A geochemical approach to the identification of a radon-affected area

The identification of a radon-affected area in the south of Yugoslavia was based on geologicalstructuraland geochemical prospecting data of radioactive and other mineral resources. An anomalousarea was recognized at a rural community Gornja Stubla (in the extreme south of Serbia), whileprospecting for uranium in the region on the margin of the large Vardar Zone geotectonic unit. Thevillage of Gornja Stubla overlies the contact of Paleogene rocks, lower Cretaceous flysch and granite.The village area is bordering on a (NW-SE) fault zone filled with brecciated rock mass which bearsthe secondary uranium mineral (autunite).The regional semidetailed and detailed geochemical prospection used lithogeochemical,hydrogeochemical, stream sediments, radiometric and atmogeochemical (soil gasses) methods. Thelithogeochemical prospecting was parallelled with the radiometric ground network measurementswhich varied within the range from 183 to 825 Bq/kg. Concentrations of natural radionuclides intrachyte, the primary uranium bearing rocks is, near the village houses, approximated U 25 g/t, Th 61g/t, and K-40 5,4%.Uranium contents in waters, near Gornja Stubla, measured during the hydrogeochemical prospecting,at trachyte/sedimentary rocks contact, varied from 0.5 to 2.2 mg/l. Semidetiled hydrogeochemical andmetallometric prospection detected in the NW of the area had an average uranium contents in waterand alluvion of 33.4 mg/l and 4.5 g/t respectively.Atmogeochemical prospecting revealed high levels of radioactive emission of over around 740 kBqm-3; radon levels, relative to seasonal variations exceeded 3000 Bq/m3 in some of the houses.