IRON+MAGNESIUM-BEARING BERYL FROM GRANITIC PEGMATITES: AN EMPA, LA-ICP-MS, MOSSBAUER SPECTROSCOPY, AND POWDER XRD STUDY

摘要

Five samples of blue, bluish green, and green Fe,Mg-enriched beryl from Li-poor granitic pegmatites [beryl-columbite (LCT) pegmatites at Kovarova and Bonenov in the Czech Republic and Val Sissone in Italy; a primitive pegmatite at Beryller, Untersulzbachtal, Austria; and a euxenite (NYF) pegmatite from the Beryl Pit, Quadeville, Ontario] were investigated using EMPA, Mossbauer spectroscopy, LA-ICP-MS, and powder XRD diffraction. The EMPA data show highly heterogeneous (Kovarova, Val Sissone) to rather homogeneous crystals (Bonenov, Beryller, Quadeville), with high variations in Al (1.51-1.91 apfu), Mg (0.01-0.31), Fe_(tot) (0.01-0.18), and Na (0.04-0.37). The substitution ~(CH)D + ~°R~(3+) <-> ~(CH)R~++ ~°R~(2+) is dominant and supported by the powder XRD data. LA-ICP-MS revealed notable concentrations of some trace elements: Cs < 7568 ppm (Kovarova), Li < 928 ppm (Quadeville), Sc < 2823 ppm (Val Sissone). Beryl samples have mostly comparable contents of Fe~(3+), ~ 25% at the O-site, but differ in the presence of Fe~(2+) at the T(2)-site. Primitive characteristics of some examined beryl (Mg/ (Mg+Fe_(tot)) = 0.37-0.68 reflect low degree of fractionation of the host pegmatite (Beryller), or high degree of Mg-contamination from host metabasites in the pegmatite dikes (Kovarova, Bonenov). The concentrations and ratios of selected elements, including Fe~(3+)/Fe~(2+), in beryl from these Li-poor pegmatites are not feasible for any implications of pegmatite-family affinity or degree of its fractionation except for Li; however, no evident correlation between Li and Cs contents was found.