Some mineralogo-geochemical aspects of outlooks of complex use of ores from deposits of U-Na formations of Ukraine.

 

Melnichenko B. *, Bondarenko S. **, Siomka V. **, Grinchenko O. ***, Ivanov B. ****

 

* Institute of geochemistry of the environment, Kiev, Ukraine; ** Institute of geochemistry, mineralogy and ore formation of M.P.Semenenko, Kiev, Ukraine; *** Kiev national Taras Shevchenko university, Kiev, Ukraine; **** GE Kirovgeology, SPE -46, Kiev, Ukraine.

 

Many uranium-ore formations of the world are often accompanied by rather considerable concentrations of different useful element which can be additionally extracted in the course of ore processing. Practically each uranium-ore formation is characterized by the presence of particular complex of colour, rare and noble metals which determine typical geochemical features of this formation and in turn indicate peculiarities of its geological evolution. Proterozoic deposits of uranium ore of Ukraine, that is genetically related to sodium-uranium (albitite) formation of hydrothermal-metasomatic deposits, are not an exception. Most uranium ore deposits and manifestations of this type contain high concentrations of scandium, rare-earth elements, vanadium and silver. Unlike geochemical and mineralogical features of scandium and rare-earth elements that have been thoroughly studied on the Zheltorechenka uranium deposit (Tarchanov 1991, Belevtsev, 1995) the behaviour of V and Ag are not widely discussed in geological literature.

Deposits of U-Na formation are widely distributed in the central part of the Ukrainian Shield, mainly within Ingul'sk geoblock. Here four uranium-ore regions are outlined known as Central (Vatutinka deposit), Novoukrainka (Novokonstantinovka deposit), Kirovograd (Severinkovka, Michurinka deposits) and Krivorozhsk-Kremenchug (Zheltorechena, Pervomaisk deposits) regions. All the uranium deposits are of the same age and were formed in the course of paleo-proterozoic (1,8 - 1.7 billion years) activization of more ancient granito-gneissic substrate. But till now there are no any widely accepted idea about the nature and conditions of their formation. Some spatial and age relations established between the process of ore mineralization and certain rock complexes or structural blocks have rather contradictory nature. That fact testifies to it, that the processes of ore-forming alkaline-sodic metasomatism developed practically on all varieties of rocks from granitoids, migmatites, gneises to ferruginous quartzites and carbonate rocks. Besides this the composition and geochemical features of the uranium ores are practically similar for all the deposits of the central part of the Ukrainian Shield. Sodic metasomatites are represented by chlorite-epidote, riebeckite, riebeckite-aegirine, aegirine, andradite-diopside, hydromica-phlogopite, carbonate-hematite albitites. Uranium mineralization is represented by brannerite, uraninite and some minerals formed as a result of metasomatic alteration of primary minerals. It is combination of the primary hypogenic and different hypergene mineralizations that caused complex mineralogic and geochemical zonation typical of many uranium deposits. But at the same time V and Ag were found present at different content in ores of practically all the urainium deposits.

Vanadium. There are no any vanadium deposits found in Ukraine.

The reliable evaluation of possible accompanying extraction of vanadium from ores of albitite type have not been performed yet. But the probable needs for this element on the nearest period (till 2010) are estimated to be about 1000-1700 tons per year. Multiple geochemical data on uranium deposits of the Inlul's geoblock indicate constant presence of the vanadium directly in ores ores or in near-ore altered rocks (Melnichnko, 1994). Some ore sites of uranium deposits of Zheltorechenka group show high vanadium contents that reach up to 1 %, with ordinary values varying from 0,05 to 0,3 %. Similar values were found on similar uranium deposits of the Kirovograd and Novoukrainka groups.

Preliminary geochemical and mineralogical investigations carried out by us on the Vatutinka deposit have shown, that vanadium is constantly present both in rich and poor ores with average contents of 0,02 to 0,07 %. It is also found, that vanadium show high concentration only in some typomorphic minerals found in uranium ores. (see Table. 1).

 

Mineral

Content of V2O3 in mineral (%)

Mineral in ores (%)

Number of analysis

Aegirine

0,10-0,49 (0,19)

5-20

12

Riebeckite

0.03 -0,32

1-10

8

Sphene

0,34-0,82 (0,54)

0,3 -3

12

Magnetite + hematite

0,15-0,90 (0,40)

0,2- 3

10

Brannerite

0,1-2,85 (1,03)

0,00-1

24

Davidite

0,25- 4,10 (1,60)

0,00-0,1

9

Lead titanates

0,40-2,75 (1,20)

0,00-0,1

7

 

Vanadium forms its own minerals, such as e-Wakefildite (CeVO4) with 18 % of V2O3, for which identification additional detailed investigations are need to be carried out. Simple calculations allow to draw some conclusions. If in the course of separation of uranium ores the fraction of vanadium bearing minerals averages 5-20 % it means, that total contents of V2O3 under the optimistical scenario can reach 0,15-0,25 %. It is not excluded, that contents of vanadium are considerably high on the other uranium deposits and therefore the importance of this problem is much higher.

Silver. This element was out of much attention for long period of time, though the facts of some silver specialisation of sodic metasomatites were established on several deposits of the Krivorozhsk-Kremenchug belt where some intervals with high silver content of more than 1 % have been found (Belevtsev J.N., 1995). Recently the ore body with high silver concentrations were oulined within foot wall of the major uranium-ore zone of the Vatutinka deposit. Spectral analysis data have shown high silver contents of 300 g\t on five-meter interval of silicified albitites in the northern part and 70 g\t on 4,8 m interval of silicified granites in the central part of the Vatutinka deposit. Silver was found as native phase and enter the compositon of matildite AgBiS2. Among associated minerals the galena, pyrite, marcasite, chalcopyrite, sphalerite as well as minerals of uranium, titanium and barium were found as predominate phases.

High concentrations of vanadium and silver in ores of U-Na formation are supplemented by geochemical spectrum of already known useful elements (TRE, Sc, Zr) which concentration is genetically associated with processes of formation of alkaline metasomatites. This fact testifies to unique feature of this formation and some peculiarities in behaviour of the specific elements (including vanadium and silver) in hydrothermal-metasomatic processes. Possible evaluation of possible extraction of silver and vanadium during the processing of uranium ores might be interpreted as urgent problem which resolved by specialists - technologist.

 

References:

Belevtsev Ya.N., Koval V.B, et. al. Genetic types and patterns of distribution of uranium deposits of Ukraine. - Kiev, Naukova dumka. 1995

Tarhanov A.V., Kudlaev A.R., Petrin A.V., Kozyr'kov V.D. Zheltorechenska vanadium-scandium deposit // Geology of ore deposits - 1991 - 33, 6 - P. 50-56.


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