Features of berillium and rare metal mineralization in syenite of the Perga deposit (Ukrainian shield)

The results of the ore and accessory minerals study in the syenite of the Perga beryllium deposit are discussed. Phenakite and genthelvite are found among Be-bearing minerals. Genthelvite of this syenite, being compared to early published data on genthelvite of the Perga deposit, is distinguished by the highest ZnO content which is close to the theoretical maximum) due to the alkaline nature of studied rock ((Na + K)/Al = 1.09). Genthelvite occurs as later mineral to phenakite or is formed by phenakite replacement at rising the alkalinity as a result of melt differentiation. Columbite with high-Mn content, Y-silicate (keiviite-(Y)?), rare-earth fluorocarbonate (bastnesite) are also found among other minerals of rare metals. The presence of fluorite and rare-earth fluorocarbonate in association with genthelvite or phenakite may indicate that Be and REE were transported in ore-bearing fluids as complex fluorine-carbonate compounds. Considering the geochemical characteristics of rocks (meta-aluminous, subalkaline and alkaline series, deep negative Euanomalies, low Sr, Ba, elevated – HFS elements) from the Sushcano-Perga region, enrichment of these rocks with rare metals and Be are related to intensive feldspar fractionation of the primary melts and due to alkaline oversaturation, volatile and rare metals (Be, Li, REE, Y, Nb, Ta) enrichment in the residual fractions of granitic or syenitic compositions. Postmagmatic alkaline solutions enriched in F and CO32- promote of Be concentration in fluid phase with its following migration and crystallization as genthelvite.