Geological position of riebeckite-containing magnetite ores of Krivoy Rog basin

The geological position of the riebeckite metasomatites at the Pervomayskoye, Annovskoye, Gleyevatskoye, Valyavkinskoye, Inguletskoye, Petrovskoye and Artemovskoye deposits of the Krivbas is controlled by faults serving as channels for metasomatizing solution filtrations. This is confirmed by a significant loss of riebeckite metasomatites abundance moving south and north of the central part of the Pervomayskoye deposit, the position of which corresponds to the intersection of two deep faults that are: the submeridional Krivoy RogKremenchug and the sublatitudinal Devladovo ones. In the productive strata of other deposits, the distribution of riebeckite metasomatites is much lower in comparison with the Pervomayskoye deposit, but their position is also determined by faults position.The fifth and sixth ferruginous horizons are characterized by the maximum distribution of riebeckite metasomatites within the Pervomayskoye deposit and form the productive iron ore rock mass. They contain ferruginous quartzites with the highest iron content, composition of which is optimal for active manifestation of riebeckite metasomatism.The process of riebeckitization occurred to much lesser extentin the stratigraphic horizons that underlie and overlay the productive rock mass and which are composed of schists and low-iron magnetite-silicate quartzites.Silicateless (micaceous hematite-magnetite, magnetite) quartzites were subjected to the most intensive riebeckitization in the ferruginous horizons: the content of riebeckite metasomatites here makesup 60-80% of the volume of ore layers. The composition of the sodium amphibole is close to stoichiometric one here. In the layers composed of cummingtonite-magnetite and magnetite-cummingtonite quartzites, the amount of riebeckite metasomatites is much lower and makes up 10-30% of their total volume. The sodium amphibole is represented here by magnesioriebeckite. Similar regularities in the distribution of riebeckite metasomatites are also typical for ferruginous horizons of all iron ore deposits in the Krivoy Rog basin.