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TitleRegional geochemical mapping in the tropical environment: bedrock reflection of Precambrian volcanosedimentary sequences in B-horizon soil strata: case studies from Nigeria/West Africa
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LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorMatheis, G; Utke, A
SourceGEOANALYSIS 90, an international symposium on the analysis of geological materials; by Hall, G E M (ed.); Geological Survey of Canada, Bulletin 451, 1993 p. 43-44, Open Access logo Open Access
PublisherNatural Resources Canada
MeetingGEOANALYSIS 90; Huntsville, Ontario; CA; June 3-7 1990
Mediapaper; on-line; digital
RelatedThis publication is contained in GEOANALYSIS 90, an international symposium on the analysis of geological materials
File formatpdf
AreaWest Africa; Nigeria
Subjectssoils science; geochemistry; soil studies; weathering; geochemical surveys; leaching; Proterozoic
Released1994 01 01
AbstractAbout one quarter of the Earth's land surface is covered by thick accumulations of lateritic soils, limiting the exposure of bedrock and leaving these regions the least explored. The most successful way to establish the badly needed geological and mineral inventories of these areas is the regional application of geochemical mapping, complemented by remote sensing and geophysics. Although chemical weathering progresses rather quickly in the tropics, extensive leaching is nearly restricted to the major elements Mg, Ca, Na, K, and partly Si. Most of the trace elements, however, retain more or less their bedrock concentrations, i.e., lithologically determined concentration ranges of the bedrock are not overruled by the weathering processes. In order to gain detailed information on the geochemical dispersion between the concealed bedrock and the uppermost soil horizons where sampling usually takes place (uppermost 60 cm of B-horizon), various orientation surveys were carried out in different climatic zones of Nigeria, ranging from the rain forest in the south to the dry Savannah in the north. The main lithological targets were late Proterozoic greenstone type associations which are host to Nigeria's gold resources and are equally important in revealing the Proterozoic geodynamic processes of the Nigerian basement complex. Vertical dispersion was studied in auger drilled soil profiles. The regional distribution patterns cover selected areas over volcanosedimentary sequences, totally about 1000 km2 at a sample density of one sample per square kilometre. Various selective leaching methods were applied to gain information on clay adsorbed, hydroxide adsorbed, and total geochemical dispersion. A comparison of the resulting geochemical maps with the most detailed published maps at scale 1:250 000 clearly demonstrated the advantage of geochemical mapping in providing more detailed information as well as pointing out inaccuracies in the existing geological maps.

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