PARAGENETIC SETTING AND CRYSTAL-CHEMISTRY OF MILARITES FROM PROTEROZOIC GRANITIC PEGMATITES IN SWEDEN

Milarite from Hogsbo, Gruvdalen, St Vika and Klintberget all occurring in NYF-pegmatites show Y+REE enrichment up to 0.8 atoms per formula u nit. Complex zonations (growth-zonation, replacement) show several min eralizing events. Milarite from Uto, having low Y + REE contents is co nsistent with the LTC-character of this pegmatite. Unit cell dimension s of of Y + REE enriched milarite show a-axis of 10.346-10.399 Angstro m as compared to Y + REE poor milarite (10.413 Angstrom). SIMS data gi ve a maximum boron content of 900 ppm for Uto samples coexisting with tourmaline. At Gruvdalen milarite has formed by breakdown of beryl.