Characteristics and Genesis of Enkafela Manganese Deposit, Dallol Area, Northern Afar Depression
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Date
2018-05-30
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Addis Ababa University
Abstract
The Enkafela manganese deposit is situated in the Afar Depression, northern Ethiopia, about 20km west of Dallol at the border with the western escarpment. The geology of the Enkafela area is characterized by marine formations of reef limestone, oolitic limestone, gypsum, conglomerates and basalt. The ore body is stratabound and lies between the reef limestone and basalt. The ore stratum is characterized by two distinctive manganese layers. The bottom is massive while the top layer is powdery/friable. The main purpose of this study is to understand the geochemical characteristics and genesis (origin) of the manganese mineralization. Geological, mineralogical and geochemical data are integrated to characterize the genesis of the manganese deposit. Based on XRD mineralogical analysis, Pyrolusite, Chalcophanite and Biernessite minerals are identified as the main ore minerals in the deposit. The geochemical analysis result indicate enriched MnO (av. 70.25wt %), Ba (>10,000ppm), Sr (>10,000 ppm) and depleted Fe2O3 (av. 0.37wt %) and transition metals. The total REE content of the massive manganese is 172.9ppm while the powdery manganese contains total REE of 7.84ppm. The massive manganese show higher REE content than the powdery manganese. Chondrite normalized REE plot show LREE enrichment for both manganese layers. The massive manganese layer shows enrichment in Ce and no anomaly in Eu. However, the powdery manganese shows depletion in Ce and Eu. The geochemical and mineralogical studies indicate that Enkafela manganese mineralization does not originate from a pure hydrothermal source or pure hydrogenic source. The massive manganese shows mixed sources, whereas the powdery manganese shows a hydrothermal source. The Ni-Co-Zn discriminating ternary diagram indicates the powdery manganese (top layer) has a hydrothermal origin and the massive manganese (bottom layer) has mixed origin (both hydrothermal and hydrogenic). Alternatively, the Fe-(Ni + Cu + Co)*10-Mn and Fe-Si*2-Mn discriminating diagrams indicate hydrothermal activity played the major role in the formation of both the powdery and massive manganese layers. Generally, the geochemical studies show the dominance of hydrothermal activity in the formation of the Enkafela manganese deposit, though seawater contribution is undeniable in the massive manganese deposit. The two manganese layers are similar genetically and formed successively from the same source.
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Keywords
Birnesssite, Chalcophanite, Enkafela, Pyrolusite, Manganese, Genesis, Hydrothermal