RELATION BETWEEN STRUCTURES AND GOLD MINERALIZATION IN NEOPROTEROZOIC GREENSTONES OF THE WERRI AREA, NORTHERN ETHIOPIA

Little work has been done on the genesis and structural associations of important gold occurrences within the Neoproterozoic greenstone belts of Ethiopia. Northern Ethiopia consists of weakly metamorphosed massive to schistose metavolcanics and meta-arenaceous units affected by four major deformational events. D1 resulted in north verging recumbent folds and reverse faults/shear planes containing quartz veins and epidote-rich silica veins/stringers. D2 deformation produced NE-SW oriented tight folds and steep W dipping axial planar foliation. D3 and D4 deformations are represented by formation of NE and NW dextral shear planes, respectively.

Gold mineralization in the Werri area occurs within quartz stringers hosted by ferru-ginous quartz chlorite schist. The stringers are folded and plunge steeply southwest, consistent with formation prior to regional D2 folding. The steep plunges of auriferous alteration zones can be correlated with folded D1 reverse shear planes. Thin sections from altered zones cut parallel to S2 show reverse northward shearing. We interpret the D2 deformation to have folded the ca. east-west striking D1 shear zones causing them to crop out as detached hinges. The NE trending D3 shearing is also auriferous, possibly associated with gold remobilization from D1 deformation zones. We suggest that lack of recognition or existence of early north-south D1 directed deformation outside of the Werri area may account, in part, for past unsuccessful exploration activities in other parts of Ethiopia.