Pejrology, Geochemistry and Mineral Occurrences of the Big Dubicha Metaultramafic Rocks, Northeast of Kibremengist, Southern Ethiopia
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Date
1999-11
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Addis Ababa Universty
Abstract
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.
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Keywords
Kibremengis