Ruby mineralization in southwest Madagascar

Gem-variety of red corundum (i.e. ruby) is produced in the Ejeda-Fotadrevo area, in southwestern Madagascar. The primary ruby deposits are closely ass ociated with basic/ultrabasic complexes within the high grade metamorphic t erranes of the Precambrian Vohibory unit. Ruby is recovered from amphibolit e and anorthosite veins within these complexes. Petrographic data and P-T e stimates indicate that the ruby-bearing rocks crystallized under granulites facies conditions of 750 - 850 degrees C and 9 - 11.5kbar, in accordance w ith the conditions recorded from the surrounding granulites. The Malagsy ru by deposits present numerous similarities with East African deposits, espec ially Tanzanian, indicating similar geological context of ruby mineralizati on and suggesting that ruby formation in both these areas resulted from a s ame mineralizing event when Madagascar was still adjacent to East Africa (K enya, Tanzania) in the Gondwanaland assembly at the end of Proterozoic time s.