BASIC PRINCIPLES OF ALLUVIAL DIAMOND EXPLORATION

There is no single, universally applicable method of target selection for alluvial diamond deposits. Climatic and geomorphic history, stratigraphy, structure and tectonic history are important factors that require study and need to be understood for each alluvial diamond province prior to target selection. What is appropriate in one part of the world may be entirely inappropriate in another, but there are some basic principles which must be followed in planning and executing any alluvial diamond exploration program. The general principles that govern any search for alluvial diamonds, the processes involved in alluvial diamond deposition and the methods and technology used in exploring for and evaluating such deposits are also discussed. The principles are illustrated, where possible, by reference to a case history of exploration for alluvial diamonds in the south-western Transvaal, South Africa. Before starting field exploration, it is important to have a comprehensive knowledge of (i) the regional geology of the drainage basin under revue; (ii) the constituent lithologies of the gravel being prospected for; (iii) the geomorphic and climatic factors which have affected the exploration area; (iv) the type of deposit to be sought; and (v) any post-depositional processes which may have affected the alluvial deposits being considered for exploration. This overall information is necessary to construct a concise, yet comprehensive regional model upon which to base any alluvial diamond exploration program. Remote sensing methods are useful, but there is no substitute for an observant, well-trained field geologist expert in mapping and air-photo interpretation. Sampling of drainages for indicator minerals has limited application in alluvial exploration. A brief review of the evaluation methods recommended for an alluvial deposit is included.