A 2ND NATURAL OCCURRENCE OF YODERITE

A second example of yoderite has been discovered in whiteschists from the Southern Chewore Hills of northern Zimbabwe. The mineral is pale g reen in colour and occurs in an equilibrium assemblage with talc + chl orite + kyanite + dravite + hematite. There is no quartz present. Reca lculated microprobe analyses give a structural formula of Mg2Al5.7Fe0. 3Si4O18 (OH)(2), similar to that obtained for the type locality at Mau tia Hill, Tanzania, i.e. Mg2Al5.6Fe0.4Si4O18 (OH)(2). Textural relatio nships and relative proportions of minerals suggest that the yoderite was formed by reaction between talc, chlorite, kyanite and hematite. E xperimental evidence suggests high-water-pressure metamorphic conditio ns at temperatures exceeding a reaction curve that extends between 13 kbar at 590 degrees C and 21 kbar at 650 degrees C. The yoderite-beari ng whiteschist is associated with a 1.4 Ga dismembered ophiolite. It i s proposed that this yoderite occurrence is associated with a relict s ubduction/suture zone.