The deposit Gemerská Poloma is located in the Gemeric Superunit of the Western Carpathians and it is currently mined for talc. Talc formed by metasomatic replacement of magnesite, together with dolomite, quartz, pyrite, and accessory minerals. Leachates of dolomite samples in 2.5 M acetic acid yield a SmNd isochron age of 271 ± 7 Ma. This age coincides with the previously published ages of the underlying, evolved granitic rocks (from 265 ± 17 to 257 ± 5 Ma, U–Th–Pb on monazite) and the UPb age of uraninite (264 ± 1 Ma) interpreted to form from fluids expelled during granite crystallization. The relationship of metasomatism and the granites is further supported by: (i) increased Li and F concentrations in the leachates from dolomite (when compared to the primary magnesite); (ii) increased total REE concentrations in dolomite (compared to magnesite) and even presence of individual REE minerals (bastnäsite) in the ore body, (iii) chondritic Y/Ho ratios, compatible with a magmatic source; (iv) the presence of skarn bodies directly above the magnesite-talc ore deposit; and (v) previously inferred low pressure of talc metasomatism, typical for contact metamorphism in shallow crustal levels. The positive europium anomalies argue for the metasomatism by the action of high-temperature (> 250 °C) hydrothermal fluids that progressively cooled below 250 °C. Thus, the observed talc metasomatism was triggered by the intrusion of the Permian granitic rocks. The Alpine processes tectonically modified the ore body, caused recrystallization and folding of the pre-existing talc and formation of new talc, and obliterated much of the evidence of the earlier processes. •Talc metasomatism of a magnesite body resulted from an interaction with a granite intrusion.•Sm–Nd radiometric dating on dolomite constrained the timing of talc metasomatism.•Dating of hydrothermal carbonates by the NdSm method yields geologically reasonable and precise ages.