The Evolution of the Čanište Epidote-Bearing Pegmatite, Republic of Macedonia: Evidence from Mineralogical and Geochemical Features

The epidote-bearing Čanište pegmatite and adjacent Upper Carboniferous granodiorites cut Precambrian gneisses, on the western slopes of the Selečka Mts., the Eastern Pelagonian zone, Republic of Macedonia. The pegmatite exhibits zonal internal structure with the following sub-units: the wall zone (amazonite microcline ± biotite, quartz), the first intermediate zone (epidote + haematite + grossular + muscovite + quartz + almandine ± zircon, beryl, microcline, quartz), the second intermediate zone (albite + quartz ± microcline) and the core (massive quartz). According to the microprobe data epidote belongs to clinozoisite subgroup with the formula (Ca1.96–1.99Mn0.02–0.03Fe2+ 0.00–0.02) (Al2.17–2.46Fe3+ 0.51–0.82Ti0.00–0.01)(Si2O7 (Si0.99–1.00Al0.00–0.01O4)O(OH). The occurrences of almandine and zircon with low U, Th and REE content, are indicative of weakly evolved granitic/granodioritic rocks. The absence of aplites suggests steady pressure conditions during the course of pegmatite crystallization. Microthermometric data combined by the two-feldspar geothermometer gained pressure from 4.8 to 5.6 kbar for the second intermediate zone. The wall zone, composed of amazonite microcline, crystallized at a temperature between 650 and 760 °C. A drop in melt temperature to below 550 °C, under the oxygen fugacity between 10–22 and 10–19.5 bar, was the principal trigger for crystallization of minerals in the first intermediate zone. The residual fluid, depleted in Ca, Fe and K, and enriched in water, Na and Si, caused deposition of the second intermediate zone (albite + quartz) at temperatures between 445 and 465 °C. The massive quartz core crystallized in the very last stage of the pegmatite evolution (T ≈ 400–480 °C) from melt residue enriched in silica, water and CO2 content