Geochemical sampling techniques in the Eastern Desert of Egypt

Abstract

This paper describes various problems in carrying out geochemical prospecting under the conditions that prevail in the Eastern Desert of Egypt. Conclusions are based on four years experience in geochemical exploration in the Eastern Desert, including studies of over 25,000 geochemical samples. In prospecting for ore deposits in stony and sandy deserts, different kinds of geochemical survey techniques can be successfully applied. In carrying out regional geochemical surveys, stream-sediment sampling in combination with panning of heavy concentrates may be used with a considerable degree of success. The method of the cold extraction of metals produces best results when the alluvial silt and argillaceous fraction (minus 0.075 mm) is sampled. Spectrographic analysis, on the other hand, provides dependable data when the minus 1-plus 0.25-mm fractions are sampled. It is established as a fact that sieving-out of the minus 0.25-mm fraction helps to get rid of aeolian sands which otherwise “dilute” anomalies. In the localities where colluvium is mixed with aeolian sand, sampling of the minus 1-plus 0.25-mm fraction considerably increases the contrast of anomalies (by 3.7 times for Sn, 3.8 for Mo, and 1.5 for Cu) and enlarges their size (4 times for Sn, 2.6 for Mo, and 2.5 for Cu). A possibility of forming of “false” anomalies in colluvium, resulting from the secondary concentration of certain heavy minerals resistant to weathering (e.g. Sn, W, Nb, Ta, Zr, etc.) was proven. This should be taken into consideration while carrying out geochemical prospecting in similar conditions.