Gold and silver accessory minerals in ultramafites of the Kyzyr-Burlyuksky ultramafic massif (Western Sayan)

Abstract

The study focuses on gold and silver accessory minerals (native silver, cuprous gold, luanheite (Ag3Hg), unspecified mineral phase (Cu,Ag,Hg), first diagnosed in dunites and apodunite serpentinites of the Kyzyr-Burlyuksky ultramafic massif, which is part of the Kurtushibin ophiolite belt of Western Sayan. The revealed ore minerals are mainly observed in the form of single hypidiomorphic, irregular microscopic precipitates (0.5– 3.0 μm) mainly inside magnetite, much less often in grains of avaruite. Typomorphic and chemical features of ore minerals, their natural setting in rock-forming silicate matrix are characterized. Formation and concentration of these accessory minerals is associated with superimposed low-temperature transformation (hydration) processes affecting original ultramafic rocks. At the same time, the presence of luanheite and an unnamed phase (Cu,Ag,Hg), along with the previously identified potarite (PdHg), is probably evidence of low-temperature conditions of mineral formation during the manifestation of epigenetic processes of serpentinization (lowgrade metamorphism) due to solutions enriched in mercury. The source of such solutions could be gabbro intrusions that penetrated later into the main ultramafic body.