Differentiated Mafic–Ultramafic Intrusions of the Zubovsky Type in the Norilsk Area: Petrochemistry, Geochemistry, and Ore Potential

Abstract

Intrusions of the Zubovsky type (1) are commonly dominated by troctolite in their ultramafic parts and have an insignificant number (if any) of ultramafic units; (2) occur among olivine and olivine-bearing gabbro-dolerites and often show evidence of a number of accumulation of cumulus olivine, (3) have weakly pronounced (if any) taxitic gabbrodolerite units; (4) include widespread leucocratic hybrid-metasomatic rocks and hybrid quartz- and cordierite-bearing norites and gabbronorites at contacts with the host aluminosilicate rocks; and (5) generally have a low ore content, with the prevalence of disseminated ore units among troctolites and ultramafic rocks, and almost complete absence of massive sulfide ores. The paper is the first to present data on the composition and Nd–Sr–Cu–S isotope-geochemical characteristics of rocks and sulfide ores from the Zubovsky-type intrusions in the Norilsk area. The silicate material of the Zub-Marksheider and Vologochan intrusions is characterized by similar Nd–Sr isotopic parameters: eNd = –1.2 ± 0.5, (87Sr/86Sri) = 0.70685 ± 0.00127, and eNd = 1.2 ± 0.8, (87Sr/86Sri) = 0.70634 ± 0.00068, respectively. These parameters are close to those of intrusions accompanied by economic ore mineralization in the Norilsk area. The whole-rock samples generally have a more ‘radiogenic’ Nd isotopic composition than that of the pyroxene and plagioclase and less ‘radiogenic’ than that of the olivine. The highest eNd value (ca. 5.3) of the olivine indicates that depleted mantle (DM) material was involved in the magma-generating processes. Copper–sulfur isotope data for sulfide ores of the Zub-Marksheider and Vologochan intrusions are remarkably different: δ34S = 1.3 ± 2.3‰, δ65Cu = –0.1 ± 0.15‰ and δ34S = 7.0 ± 1.2‰, δ65Cu = –0.7 ± 0.3‰, respectively. The Cu isotope composition of the sulfide mineralization of both intrusions is close to that of massive and disseminated sulfide ores from the Talnakh deposit in the Norilsk area. The sulfur isotope data suggest that the host rocks had little effect on sulfide mineralization. The identified Nd–Sr–S–Cu isotope-geochemical parameters of the rocks and ores are an important indicator of the potential for rich PGE–Cu–Ni sulfide ores.