Mineral Paragenesis, formation stages and trace elements in sulfides of the Olympiada gold deposit (Yenisei Ridge, Russia)

Abstract

The mineral sequence and LA-ICP-MS study of the trace-elements distribution in chalcogenides (arsenopyrite, pyrite, pyrrhotite, sphalerite, chalcopyrite, ullmannite, tetrahedrite, berthierite, stibnite, gudmundite, jamesonite) of the Olympiada gold ore deposit (Yenisei Ridge, Russia) are presented. The deposit was formed in three stages, separated by tectonic breaks. Early (I) corresponds to the paragenesis of acicular arsenopyrite + pyrite + pyrrhotite. At the stage of base-metal sulfides (II), the deposition of the bulk of chalcopyrite, sphalerite and galena occurred. Mineral associations of these stages determined the gold-arsenic (Au-As) type of ores. The stage of late sulfides (III) is characterized by the paragenesis of antimony minerals (stibnite + berthierite + gudmundite) and corresponds to the gold-antimony (Au-Sb) ore type. Commercial concentrations of gold were formed at the early sulfides stage in the lattice bonded and nanosize mode in acicular arsenopyrite (12.5–1,512 ppm). The progress of the ore deposition process with the formation of late polymetallic and stibnite-berthierite mineralization led to recrystallization of early sulfides (prismatic arsenopyrite Au ∼ 36.4 ppm → dipyramidal arsenopyrite Au ∼ 0.5 ppm), remobilization and re-deposition of gold in a native form. Pyrite of the deposit does not contain significant amounts of gold (∼0.4 ppm). Silver is absent in early sulfides, but is concentrated in tetrahedrite (348.0–3,811 ppm), jamesonite (0.1–7.7 ppm), berthierite (0.1–2.3 ppm) and stibnite (0.2–2.0 ppm) of the later stage (III). Early sulfides (stage I) are characterized by the As-Au-W-Se-Te geochemical association; polymetallic sulfides (stage II) — by the Cu-Zn-Pb-Cd-In association; and late sulfides (stage III) — by the Sb-Co-Ni-Te-Bi-Pb-Hg-Ag association.