric surveys and was equal to 305 m above topography for the single draped survey. Reprocessing included digitizing the old contour data, improved levelling by means of microlevelling in the frequency domain, and re-reduction to a common reference field based on the DGRF90 model. A multi-frequency grid procedure was then applied to obtain a coherent and merged total intensity magnetic anomaly map. The shaded relief map covers an area of approximately 380 000 km². This new compilation provides a regional image of the location and spatial extent of the Cenozoic alkaline magmatism related to the TAM–Ross Sea rift, Jurassic tholeiites, and crustal segments of the Early Palaeozoic magmatic arc. A linear, approximately 100-km wide and 600-km long Jurassic rift-like structure is newly identified. Magnetic fabric in the Ross Sea rift often matches seismically imaged Cenozoic fault arrays. Major buried onshore pre-rift fault zones, likely inherited from the Ross Orogen, are also delineated. These faults may have been reactivated as strike-slip belts that segmented the TAM into various crustal blocks.     

Strengthening Western Gondwanan correlations: A Brazilian Dicynodont (Synapsida,Anomodontia) in the Middle Triassic of Namibia

Terrestrial Middle Triassic strata occur throughout continental Africa and are particularly well exposed in South Africa, Tanzania, Zambia, and Namibia. The youngest age for all these African deposits is widely accepted as early Middle Triassic (Anisian). Fossils collected recently from the uppermost strata of the upper Omingonde Formation in Namibia highlighted the presence of Chiniquodon, a carnivorous cynodont previously only found in Ladinian-Carnian aged rocks of South America. In addition, work in progress indicates that a large archosaur, originally reported as Erythrosuchus, also discovered from levels close to the top of this unit, is in fact a rauisuchian, a group of archosaurs well known from Ladinian-Carnian beds of southern South America. Here we present the first record of the tuskless dicynodont Stahleckeria potens from the top of the upper Omingonde Formation in central Namibia. This taxon was up until now only known from the Ladinian Dinodontosaurus Assemblage Zone of the Santa Maria Formation in southern Brazil. Thus, compelling evidence for a Ladinian age for the upper levels of the upper Omingonde Formation is provided by two therapsid and one archosaur taxa. The tetrapod fauna of the upper Omingonde Formation partially fills the gap of the well-documented hiatus (Ladinian gap), prevalent throughout the Karoo basins of south and central Africa. The presence of the same therapsid taxa in the Namibian Waterberg Basin and the Paraná Basin of Brazil during Middle Triassic suggests that these basins were biogeographically linked through a series of interconnecting lowlands, with no major ecological, climatic and/or physical barriers.     

Lithostratigraphy, basin development, base metal deposits, and regional correlations of the Neoproterozoic Nguba and Kundelungu rock successions, central African Copperbelt

The Neoproterozoic Katangan Supergroup comprises a thick sedimentary rock succession subdivided into the Roan, Nguba, and Kundelungu Groups, from bottom to top. Deposition of both Nguba and Kundelungu Groups began with diamictites, the Mwale/Grand Conglomérat and Kyandamu/Petit Conglomérat Formations, respectively, correlated with the 750 Ma Sturtian and (supposedly) 620 Ma Marinoan/Varanger glacial events. The Kaponda, Kakontwe, Kipushi and Lusele Formations are interpreted as cap-carbonates overlying the diamictites. Petrographical features of the Nguba and Kundelungu siliciclastic rocks indicate a proximal facies in the northern areas and a basin open to the south. The carbonate deposits increase southward in the Nguba basin. In the southern region, the Kyandamu Formation contains clasts from the underlying rocks, indicating an exhumation and erosion of these rocks to the south of the basin. It is inferred that this formation deposited in a foreland basin, dating the inversion from extensional to compressional tectonics, and the northward thrusting. Sampwe and Biano sedimentary rocks were deposited in the northernmost foreland basin at the end of the thrusting. The Zn–Pb–Cu and Cu–Ag–Au epigenetic, hypogene deposits occurring in Nguba carbonates and Kundelungu clastic rocks probably originate from hydrothermal resetting and remobilization of pre-existing stratiform base metal mineralisations in the Roan Group.     

The Neoproterozoic Mwashya–Kansuki sedimentary rock succession in the central African Copperbelt, its Cu–Co mineralisation, and regional correlations

Rocks of the Neoproterozoic Mwashya Subgroup (former Upper Mwashya) form the uppermost sedimentary unit of the Roan Group. Based on new field and drill hole observations, the Mwashya is subdivided into three formations: (1) Kamoya, characterized by dolomitic silty shales/siltstones/sandstones and containing a regional marker (the “Conglomerate de Mwashya” bed or complex); (2) Kafubu, formed by finely bedded black carbonaceous shales; and (3) Kanzadi, marked by feldspathic sandstones. Rocks of the Mwashya Subgroup are overlain by the Sturtian age Grand Conglomérat diamictite (equivalent to the Varianto/Brazil and Chuos/Namibia diamictites), and conformably overlie rocks of the Kansuki Formation (former Lower Mwashya), a carbonate unit containing volcaniclastic beds. New geochemical data confirm the continental rift context of this magmatism, which is contemporaneous with rift-related volcanism of the Askevold Formation (Nosib Group, Namibia). A gradational lithological transition between rocks of the Kansuki and the underlying Kanwangungu Formations, and similar petrological composition of these two formations, support the hypothesis that the Kansuki is the uppermost unit of the carbonate-dominated Dipeta/Kanwangungu sequence, and does not form part of the Mwashya Subgroup. Base metal deposits, mostly hosted in rocks of the Kansuki Formation, include weakly disseminated early-stage low-grade Cu–Co mineralisation, which was reworked and enriched, or initially deposited, by metamorphic fluids associated with the Lufilian orogenic event.     

赞比亚铜带省铜矿成因分析

中非(赞比亚―刚果(金))沉积型铜矿以其拥有高品位的大型超大型铜、钴矿床和众多的世界级铜矿山而闻名于世。铜矿类型可分为沉积型铜矿、热液脉型铜矿、变质热液型铜矿三类。沉积型铜矿床形成后,受到深部含矿岩浆热液的侵入形成脉状铜矿,可能还有斑岩型铜钼矿的成矿作用,叠加富集原有的沉积型铜矿床。硫同位素结果显示,硫源主要为成岩硫化物和海水硫酸盐的混合硫,受到深源岩浆或岩浆热液叠加改造。沉积型铜矿成矿年龄880~735Ma,后期岩浆热液型铜钼矿成矿年龄为514~502Ma。这些发现对进一步认识总结中非铜矿带上的矿床成因及成矿规律具有重要意义。