Natural radioelement concentration in the Troodos Ophiolite Complex of Cyprus

Résumé : High-resolution gamma-ray spectrometry was exploited to determine naturally occurring thorium (Th), uranium (U) and potassium (K) elemental concentrations in the whole area covered by the Troodos Ophiolite Complex of Cyprus. For that purpose, a total of 59 samples from surface soils and 10 from the main rock formations of the region of interest were analysed. Elemental concentrations were determined for Th (range from 2.5x10^-3 ppm to 2.0 ppm), U (from 8.1x10^-4 ppm to 0.6 ppm), and K (from 1.3x10^-4 % to 1.0 %). The average values (A.M +- S.D.) derived are (0.24 +- 0.34) ppm, (0.10 +- 0.10) ppm and (0.21 +- 0.24) %, for Th, U, and K, respectively, in the soils, and (0.52 +- 0.17) ppm, (0.17 +- 0.11) ppm and (0.49 +- 0.87) % in the rocks. From these values, a radioactivity (radioelement) loss of nearly 50% is estimated in the underlying surface soils due to bleaching and eluviation during weathering of the rocks. The measured Th/U ratio exhibits values between 2 and 4, whereas the K/Th ratio is highly variable ranging between 1.5x10^3 and 3.0x10^4.