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GEOSTATISTICAL ASSESSMENT AND RESOURCE CLASSIFICATION OF THE OUM DHEROUA (ISLAMIC REPUBLIC OF MAURITANIA) STRONTIUM-URANIUM SURFICIAL TYPE OCCURRENCE

I. Virshylo, V. Zagnitko, D. Kravchenko, А. В. Андреев, М. Kurylo

Abstract

The issues of the spatial distribution of complex occurrence of surficial type uranium and strontium mineralization are presented. In this study, we show the preliminary results of complex processing of remote sensing and ground data, including detailed geological mapping, geochemical and mineralogical assays, geophysics made by analysis in GIS. We found a significant variation in commodities co-distribution, which impacts the resource classification. The investigated area is located in arid conditions of south-west Sahara, in the northern-western part of the Precambrian Reguibat shield. Generally, Mauritania is a very perspective country for the discovery of different types of uranium deposits. There are several good surficial type deposits explored in the northern-eastern part with a strong aerogeophysical anomalous pattern of this part of the Reguibat shield. But the northern-western part has only a few known occurrences. In our opinion, the area is underexplored due to hard climate and infrastructure conditions but has some advantages like a short distance to Nouadhibou seaport, a flat area without any significant settlements, etc. The site discussed was firstly discovered in 2013 after the remote analysis of aerospectral data during the short field reconnaissance with the ground radiometric survey. Next in 2015-2019, this site was prospected by ground radiometry and spectrometry, trenches, and ongoing drilling. The results show some specific features of ore bodies: 1) predominance of ?alcium uranium vanadate (tyuyamunite) over more usual potassium ones (carnotite); 2) significant geochemical anomalies of strontium (mostly in form of strontianite) ? up to 8%; 3) bad correlation of ore bodies with current hydrography ? dry streams (?wadi?) and lakes. We discover a spatial variance in the distribution of uranium and strontium where the last is spread widely. The paleo-valleys relief is varying in the range of 3-14 meters and mineralization mostly concentrated in depth?s range 3-7 meters. It was discovered at least four ore bodies. The main ore body was explored by 57 drillholes and two trenches, we estimate about 80t of indicated resources of U3O8 with 100 ppm cut-off grade. But there are still big uncertainties in the shape of ore bodies, cut-off grades both for strontium and uranium, especially in case of strontium evaluation as the main commodity. The question of resource classification in connection to geostatistical results was discussed.

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DOI resolver: doi.org/10.5593/sgem2020/1.2/s03.016

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