Genesis of rare-earth and barium, strontium mineralization in west transbaikalia carbonatites

摘要

Rare-earth and barium-strontium carbonatites in West Transbaikalia are associated with potassic alkaline rocks and occur as dykes, sheets and steeply dipping breccia bodies. Bastnasite phenocrysts in fluorite-bearing carbonatites are throught to be the result of magmatic crystalization. REE-bearing barium-strontium carbonatites contain apatite, monazite and allanite. Barium and strontium minerals developed as a result of melt-liquid immiscibility into sulfate and calcite phases. Hight fluid-saturation of the melt led to further autometasomatic and hydrotheraml processes, promoting the formation of a potential ore deposit, mainly of strontium. Interaction between the carbonatites and a fluid phase has contributed to shifts in isotopic composition of oxygen, carbon and sulfur. In several deposits, contamination by crustal material has occurred and is observable in the isotopic ratios of oxygen and strontium. THe studies have been carried out under support of the Russian Fund for Fundamental Research (grants 96-05-65715, 98-05-65651, 99-05-64435).