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.
