The paper presents results of Ar and He isotopic studies in rocks and sulfide ores of the Late Precambrian Dovyren dunite-troctolite layered intrusion (Northern Baikal region). The ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios in the intrusion are similar to those in other mafic intrusions in the continental crust, and the gases in fluid inclusions bear a significant crustal component. The lowest ³He/⁴He and ⁴⁰Ar/³⁶Ar ratios in sulfide ores hosted by the intrusion, about those in crustal fluids, indicate involvement of the latter in magmatic mineralization.