Metamorphism and gold mineralization of the Kenticha-Katawicha area: Adola belt, southern Ethiopia

I present geological and mineral chemistry results aiming at understanding the relationship between metamorphism and gold mineralization in the N-trending Neoproterozoic Kenticha-Katawicha area in the Adola belt of southern Ethiopia. The Kenticha-Katawicha area comprises low-grade metamorphic rocks including pelitic schists, marble, graphite schists and Fe-Mn quartzites (Kenticha marine metasedimentary rocks) and serpentinites and talc-tremolite-chlorite schists with podiform chromites (Kenticha ophiolite). Lenses of high-grade amphibolite schist are also locally present within the Kenticha-Katawicha area. These rocks are sandwiched between high-grade para- and ortho-gneisses, migmatites, schists and amphibolites. Post-orogenic granites intrude the metamorphic sequences. Mineral assemblages and textural data obtained from the high-grade rocks indicate that the dominant metamorphic condition is of upper amphibolite facies. Garnet-biotite (garnet-core-matrix-biotite) and amphibole-plagioclase geothermometry gave estimates for peak metamorphic temperatures of 630-650 degrees C and pressure of 7 kbar for the high-grade rocks. On the other hand, the low-grade rocks recrystallized in the greenschist facies conditions. The estimated peak T-P values for the high-grade rocks suggest a burial to similar to 25 kin depth and a clockwise P-T path is deduced from mineral thermometry and the textural and paragenetic relations. This combined with the geochemistry of the magmatic rocks and clockwise P-T is consistent with a collision setting in which rocks of the calc-alkaline, volcanic-arc, and oceanic fragments are assembled. In the study area, gold occurs in quartz veins and veinlets in lenses of biotite schists within ultra-mafic rocks that are confined to shear zones. Fluid inclusion studies of gold quartz veins and veinlets indicate a H2O- and CO2-rich fluid with low salinity (< 5 wt% NaCl equivalent). The gold mineralization in the area is post-peak regional metamorphism and is associated with the low-grade wall-rock alteration. (c) 2006 Elsevier Ltd. All rights reserved.