Geology, mineralogy and geochemistry of serpentinites from Kenticha area, southern Ethiopia, and associated Ni-mineralization

摘要

The Kenticha area which belongs to the Adola belt of southern Ethiopia comprises four lithological units namely serpentinites, massive talc unit, talc-chlorite-tremolite schist and pegmatites. Detailed petrographic studies of serpentinites revealed the presence of primary (forsterite and clinopyroxene) and secondary (serpentine, talc, actinolite and chlorite) silicate minerals. The presence of relict olivine and clinopyroxenes indicate that serpentinites are derived from dunites and peridotites. Ore microscopic studies also reveal the presence of chromite, magnetite and small sulphide inclusions. Geochemical investigations of the Kenticha ultramafic bodies indicate that they crystallized from mantle-derived magmas affected by crustal contamination. Some drill core samples of the serpentinites show highly anomalous values of Ni (up to 2.9%). The Ni mineralization is associated with garnierite and probably resulted from siliceous and carbonaceous hydrothermal remobilization processes. The hydrothermal alteration may be related to the intrusion of nearby Ta-bearing pegmatites for the reason that Ni and Cr values as well as siliceous and carbonaceous alteration phenomena are highest close to the pegmatite bodies.