Evolution of the Kara Ore-Magmatic System (Eastern Transbaikalia, Russia): Experience in Applying Small-Scale Geochemical Survey

The article discusses a novel methodological approach to deciphering the evolution of ore-magmatic systems (OMS), based on the study of geochemical fields associated with different stages of the evolution of the magma chamber, accompanied by ore mineralization. As the material for research, we used the results of geochemical dispersion train surveys within the Kara ore cluster (Eastern Transbaikalia). The analysis of features of the composition and sequence of identification of geochemical fields made it possible to consider in more detail the evolution of the Kara OMS. It was found that we are dealing with a highly eroded rare metal OMS created in two ore formation stages. The first ore formation stage is associated with the evolution of the upper magma chamber (apical part of the Kara–Chacha massif). The main useful component of this OMS was Mo. The second stage is associated with the evolution of the lower magma chamber. This was also rare-metal mineralization; its profiling elements were W and Mo, but the main useful component is Au. It was found that Au is mobile at two evolutionary stages of the late OMS and accumulates when one stage of mineralization overprints the other. Granitoids of the Kara–Chacha massif can be considered the source of Au. No less probable is the hypothesis of its input together with B from the lower levels of the magmatic system, or as part of transmagmatic fluids from without.