NEOPROTEROZOIC STRUCTURES AND THEIR CONTROLS ON GOLD MINERALIZATION IN NORTHERN ETHIOPIA-EVIDENCE FOR AN EARLIER E-W STRUCTURES BY YONATHAN ADMASSU, NATIONAL MINING CORPORATION- GOLD PROJECT, ADDIS ABABA, ETHIOPIA

The closure of the Mozambique ocean ~750~650ma subsequently led to the collision of the ANS with pre-neoproterozoic centinental blocks of East and West Gondwana.

Abdelselam & Stern 1996 states that deformational belts are associated with 1)arc-arc and arc-centinental sutures 2)post accretionary shortening belts and north west trending strike slip faults. The earliest structures are associated with arc-arc sutures. These arc-arc sutures (~800-700ma) are oriented east to northeast in the northern part of the ANS and north to northeast in the southern part of the ANS.

Arc-continental sutures are north trending deformational belts which formed as a result of the closure of the Mozambique ocean ~750-650ma.

The post accretionary structures which developed ~ 650-550ma are marked by early north trending shortening and late strike slip faults with associated shear zones.

According to my studies in Northern Ethiopia (Southern ANS), the earliest structures are not north-north east as they are supposed to be related to the north –north east arc-arc sutures in southern ANS(Drury and Benhe 1993; Berhe 1990; Abdelselem and stern 1996; vail 1983,1985; kroener et al 1987). The earliest structures in northern Ethiopia are however found to be a result of a N-S tectonic transport. This N- S compression produced early E-W recumbent north verging folds and late steep northward thrusting.

The east-west folds and thrust planes are later folded by E-W compression, which resulted in N-NE trending open-tight folds. These structures are caused by the closure of the Mozambique Ocean and subsequent collision of east and west Gondwana. The E-W compression, culminated with the development of N-NE oriented steep thrusting towards the east.

The latest structures are NW and NE trending shear zones.

The earliest E-W trending northward thrusting and shearing are found to be the controlling structures for the deposition of gold. The later E-W compression folded these zones to be steeply plunging ore bodies.