An abandoned mine located in the Zlate Hory ore district is now used for speleotherapy. A detailed petrographical study along with extensive gamma-ray spectrometry measuring concentrations of naturally occurring radioactive elements (K, U and Th) was conducted in the mine in order to analyze the interrelationship between modal composition and radioactivity of the rocks. Authors warn of a potentially higher concentrations of ²²²Rn in the subsurface atmosphere of the speleotherapeutic medical facility.