Skarn-borosilicate giant deposits: derivates of the fluid-hydrothermal reworking of atoll fragments in a subduction melange of Mesozoic orogenic belts of Asia
Geological observations coupled with geochemical, isotopic and thermobaric-geochemical research of danburite ores of skarn-borosilicate deposits unique in their reserves in the Sikhote-Alin (Dalnegorskoe) and in the Pamir (Ak-Arkhar) indicated lagoonal 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 Dalnegorskoe deposit, the fact that boron is mobilized by skarn-forming solutions from evaporite accumulations is directly confirmed by isotopically heavier composition of boron (δ11В = +17.7 ‰) corresponding to marine evaporites, and a typical enrichment of fluid in lithium.