Ore-bearing magmatism at the Ermakov beryllium deposit in the western Transbaikal Region: Age, magma sources, and relationships to ore mineralization

We have determined the Rb-Sr isotopic ages of magmatic rocks and ores from the Ermakov deposit and established the following succession of formation f rom the early to the late stages: (1) formation of the host rocks represent ed by crystalline schists, sandstones, and dolomites; (2) the preore stage, which includes the formation of gabbroids (318 +/- 2 Ma), fine- to medium- grained granites (283 +/- 30 Ma), and gneissic granites with a U-Pb zircon age of (261 +/- 5 Ma); (3) the synore magmatic stage, which includes the fo rmation of basites, syenite-granites, and alkaline granites (255 +/- 5 Ma); phlogopite micaites (255 +/- 1, Ma); vesuvian skarns and ore bodies; and l eucogranites of the Shtok massif (224 +/- 1 Ma). Felsic dike formation was attributed to the postore stage. Field and isotopic studies showed that Be mineralization of the Ermakov deposit was genetically related to the associ ation of rocks represented by basites, syenites, and alkaline granites; sal t melts and brines (including carbonatite-like) also took part in the Be mi neralization. Magmatic and ore-forming processes at the Ermakov deposit, as well as the formation of grabens and dike swarms in this region, were rela ted to intracontinental rifting due to the early Mesozoic Central Asian man tle plume.