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Stream-sediment geochemical prospecting for uranium in the paleozoic of the Belgian ardennes
Journal o f Geochemical Exploration, 19 (1983) 125--126
125
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
STREAM-SEDIMENT GEOCHEMICAL P R O S P E C T I N G F O R URANIUM IN T H E P A L E O Z O I C OF T H E B E L G I A N A R D E N N E S
H. MARTIN', J.P. LEFIN', L. DEJONGHE 2 and J. HENRY 2 ' Laboratoire, de G$ochimie, Universit~ de Louvain, Batiment Mercator, Place L. Pasteur 3, 1348 Louvain-la-Neuve (Belgium) 2 Geological Survey o f Belgium, Brussels (Belgium)
(Received June 14, 1983)
ABSTRACT During the years 1979 and 1980, a preliminary program of uranium e x p lo r atio n in the Paleozoic of the Belgian Ardennes was carried out u n d e r the sponsorship of the Commission of E u r o p e a n Communities. The Laborat o r y of Mineralogy of the Pol yt echni c F a c u l t y o f Mons was charged with the radiometric section of the program, the G e o c h e m i s t r y L a b o r a t o r y of the Free University of Brussels with the h y d r o g e o c h e m i c a l exploration, and the G e o c h e m i s t r y L a b o r a t o r y of the University of Louvain with the stream sediment exploration. The Geological Survey of Belgium had the responsibility for coordinating the three programs, the statistical and c o m p u t e r treatm e n t o f the data, and the compilation of the different maps. Orientation studies at the G e o c h e m i s t r y L a b o r a t o r y of the University of Louvain showed t ha t a positive geochemical response for uranium could be obtained with bank sampling, which consists of collecting colluvium and alluvium on b o t h sides of the rivers. This necessitates a large sampling density of a b o u t one sample per km 2 (10 205 samples from an area of 11 000 km2). The f r e q u e n c y distribution of the values of uranium follows the lognormal law with a geometric mean of 1.06 ppm and a threshold of 2.36 ppm (P = 0.954). The anomalies ( > 3 ppm) fall into three main areas each in a di fferent geological setting: (1) at t he periphery of the Cambro-Silurian Massif of Stavelot; (2) within the transition beds bet w een the Visean and Namurian; and (3) in the lower Devonian o f the central Ardennes. The first two areas coincide with zones o f know n radiometric anomalies and of the o ccu r r ence of uraniferous minerals. In the third zone, follow-up w or k has led t o the discovery of a uraniferous mineral assemblage consisting of a weathered mass of iron oxide, leucoxene and phosphates. Statistical analyses o f the results indicate no significant relationship b e t w e e n U and either organic car bon or Mn, a negative correlation between
0375-6742/83/$03.00
© 1983 Elsevier Science Publishers B.V.
126 U and carbonate and pH, and a good positive correlation between ~ and Ca, V and Fe. The last correlation m a y indicate an association of U, V, and Cu with iron oxides f o r m e d during meteoric alteration.
125
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
STREAM-SEDIMENT GEOCHEMICAL P R O S P E C T I N G F O R URANIUM IN T H E P A L E O Z O I C OF T H E B E L G I A N A R D E N N E S
H. MARTIN', J.P. LEFIN', L. DEJONGHE 2 and J. HENRY 2 ' Laboratoire, de G$ochimie, Universit~ de Louvain, Batiment Mercator, Place L. Pasteur 3, 1348 Louvain-la-Neuve (Belgium) 2 Geological Survey o f Belgium, Brussels (Belgium)
(Received June 14, 1983)
ABSTRACT During the years 1979 and 1980, a preliminary program of uranium e x p lo r atio n in the Paleozoic of the Belgian Ardennes was carried out u n d e r the sponsorship of the Commission of E u r o p e a n Communities. The Laborat o r y of Mineralogy of the Pol yt echni c F a c u l t y o f Mons was charged with the radiometric section of the program, the G e o c h e m i s t r y L a b o r a t o r y of the Free University of Brussels with the h y d r o g e o c h e m i c a l exploration, and the G e o c h e m i s t r y L a b o r a t o r y of the University of Louvain with the stream sediment exploration. The Geological Survey of Belgium had the responsibility for coordinating the three programs, the statistical and c o m p u t e r treatm e n t o f the data, and the compilation of the different maps. Orientation studies at the G e o c h e m i s t r y L a b o r a t o r y of the University of Louvain showed t ha t a positive geochemical response for uranium could be obtained with bank sampling, which consists of collecting colluvium and alluvium on b o t h sides of the rivers. This necessitates a large sampling density of a b o u t one sample per km 2 (10 205 samples from an area of 11 000 km2). The f r e q u e n c y distribution of the values of uranium follows the lognormal law with a geometric mean of 1.06 ppm and a threshold of 2.36 ppm (P = 0.954). The anomalies ( > 3 ppm) fall into three main areas each in a di fferent geological setting: (1) at t he periphery of the Cambro-Silurian Massif of Stavelot; (2) within the transition beds bet w een the Visean and Namurian; and (3) in the lower Devonian o f the central Ardennes. The first two areas coincide with zones o f know n radiometric anomalies and of the o ccu r r ence of uraniferous minerals. In the third zone, follow-up w or k has led t o the discovery of a uraniferous mineral assemblage consisting of a weathered mass of iron oxide, leucoxene and phosphates. Statistical analyses o f the results indicate no significant relationship b e t w e e n U and either organic car bon or Mn, a negative correlation between
0375-6742/83/$03.00
© 1983 Elsevier Science Publishers B.V.
126 U and carbonate and pH, and a good positive correlation between ~ and Ca, V and Fe. The last correlation m a y indicate an association of U, V, and Cu with iron oxides f o r m e d during meteoric alteration.