The Kola region (NE of Fennoscandian Shield) has high uranium potential. The most promising structures within the Kola region in respect to uranium enrichment are the Litsa area and the Salla-Kuolajarvi zone. The principal objective of the present study was to define sequence and timing of uranium deposition within these areas. Isotopic (U-Pb and Rb-Sr) exploration of the rocks from Skal’noe and Dikoe U occurrences of the Litsa area and Ozernoe occurrences of the Salla-Kuolajarvi zone was carried out. As it follows from isotopic dating, the principal stages of uranium mineralization had taken place 2.3–2.2, 1.75–1.65, and 0.40–0.38 Ga ago, simultaneously with the stages of alkaline magmatism in the Kola region, which provided the uranium input. Uranium mineralization was related to hydrothermal and metasomatic events under medium to low temperature of ~550 °С at 2.3 Ga to ~280 °С at 0.4 Ga.

No abstract

Zircon grains from various metagranitoids (plagio- and monzo-granites, gneisses, metasomatic rocks, and pegmatoid veins) from the Skal’noe and Dikoe sites of the Litsa uranium ore area (Kola Region, Russia) were studied in order to reconstruct the sequence and timing of events in the area and to observe effects of hydrothermal process related to uranium mineralization on structure and composition of zircon. Individual zircon grains were studied by means of laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS), ion microprobe and Raman spectroscopy. Isotopic LA–ICPMS data for the Skal’noye and Dikoe ore occurrences suggest the following age sequence of events in the area: intrusion of plagiogranites—2829 ± 12 Ma, formation of magmatic protolith of gneisses—2781 ± 17 Ma, metamorphism of plagiogranites—2636 ± 34 Ma; intrusion of monzogranites and pegmatoid veins—2549–2526 Ma, hydrothermal event with uranium input—2276 ± 21 Ma, last metamorphism of plagio- and monzo-granites—1892–1696 Ma. Ore-bearing rocks in the area are pegmatoid veins and quartz–feldspar metasomatites which contain uraninite. During a 2.3 Ga hydrothermal process, newly formed zircon rims grew simultaneously with the precipitation of uraninite in the veins and metasomatites. These rims are characterized by high U and rare earth elements (REE) contents (up to 6560 and 8760 ppm, respectively), dark cathodoluminescence, low Th-U ratios (0.1–0.007) and a flat LREE-enriched pattern, in some cases inherited from minerals, dissolved during a hydrothermal event (magmatic plagioclase and probably monazite). Hydrothermal zircon rims grew with partial dissolution of the magmatic zircon, as evidenced by the rounded and curved shapes of zircon cores. The degree of alteration caused by hydrothermal events depends on the uranium content in the pre-existing zircon. The effects of zircon alteration and newly formed zircon composition reflect the redistribution of uranium in rocks.

No abstract

Ìåòîäîì ðåíòãåíîâñêîé òîìîãðàôèè èññëåäîâàíû äâà îáðàçöà ïåñ÷àíèêîâ, ðàíåå èçó÷åííûõ ìåòîäîì àêóñòîïî-ëÿðèñêîïèè ñ îïðåäåëåíèåì òèïà óïðóãîé ñèììåòðèè è ïðîñòðàíñòâåííîãî ïîëîaeåíèÿ ýëåìåíòîâ óïðóãîé ñèììåòðèè ïîðîä. Ñðàâíåíèå ðåçóëüòàòîâ èññëåäîâàíèÿ ïîêàçàëî ïðîñòðàíñòâåííîå ñîâïàäåíèå ðàíåå óñòàíîâëåííûõ ýëåìåíòîâ óïðóãîé ñèììåòðèè ñ ñèñòåìíîé îðãàíèçàöèåé íåîäíîðîäíîñòåé (òåêñòóðà, ïîðèñòîñòü, ìèêðîòðåùèíîâàòîñòü), êîòî-ðûå ëåãêî âèçóàëèçèðóþòñÿ íà ðåíòãåíîâñêèõ òîìîãðàììàõ.Êëþ÷åâûå ñëîâà: ðåíòãåíîâñêàÿ òîìîãðàôèÿ, àêóñòîïîëÿðèñêîïèÿ, óïðóãàÿ àíèçîòðîïèÿ ïîðîä, óïðóãàÿ ñèììåòðèÿ. IDENTIFICATION OF ELASTIC SYMMETRY ELEMENTS IN ANISOTROPIC ROCK SAMPLES BY X-RAY TOMOGRAPHY V. L. Ilchenko Geological Institute of the Kola Scientific Center of the Russian Academy of Sciences, ApatityTwo samples of sandstones were studied by means of X-ray tomography, which had been previously studied by acoustopolariscopic method with determination of spatial position of the elastic symmetry elements and type of elastic symmetry of rocks. Comparison of the obtained results showed the spatial coincidence of previously studied elements of elastic symmetry with the system organization of irregularities (texture, porosity, microfractures), easily visualized on X-ray tomograms.

No abstract

A relation of uranium mineralization to structural, textural and physical properties of rocks was investigated using two uranium ore occurrences (Beregovoe and Dikoe) in the Litsa ore area (Kola region, Russia) as an example. Study of the rock samples collected on the surface was carried out using X-ray computer tomography (CT), petrography and petrophysics. Petrophysical properties (density and elastic anisotropy index) as well as petrographic characteristics of 25 rock samples were studied; six samples from this collection were studied by CT method. The samples from the Beregovoe site display general positive correlation between magnitude of the elastic anisotropy index and uranium concentration. The samples from the Dikoe ore occurrence, however, do not follow this trend. Comparison of CT data with that obtained from petrophysical measurements shows that the elastic anisotropy index can be low in highly deformed rock, if microfractures and micropores were sealed with secondary (including uranium) minerals; while the uneven distribution of the heavy mineral phases in weakly deformed rock can significantly increase its elastic anisotropy. The CT method combined with petrographic and petrophysical methods has proved to be useful for studying ore deposits. In particular, the CT method allows the influence of spatial variations of minerals of different specific weight on the elastic properties of rocks (elastic anisotropy) to be ascertained. The data obtained for the Litsa area suggest the course of further research involving the construction of geological structural models of the crust blocks with subsequent selection of areas with the most favorable conditions for the formation of uranium ore.

No abstract