Petrochemistry of corundum-bearing rocks from montepuez deposits, mozambique

Abstract

Montepuez corundum deposits situated in the northeastern Mozambique is geologically occupied by parts of Neoproterozoic Mozambique Belt in which is classified as Montepuez Complex. It is composed of high grade metamorphic rocks belonging to amphibolite facies that is mainly characterized by amphibolite and gneiss. Amphibolite is distinctively divided into corundum-bearing amphibolite and corundum-barren amphibolite. Corundum-bearing amphibolite is composed essentially of amphibole, spinel and plagioclase with minor amounts of garnet, mica and corundum. Moreover, some corundum-bearing amphibolites have been altered to contain significant mica and clay minerals. These altered rocks are crucially associated with pegmatite. Apart from corundum absence and with/without garnet occurrence, the other mineral assemblages are similar. On the other hand, gneiss is composed of plagioclase, alkali-feldspar, quartz, amphibole, biotite and garnet. Geochemically, these rocks appear to have different protoliths such as basic rock origin of amphibolite and quartzo-feldsparthic to pelitic rocks for gneiss. Based on geothermobarometry, these rocks should have undertaken high-grade metamorphism belonging to amphibolite facies with P-T estimations of 10.5-11 kbar and~550– 600 oC for corundum-bearing amphibolite, 10.5-11.5 kbar and 450-550 oC for Corundum-barren amphibolite and 9-9.5 kbar and 550-600 oC for gneiss.