Spectrochemical study of potential source minerals of radon anomaly

Abstract

In the Velence Mts. one of the highest indoor radon concentrations was detected in Hungary. In this study, we identify the potential source minerals of radon measured at several locations in the Velence Mts. Two basic types of samples have been collected representing the bedrock of the studied area: (1) massive granite; and (2) granite rubble. The U- (2.5–5.4 ppm) and the Th-concentrations (16.9–23.3 ppm) of the bulk rock samples are above the average of the upper continental crust, which is dominated by granites (U: 2.8 ppm, Th: 10.7 ppm). Four types of U- and/or Th-bearing mineral phases, which can be considered as potential source of radon, have been identified in the studied samples: allanite, monazite-group minerals, zircon and xenotime. Based on our study, the monazite-group minerals and, in the massive granite samples allanite are the most likely source of radon. Our petrographical and geochemical results suggest that monazite-group minerals formed by the alteration of primary U–Th-bearing allanite when the massive granite became granite rubble. This process could happen in the surface (or near the surface) in the geological past and happens recently during our life.