TITLE:
Gold and Silver Minerals and Conditions of Their Formation at the Dorozhnoye Deposit (Magadan Region, Russia)
AUTHORS:
N. E. Savva, G. А. Palyanova, Е. Е. Kolova
KEYWORDS:
Dorozhnoye Deposit, Au-Ag Minerals, Genesis, Eh-pH Diagrams
JOURNAL NAME:
Natural Resources,
Vol.5 No.9,
July
31,
2014
ABSTRACT: This paper presents the brief geological and
mineralogical characteristics of the Dorozhnoye mesothermal gold
ore deposit (Magadan Region, Russia). The gold and silver minerals are represented
by electrum (530‰ - 700‰), freibergite, stephanite, pyrargyrite and
Bi-diaphorite. The homogeneous fluid inclusions enable one to determine that
the quartz-molybdenite veins were formed at a temperature of 340°C to 140°C,
and that the quartz-sulfide gold ore veins were formed at a temperature of 165°C
to 125°C. It is assumed that the fluid had a mixed composition and evolved from
K-chloride and K-carbonate to Na-chloride. The hypergenesis zone contains: high
fineness gold (800‰ - 950‰), petrovskaite (AgAuS) and uytenbogaardtite (Ag3AuS2)
associated with goethite and melanterite. The surface waters contain: Ca++ up to 293 mg/L, HCO3 up to 125 mg/L, SO4 up to 777 mg/L;
рН is 5.8 to 7.2. Thermodynamic calculations have been conducted and Eh-pH
diagrams have been built for the Au-Ag-S-H2O system at 25°C and 100°C
(p = 1 bar) to reveal gold and silver stability
fields. Au-Ag sulfides at the Dorozhnoye deposit are formed under oxidizing
conditions and an acidic environment with dominating sulfates.