Geobotany, biogeochemistry and geochemistry in mineral exploration on the western fringes of the kalahari desert with specific reference to the detection of copper mineralization beneath transported overburden

Abstract

The investigations outlined in this thesis were conducted in an attempt to establish the role of biogeography/geobotany, geochemistry and biogeo-chemistry in the detection of copper mineralization in bedrock concealed by transported material. To aid the interpretation of the results a detailed study of the physical background of the study area was necessary. Orientation studies were carried out overmineralized tilloid and mineralized lava, and comprised the mapping and/or recording of vegetation along transects, the establishment of plant species suitable for biogeochemistry and the copper content of various mesh fractions of the soil. Analytical techniques suitable for plant and soil sample analysis were also investigated. A regional biogeo-chemical/geochemical programme was carried out to locate extensions to known mineralization and also additional areas of mineralization. The biogeographical/geobotanical studies reveal the composition of anomalous and background vegetation units and indicate the influence of relief, drainage and lithology on plant species distribution. Over mineralized tilloid two plant species emerge as specific indicators of copper toxicity in the soil. The extent of the overburden limits the use of geobotany as a prospecting tool as vegetation is generally found to reflect overburden and soil types rather than concealed bedrock. Geochemistry, comprising analysis of the -270 mesh fraction of the soil by the acid leaching/atomic absorption spectrophotometry method, is found to give satisfactory results in areas of near surface bedrock. The value of biogeochemistry in areas of thick overburden is discussed, and of the tree and shrub species investigated Phaeoptilum spinosum is found to be the most suitable for further biogeochemical work. Dry ashing/acid digestion followed by atomic absorption spectrophotometry is a suitable method of analysis for plant samples. The limited success obtained in the regional biogeochemical/geochemical survey is probably due to the absence or low grade of mineralization in the tilloid and the lens-like occurrence of mineralization in the lava.