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Gold-bearing ore occurrences and deposits in jasperoids are objects of a new unconventional type widespread in the West Kalba auriferous belt in eastern Kazakhstan. We present original data on the structural and geologic position and mineralogy of gold-bearing jasperoids of the Baybura ore field, which is a standard object of this type in eastern Kazakhstan. Gold-bearing jasperoids are localized here in shale-carbonate strata of island-arc type (C 1 ) that underwent metasomatism in superintrusive zones of the Kunush complex plagiogranites (C 3 ). Free finely dispersed gold shows typical signs of hypogenous changes. The content of Au varies from 0.1 to 33.5 ppm, and that of Ag, from 0.05 to 2.5 ppm. Based on the data obtained, a geologo-genetic model of the formation of the Baybura gold-bearing jasperoids is proposed. According to the model, the ore deposition is related to the impact of juvenile fluids of plagiogranitic magma on carbonate substrate. The main factors determining the evolution of gold-bearing metasomatites are their localization in zones of high tectonic activity and a drastic change in the acidity-alkalinity regime of solutions in the carbonate environment. Native gold grains are extremely fine and thin and contain a permanent impurity of Hg (0.2-0.7 wt.%). In mineralogical and geochemical features the gold mineralization of the Baybura ore field is similar to that of the Suzdal' deposit and can be assigned to the Carlin type.

—The Lugokanskoe deposit is located in southeastern Transbaikalia and has been studied for a long time by many researchers. However, the type of its formation is still debatable. In this paper we study the mineral composition of ores by modern methods, recognize and describe the main gold mineral assemblages, and present detailed data on the chemical composition of native gold and sulfide minerals and their isotope composition. We have established that gold–pyrite–chalcopyrite–arsenopyrite and gold–bismuth parageneses localized in skarn deposits are the main productive assemblages. Study of the sulfur isotope composition of sulfide minerals has shown an endogenous source of sulfur of the ore minerals. The carbon and oxygen isotope compositions of carbonates of ore-bearing veins indicate the participation of a magmatic fluid. The established age of the gold mineralization and igneous rocks of the Shakhtama complex, together with direct geological observations, points to their spatial, temporal, and genetic relationships. According to their petrochemical and geochemical characteristics, the igneous rocks of the Shakhtama complex are I-type ilmenite (reduced) granitoids. Study of fluid inclusions by heating and cooling and Raman spectroscopy has shown that the mineral formation was accompanied by a gradual decrease in the content of salts in the ore-forming fluids and by a decrease in their homogenization temperatures. Optical observations demonstrate that the fluid was heterogeneous at the early stages of the mineral formation. The evolution of the ore system was accompanied by a change in the gas phase composition of fluid inclusions from predominantly nitrogen–carbon dioxide to essentially aqueous, with carbon dioxide impurity (H2O + CO2 ± N2 → H2O ± CO2). The research data testify to the magmatic nature of fluids and the participation of meteoric waters at the late stages of the ore-forming process. The data obtained have led to the conclusion that the Lugokanskoe gold deposit is related to reduced intrusions formed at a shallow depth.

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The Chauvai Hg-Sb deposit is a striking example of combining two contrasting types of mineralization in space: mercury-antimony and gold ones. The article studies the spatial-temporal and genetic relationships of goldore and mercury-antimony mineralization based on a complex of both traditional geological and mineralogicalgeochemical methods, as well as modern instrumental methods for analyzing the mineral composition. Two types of ores with clear structural confinedness have been found at the deposit: a) mercury-antimonic (cinnabarantimonite) ores, associated with jasperoid breccias and manifested exclusively along the tectonic contact of limestone of the Alai section and terrigenous rocks of the Tolubai Formation, and b) gold- sulphide (arsenopyritepyritic) ores, localized in slightly modified carbonate-terrigenous rocks of the Tolubai Formation, overlying the plane of tectonic contact. Ore formation occurred during the following stages: in the late diagenetic, without interruption passing into the catagenetic-hydrothermal, characterized by the formation of gold mineralization, and then in the later hydrothermal-telethermal, characterized by the development of Hg-Sb mineralization. It is established that the main carrying agent of invisible gold (“invisible gold”) in ores is framboidal and idiomorphic pyrite and, especially, its high-arsenic varieties. A set of conducted studies has shown that the gold ore and mercury-antimony mineralization is broken in time and is genetically associated with various hydrothermalmetasomatic processes, and the Chauvai deposit can be classified as a Carlin-like type.