Comparison between natural radioactivity levels and geochemistry of some granitoids in western Turkey

Granitoids commonly include K-feldspar, biotite and zircon, apatite, titanite, allanite, and xenotime crystals, which are known to contain common radioactive elements. Radioactive isotopes of K-40, U-238, and Th-232 can be harmful to human health with increasing dosage and their quantification should be well defined to assess the suitability of wall-rock granitoids for indoor and outdoor purposes. In this study, it is aimed to correlate the possible relationship between concentrations of natural radionuclides and SiO2, Na2O, K2O, and CaO together with elements U, Th, Zr, Y, Ba, Rb, and Sr to provide a basic approach to the compatibility of geochemical data with natural radioactivity levels of granitic to dioritic rocks in western Turkey. Ra-226, Ac-228, and K-40 radioactivity concentrations of the granitoid samples from seven locations range between 15.6 +/- 1.5 and 139.7 +/- 11.2, 12.0 +/- 1.1 and 93.4 +/- 9.0, and 297.5 +/- 15.5 and 880.2 +/- 47.5 Bq/kg, respectively. The lowest Ra-226, Ac-228, and K-40 values occur in the Karaburun granitoids while the Buldan granitoids have the highest values. Our data confirm that the silica-rich acidic granitoids have higher natural radioactivity levels than silica-poor basic granitoids and high natural radioactivity levels have been closely associated with high SiO2, Na2O, K2O, Rb, and Ba contents, which may be explained by postmagmatic events of metasomatism and alteration. CaO, Sr, Y, and Zr do not show any correlation with natural radioactivity levels. Natural radioactivity parameters of the studied granitoids are within the safe dosage limits specified in international standards and are safe for use as construction materials. However, metasomatized or strongly altered granitoids may have elevated natural radioactivity levels and hence careful attention is needed for such granitoids.