X-Ray Computed Microtomography of Sulfide Minerals: Studies of Microinclusions and Implications for the Sm–Nd Dating of Ore Genesis

A microtomographic study of the internal structure of sulfide minerals from the ore-bearing rock varieties of two economically significant deposits in the Arctic zone of the Russian Federation, disseminated ore of the Pilgujarvi Cu–Ni deposit (Pechenga) and metalliferous gabbronorites of the platinum-bearing Fedorovo–Pansky complex (Kola Peninsula), was carried out. It was shown that all sulfide samples studied had a homogeneous structure without obvious defects or silicate inclusions larger than 1 µm. The absence of silicate microinclusions larger than one micron in sulfides testifies to the isomorphism of rare earth element (REE) occurrence in sulfides and eliminates, to a certain extent, the debatable problem of the influence of microinclusions on the results of Sm–Nd isotope-geochronological studies of sulfides. The presence of smaller (10–500 nm) silicate microinclusions is, with a high degree of probability, unable to control the total REE budget in a sulfide mineral. The conclusion of the absence of a significant effect of microinclusions on the obtained ages is confirmed by the results of Sm–Nd dating using sulfides from the same mineral aliquots: the Sm–Nd ages of the ores of the Pilgujarvi Cu–Ni deposit were estimated at 1965 ± 87 Ma; and the ore-bearing gabbronorites of the Fedorovo-Pansky complex, at 2482 ± 61 Ma. This agrees well with the datings obtained earlier using other isotopic systems (U–Pb, Re–Os).