The Characterisation of Ultramafic Bodies in Ethiopia
Abstract
The laterites over the Yubdo ultramafic body (Welega Province) have been mined for PGEs and Au since the early 1900s and the mineralisation here has been well documented. However, other ultramafics are known and artisans mine Pt and Au grains from streams draining a much wider area. This presentation outlines the analysis of terrain to identify ultramafic bodies and the use of geochemical data to describe these bodies. The poor exposure (<5%) in this area means that traditional mapping techniques are of limited use and published maps are known to have significant omissions and inaccuracies. When viewed from the ground, it is clear that the geology exerts a strong influence on the nature of the landform around Yubdo. The terrain was viewed using Aerial Photographs and classified according to properties known to be related to the subsurface geology; topography, relative image tone and texture, vegetation and land use, drainage pattern and erosion. This technique allowed fourteen photomorphic regions to be mapped: Basalt (3 types), Basement (9 types) and Ultramafic (2 types). Ultramafic terrain is characterized by a lack of cultivation, very sparse vegetation and very coarse drainage pattern. The bodies identified were confirmed as ultramafic during a ground truth survey. Over 1000 soil samples and 500 rock samples covering the area around and north of Yubdo have been collected and characterize the ultramafic bodies and this helps to determine the conditions of their formation. The Yubdo ultramafic body was previously considered to be an ophiolite sliver but is now widely regarded as an Alaskan type intrusion. The data presented here supports this. The geochemical data will be used to test the idea that other smaller ultramafic bodies are pre-tectonic ophiolite as opposed to syn or post tectonic Alaskan type intrusions. This has implications for PGE prospectivity north into the Arabian Nubian Shield and south to the Mozambique belt and mafic-ultramafic bodies in the Yubdo area can be compared to similar Ultramafic bodies found in the Urals, W Russia.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....1345J