The Lithological Mapping theme (1984-1988) was undertaken as part of the GARS Africa Project to improve lithological mapping in tropical environments through the integration of data from a variety of remote sensing systems. The theme was mainly a scientific research programme devoted to image processing and field control of satellite imagery. The research was also aimed at establishing a closer link between research that was related to fundamental geological investigations and those of the metallogenic aspects of the Kibaran region, and with an aim to improve the correlation between sedimentary formations relating to the Kibaran cycle in the different countries of the African region.

Landsat image-©Philippe Trefois

Objective of the Lithological Mapping theme The Lithological Mapping theme was aimed at improving the interpretation of the lithology, structure and mineralisation of the Kibaran and Ubendian fold belts in Africa using advanced remote sensing technology.

Aims of the theme

The theme focused on assessing the capability of using advanced remote sensing data for detecting mineral assemblages, alteration zones and geobotanical indicators for a range of litho-structural analyses:

• Discrimination of lithological units within metasedimentary complexes
  
• Recognition of different types of intrusive rocks
  
• Influence of tropical weathering on characteristic mineral assemblages of rocks and soils
  
• Recognition of mineral alteration zones
  
• Differentiation of Precambrian and overprinted Cenozoic structures
  
• Recognition of structural control on mineralisation
  
• Determination of spectral properties of geologic materials by radiometric measurements

Geological Setting

The Lithological Mapping theme was performed in Africa in the Precambrian terranes of the Kibaran fold belt in Burundi and the Ubendian fold belt in Tanzania. These are dominated by lateritic soils and vegetation that varies from tropical rain forest to savannah.

The Ubendian fold belt consists of a variety of lithological units covered by a relatively homogeneous vegetation layer and this formed the focus of initial investigations.

The Kibaran fold belt (Middle Proterozoic) has a more complex character and the research focused on the discrimination of granites, basic rocks and shear zones in northern Burundi and also on the use of geobotanical indicators for the discrimination of mineral alteration zones in central Burundi.

The Kibaran fold belt is rich in Gold (Au), Tin (Sn), Tungsten (W), Niobium (Nb), Tantalum (Ta), Nickel (Ni), Platinum (Pt) and rare earth mineralisations. The tectonic events and emplacement of plutons that affected the Kibaran belt range from 1400Ma to 1000Ma, which is similar to the major orogenic evolution associated with the Urumides range in Zambia and the Lurio belt in Mozambique and Malawi.

Methodology adopted for Lithological Mapping

Lithological mapping was performed using a combination of field survey and spectral analysis of remote sensing data from Landsat MSS, Landsat TM and SPOT.

Publications

Results from the Lithological Mapping Phase of the GARS-Africa Project were published in two volumes of the Bulletin (annals) of MRAC:

• Volume I (1988): “Image analysis, geological control and radiometric survey of Landsat TM data in Tanzania”
  
• Volume II (1989) “Spectrométrie à haute résolution in situ et analyse d’image LANDSAT et SPOT au Burundi”
  
  For more information, please visit MRAC

International Collaboration

University of Bujumbura, Burundi (Geological Department)
University of Dar-es-Salaam, Tanzania (Geological Department)
Bundersanstalt für Geowissenshaften und Rohnstoffe (BGR), Germany
Bureau de Recherches Géologiques et Minières (BRGM), France
Ecole National Supérieure des Mines (CTAMN), France
Musée Royal de l’Afrique Centrale (MRAC), Belgium
Université de Nice, France
Université de Paris-VI, France

Coordination was carried out by MRAC and BGR