FERUVITE FROM LEPIDOLITE PEGMATITES AT RED-CROSS LAKE, MANITOBA

Feruvite occurs in the Ca-rich exocontacts of lepidolite-subtype grani tic pegmatites in the Red Cross Lake pegmatite field, northeastern Man itoba. The pegmatites intrude meta-andesitic to metabasaltic host-rock s. In addition to tourmaline, exocontacts contain Cs- and Rb-rich biot ite, Fe-rich muscovite, epidote, apatite, Ca-rich garnet, titanite, ca lcite, quartz and arsenopyrite. The tourmaline is commonly zoned, with a core of feruvite surrounded by schorl or dravite, and rimmed by uvi te. The most extreme composition of feruvite analyzed is (Ca0.56Na0.39 )(Sigma 0.95) (Fe1.962+Mg0.81Ti0.04Mn0.01)(Sigma 3.00)(Al5.31Mg0.69)(S igma 6.00)(BO3)(3)Si6.07O18 [(OH3.51)F-0.49](Sigma 4.00); the X, Y, an d Z sites are dominated by Ca, Fe and Al, respectively. Magnesium is a significant component at the Y and Z sites. In plane-polarized light, uvite and dravite are mainly pale blue or blue, and feruvite and scho rl are mainly dark blue. Brown schorl and feruvite tend to be rich in Ti. The meta-andesitic and metabasaltic wallrocks provided the Fe and Ca for contact-metasomatic reactions between the wallrocks and the int ruding pegmatite to produce feruvite.