Petrogenetic and geochemical behavior of the Neoproterozoic low-grade metamorphic rocks from Ropi Megada area in Bule Hora Belt, Southern Ethiopia

Abstract

The granite gneiss complexes and mafic-ultramafic-sedimentary ophiolitic belts are mostly exposed in southern Ethiopia, but the Bule Hora ophiolitic belt is not well studied yet. For the first time, this paper reveals the petrogenesis and geochemical nature of the rocks from the Ropi Megda area in the Bule Hora ophiolitic belt, southern Ethiopia, through ore rock geochemical and field studies. Major oxides and trace elements were analyzed using ICP-MS and ICP-AES to understand the geochemical trends, petrogenesis and tectonic settings of the Ropi Megada. The SiO2 and TiO2 content in the hornblende-biotite-quartz-plagioclase schist range from 35 to 50 wt % and 0.07–6.38 wt %, respectively. Among the major oxides, Fe2O3, MgO, CaO show negative trends with silica content. Similarly, some trace elements like V and Sr show negative trends with SiO2. The rocks are LREE-enriched and HREE-depleted [(La/Yb)N = 0.64–12.77], with a positive Eu anomaly [(Eu/Eu*)N = 0.56–2.32]. Hornblende-biotite-quartz-plagioclase schist has higher gold content (0.001–0.489 ppm) than the biotite-quartz-feldspathic gneiss (0.001–0.003 ppm). Based on the geochemical and field data, the brittle-ductile deformations and hydrothermal fluid reactions with the ophiolitic rocks might have been the primary agents for the gold leaching and transportation from the source to the deposit in the sheared and fractured zone within the host rocks. Hornblende-biotite-quartz-plagioclase schist and quartz-hornblende-biotite schist geochemical data studies from the Ropi Megada area, supposedly associated with the upper mantle composition, show tholeiitic, calc-alkaline, metaluminous, and boninite affinity that formed in the island arc and mid-oceanic ridge basalt tectonic settings.