Structural controls on the Co and Ni-bearing arsenides from the Bou Azzer mine (Case of Aït Ahmane F53 vein deposit): Implications for mineral exploration

Abstract

The mining district of Bou Azzer is located in the central part of the Anti-Atlas, which is on the northern margin of the West African craton. Located about hundred kilometers southwest of the Ouarzazate city, the Bou Azzer inlier crops out along the major fault of the Anti-Atlas. In the eastern part of the Bou Azzer mining district, the "F53 vein deposit", in the Aït Ahmane area, represents one of the richest cobalt ore deposit; with production of more than 200 tons of cobalt per month. This study aims to define the different faults controlling the mineralization in the F53 vein deposit. In this work, we use the ArcPad mobile application to map faults, veins and geological formations and the digital collection of geological data (e.g., alterations, structural measurements, etc.) in the field. Then, we use the Win-Tensor software for structural analysis and reconstruction of paleostress. The results of this study indicate that the mineralization in the F53 vein deposit is structurally controlled by two main types of faults. The first one corresponds to overlapping faults with sinistral strike-slip component oriented N110° to N120° formed during the Pan-African orogenic event with a NNE-SSW to NE-SW of a maximum subhorizontal stress (σ1), and with N00 to N40° tension gashes. These faults control the mineralization located along the contact between the serpentinized peridotites and the quartz diorite. This type of mineralization named "Contact mineralization”, has massive to brecciated texture and are rich in Co–Ni–Fe arsenides. The second type correspond to a reactivation of tension gashes oriented N00° to N40° as reverse faults during a shortening phase, probably of Variscan age, with horizontal NW-SE trending maximum stress (σ1) and subvertical minimum stress (σ3). These faults oriented N00° to N40° control the vein-type mineralization, which has a banded texture and appears in the form of mineralized quartz-carbonate veins intersecting the quartz diorite. These mineralized faults N00° to N40° directions are transverse to the N120° fault contact between the serpentinized peridotites and the quartz diorite.