Pejrology, Geochemistry and Mineral Occurrences of the Big Dubicha Metaultramafic Rocks, Northeast of Kibremengist, Southern Ethiopia

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Addis Ababa Universty


The Big Dubicha metauitramafic mass is part of thy, east;,:l'n belt (Kenticha belt)Of, Adola area. Lithologic units in the area include; biotite - muscovite - quartz schist, chlorite schist, taic schist and tremolite - actinolite - talc - serpentine schist. Mineral assemblages of the Big Dubicha altered ultramafic rocks are characteristic of lower greenschist facies, representing serpentinization, chloritization and carbonation reactions among others. These reactions are the result of low temperature water-rock interactions. The metamorphic mineral assemblages of the enveloping metamorphosed sedimentary rock fall within lower to middle amphibolite facies, suggesting the presence of allofacial relationship between the Big Dubicha altered ultramafic rocks versus the enveloping rock. In addition shallow angle westward dipping foliation is related to the thrusting event. Whole rock geochemical data examined in the system CaO - MgO - Si02 - H20 - CO2 for" tremolite - actinolite - talc - serpentine schist and chlorite schist suggest harzburgitic and dunitic anhydrous mineralogy, together with the limited metamorphic and structural observations, the Big Dubicha altered uitramafic rocks represent a slice or fragmcnt 01 subcontinental mantle lithosphere, From the geochemical maps of soil samples, anomalous zones of Ni, Cr, Co, Mn, and Zn are observed along the strongly deformed and serpentinized tremolite - actinolite - talc -serpentine schist, indicating insitu weathering (lateritization) of the bedrock was responsible for the' observed mineral occurrences.