Radon in soils has been tested for the exploration of copper-cobalt deposits of the Shaba crescent where uranium is often a pathfinder element. A very simple technique has been developed using a charcoal detector and a reading by a

portable scintillator

Charlet, J. M.

Makabu, K.

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IL NUOVO CIMENTO Maggio-Agosto 1999VOL. 22 C, N. 3-4Radon in mining exploration of the deposits of the Shaba Copperbelt(République du Congo, Africa) (*)J. M. CHARLET (1) and K. MAKABU (2)(1) Faculté Polytechnique de Mons - Mons, Belgium(2) Université de Lubumbashi - Lubumbashi, Republic of Congo(ricevuto il 9 Giugno 1998; approvato il 18 Dicembre 1998)Summary. — Radon in soils has been tested for the exploration of copper-cobaltdeposits of the Shaba crescent where uranium is often a pathfinder element. A verysimple technique has been developed using a charcoal detector and a reading by aportable scintillator.PACS 29.40 – Radiation detectors.PACS 91.35.Gf – Structure of the crust and upper mantle.PACS 89.60 – Environmental studies.PACS 01.30.Cc – Conference proceedings.1. – IntroductionUranium is often associated with the copper-cobalt deposits of the Southern Shaba(see fig. 1) of the «Republique du Congo» (Gauthier et al., 1989). It can constitute auseful indicator of the hidden or buried mineralizations in consideration of thebehaviour of the gas products by disintegration (radon, helium).However, radiometric anomalies can also be related to lateritic soils well known inAfrica (Samama, 1984). The discovery of U-occurrences in ferralitic environment of theLubumbashi area (Makabu et al., 1990) leads to a question:These anomalies can represent secondary dispersion patterns above high-gradeprimary occurrences or result from processes of concentration on ordinary sourcerocks?To discuss this problem we have undertook a radon and radiometric exploration ona Cu-Co deposit situated near the mining town of Lubumbashi (Luiswishi deposit).The Luiswishi deposit has been the subject of a complete study in the thesis of Loris(Loris et al., 1997; Charlet et al., 1997).(*) Paper presented at the “Fourth International Conference on Rare Gas Geochemistry”,Rome, October 8-10, 1997.G Società Italiana di Fisica 497J. M. CHARLET and K. MAKABU498Fig. 1. – Distribution of uranium deposits or occurrences in the Shaba Crescent (after Gauthier etal., 1989).A typical profile of radioactivity (fig. 2) in a quarry shows a high U concentration inthe «RAT grey» formation (REDOX front) where mineralizations are developed.2. – Application of the radon methodApplication of gas methods in developing countries requires a low-cost, efficient andnot complex method. We have developed a charcoal detector allowing reading by aportable scintillator that many mining companies use for the radiometric prospectionby foot. In 1995 a first test has allowed to compare the measures of radon concentrationon field with a portable system (a total-count scintillator and some lead pieces to reducethe background) and in the Mons laboratory with a gamma-ray spectrometer. The dayafter the recovery of the detectors, the return by plane allowed to count the detectorsat Mons. Correlation between both the systems of measurement was excellent (r 240.990) and support the generalization of in situ reading in Shaba (Charlet and Makabu,1996).Two traverses and some sites at the bottom of the quarry (points 23-24) have beenstudied in 1995 and 1996.A typical radon profile in soils (fig. 3) shows a very high anomaly at the top of the«RAT grey» and a general shape similar to the radiometric profile (fig. 2).RADON IN MINING EXPLORATION OF THE DEPOSITS ETC. 499Fig. 2. – A typical radioactivity traverse in the Luiswishi deposit (RAT lilas: dolomitic, chloriticsiltstones with hematite, RAT gris: dolomitic, chloritic siltstones with organic matter and sulfides,RSF-RSCA: siliceous dolostones, SD: dolomitic shales).Fig. 3. – Radon and radiometric traverse.J. M. CHARLET and K. MAKABU5003. – Comparison between radon and radioactivity in soilsDuring the field survey, radioactivity has been measured at the bottom of the holeswhere the charcoal detectors have been put down. Besides soils were sampled and ag-ray spectrometry was performed at Mons.From the traverse 1 (see fig. 3) a comparison between radon and hole-radioactivityshows some correlation but lower than with the radiometric profile of the deposit (fig. 2).For example, the high radioactivity of points 11-12 is linked with «colluvium» of«RAT grey» covering the «RAT lilas» formation.A statistical study of the results shows (table I) three different behaviours:– A good correlation between radon-U concentration and total count of thesuperficial formations. In this first case the radon source is close. The application of theradon technique accentuates the geochemistry anomalies in soils (traverse 1).– A bad correlation between radon and radioelements content of the superficialformations where the radon source is distant (traverse 2).– A breaking of the correlation of traverse 1 when some sites at the bottom of thequarry (points 23-24) are added. In that zone wastes with high grade of U cover anon-uraniferous formation (similar to a pedology anomaly).TABLE I. – Correlation radon-radioactivity in soils and g-ray spectrometry of soils samples.Correlationcoefficient (r 2 )Traverse 1 radonradonradonradoactivity in holeseU (ppm)Th (ppm)0.7890.61720.723Traverse 11pts23-24 radonradonradoactivity in holeseU (ppm)0.3820.277Traverse 2 radonradonradonradoactivity in holeseU (ppm)Th (ppm)0.2700.2780.01334. – ConclusionsThe results show a possibility to distinguish superficial uraniferous concentrationslinked with pedology and deeper concentrations linked with copper-cobalt-uraniummineralizations. They suggest the use of radon methods to prospect deposits of theShaba copperbelt in a tropical environment where the difficulty is that anomalies canbe present in the lateritic terrains, in the absence of deposits.RADON IN MINING EXPLORATION OF THE DEPOSITS ETC. 501R E F E R E N C E SSAMAMA J. C., Uranium in ferralitic terranes, in Superficial uranium deposits (I.A.E.H.,Vienna) 1984, pp. 53-59.GAUTHIER G., FRANC¸OIS A., DELIENS M. and PIRET P., The uranium deposits of the Shaba region,Zaïre, The Mineralogical Record, 20 (1989) 265-288.MAKABU K., CHARLET J. M., DOREMUS P. and QUINIF Y., Comportement des radioéléments dansquelques formations latéritiques des environs de Lubumbashi (Shaba, Zaïre). Application àla prospection des gisements Cu-Co-U, Ann. Soc. Geol. Belg., 113 (1990) 315-327.CHARLET J. M. and MAKABU K., Le radon en prospection minière, application à la recherche desminéralisations de la province cuprocobaltifère du Shaba (Congo), Bull. Soc. Belge Geol.,105 (1996) 5-14.CHARLET J. M., LORIS N. B. T. and QUINIF Y., Etude radiométrique des roches encaissantes dugisement de Lwiswishi (Shaba, Zaïre), relation avec les minéralisations uranifères, Actesdu colloque International Cornet (Acad. Royale Sc. d’ Outre-Mer) 1997, pp. 269-283.LORIS N. B. T., CHARLET J.M., PECHMANN E., CARL C., CHABU M. and QUINIF Y., Caractéristiquesminéralogiques, cristallographiques, physico-chimiques et âges des minéralisationsuranifères de Lwiswishi (Shaba, Zaïre), Actes du Colloque International Cornet (Acad.Royale Sc. d’ Outre-Mer) 1997, pp. 285-306.

Radon in mining exploration of the deposits of the Shaba Copperbelt

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Radon in mining exploration of the deposits of the Shaba Copperbelt

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