Scheelite of the Bystrinskoe Skarn-Porphyry Cu–Au–Fe Deposit, Eastern Transbaikal Region, Russia: Genetic Implications

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.