Albitites of the Kryvyi Rig-Kremenchug Zone
Syomka V.A, Velikanov Ju.F, Velikanova O.Ju.
N.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation National Academy of Sciences of Ukraine, Kyiv
Deposits of sodium-uranium formation occur in all Precambrian shields of the world. They are confined to the tektono-metasomatic zones developed among the rocks different in composition of amphibolite facies, they are considerably granitized and are of Paleoproterozoic age. Uranium ores are formed by metasomatic way among albitites or albititesated crystalline slates, gneisses, migmatites, granites and ferriferrous quartzite's. Age of ore mineralization by different definitions is from 1.6 billion years to 1.8 billion years, depth more than 2-2.5 km, scope from 0.9-1.0 km to 1.2-1,5 km .
Uranium deposits of sodium-uranium formation are widely developed within the Kryvyi Rig-Kremenchug synclinal structure . Processes of albites metasomatism are most intensively shown in the northern part of the structure – in the Lenin, Pervomaisk mines in the East Annove strip and Zhovta Richka iron-ore deposit. Albititesation is displayed in metasomatic albite replacement of various rocks on Gdantsevo and Saksahan' suites of Paleoproterozoic Kryvyi Rig series, metamorfized in the conditions of green-slate and epidot-amphibolite facies.
Albitites formed during metasomatic replacement of micaceous slates of the Gdansk suite are homogeneous in their mineral structure and are composed by albite, glaucophane, and hydrobiotite; minor ones – by actinolite, tremolite, chlorite; accessory – by apatite, zircon, grothite and rutile. In the rocks of Saksahan′ suite processes albititesation are confined to ferriferrous quartzites and magnetite-amphibolous, amphibolous, garnet-amphibolous and micaceous slates dividing them. The basic varietes of sodium-metasomatites are albitites, aegirinites, riebeckitisated and albititesated magnetite-amphibol slates. Albitites consist from albitite, by 80-90%, alkaline amphiboles, aegirine, quartz, magnetite, biotite, hydrobiotite, chlorite, calcite and accessory malacon, apatite and grothite (sphene) are present in them in subordinate quantity.
Formation of uranium ores which occur, not only in albititesated rocks but also in more cold products of calcium-magnesian and silicium-alkaline metasomatism is connected with albititesation processes in the rocks of Kryvyi Rig series . Albititesated rocks are transitive ones between albitites and enclosing ferriferrous quartzites. Both minerals of initial rocks (magnetite, cummingtonite) and neogenic ones (albite, crossite, rodusite, aegirine, chlorite, hydromicas) in them are noted. The uranium mineralization is presented by silicates and uranium oxides in them. Products of calcium-magnesian metasomatism are developed at average depths. They form large lenticular bodies on magnetite-amphibole slates and ferriferrous quartzites. Their mineral composition – magnetite, martite, hematite, dolomite, alkaline amphiboles, talc, biotite, chlorite, garnet. Industrial uranium ferriferrous-carbonate ores in which the main mineral is uraninite are connected with calcium-magnesian metasomatism. The latest metasomatites fill cracks, secant sodium-carbonate metasomatites and metamorphic rocks and consist of quartz, and biotite, muscovite, feldspars, calcite, chlorite, hydromicas, graphite and organic substance occur in subordinate quantity. The ore mineralization is presented in them by nasturan, coffinite, magnetite, mushketovit, iron hydroxides, pyrite, marcasite, chalcopyrite.š
Some deposits of sodium-uranium formation are characterised by complex ore mineralization, for example, uranium ores of the Zhovta Richka deposit are substantially enriched with V, Sc and TR and have the age of 1.77 billion years [4, 5]. Concerning the age of other uranium deposits defined by K-Ar method, they change in the limits from 1.7 billion years by riebeckite from the Frunze mine  to 1.82 billion years on hydrobiotite from Northern Kryvyi Rig Region .
Deposits of sodium-uranium formation of Kryvyi Rig-Kremenchug synclinale structure were formed at Paleoproterozoic stage of tektono-magmatic activization of the Ukrainian Shield in the subduction zone of Archeane Middle-Dnieper megablock under Paleoproterozoic Ingul megablock.
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