Physical and chemical conditions for the formation of mercuric gold within Au-Hg deposits (thermodynamic modeling)

Purpose. To carry out computer thermodynamic modeling of gold and mercury behaviour in the context of their common occurrence and formation of mercuric gold in hydrothermal solutions Cl– – HCO3– – Na+ and Cl– – Na+ – Ca2+ with the use of “Chiller” programme. Methods. Physical and chemical parameters of ore-forming solutions have been used as the initial data for the modeling. They were obtained relying upon the analysis of fluid ore inclusions in the neighbourhood of surface Au-Hg deposits; fluid inclusion studies (i.e. thermometry, cryometry, RS-spectroscopy, ICP-MS-LA) were applied. High metal-bearing hydroterms according to Au (I) within 200 – 100°С temperature interval is determined by means of hyperalkalinity of hydrothermal solutions as well as stability of dihydrosulphide (i.e. Au(HS)2–) complex under the conditions providing transport of gold to low-temperature (150 – 100°С) ore deposition typical for Au-Hg deposits. Findings. Relying upon the previously obtained data of fluid inclusion studies and thermodynamic modeling, basic geological and geochemical conditions of occurrence have been identified; physical and chemical factors defining gold deposits with different mercury content have been determined. Originality. Computer thermodynamic modeling of common Au and Hg behaviour in hydrothermal process made it possible to demonstrate specifics of physical and chemical parameters of formation of complex gold-mercury ores. For the first time, uniqueness of free gold composition for various types of Au-Hg deposits has been determined on the basis of proper data and data by scientific sources. The results, obtained in the process of the studies, made it possible to expand substantially available concepts of their genesis to be important for the development of genetic models of ore-forming systems of Au-Hg deposits. Practical implications. Composition of gold and its mercury content may be used practically in the process of prospecting activities as a criterion to determine the occurrence of one of prospective industrial types of gold ores (Carlin-type) – finely disseminated gold and mercury ore grade mineralization – as well as formation depth and estimation of erosion level of ore bodies.