Selective Neodymium Enrichment of Sulfides as a “Fingerprint” of Late Processes of Ore-Formation: Insight into Sm-Nd Isotopes for Sulfides from Magmatic Cu-Ni-PGE Complexes and Hydrothermal Pb-Zn, Au-Mo, and Gold Deposits

Abstract

The effect of enrichment with Nd in sulfides from magmatic Cu-Ni-PGE complexes and sulfide ores from hydrothermal Pb-Zn, Au-Mo, and gold deposits was found and characterized. This paper concerns the report and analysis of isotopic geochemical data on the sulfide ores from the large Paleoproterozoic mafic–ultramafic magmatic Cu-Ni-PGE complexes of Fennoscandia and the literature data on sulfide ores from the Qingchengzi Pb-Zn deposit (northeastern China), Tokuzbay gold deposit (southern Altai, northwestern China), and Dahu Au-Mo deposit (central China). The mineral/rock partition coefficients for Nd and Sm (the DNd/DSm ratio) are defined as a prospective tool for the reconstruction of the sulfide mineral formation and geochemical substantiation of possible sources of ore-forming fluids for deposits of various genetic types. The observed selective Nd accumulation indicates either hydrothermal or metamorphic (metasomatic) impact, which is associated with increased Nd mobility and its migration or diffusion. Due to this process, there is a relative Nd accumulation in comparison with Sm and a consequent increase in the DNd/DSm ratio. At the isotopic system level, this leads to a sufficient decrease in the Sm/Nd ratio for the secondary sulfides of such kind. The revealed effect may serve as an isotopic geochemical marker of recent processes. These processes are quite frequently associated with the most important ore formation stages, which bear the commercially valuable concentrations of ore components. Sulfides from magmatic Cu-Ni-PGE complexes are more characterized by the selective accumulation of Nd in the sequential sulfide mineral formation. For sulfides from hydrothermal deposits, the effect of Nd enrichment is more intense and closely related to ore-forming fluids, under the influence of which sulfide mineralization is formed in multiple stages. The study aims at expanding the knowledge about fractionation and the behavior of lanthanides in ore-forming processes and allows the development of additional criteria for the evaluation of the ore potential of deposits with different geneses, ages, and formation conditions.