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Natural radioelement concentration in the Troodos
Ophiolite Complex of Cyprus
Michalis Tzortzis and Haralabos Tsertos*
Abstract
High-resolution −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 2.510−3 ppm to 2.0 ppm), U (from 8.110−4 ppm to 0.6 ppm), and K (from 1.310−4 % 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 1.5103 and 3.0104.
The main external source of irradiation to the human body is represented by the gamma radiation emitted by naturally occurring radioisotopes, also called terrestrial environmental radiation. These radioisotopes, such as 40K and the radionuclides from
the 232Th and 238U series and their decay products, exist at trace levels in all ground formations. Therefore, natural environmental radioactivity and the associated external exposure due to gamma radiation depend primarily on the geological and geographical conditions, and appear at different levels in the soils of each different geological region (UNSCEAR 2000 Report, and further references cited therein). The
specific levels of terrestrial environmental radiation are related to the geological composition of each lithologically separated area, and to the content in thorium (Th), uranium (U) and potassium (K) of the rock from which the soils originate in each area. The island of Cyprus is located in the eastern basin of the Mediterranean Sea and extends to an area of about 9,300 km2. Its characteristic geological formations can be
classified into two broad main categories: those that belong to an ophiolite complex (extending to an area of about 3000 km2) and those of sedimentary origin (Figure 1). The Cyprus ophiolite is one of the best preserved and most intensively studied ophiolite complexes in the world, and is known as the Troodos Massif or Troodos Ophiolite Complex (Moores and Vine, 1971; Robinson and Malpas, 1998).