Abstract
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.
Highlights
Riebeckitized magnetite quartzites constitute a significant part of the productive strata at the Pervomayskoye, Annovskoye, Inguletskoye, Petrovskoye, and Artemovskoye deposits in the Krivoy Rog basin
Their formation is associated with epigenetic process of sodium metasomatism, which is about 1.8 billion years old and which occurred at an interval of about 400 million years after the dynamothermal metamorphism of the rocks of the banded iron formation (2.2 billion years)
Issues of their geological position, structure of metasomatic bodies were considered in the works (Polovinkina, 1953;Eliseyev, e. a., 1961;Aleksandrov, 1963;Kushev,1972;Nikolskiy, 1973;Evtekhov, e. a., 1980;Evtekhov, e. a., 1988;Pirogov, e. a.,1989;Chadwick, e. a.,1986).The authors came to the conclusion of regularities existing in the arrangement of the bodies of riebeckite metasomatites, they are as follows: 1) the overwhelming majority of them tendsspatially towards the ferruginous horizons of the Saksagan suite; 2) ferruginous quartzites of the central zones, as well as cummingtonite-magnetite, magnetitecummingtonite quartzites of the peripheral zones of ferruginous horizons, were subject of maximum riebeckitization; 3) the position of the bodies of riebeckite metasomatites in the sections of the ferruginous horizons is controlled byfaulting, which played the role of supply channels for metasomatizing carbon dioxide-sodium hydrothermal solutions
Summary
Riebeckitized magnetite quartzites constitute a significant part of the productive strata at the Pervomayskoye, Annovskoye, Inguletskoye, Petrovskoye, and Artemovskoye deposits in the Krivoy Rog basin. Riebeckitized magnetite quartzites are the main mineral variety of ores at Pervomayskoye, Petrovskoye, and Artemovskoye deposits – they account for up to 60% of the total mass of the productive strata at these deposits.
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