TY - JOUR

T1 - Gold and silver minerals in low-sulfidaton ores of the Julietta deposit (northeastern Russia)

AU - Palyanova, G. A.

AU - Savva, N. E.

AU - Zhuravkova, T. V.

AU - Kolova, E. E.

PY - 2016/8/1

Y1 - 2016/8/1

N2 - Gold- and silver-containing pyrites of the Tikhii area at the Julietta deposit (Engteri ore cluster, Magadan Region) were studied by optical and scanning electron microscopy and electron probe microanalysis. One- or two-phase rounded microinclusions consisting of electrum (450-680%c) and/or galena or of petrovskaite and/or uytenbogaardtite, galena, and sphalerite have been found in early pyrites. Later As-pyrites (up to 2.6 wt.% As) contain multiphase xenomorphic microinclusions of acanthite, uytenbogaardtite, freibergite, argentotetrahedrite-tennantite, naumannite, petzite, selenopolybasite-selenostephanite, tellurocanfieldite, and other ore minerals localized in pores, cracks, and interstices. Pyrites that underwent hypergene alterations have rims and veinlets formed by acanthite, goethite, anglesite, plattnerite, and native silver. The presence of rounded ore mineral microinclusions and large pores in the early pyrites suggests the participation of volatiles in the mineral formation and the uptake of large amounts of impurities by pyrite under high-gradient crystallization conditions. The thermobarogeochemical studies of fluid inclusions in quartz have shown that the ore zone formed under boiling-up of hydrothermal medium-concentration NaCl solutions at 230-105 °C. The results of thermodynamic calculations evidence that Ag-Au-S-Se minerals formed under decrease in temperature and fugacity of sulfur (log1Q/S2 = -22 to -9) and selenium (log1Q/Se2 = -27 to -14) and change of reducing conditions by oxidizing ones in weakly acidic to near-neutral solutions.

AB - Gold- and silver-containing pyrites of the Tikhii area at the Julietta deposit (Engteri ore cluster, Magadan Region) were studied by optical and scanning electron microscopy and electron probe microanalysis. One- or two-phase rounded microinclusions consisting of electrum (450-680%c) and/or galena or of petrovskaite and/or uytenbogaardtite, galena, and sphalerite have been found in early pyrites. Later As-pyrites (up to 2.6 wt.% As) contain multiphase xenomorphic microinclusions of acanthite, uytenbogaardtite, freibergite, argentotetrahedrite-tennantite, naumannite, petzite, selenopolybasite-selenostephanite, tellurocanfieldite, and other ore minerals localized in pores, cracks, and interstices. Pyrites that underwent hypergene alterations have rims and veinlets formed by acanthite, goethite, anglesite, plattnerite, and native silver. The presence of rounded ore mineral microinclusions and large pores in the early pyrites suggests the participation of volatiles in the mineral formation and the uptake of large amounts of impurities by pyrite under high-gradient crystallization conditions. The thermobarogeochemical studies of fluid inclusions in quartz have shown that the ore zone formed under boiling-up of hydrothermal medium-concentration NaCl solutions at 230-105 °C. The results of thermodynamic calculations evidence that Ag-Au-S-Se minerals formed under decrease in temperature and fugacity of sulfur (log1Q/S2 = -22 to -9) and selenium (log1Q/Se2 = -27 to -14) and change of reducing conditions by oxidizing ones in weakly acidic to near-neutral solutions.

KW - Au- and Ag-containing pyrites

KW - Au-Ag chalcogenides (acanthite, naumannite, uytenbogaardtite, and petrovskaite)

KW - electrum

KW - genesis

KW - physicochemical parameters of ore formation

UR - http://www.scopus.com/inward/record.url?scp=84996483723&partnerID=8YFLogxK

U2 - 10.1016/j.rgg.2016.08.005

DO - 10.1016/j.rgg.2016.08.005

M3 - Article

AN - SCOPUS:84996483723

VL - 57

SP - 1171

EP - 1190

JO - Russian Geology and Geophysics

JF - Russian Geology and Geophysics

SN - 1068-7971

IS - 8

ER -