Elastic Anisotropy and Internal Structure of Rocks from the Uranium Ore Occurrences of the Litsa Ore Area (Kola Region, Russia)

Vadim L Il’Chenko,Maria A Gannibal

doi:10.3390/geosciences9070284

Vadim L Il’Chenko, Maria A Gannibal

Open Access

https://doi.org/10.3390/geosciences9070284

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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.

Highlights

The most important role in the formation of mineral deposits is played by tectonic disruptions, fractures and other heterogeneities of the Earth’s crust, which act as reservoirs or migration routes for ore-forming fluids
Spatial variations of rock fracturing determine the anisotropy of its permeability; for example, type of elastic symmetry will directly affect the results of geotechnological experiments on the possibility of extraction of the ore component by the method of underground leaching
All samples studied were collected from felsic rocks; their average density (2.6–2.7 g/cm3 ) corresponds to the reference data [21]

Summary

Introduction

The most important role in the formation of mineral deposits is played by tectonic disruptions, fractures and other heterogeneities of the Earth’s crust, which act as reservoirs or migration routes for ore-forming fluids. The tectonic disturbances are often developed around geological bodies or the areas with contrast physical properties as compared to the surrounding rocks: these are either denser intrusive bodies, or zones with increased amount of pores or cavities of natural or artificial origin. The systems of cracks and pores in rock samples, as a rule, coincide with the spatial position of the elements of elastic symmetry (axis, plane); that is, the type of elastic symmetry and the value of the elastic anisotropy index of rocks is reflected in the actual fracturing or porosity. Spatial variations of rock fracturing determine the anisotropy of its permeability; for example, type of elastic symmetry will directly affect the results of geotechnological experiments on the possibility of extraction of the ore component by the method of underground leaching.

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