Aluminium phosphates in muscovite-kyanite metaquartzites from Passo di Vizze (Alto Adige, NE Italy)

A metaquartzite horizon with aluminium phosphates extends over several km in the Penninic Lower 'Schieferhulle' units of the Tauern Window at the Passo di Vizze; it contains the following mineral association: A) pale blue lazulite, colourless crandallite-goyazite, apatite, tourmaline, B) dark blue lazulite, colourless svanbergite-goyazite, bearthite, apatite, celestine, and C) staurolite, chlorite and tourmaline. EPMA results show that lazulite has X (sub Mg) 0.95-0.75 in type A assemblages and 0.65-0.55 in type B. (Sr,Ca)-bearing Al phosphates form a quaternary solid solution series between crandallite-goyazite and woodhouseite-svanbergite and a binary one between bearthite and goedkenite; the quarternary phase or type A has X (sub Sr) [= Sr/(Sr + Ca)] 0.35-0.95 and X (sub p) [= (P-1)/(P-1 + Si)] 0.45-0.90, indicating a main solid solution series between crandallite and goyazite; in the type B association this phase has X (sub Sr) 0.95-0.99 and X (sub p) 0.29-0.90, showing a solid solution series between svanbergite and goyazite. Tourmaline shows a variation of X (sub Mg) from core to rim of 0.15-0.55 in type A and 0.48-0.70 in the much less common type C. Euhedral apatites are Sr-rich (up to 2.98 wt.%) but small, anhedral apatites are Sr-poor. The protolith of these rocks was probably a sabkha-like sediment with Na leached by flood waters.