Summary:
The Boumadine deposit is described as shallow mineralizing system similar to volcanic-hosted epithermal veins developed in subaerial resurgent caldera environments (Bouabdellah and Levresse, 2016; Abia et al., 2003).
Mineralization is structurally controlled, consisting of zones of vuggy quartz and veins, veinlets, and tectonic-hydrothermal breccias.
Three successive and overlapping stages of mineralization are distinguished (Ait Saadi, 1992; Abia et al., 2003; Bouabdellah and levresse, 2016). The origin of the mineralization is probably the mixing between ascending deep seated fluid and meteoric waters that have generated precipitation of precious- and associated base-metal mineralization.
The Boumadine mineralization is structurally controlled and comprises a system of subvertical veins, veinlets, cemented breccias within veins and filling of tension gashes veins. Mineralized structures occur exclusively within the rhyolitic sequence of the Tamerzaga Formation.
The orientation of the mineralized structures is related to Ediacaran transcurrent tectonics represented by N30 to N-S strike-slip fault zones (Freton, 1988; Ait Saadi, 1992; Abia et al., 1999, 2003). The mineralization and associated alterations are developped at the proximity of magmatic vents. Alteration, which appears around the mineralization, develops an assemblage of major quartz and white micas with minor quantities of chlorite and calcite (Ait Saadi, 1992).
At least five mineralized vein systems are documented at Boumadine deposit. IMARIREN zone, Tizi, NORD zone, CENTRE zone and SUD zone. The rich mineralization tends to occur where NNE, NNW and the textural features indicate that mineralization took place in open space with a relatively shallow mineralizing system (Abia et al., 1999).
All of the mineralized veins display more or less similar mineral assemblages. The mineral sequence established on the crosscutting relationships show three stages of mineralization (Abia et al., 2003; Bouabdellah and Levresse, 2016).
Stage I is characterized by the mineral assemblage dominated by massive pyrite with banded appearance, pyrrhotite, cassiterite and arsenopyrite emplaced under N160 E shortening.
The stage II is characterized by the precipitation of sphalerite, chalcopyrite, calcite, quartz, tetrahedrite-tennantite, silver, gold and Bismuth hosted in massive quartz veins, stock work veins and hydrothermal breccias. Gold is mostly distributed in pyrite and arsenopyrite crystals, and less frequently in galena and sphalerite. Galena is mainly present as a cement of the earlier brecciated sulfides and partially dissolving the arsenopyrite, pyrite and sphalerite. Quartz crystals are filling cavities within all pre-existing sulfides and mainly associated with small euhedral arsenopyrite crystals. Structural and textural data indicate that mineralization took place during the late Neoproterozoic as a result of open-space filling.
The stage III is resulting from the oxidation of primary sulphides and consists of minor amounts of goethite, and jarosite with traces of hematite.
These data further suggest that the Boumadine deposit represents a relatively shallow mineralizing system that was open to the surface, and is similar to volcanic-hosted epithermal veins developed in subaerial resurgent caldera environments (Abia et al., 2003).