Tourmalines in the Namacotche Li-Cs-Ta granitic pegmatite group, Mozambique: crystal chemistry and origin

The field work, backscattered electron images and detailed microanalyses of three generations tourmaline from the Namacotche LCT pegmatites allows de distinction between compositional magmatic hydrothermal tourmalines. generation 1 occurs in outer intermediate zone pegmatite. It consists zoned crystals with an oscillatory inner core foitite schorl, schorl Fe-rich fluor-elbaite rim. Unzoned occur All are derived by fractionation a (Al, Li, B)-rich pegmatite melt. However, rim some compositions unzoned show evidence fluids, as they plot outside trends. 2 They have pink green has higher YFe2+, Na, F contents YFe2+/(YFe2++Licalc.) value lower Si, YAl, Licalc. X-site vacancy contents, X-vacancy/(Na+X-vacancy) than core. Both zones hydrothermal. is overgrowth. gemmy 3 sheared breccia blasts clasts cookeite matrix. depend mainly on fluid-rich environment low temperatures (280-150ºC). Some cycle may result dissolution due to reaction late fluids chemical disequilibrium, followed growth temperature fluids. evolution b c implies that reacting were undergoing becoming richer Li poorer Fe2+ during crystallization pegmatites.