Summary:
The iron ore deposits are located within the southern part of the Krivorozhsky iron-ore basin. The iron mineralization at Novokryvorizke and Valyavkinske deposits is hosted by early Proterozoic rocks containing multiple altered ferruginous quartzite strata with shale layers. The major iron ore bearing units in the open pit mines have a carbonate-silicate-magnetite composition. In addition, oxidized, iron-rich quartzite is mined simultaneously with primary ore and is stored separately for possible future processing. Only the magnetite mineralization is included in the 2021 open pit iron ore reserve estimates. The high-grade iron ore of the Kirova deposit is hosted by a ferruginous quartzite with martite and jaspilite.
The iron-formation succession at Kryvyi Rih/Krivoy Rog consists of seven members having a total thickness of ~1300 m (Alexandrov, 1973).
The Kryvyi Rih Basin contains mostly Precambrian sedimentary-metamorphic rocks and is divided into three suites. The middle suite, with a thickness of up to 2,000 m, is the main ore-bearing formation. It consists of seven to eight seams of ferruginous quartzites (represented by hematites, magnetites, and mixed hematite-magnetite varieties) and schists. The average iron content is 30–40 percent in the ferruginous quartzites and 25–30 percent in the magnetite varieties (which compose 20 percent of the total quartzite reserves). Rich iron-ore bodies are dispersed throughout the ore-bearing formation. The ore is formed in columnar, lenticular, and pocket-like bodies that descend to a depth of over 1,000 m. In several places the bodies merge into large sloping ore beds. The rich ores are divided into magnetite, martite, and hematite-martite ores. The last two varieties have an average iron content of 63.7 percent and make up more than half of all reserves.
It lies within the valley of the Ingulets River and its tributaries, the Saksagan and the Zheltaya, and extends in a NNE direction over an interval of about 100 km. The basin is developed within the crystalline basement of the Kurainian massif, comprising Archaean gneisses, granites, migmatites, amphibolites and schists exposed to the west and east of the 2200-2000 Ma Palaeoproterozoic Krivbass geosyncline. The Proterazoic Krivoi Rog Series within the Krivbass is divided into three sections:
1) a lower arkose-quartzite and phyllitic sequence, with a horizon of talc schists;
2) a middle, ore-bearing ferruginous quartzite (banded iron formation - BIF) and slate sequence, which includes includes nine BIF horizons intercalated with quartz-sericite, chlorite-sericite, slates and microquartzites;
3) an upper, quartzite-sandstone-slate sequence with lenses of marble.
The Krivoi Rog Series is folded it no a complex synclinorial structure of synclinal and anticlinal folds with dips on the limbs of 45 to 80°, for the most part with a keel shaped synclinal closure plunging at up to 40° northwards. The limbs of the major synform has been intruded by Proterozoic granite and are cut by longitudinal faults or overthrusts, resulting in the ore-bearing units being segregated along the north-south strike of the basin to form the: i). southern-most Inguletsky, ii). the Saksagan or Main, iii). the Pervomaisk, iv). Annovsk, and v). the northern Zheltorechensk and Popel'nostovsk ore fields. The largest reserves of high grade ores are concentrated in the Saksagan ore field where the ore-bearing middle unit attains a thickness of up to 2000 m and contains up to eight BIF seams.
The BIFs (locally termed 'ferruginous quartzites') comprise magnetite, magnetite-hematite, and hematite varieties, the most economically significant being the unoxidized magnetite and magnetite-hematite varieties. The high grade ores consist mainly of iron oxides and hydroxides which form column-like, less commonly stock-, and lens-like, and more rarely layer-like segregations and bodies within the BIF units, the characteristics of which vary from location to location within the basin. This high grade ore was formed by the leaching of quartz and oxidation of iron silicates within the BIFs.