Browsing Research articles (Dept of Geology) by Title
Previous Page
Now showing items 11-30 of 30
-
Cailteux, J.L.H.; Kampunzu, A.B.; Lerouge, C.; Kaputo, A.K.; Milesi, J.P. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2005)[more][less]
Abstract: The Neoproterozoic central African Copperbelt is one of the greatest sediment-hosted stratiform Cu–Co provinces in the world, totalling 140 Mt copper and 6 Mt cobalt and including several world-class deposits (P10 Mt copper). The origin of Cu–Co mineralisation in this province remains speculative, with the debate centred around syngenetic–diagenetic and hydrothermal-diagenetic hypotheses. The regional distribution of metals indicates that most of the cobalt-rich copper deposits are hosted in dolomites and dolomitic shales forming allochthonous units exposed in Congo and known as Congolese facies of the Katangan sedimentary succession (average Co:Cu = 1:13). The highest Co:Cu ratio (up to 3:1) occurs in ore deposits located along the southern structural block of the Lufilian Arc. The predominantly siliciclastic Zambian facies, exposed in Zambia and in SE Congo, forms para-autochthonous sedimentary units hosting ore deposits characterized by lower a Co:Cu ratio (average 1:57). Transitional lithofacies in Zambia (e.g. Baluba, Mindola) and in Congo (e.g. Lubembe) indicate a gradual transition in the Katangan basin during the deposition of laterally correlative clastic and carbonate sedimentary rocks exposed in Zambia and in Congo, and are marked by Co:Cu ratios in the range 1:15. The main Cu–Co orebodies occur at the base of the Mines/Musoshi Subgroup, which is characterized by evaporitic intertidal–supratidal sedimentary rocks. All additional lenticular orebodies known in the upper part of the Mines/Musoshi Subgroup are hosted in similar sedimentary rocks, suggesting highly favourable conditions for the ore genesis in particular sedimentary environments. Prelithification sedimentary structures affecting disseminated sulphides indicate that metals were deposited before compaction and consolidation of the host sediment. The ore parageneses indicate several generations of sulphides marking syngenetic, early diagenetic and late diagenetic processes. Sulphur isotopic data on sulphides suggest the derivation of sulphur essentially from the bacterial reduction of seawater sulphates. The mineralizing brines were generated from sea water in sabkhas or hypersaline lagoons during the deposition of the host rocks. Changes of Eh–pH and salinity probably were critical for concentrating copper–cobalt and nickel mineralisation. Compressional tectonic and related metamorphic processes and supergene enrichment have played variable roles in the remobilisation and upgrading of the primary mineralisation. There is no evidence to support models assuming that metals originated from: (1) Katangan igneous rocks and related hydrothermal processes or; (2) leaching of red beds underlying the orebodies. The metal sources are pre-Katangan continental rocks, especially the Palaeoproterozoic low-grade porphyry copper deposits known in the Bangweulu block and subsidiary Cu–Co–Ni deposits/occurrences in the Archaean rocks of the Zimbabwe craton. These two sources contain low grade ore deposits portraying the peculiar metal association (Cu, Co, Ni, U, Cr, Au, Ag, PGE) recorded in the Katangan sediment-hosted ore deposits. Metals were transported into the basin dissolved in water. The stratiform deposits of Congo and Zambia display features indicating that syngenetic and early diagenetic processes controlled the formation of the Neoproterozoic Copperbelt of central Africa. URI: http://hdl.handle.net/10311/387 Files in this item: 1
Kampunzu2005GenesisSediment.pdf (2.837Mb) -
Ranganai, R.T.; Kampunzu, A.B.; Atekwana, E.A.; Paya, B.K.; King, J.G.; Koosimile, D.I.; Stettler, E.H. (Royal Astronomical Society. http://www.wiley.com/bw/journal.asp?ref=0956-540X&site=1, NaN, 2002)[more][less]
Abstract: The Limpopo Belt of southern Africa is a Neoarchean orogenic belt located between two older Archean provinces, the Zimbabwe craton to the north and the Kaapvaal craton to the south. Previous studies considered the Limpopo Belt to be a linearly trending east-northeast belt with a width of ~250 km and ~600 km long. We provide evidence from gravity data constrained by seismic and geochronologic data suggesting that the Limpopo Belt is much larger than previously assumed and includes the Shashe Belt in Botswana, thus defining a southward convex orogenic arc sandwiched between the two cratons. The 2 Ga Magondi orogenic belt truncates the Limpopo–Shahse Belt to the west. The northern marginal, central and southern marginal tectonic zones define a single gravity anomaly on upward continued maps, indicating that they had the same exhumation history. This interpretation requires a tectonic model involving convergence between the Kaapvaal and Zimbabwe cratons during a Neoarchean orogeny that preserved the thick cratonic keel that has been imaged in tomographic models. URI: http://hdl.handle.net/10311/326 Files in this item: 1
Ranganai_GJI_2002.pdf (1.361Mb) -
Jourdan, F.; Fe´raud, G.; Bertrand, H.; Kampunzu, A.B.; Tshoso, G.; Le Gall, B.; Tiercelin, J.-J.; Capiez, P. (Elservier www.elsevier.com/locate/epsl, NaN, 2004)[more][less]
Abstract: The lower Jurassic Karoo–Ferrar magmatism represents one of the most important Phanerozoic continental flood basalt (CFB) provinces. The Karoo CFB province is dominated by tholeiitic traps and apparently radiating giant dyke swarms covering altogether ca. 3 106 km2. This study focuses on the giant N110j-trending Okavango dyke swarm (ODS) stretching over 1500 km across Botswana. This dyke swarm represents the main (failed) arm of the so-called Karoo triple junction that is generally considered as a key marker of the impingement of the Karoo starting mantle plume head. ODS dolerites yield six new plagioclase 40Ar/39Ar plateau (and miniplateau) ages ranging from 178.7F0.7 and 180.9F1.3 Ma. The distribution of the ages along a narrow Gaussian curve suggests a short period of magmatic activity centered around 179 Ma, i.e., f5 Ma younger than the emplacement age of Karoo mafic magmas in the southern part of the Karoo CFB province (f184). This age difference indicates that Karoo magmatism does not represent a short-lived event as is generally the case for most CFB but lasted at least 5Ma over the whole province. In addition, small clusters of plagioclase separated from 28 other dykes and measured by ‘‘speedy’’ step-heating experiments (with mostly two to three steps), gave either ‘‘Karoo’’ or Proterozoic ages. Integrated ages of the Proterozoic rocks range from 851F6 to 1672F7 Ma, and one plateau age (959.1F4.6 Ma) and one possibly geologically significant weightedmean age (982.7F4.0 Ma) were obtained. Proterozoic and Karoo mafic rocks are petrographically similar, but Proterozoic dykes display clear geochemical differences (e.g., TiO2 < 2.1%) with the Karoo high-Ti ODS (TiO2>2.1%). Geochemical data combined with available Ar/Ar dates allow the identification of the two groups within a total set of 77 dykes investigated: f10% of the bulk ODS dykes are Proterozoic. Thus, the Jurassic Karoo ODS dykes were emplaced along reactivated Proterozoic structures and there is no pristine Jurassic Nuanetsi triple junction as commonly proposed. This throws into doubt the validity of the ‘‘active plume head’’ Karoo CFB rift models as being responsible for the observed ‘‘triple junction’’ dyke geometry URI: http://hdl.handle.net/10311/383 Files in this item: 1
Kampunzu2004KarooTripleJunction.pdf (1.306Mb) -
Cailteux, J.L.H.; Kampunzu, A.B.H.; Batumike, M.J. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2005)[more][less]
Abstract: The Neoproterozoic Katangan R.A.T. ("Roches Argilo-Talqueuses") Subgroup is a sedimentary sequence composed of red massive to irregularly bedded terrigenous-dolomitic rocks occurring at the base of the Katangan succession in Congo. Red R.A.T. is rarely exposed in a continuous section because it was affected by a major layer-parallel de´collement during the Lufilian thrusting. However, in a number of thrust sheets, Red R.A.T. is in conformable sedimentary contact with Grey R.A.T which forms the base of the Mines Subgroup. Apart from the colour difference reflecting distinct depositional redox conditions, lithological, petrographical and geochemical features of Red and Grey R.A.T. are similar. A continuous sedimentary transition between these two lithological units is shown by the occurrence of variegated to yellowish R.A.T. The D. Strat. "Dolomies Stratifie´es" formation of the Mines Subgroup conformably overlies the Grey R.A.T. In addition, a transitional gradation between Grey R.A.T. and D. Strat. occurs in most Cu–Co mines in Katanga and is marked by interbedding of Grey R.A.T.-type and D. Strat.-type layers or by a progressive petrographic and lithologic transition from R.A.T. to D. Strat. Thus, there is an unquestionable sedimentary transition between Grey R.A.T. and D. Strat. and between Grey R.A.T. and Red R.A.T. The R.A.T. Subgroup stratigraphically underlies the Mines Subgroup and therefore R.A.T. cannot be comprised of syn-orogenic sediments deposited upon the Kundelungu (formerly ‘‘Upper Kundelungu’’) Group as suggested by Wendorff (2000). As a consequence, the Grey R.A.T. Cu–Co mineralisation definitely is part of the Mines Subgroup Lower Orebody, and does not represent a distinct generation of stratiform Cu–Co sulphide mineralisation younger than the Roan orebodies. URI: http://hdl.handle.net/10311/391 Files in this item: 1
Kampunzu2005Lithostratigraphic.pdf (1.922Mb) -
Kampunzu, A.B.; Tombale, A.R.; Zhaia, M.; Bagai, Z.; Majaule, T.; Modisi, M.P. (Elsevier www.elsevier.com/locate/lithos, NaN, 2003)[more][less]
Abstract: The Neoarchaean Tati granite–greenstone terrane occurs within the southwestern part of the Zimbabwe craton in NE Botswana. It comprises 10 intrusive bodies forming part of three distinct plutonic suites: (1) an earlier TTG suite dominated by tonalites, trondhjemites, Na-granites distributed into high-Al (Group 1) and low-Al (Group 2) TTG sub-suite rocks; (2) a Sanukitoid suite including gabbros and Mg-diorites; and (3) a younger high-K granite suite displaying I-type, calc-alkaline affinities. The Group 1 TTG sub-suite rocks are marked by high Sr/Y values and strongly fractionated chondrite-normalized rare earth element (REE) patterns, with no Eu anomaly. The Group 2 TTG sub-suite displays higher LREE contents, negative Eu anomaly and small to no fractionation of HREE. The primordial mantle-normalized patterns of the Francistown TTGs are marked by negative Nb–Ti anomalies. The geochemical characteristics of the TTG rocks are consistent with features of silicate melts from partial melting of flat subducting slabs for the Group 1 sub-suite and partial melting of arc mafic magmas underplated in the lower crust for the Group 2 sub-suite. The gabbros and high-Mg diorites of the Sanukitoid suite are marked by Mg#>0.5, high Al2O3 (>>16%), low TiO2 ( < 0.6%) and variable enrichment of HFSE and LILE. Their chondrite-normalized REE patterns are flat in gabbros and mildly to substantially fractionated in high-Mg diorites, with minor negative or positive Eu anomalies. The primordial mantle-normalized diagrams display negative Nb–Ti (and Zr in gabbros) anomalies. Variable but high Sr/Y, Sr/Ce, La/Nb, Th/Ta and Cs/La and low Ce/Pb ratios mark the Sanukitoid suite rocks. These geochemical features are consistent with melting of a sub-arc heterogeneously metasomatised mantle wedge source predominantly enriched by earlier TTG melts and fluids from dehydration of a subducting slab. Melting of the mantle wedge is consistent with a steeper subduction system. The late to post-kinematic high-K granite suite includes I-type calc-alkaline rocks generated through crustal partial melting of earlier TTG material. The Neoarchaean tectonic evolution of the Zimbabwe craton is shown to mark a broad continental magmatic arc (and related accretionary thrusts and sedimentary basins) linked to a subduction zone, which operated within the Limpopo– Shashe belt atf2.8–2.65 Ga. The detachment of the subducting slab led to the uprise of a hotter mantle section as the source of heat inducing crustal partial melting of juvenile TTG material to produce the high-K granite suite. URI: http://hdl.handle.net/10311/381 Files in this item: 1
Kampunzu2003Majorandtrace element.pdf (2.863Mb) -
De Waele, B.; Kampunzu, A.B.; Mapani, B.S.E.; Tembo, F. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2006)[more][less]
Abstract: The Mesoproterozoic Irumide belt is a northeast-trending structural province stretching from central Zambia to the Zambia–Tanzania border and northern Malawi. Mesoproterozoic and Neoproterozoic transcurrent shear zones within reactivated parts of the Palaeoproterozoic Ubendian belt define its northeastern limit. The northwestern margin is defined by the largely undeformed basement lithologies of the Bangweulu block. An intensely folded and sheared zone at the southeastern margin of the Mporokoso Group sedimentary depocentre on the Bangweulu block, interpreted to have developed above a thrust at the basement-cover interface, indicates that far-field effects of the Irumide Orogen also affected the southeastern part of the Bangweulu block sedimentary cover. To the west and southwest, Irumide and basement lithologies were reworked by the Damara–Lufilian–Zambezi Orogen within the Neoproterozoic Zambezi and Lufilian belts. The Choma–Kalomo block, previously regarded as the southwesterly continuation of the Irumide belt, is a distinct Mesoproterozoic province, while a succession of structurally juxtaposed tectonic terranes in eastern Zambia record a deformation event related to the Irumide Orogen. The lithological units identified in the Irumide belt include: (1) limited Neoarchaean rocks emplaced between 2.73 and 2.61 Ga and representing the oldest rocks in the Bangweulu block; (2) ca. 2.05–1.85 Ga volcano-plutonic complexes and gneisses representing the most important components in the Bangweulu block; (3) an extensive quartzite–metapelite succession with minor carbonate forming the Muva Supergroup, and deposited at ca. 1.85 Ga; (4) granitoids emplaced between 1.65 and 1.55 Ga; (5) a minor suite of anorogenic plutons (nepheline syenite and biotite granite) restricted to the far northeastern Irumide belt and emplaced between 1.36 and 1.33 Ga; (6) voluminous syn- to post-kinematic Irumide granitoids emplaced between 1.05 and 0.95 Ga. Crustal shortening and thickening in the Irumide belt are shown by northwestward-directed thrusts and related folds and metamorphic parageneses recording a clockwise medium-pressure/medium-temperature P–T–t path. Metamorphic grades range from greenschist facies in the foreland to the northwest to upper amphibolite facies in the southeast, with local granulites. Peak metamorphism is diachronous across the belt and bracketed between 1.05 in the southeast and 1.02 Ga in the northwest. URI: http://hdl.handle.net/10311/398 Files in this item: 1
-
Becker, T.; Schreiber, U.; Kampunzu, A.B.; Armstrong, R. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2006)[more][less]
Abstract: Two main Mesoproterozoic provinces occur in southern Namibia: (1) The high-grade Namaqua Metamorphic Complex (NMC) composed of a supracrustal sedimentary succession and interpreted as a passive margin sequence in the west of the Kalahari craton; (2) The Sinclair Group and its northeastern correlatives, composed of two main magmatic and metamorphic units, reflecting northeast-directed subduction, which started before 1.37 Ga and lasted until about 1.1 Ga. These two units were tectonically juxtaposed during the 1.1– 1.03 Ga Namaqua orogenic event. The Kairab–Kumbis Metamorphic Complex comprises metasedimentary and metavolcanic rocks intruded by the 1.37 Ga arc-related Aunis tonalite. The mafic volcanic rocks from this complex have geochemical features of island arc calcalkaline basalts; they were emplaced and metamorphosed along an active margin before 1.37 Ga. The 1.2–1.1 Ga low-grade unmetamorphosed volcanic and immature sedimentary rocks of the Sinclair Group and its northwestern equivalents rest disconformably on the Kairab–Kumbis Complex. They occur in fault-bounded depocenters defining a regional arc-shape structure up to 100 km-wide and with a minimum length of 2000 km. The plate tectonic setting of this arc is best constrained by the composition of volcanic rocks from the 1.2 Ga Barby Formation and coeval granitoids; they comprise high-K calcalkaline rocks suggesting emplacement in an active continental margin setting. The final stage of this continental arc evolution is recorded in the <1.1 Ga tholeiites of the Opdam Formation. High Ti-content and flat REEpatterns in the tholeiites suggests an extensional event, whereas high Th/Ta and La/Nb ratios, low Ce/Pb values and negative anomalies for Nb–Ta suggest a subduction-related setting for the mantle source from which the mafic magmas were derived. Docking of continents led to the slab detachment, allowing interaction between the asthenospheric mantle and the mantle wedge enriched during the subduction process. The magmatic underplating related to this event induced the genesis of large-scale batholitic granitoid bodies in the NMC and a 1.1–1.0 Ga high-grade LP/HT metamorphism, with mineral assemblages indicating an anti-clockwise P–T–t path. URI: http://hdl.handle.net/10311/385 Files in this item: 1
Kampunzu2006RocksofNamibia.pdf (3.444Mb) -
Cailteux, J.L.H.; Kampunzu, A.B.; Lerouge, C. (Elsevier www.elsevier.com/locate/gr, NaN, 2007)[more][less]
Abstract: 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. URI: http://hdl.handle.net/10311/399 Files in this item: 1
Kampunzu2007Neoproterozoic Mwashya.pdf (2.801Mb) -
Le Gall, B.; Tshoso, G.; Dyment, J.; Kampunzu, A.B.; Jourdan, F.; Fe´raud, G.; Bertrand, H.; Aubourg, C.; Ve´tel, W. (Elsevier www.elsevier.com/locate/jsg, NaN, 2005)[more][less]
Abstract: The structural organization of a giant mafic dyke swarm, the Okavango complex, in the northern Karoo Large Igneous Province (LIP) of NE Botswana is detailed. This N1108E-oriented dyke swarm extends for 1500 km with a maximum width of 100 km through Archaean basement terranes and Permo-Jurassic sedimentary sequences. The cornerstone of the study is the quantitative analysis of NO170 (exposed) and NO420 (detected by ground magnetics) dykes evidenced on a ca. 80-km-long section lying in crystalline host-rocks, at high-angle to the densest zone of the swarm (Shashe area). Individual dykes are generally sub-vertical and parallel to the entire swarm. Statistical analysis of width data indicates anomalous dyke frequency (few data !5.0 m) and mean dyke thickness (high value of 17 m) with respect to values classically obtained from other giant swarms. Variations of mean dyke thicknesses from 17 (N1108E swarm) to 27 m (adjoining and coeval N708E giant swarm) are assigned to the conditions hosting fracture networks dilated as either shear or pure extensional structures, respectively, in response to an inferred NNW–SSE extension. Both fracture patterns are regarded as inherited brittle basement fabrics associated with a previous (Proterozoic) dyking event. The Okavango N1108E dyke swarm is thus a polyphase intrusive system in which total dilation caused by Karoo dykes (estimated frequency of 87%) is 12.2% (6315 m of cumulative dyke width) throughout the 52-km-long projected Shashe section. Assuming that Karoo mafic dyke swarms in NE Botswana follow inherited Proterozoic fractures, as similarly applied for most of the nearly synchronous giant dyke complexes converging towards the Nuanetsi area, leads us to consider that the resulting triple junction-like dyke/fracture pattern is not a definitive proof for a deep mantle plume in the Karoo LIP. URI: http://hdl.handle.net/10311/400 Files in this item: 1
Kampunzu2005Okavangogiant.pdf (3.456Mb) -
Mapeo, R.B.M.; Ramokate, L.V.; Corfu, F.; Davis, D.W.; Kampunzu, A.B. (Elsevier Ltd. www.elsevier.com/locate/jafrearsci, NaN, 2006)[more][less]
Abstract: The Okwa Basement Complex crops out at the northwestern edge of the Kaapvaal craton within the Okwa Inlier, an isolated exposure of Precambrian basement in the Kalahari Desert. New U–Pb zircon dating was performed on all the major Palaeoproterozoic lithologies of the complex. Results are 2055.3 ± 1.3 Ma for augen gneiss, 2056.3 ± 1.3 Ma for foliated monzogranite and 2057 ± 2 Ma for microgranite. A meta-rhyolite gives an age of 2055 ± 4 Ma, based on one concordant zircon, and contains an inherited zircon with an age of 2101 ± 4 Ma. All precisely dated rocks are indistinguishable in age at 2056 ± 2 Ma. This age can be broadly correlated with Palaeoproterozoic geologic events in the Magondi belt at the northwest margin of the Zimbabwe craton and the Triangle Shear Zone in the Limpopo belt. However, the most precise correlation is with the Bushveld Complex, whose age is indistinguishable from that of the Okwa Basement Complex. This suggests a link between marginal and intra-cratonic Bushveld-age magmatism on the Kaapvaal craton. URI: http://hdl.handle.net/10311/272 Files in this item: 1
The Okwa basement complex.pdf (5.655Mb) -
Ringrose, S.; Kampunzu, A.B.; Vink, B.W.; Matheson, W.; Downey, W.S. (John Wiley & Sons, Ltd. http://www3.interscience.wiley.com/journal/117935722/grouphome/home.html, NaN, 2002)[more][less]
Abstract: Quaternary sedimentation in the Moshaweng dry valley of southeastern Botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses. Stratigraphic evidence reveals an 'upper surface (1095 m) containing abundant sil-calcrete, an intermediate surface (1085 m) in which sil-calcrete underlies nodular calcrete and lower (1075 m) surface in which sil-calcrete and nodular calcrete are interbedded. This subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing Si02 content (and increasing CaC03 content) with depth from the highest to the lowest surface levels. The calcretes and sil-calcretes represent modifications of pre-existing detrital Kalahari Group sand and basal Kalahari pebbles which thinned over a Karoo bedrock high. Modification took place during wet periods when abundant Ca++ -rich groundwater flowed along the structurally aligned valley system. With the onset of drier conditions, water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m. A major geochemical change resulted in the preferential silicification of the nodular calcrete deposits. Conditions for silica mobilization may be related to drying-induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile. As calcretization and valley formation progressed to lower levels, silica release took place on a diminishing scale. Thermoluminescence dating infers a mid-Pleistocene age for sil-calcrete formation suggesting that valley evolution and original calcrete precipitation are much older. Late st~ge dissolution of CaC03 from pre-existing surface calcretes or sil-calcretes led to the formation of pedogenic case-hardened deposits during a time of reduced flow through the Moshaweng system possibly during the upper or late Pleistocene. URI: http://hdl.handle.net/10311/310 Files in this item: 1
Ringrose_ESPL_2002.pdf (3.095Mb) -
Ringrose, S.; Harris, C.; Huntsman-Mapila, P.; Vink, B.W.; Diskins, S.; Vanderpost, C.; Matheson, W. (Elsevier www.elsevier.com/locate/sedgeo, NaN, 2009)[more][less]
Abstract: Trace elements togetherwith some O and C isotope analysiswere 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 silcretisationmay be similar to that occurring in Botswana at present being dry semi-arid with lowseasonal 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 ofmajor humid events interspersedwithmore normal semi-arid palaeo-climateswith an exception obtained from isotope data, of drier and cooler conditions than usual for the region around 80–90000 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. URI: http://hdl.handle.net/10311/560 Files in this item: 1
RINGROSE2009Makgadikgadi Pans.pdf (3.500Mb) -
Milesi, J.P.; Toteu, S.F.; Deschamps, Y.; Feybesse, J.L.; Lerouge, C.; Cocherie, A.; Penaye, J.; Tchameni, R.; Moloto-A-Kenguemba, G.; Kampunzu, H.A.B.; Nicol, N.; Duguey, E.; Leistel, J.M.; Saint-Martin, M.; Ralay, F.; Heinry, C.; Bouchot, V.; Mbaigane, J.C. Doumnang; Kula, V. Kanda; Chene, F.; Monthel, J.; Boutin, P.; Cailteux, J. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2006)[more][less]
Abstract: This paper is prepared within the frameworks of IGCP Project 470 and the associated BRGM scientific project ‘‘Africa 1999–2004’’ to accompany the 1:4,000,000 scale map ‘‘Geology and major ore deposits of Central Africa, presented at the 20th Colloquium of African Geology in Orleans in June 2004. It incorporates geological and metallogenic data from eight countries in Central Africa (Angola, Cameroon, Chad, Central African Republic, Congo Brazzaville, Democratic Republic of Congo (DRC), Equatorial Guinea and Zambia). The map is a harmonised and geo-referenced preliminary map, based on a GIS at 1:2,000,000 scale, and focusses on the spatial and temporal distribution of selected major deposits. URI: http://hdl.handle.net/10311/384 Files in this item: 1
Kampunzu2006MajorOreDeposits.pdf (2.307Mb) -
Batumike, M.J.; Kampunzu, A.B.; Cailteux, J.H. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2006)[more][less]
Abstract: The Nguba and Kundelungu Groups constitute the middle and upper parts of the Neoproterozoic Katangan Supergroup, respectively, and consist of conglomerates, sandstones, mudrocks and carbonates. During deposition, the Katangan basin received sediments originating from both northern and southern sources. The Nguba and Kundelungu Groups siliciclastic rocks have elemental abundances and ratios suggestive of a relatively felsic TTG source, although slightly more mafic compositions occur in the Nguba Group and the overlying ‘‘Petit Conglome´rat’’ Formation at the base of the Kundelungu Group. Modal compositions of the Nguba Group rocks indicate a basement uplift provenance, and geochemical parameters indicate the source of both the Nguba and Kundelungu Groups had an active continental margin character. Source area weathering was moderate in the Nguba Group. Low Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) indices and relatively uniform chemical compositions of the ‘‘Grand Conglome´rat’’ and the ‘‘Petit Conglome´rat’’ Formations lying respectively at the bases of the Nguba and Kundelungu Groups are compatible with deposition in a cool or frigid climate, and support their presumed petrographic based glaciogenic origin. High CIA and PIA indices in Upper Kalule rocks in the middle part of the Kundelungu Group point to the intensification of source weathering, possibly under tropical to subtropical climate under steady state conditions. Geochemical similarities between the Nguba Group and the ‘‘Petit Conglome´rat’’ are compatible with a change from an extensional setting to compression, with derivation of the ‘‘Petit Conglome´rat’’ by reworking of the underlying units during basin inversion. Change in provenance signatures and weathering indices in the Upper Kalule Formation may reflect reduced tectonism and resumption of supply of more weathered extrabasinal detritus, similar to that which fed the basal Roan Group. Overall the data suggest derivation mainly from pre-Katangan Proterozoic sources with continental arc characteristics. The adjacent Paleoproterozoic Ubendian Belt, particularly the Bangweulu block calcalkaline plutonic and volcanic province, is a suitable candidate as the source for the Nguba and Kundelungu Group sedimentary rocks. However, Mesoproterozoic and Archaean terrains have also contributed a minor component to the basin. URI: http://hdl.handle.net/10311/392 Files in this item: 1
Kampunzu2006Petrologyandgeochemistry.pdf (1.585Mb) -
Moges, S.A.; Alemaw, B.F.; Chaoka, T.R.; Kachroo, R.K. (Elsevier, www.elsevier.com/locate/pce, NaN, 2007)[more][less]
Abstract: This paper is aimed at developing a geostatistical model to improve interpolated annual and monthly rainfall variation using remotely- sensed cold cloud duration (CCD) data as a background image. The data set consists of rainfall data from a network of 704 rain gauges in the Rufiji drainage basin in Tanzania. We found ordinary kriging to be a robust estimator due mainly to its inherent nature of including the non-stationary local mean during estimation. Parameter sensitivity analysis and examination of the residuals revealed that the parameter values of the variogram viz., the nugget effect, the range, sill value and maximum direction of continuity, as long as they are in acceptable ranges, and any different combination of these parameters, have low effect on model efficiency and accuracy. Rather, the use of remotely-sensed CCD data as a background image is found to improve the interpolation as compared to the estimation based on observed point rainfall data alone. The study revealed the improvement in terms of Nash–Sutcliffe model performance index (R2) by using CCD as external drift with kriging provided an R2 of 64.5% compared to the simple kriging and ordinary kriging, which performed with efficiency of 60.0% and 61.4%, respectively. For each case, parameter sensitivity analysis was conducted to investigate the effect of the change in the parameters on the model performance and the spatio-temporal interpolation results. URI: http://hdl.handle.net/10311/500 Files in this item: 1
MOGES2007Rainfall interpolation.pdf (1.188Mb) -
Kampunzu, A.B.; Cailteux, J.L.H.; Kamona, A.F.; Intiomale, M.M.; Melcher, F. (Elsevier www.elsevier.com/locate/oregeorev, NaN, 2009)[more][less]
Abstract: Stratabound epigenetic sulphide Zn–Pb–Cu ore deposits of the Central African Copperbelt in the Democratic Republic of Congo and Zambia are mostly hosted in deformed shallow marine platform carbonates and associated sedimentary rocks of the Neoproterozoic Katanga Supergroup. Economic orebodies, that also contain variable amounts of minor Cd, Co, Ge, Ag, Re, As, Mo, Ga, and V, occur mainly as irregular pipe-like bodies associated with collapse breccias and faults as well as lenticular bodies subparallel to bedding. Kipushi and Kabwe in the Democratic Republic of the Congo and Zambia, respectively, are the major examples of carbonate-hosted Zn–Pb–Cu mined deposits with important by-products of Ge, Cd, Ag and V in the Lufilian Arc, a major metallogenic province famous for its world-class sediment-hosted stratiform Cu–Co deposits. The carbonate-hosted deposits range in age from Neoproterozoic to early Palaeozoic (680 to 450 Ma). The formation of the relatively older Neoproterozoic deposits is probably related to early collision events during the Lufilian Orogeny, whereas the younger Palaeozoic deposits may be related to post-collisional processes of ore formation. Fluid inclusion and stable isotope data indicate that hydrothermal metal-bearing fluids evolved from formation brines during basin evolution and later tectonogenesis. Ore fluid migration occurred mainly along major thrust zones and other structural discontinuities such as karsts, breccias and faults within the Katangan cover rocks, resulting in ore deposition within favourable structures and reactive carbonates of the Katangan Supergroup. URI: http://hdl.handle.net/10311/380 Files in this item: 1
Kampunzu2009Sediment-hosted Zn.pdf (4.792Mb) -
Ringrose, S.; Huntsman-Mapila, P.; Kampunzu, A.B.; Downey, W.; Coetzee, S.; Vink, B.W.; Matheson, W.; Vanderpost, C. (Elsevier www.elsevier.com/locate/palaeo, NaN, 2005)[more][less]
Abstract: This work considers new evidence for palaeo environmental change taking place during the Pleistocene in northern Botswana. Duricrusted strandlines along the northeastern margin of Sua Pan provide palaeo-environmental data pertaining to the Makgadikgadi subbasin (MSB) with inferences regarding the larger Makgadikgadi–Okavango–Zambezi (MOZ) rift depression. Field, XRD and geochemical data show that MSB strandlines comprise calcretes (LU1 type), MgO-rich calcretes with silica (LU2 type), sil-calcrete (LU3 type) and silcrete (LU4 type). Early freshwater episodes appear to have been followed by calcrete-dominated drying phases interspersed with repeated silcretisation. Calcretisation through pan littoral sediments may have been both biogenically and environmentally induced. Calcite precipitation was in part controlled by the Mg/Ca ratio of pore water in the pan littoral zone suggesting closed basin type evaporative conditions, which were followed by a major desiccation interval. Phases of silcrete precipitation appear to be related to periods when the geochemistry of the lake littoral more closely resembled present-day Na–CO3–SO4–Cl-type brines. Silica saturated acidic, moderately saline groundwater preceded Si precipitation which took place as the pH reduced. Si mobilisation occurred (inter alia) as a result of quartz grain dissolution enhanced by diatoms, bacteria and algal growth in the moist pan littoral. SiO2-rich pore waters migrated through cracked and desiccated calcrete into areas of lower salinity and lower pH resulting in preferential calcite removal and silcrete precipitation. Approximate TL dates imply that exposed littoral sand underwent calcretisation during the drying phases of extensive palaeo-lakes which occurred prior to 110 ka, 80–90 ka and 41–43 ka. These wet periods compare fairly well with Vostok core chronologies for southern Africa. URI: http://hdl.handle.net/10311/794 Files in this item: 1
Kampunzu2006Sedimentological.pdf (3.498Mb) -
Laletsang, K.; Modisi, M.P.; Shemang, E.M.; Moffat, L.; Moagi, O.R. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2007)[more][less]
Abstract: A seismic refraction analysis was carried out on data acquired on an 8.5 km profile at Lake Ngami, NW Botswana, to determine the structure and stratigraphy underlying the lake. The seismic spread comprised a 48-channel seismograph with a 9.5 m receiver and source spacing. The seismic source comprised 10 hammer blows on an aluminum plate, from which a vertical stack was recorded. The data were processed with WinSismTM version 10 program using the intercept time method. A total field magnetic survey was also carried out along the same line. The seismic refraction profile shows a low velocity layer (400–1600 m/s) extending from the surface at the southern end of the line to a maximum depth of 30 m in the middle of the profile, returning to a depth of 20 m from 4.5 km to the northern end of the line. The low velocity layer consists of the unconsolidated sediments and is underlain by more compact and saturated material with seismic velocities of 1600–3600 m/s. This material is interpreted to comprise semi- to fully consolidated sandstone. The base of these sandstones, however, could only be mapped near the southern end of the line out to 2 km. High seismic velocity rocks (3600–5000 m/s), interpreted to be weathered to fresh basement, were mapped below the sandstones at the southern end of the line. The magnetic profile shows a high at the beginning of the line which progressively declines to a low at 3 km. The field strength increases rapidly over the next 1.5 km to reach a plateau level at 4.5 km. The magnetic high at the beginning of the line corresponds to shallow basement which is mapped in the refraction profile. The magnetic low at 3 km is indicative of a thickened sediment section at this location. The southern end of the line with high seismic velocities comprises basement rocks located in the footwall block of the Kunyere Border Fault of the Okavango Rift. The step-wise downthrown hanging wall block consists of the low to intermediate velocity basin deposits in the northern part of the profile. URI: http://hdl.handle.net/10311/376 Files in this item: 1
Modisi2007ShallowSeismic.pdf (656.3Kb) -
Lerouge, C.; Cailteux, J.; Kampunzu, A.B.; Milesi, J.P.; Fle´hoc, C. (Elsevier www.elsevier.com/locate/jafrearsci, NaN, 2005)[more][less]
Abstract: Luiswishi is a Congo-type Neoproterozoic sediment-hosted stratiform Cu–Co ore deposit of the Central Africa Copperbelt, located northwest of Lubumbashi (DRC). The ores form two main Cu–Co orebodies hosted by the Mines Subgroup, one in the lower part of the Kamoto Formation and the other at the base of the Dolomitic Shales Formation. Sulphides occur essentially as early parallel layers of chalcopyrite and carrolite, and secondarily as late stockwork sulphides cross-cutting the bedding and the early sulphide generation. Both types of stratiform and stockwork chalcopyrite and carrolite were systematically analyzed for sulphur isotopes, along the lithostratigraphic succession of the Mine Series. The quite similar d34S values of stratiform sulphides and late stockwork sulphides suggest an in situ recrystallization or a slight remobilization of stockwork sulphides without attainment of isotopic equilibrium between different sulphide phases (chalcopyrite and carrolite). The distribution of d34S values ( 14.4& to +17.5&) combined with the lithology indicates a strong stratigraphic control of the sulphur isotope signature, supporting bacterial sulphate reduction during early diagenesis of the host sediments, in a shallow marine to lacustrine environment. Petrological features combined with sulphur isotopic data of sulphides at Luiswishi and previous results on nodules of anhydrite in the Mine Series indicate a dominant seawater/lacustrine origin for sulphates, precluding a possible hydrothermal participation. The high positive d34S values of sulphides in the lower orebody at Luiswishi, hosted in massive chloritic–dolomitic siltite (known as Grey R.A.T.), fine-grained stratified dolostone (D.Strat.) and silicified-stromatolitic dolomites alternating with chloritic–dolomitic silty beds (R.S.F.), suggest that they were probably deposited during a period of regression in a basin cut off from seawater. The variations of d34S values (i.e. the decrease of d34S values from the Kamoto Formation to the overlying Dolomitic Shales and then the slight increase from S.D.2d to S.D.3a and S.D.3b members) are in perfect agreement with the inferred lithological and transgressive–regressive evolution of the ore-hosting sedimentary rocks [Cailteux, J., 1994. Lithostratigraphy of the Neoproterozoic Shaba-type (Zaire) Roan Supergroup and metallogenesis of associated stratiform mineralization. In: Kampunzu A.B., Lubala, R.T. (Eds.), Neoproterozoic Belts of Zambia, Zaire and Namibia. Journal of African Earth Sciences 19, 279–301]. URI: http://hdl.handle.net/10311/390 Files in this item: 1
Kampunzu2005SulpherIsotope.pdf (1.156Mb) -
Huntsman-Mapila, P.; Ringrose, S.; Mackay, A.W.; Downey, W.S.; Modisi, M.; Coetzee, S.H.; Tiercelin, J.-J.; Kampunzu, A.B.; Vanderpost, C. (Elsevier, www.sciencedirect.com, NaN, 2006)[more][less]
Abstract: Sediment samples from a continuous 4.6m profile in the dry bed of Lake Ngami in NW Botswana were analysed for geochemistry and dated using both 14C and TL methods. Certain units in the profile were found to be diatom rich and these, with the geochemical results, were used as indicators of high and low lake levels within the basin. The Lake Ngami sediments contain a high proportion of SiO2 (51–92.5 wt%, avg. 72.4 wt%) and variable levels of Al2O3 (2.04–17.2 wt%, avg. 8.88 wt%). Based on elevated Al2O3 and organic matter (LOIorgC) results, lacustrine conditions occurred at ca. 42 ka until 40 ka and diatom results suggest that relatively deep but brackish conditions prevailed. At 40 ka, the lacustrine sedimentary record was terminated abruptly, possibly by tectonic activity. At ca. 19 ka, shallow, aerobic, turbulent conditions were prevalent, but lake levels were at this time increasing to deeper water conditions up until ca. 17 ka. This period coincides with the Late Glacial Maximum, a period of increased aridity in the central southern Africa region. Generally, increasing Sr/Ca ratios and decreasing LOIorgC and Al2O3, from ca. 16 to 5 ka, suggest decreasing inflow into the basin and declining lake levels. Based on the enrichment of LREE results, slightly alkaline conditions prevailed at ca. 12 ka. Diatom results also support shallow alkaline conditions around this time. These lake conditions were maintained primarily by local rainfall input as the region experienced a warmer, wetter phase between 16 and 11 ka. Lake levels rose rapidly by 4 ka, probably in response to enhanced rainfall in the Angolan catchment. These results indicate that lake levels in the Lake Ngami basin are responding to rainfall changes in the Angolan catchment area and local rainfall. The results confirm that the present-day anti-phase rainfall relationship between southern Africa and regions of equatorial Africa was extant during the late Quaternary over the Angolan highlands and NW Botswana. URI: http://hdl.handle.net/10311/891 Files in this item: 1
Modisi2006SedimentaryRecord.pdf (1.674Mb)
Previous Page
Now showing items 11-30 of 30