Gold Mineralzation from Calcite-Dolomite Carbonatite of the Guli Massif (Maimecha-Kotui Province, Polar Siberia): First Results

Abstract

Complex gold-iridium-osmium placer deposits associated with the Guli massif of ultramafic, alkaline rocks and carbonatites are located within the Maimecha-Kotui province in the northern part of the Siberian Platform. Unlike natural Os-Ir alloys, which are genetically related to ultramafic rocks, the bedrock source of gold remains controversial. We report, for the first time, morphological and compositional features of gold mineralization from calcite-dolomite carbonatite of the Guli massif. Gold minerals are represented by natural Au-Ag alloys containing gold (69.64–88.57 wt %) and silver (11.73–30.83 wt %) with low concentrations of copper (up to 0.18 wt %), which predominate over minerals of the system Au–Cu–Ag (e.g., natural alloys Au_0.74Cu_0.14Ag_0.12 and Ag_0.51Au_0.47Cu_0.02, tetra-auricupride (AuCu) and auricupride (Cu₃Au)). Gold minerals are characterized by an early pentlandite-troilite-chalcopyrite association that form polyphase euhedral inclusions. Later galena (PbS) occurring in the form of subhedral monophase inclusions is replaced by cerussite (PbCO₃). The revealed similarity of gold minerals and mineral assemblages in gold from calcite-dolomite carbonatite with those of gold minerals from placer deposits of the Guli massif indicates that derivatives of ijolite-carbonatite magmatism played a significant role in gold ore formation.