and Formation Conditions of the Kyuchus Gold
Mercury Deposit (Sakha, Russia)
R. O. Berzon*, I. A. Bryzgalov**, V. O. Konyshev*, T. V. Meshcherina*, and A. N. Nekrasova*
* Central Research Institute of Geological Exploration for Base and Precious Metals (TsNIGRI),
Varshavskoye sh., 129b, Moscow, 113545 Russia
** Moscow State University, Vorob’evy gory, 119899 Moscow
Received January 20, 1999
Abstract—The results of a comprehensive study of the Kyuchus gold–mercury deposit located within the
Momsk rift structure are considered. Genetical features of the Au–Hg, Sb, and Hg mineralization are charac-
terized. Ore bodies of the deposit are located in the black shale sequence of Middle Triassic age, which is folded
in an anticline. The fold is crossed by a complicated diagonal system of the branching brecciation and shear
zones. The carbonate–quartz veins and lenses with a sulfide mineralization are observed in these zones. They
are surrounded by a halo of sericite–carbonate metasomatites with disseminated pyrite and arsenopyrite. Four
principal successively formed mineral assemblages, are distinguished in the deposit, namely: (1) pyrite–arse-
nopyrite with finely dispersed gold, (2) stibnite–quartz with finely dispersed and native gold, (3) cinnabar–met-
acinnabarite–kaolinite with mercury gold, and (4) carbonate (postproductive). The composition and internal
structure of native gold, ore, and mercury-bearing minerals were investigated in detail by electron microprobe
analysis. Mineralogical, geochemical, and isotope data indicates that mineral assemblages at the deposit were
precipitated from fluids which contained isotopically identical oxygen and carbon of a juvenile origin and sulfur
compositionally close to meteoritic standard. The mineral-forming process occurred at the temperature drop
from 300 to 100°C and below, pressure decrease, and at an increasing alkalinity and oxidation–reduction poten-
tial in an unstable physicochemical environment. Geological, mineralogical, and geochemical features of the
Kyuchus deposit are similar to those of deposits hosted by black shale sequences as well to those of the telether-
mal antimony–mercury occurrences. These facts evidence its polygenous and, possibly, polyhronous nature.
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