DIAMOND EXPLORATION IN GLACIATED TERRAIN - A RUSSIAN PERSPECTIVE

Glacial and glaciofluvial deposits are widely developed in the Arkhang elsk and Middle Timan areas of the North Russian craton, where numerou s kimberlite pipes have been found during the last two decades. These deposits often overlie the pipes and make diamond exploration (particu larly mineralogical prospecting) very difficult. They include ground m oraine (monolithic till and scaly till facies), end moraines, and glac iofluvial and lake sediments. Kimberlite indicator minerals define hal oes of different types in these deposits. Short-distance haloes (1-3 k m) form in basal till in the immediate vicinity of pipes, and in glaci ofluvial sediments of the alluvial stream facies. They are very small, which makes them difficult to find. Long-distance dispersal trains, e xtending up to 50-70 km from the sources, are observed in glaciofluvia l sediments such as eskers, related to streams overloaded with elastic material. Detached haloes, which have lost their relation to the prim ary sources, usually are observed in end moraines and modern beach sed iments. They reflect the averaged mineralogical composition of all the moraines of the area and thus are useful primarily during reconnaissa nce exploration. Pyrope and chromite grains in glacial and glaciofluvi al 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 pri mary (kimberlitic) source.