FRACTIONAL STRUCTURE AND MINERALOGICAL FEATURES OF PSEPHYTIC DEPOSITS – POTENTIAL RESERVOIRS OF DIAMOND IN THE NORTH-WESTERN PART OF THE UKRAINIAN SHIELD. Part 3. PIVDENNO-ZAKHIDNA (OVRUTSKA) AND MIZHRICHYNSKA AREAS

Abstract

Geologists of the Zhytomyrska Geological Exploration Expedition distinguished the Pivdenno-Zakhidna area in the south-western part of the Ovrutska structure for the search for diamond bearing deposits. The reason for this was the presence of different-age rudaceous rocks – conglomerates, gritstones and coarse-grained sandstones of the Verkhniozbrankivska member of Paleoproterozoic age and Quaternary pebble-sand deposits that overlap the Precambrian rocks everywhere in the region. In the interfluve of Uzh–Zherev, geologists have identified the Mizhrichynska area for the discovery of Cenozoic diamond placers. The reason for this was the discovery of diamonds and their paragenetic satellites in the rudaceous sediments of the fluvial and floodplain facies from the paleovalley of the river Uzh during previous geological surveys at a scale of 1:50,000. Detailed lithologic-mineralogical studies of terrigenous rocks have been made on the mate-rial of ordinary, large-volume and small-volume samples from the wells and dug holes. It is de-termined that the distribution of heavy fractions in sediments and clastogene minerals in them depends on the deposits fractional structure, their facies membership and development area. Par-agenetic and gravitational diamond satellites (pyrope, chrome-spihellids, picroilmenite, stauro-lite, etc.), found in the sediments of both facies, according to their typomorphic features do not correspond to the association of the diamond-bearing facies. In addition, their low content, small size (except staurolite), surface features and the degree of roundness show their long stay far from the original source and possible proceeds from older intermediate collectors. Consequently, their search value is low.