Geology

Geology

The Assaleyta permit includes several acidic injections part of the “rhyolites belt” injected along the rift margin striking ~N130. The main prospect on the Assaleyta permit is located at the South West corner of the permit, along the Asa Leyta valley, which is the result of the weathering of a volcanic dome. The volcanic dome is associated with hydrothermal activity with some part still active as fumarole.

The prospect is bound by major structures, on the South West side an alteration structures striking ~N130, 3km long with hydrothermal footprint, separate the felsic injection with the basalt. On the North East side, it is the rift normal fault with around 100m of vertical movement visible on the topography. The South East is bound by two structures striking ~N050 forming the two valleys of Asa Leyta and Data Leyta (around Porcupine Hill). The North West part of the prospect is gently covered by a thick fresh basalt boulders hiding any structures or injections.

Two zones have been defined during the various phase of work, they both belong to the same hydrothermal system crosscutting various intrusions from trachytes to rhyolites. The two zones (Red Eagle Mountain and Porcupine Hill) are separated by a deep valley, probably a major structure linked to the micro-block (Dimbir-Asal-Ghoubbet) rotation to accommodate the curve of the rift. The Black Mamba structure is located north of Red Eagle Mountain.

Figure 14. Geological map of Assaleyta

The zones are:

Porcupine Hill:

Zone south-east of the valley, where most of the veins are found hosted in trachytes and basalts, rhyolites are minimal and seen only in hydrothermal breccias and floats around the area. This zone presents all the outcrops along the NW-SE fault and the river cliff NE-SW, the rocks are strongly altered from clay alteration to strong silicification, with active fumaroles. Most of the hill is covered by fresh unaltered basalt.

Figure 15. Landscape view of Porcupine Hill, with Porcupine valley on the right

Figure 16. Landscape view of Porcupine Valley and Red Eagle Mountain with annotations

Red Eagle Mountain:

Hunting ground of the local Egyptian eagles, the zone north-west of the valley is covered by rhyolites, pyroclastic flows and their associated veins and breccias. The base of the mountain is made of a thick sediment deposits with basalt flows. This zone is mainly covered by oxidized rhyolite talus giving its unmistakable red colour, outcrops are limited to the cliff formed by the thickest flows.

Figure 17. Rhyolite Dome on Red Eagle Mountain.

Black Mamba:

Dark structure standing out of the topography below the Red Eagle Mountain in the northern area, the structure is a thick breccia hosting high grades quartz veins, the extension of the structure is not yet known as most of the outcrop lies below a thick layer of scree from the erosion of Red Eagle Mountain.

Figure 18. Black Mamba structure with annotations

Figure 19.Black Mamba structure

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