Amazarkan gold deposit: conditions of formation, sources of ore substance (Eastern Transbaikalia)

Abstract

Relevance. The need to clarify the sources and conditions of formation of gold mineralisation of the Amarzakan gold deposit. The characteristic feature of the deposit is the spatial combination of gold mineralisation and small intrusions of the middle and basic composition of the Amudzhikan complex. Aim. Determination of physico-chemical conditions and nature of the source of the ore substance of the Amazarkan deposit. Methods. ICP-MS method and standard chemical analysis were used to determine the elemental composition of rocks. Sulfur isotope composition of sulfides was obtained using gas-source mass-spectrometry and fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and by FTIR spectroscopy at the Centre for Collective Use of Multi-element and Isotope Studies of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). The oxygen isotope composition was determined at the Geological Institute of the Siberian Branch of the Russian Academy of Sciences (Ulan-Ude) using the MIR 10-30 laser heating system with a 100-watt CO2 laser and a wavelength of 10.6 µm in the infrared region in the presence of BrF5 reagent. Results. The authors have established the spatial confinement of ore zones to Mesozoic dikes of the Amudzhikan complex (J2-3). The Eu/Sm and Eu/Eu* ratios in the dikes indicate fractionation of magmatic melts in the sources at the level of the lower continental crust and low degree of their differentiation. The character of REE distribution in the rocks of dikes of the Amudzhikan complex is similar to the distribution of REE in the ores of the deposit. Eu/Sm–Eu/Eu* figurative points of compositions of ore veins and granodiorites of the Amudzhikan complex form a single trend. Dykes of the Amuzhikan complex are characterized by increased Au content from 0.026 to 1.171 g/t. These data suggest a paragenetic link between Au mineralization and rocks of the Amudzhikan complex. Ore veins of productive stages of ore formation were formed at temperatures ranging from 125 to 410°C. The calculated S and O isotopic composition of the ore-forming fluid in equilibrium with pyrite and quartz, as well as the Co/Ni>1 ratio in the ores indicate the presence of a magmatic component in its composition.

Keywords

• Amazarkan gold deposit
• ore associations
• oxygen and sulfur isotopes
• indicator ratios of elements
• magmatic sources
• fluid inclusions