Geological observations coupled with geochemical, isotope, and thermobarogeochemical research on danburite ores of unique skarn borosilicate deposits in their reserves in the Sikhote-Alin (Dalnegorsk) and in the Pamir (Ak-Arkhar) indicate lagoon strata and evaporites in the form of atoll fragments within the Mesozoic subduction mélange as the most probable boron source, which preceded the skarn formation. At the Dalnegorsk deposit, the fact that boron is mobilized by skarn-forming solutions from evaporite accumulations is directly confirmed by the heavier isotope composition of boron (δ11B = +17.7 ‰), which corresponds to marine evaporites, and a typical Li-rich fluid.