Том 61, № 6 (2019)

The distribution of major gold deposits in the Earth’s history is discussed. The primary heterogeneity of the Archean crust in terms of gold mineralization is demonstrated. Characteristics of the main auriferous metallogenic epochs are given. The predominant associations of the orogenic gold deposits with volcanogenic massive sulfide and copper–nickel deposits during the early periods of the Earth (Archean–Proterozoic) and those with tungsten, molybdenum, copper, antimony, mercury, and tin during the Phanerozoic are demonstrated. The analysis of the distribution of the mineralogical and geochemical types of gold mineralization proper also demonstrates their substantial diversity in the Phanerozoic compared to the Precambrian. These data reflect the mantle–crustal origin of gold mineralization in general and attest to an increase in the contribution of the crustal material into gold mineralization with the age of the Earth. The known gap in lode gold formation (1.7–0.8 Ga), which was caused by the stable cratonic regime of the long-lived Columbia (Nuna)–Rodinia supercontinent is discussed.

Heterogeneous rhythmic–zonal aggregates of tennantite-IV partly or completely replacing early homogeneous Zn-tetrahedrite-I grains and euhedral (Fe–Zn)-tennantite-I crystal were found in ores of the Darasun gold deposit. The different stages of fahlore replacement were observed. This initiates at grain boundaries and is terminated by a complete transformation into pseudomorphic, newly formed (Zn–Fe)-tennantite-IV aggregates surrounded by Zn-tetrahedrite-IV. These aggregates closely associate with bournonite and galena, and their precipitation initiated the formation of pseudomorphs. As is evident from the results of EMPA, (Fe–Zn)-tetrahedrite enriched in As in relation to Zn-tetrahedrite-I was precipitated at the initial stage. Tennantite with wide variations in the Sb/(Sb + As) and Fe/(Fe + Zn) ratios predominates in zonal heterogenous aggregates. There is a negative correlation between Sb/(Sb + As) and Fe/(Fe + Zn) ratios in (Fe–Zn)-tetrahedrite–tennantite-IV. In all sites, there is a miscibility gap between As and Sb and a sharp decrease in Sb/(Sb + As) ratio and increase in Fe/(Fe + Zn) ratio at the contact between Zn-tetrahedrite-I and newly formed (Fe–Zn)-tetrahedrite–tennantite-IV. The sharp zigzag boundaries between Zn-tetrahedrite-I and tennantite-IV and pores in newly formed aggregates provide evidence for coupled dissolution–precipitation reactions. The dissolution was initiated by disequilibrium between Zn-tetrahedrite-I and undersaturated fluid due to the precipitation of galena and bournonite. The precipitation of tetrahedrite–tennantite-IV occurred under the conditions of oscillation in Sb/(Sb + As) and Fe/(Fe + Zn) ratios due to the gradient of concentrations in the fluid. The temperature of crystallization of zonal heterogenous tennantite-IV aggregates ((134–161) ± 20°С) was calculated by the sphalerite–fahlore geothermometer. Instability of early Zn-tetrahedrite-I results from hydrothermal fluid cooling, decrease in fluid salinity, and change in the tetrahedrite and tennantite solubility due to the evolution of the conditions of semimetal migration.

The first results of optical microscopy, cathodoluminescence (CL), ultraviolet fluorescence (UV), electron-probe microanalysis (EPMA), and laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICPMS) study of scheelite from quartz–molybdenite and quartz–carbonate–sulfide veins and veinlets (porphyry type), as well as the magnetite–sulfide massive, veinlets, and disseminated (skarn type) associations, of the Bystrinskoe skarn-porphyry Cu–Au–Fe deposit in the Eastern Transbaikal region, one of the largest gold–copper porphyry deposits in Russia, are reported. Despite the fact that scheelite is not a major ore mineral, it is found almost everywhere. This makes it possible to identify its crucial genetic features in both the two types of mineralization and the deposit as a whole. It is shown that scheelite from different types of mineralization has clearly determined individual characteristics, differing in abundance, associated minerals, CL and UV color, composition and concentrations of major and trace elements, and REE distribution patterns. These crucial features testify to a significant difference in the formation conditions of the studied mineralization types and reveal the dependence on the physicochemical and compositional parameters of the mineral-forming environment. This allows one to consider scheelite as a fundamentally important genetic indicator of the mineral-forming environments' evolution. Crucially important are the molybdenum concentration in scheelite and the type and shape of REE-spectra, which are generally controlled by mineral-forming fluid chemistry, the incorporation of REE in the structure of the mineral, and variations in the redox properties of the mineral-forming fluid.