DIAMOND EXPLORATION IN GLACIATED TERRAIN - A RUSSIAN PERSPECTIVE

Glacial and glaciofluvial deposits are widely developed in the Arkhangelsk and Middle Timan areas of the North Russian craton, where numerous kimberlite pipes have been found during the last two decades. These deposits often overlie the pipes and make diamond exploration (particularly mineralogical prospecting) very difficult. They include ground moraine (monolithic till and scaly till facies), end moraines, and glaciofluvial and lake sediments. Kimberlite indicator minerals define haloes of different types in these deposits. Short-distance haloes (1-3 km) form in basal till in the immediate vicinity of pipes, and in glaciofluvial sediments of the alluvial stream facies. They are very small, which makes them difficult to find. Long-distance dispersal trains, extending up to 50-70 km from the sources, are observed in glaciofluvial sediments such as eskers, related to streams overloaded with elastic material. Detached haloes, which have lost their relation to the primary sources, usually are observed in end moraines and modern beach sediments. They reflect the averaged mineralogical composition of all the moraines of the area and thus are useful primarily during reconnaissance exploration. Pyrope and chromite grains in glacial and glaciofluvial sediments show specific surface features reflecting mechanical and chemical alteration during their transport. These features may be used to recognise the mode of transport and possible distance from the primary (kimberlitic) source.