Boumadine (Au, Ag, Zn, Pb, Cu)
The Boumadine mine is accessible year long from highway N10 through the town of Tinejad and by travelling southward for 13 km on a sturdy dirt and gravel road. There are numerous dirt roads and paths that lead to former shafts, adits and other remains of the mining installations.
The Boumadine polymetallic deposit (Au, Ag Zn, Pb, Cu,) is located within the Ougnat Proterozoic window (“boutonnière”) in western Morocco (Figure 1). The Ougnat basement is composed of folded and schistose metasedimentary rocks cut by late granodioritic plutons. It is unconformably overlain by Late Proterozoic volcanosedimentary sequences (PIII). The basal sequence is made of ignimbrite sheets, vitroclastic tuffs, and intercalations of andesite flows forming the Tamerzaga-Timrachine Formation (TTF) (Figure 2). The top ignimbrite sheet is strongly silicified. The TTF is invaded by swarms of gabbroic to andesitic dykes, principally oriented-N160°E, followed by injections of rhyolitic intrusions (domes ?) and dykes. The Boumadine deposit is contained within the TTF which is covered by shallow lacustrine sedimentary and minor volcanic rocks (Isilf-Ouinou-Oufrouh formation; IOF). The deposition of ignimbrite sheets, controlled by N30°E structures, characterizes the overlying Aoujane-Aissa-Akchouf Formation; the top of which is constituted of episodic clastic sedimentary rocks and mafic to intermediate flows. Phanerozoic rocks overlie the Proterozoic assemblages.
The polymetallic mineralization at Boumadine extends at least for 4 km on the surface. The mineralized zones consist of 1 to 4 m-wide N160°E-oriented lenses/veins dipping sharply (> 70°) to depths of 350 m and spatially associated with the TTF (Figure 2).The veins contain massive pyrite, sphalerite, arsenopyrite, and galena with subordinate amounts of chalcopyrite, cassiterite, silver-rich sulfosalts, stannite, enargite, bismuthinite, native silver, tin, copper and bismuth. The upper 40 m are affected by supergene alteration (Fe-hydroxyde-rich ‘‘mantos’’), that were near completely mined by artisanal workers (Figure 3).The felsic volcanic hosts display a silicic-argillic alteration halo, 40-100 m wide, which overprints the pervasive propylitised rocks and confers a bleached aspect to the halo (Figure 2). This alteration zone contains an assemblage of quartz-sericite-pyrite with pyrite decreasing away from the veins. The Boumadine deposit is interpreted as low-intermediate sulphidation epithermal silver-gold base metal deposit, with the potential of discovering Cu±Au porphyry-type mineralization at depth.
There are two principal mineralizing stages controlled by the strain applied to the TTF volcanosedimentary assemblage. The first mineralizing event involved the deposition of massive pyrite, occasionally banded, succeeded by the injection of parallel veinlets of arsenopyrite in the first stage pyrite. These veins were formed under a N160°E shortening strain. The second stage of mineralization first involved crystallization of sphalerite and galena cementing the first stage sulphides or occurring as vein filling material forming banded ore (Figure 4). The latest mineralization stage started with the deposition of quartz in dissolution cavities and as crosscutting veinlets, followed by crystallization in decreasing abundance of: grey copper, argentopyrite, schapbachite, pyrargyrite, polybasite and native antimony-silver-bismuth (Figure 5). Emplacement of polymetallic and precious metal veins is consistent with a N30°E shortening direction.
XV–XVIth centuries- Portuguese (?) workers have mined out the limonitic mantos, searching for ochre and precious metals.
1964-1975- The Central and North Zones were principally investigated by the BRPM. A total of 30,560 m of surface and underground drillcores were collected accompanied by the excavation of 387 m of shafts and 3,095 m of galleries. A Historical Resources estimate was established after extensive core analyses and chip sampling in the adits.
1975-1984- More underground exploration on the Central Zone and development of the South and Tizi zones by the BMPR. Up to 1,030 m of surface and underground cores were extracted and 140 m of shafts with 1,885 m of galleries were excavated. The exploration work contributed to expand the Historical Resources which was then established at 4,096, 500 t of ore.
1985-1992- More surface drilling and underground work to explore and develop the Central and South zones were undertaken by the BMPR. The work consisted of 1,570 m of drillcore, 111 m of shaft, and 187m of raise. 261,485 t @ 3.8 % Zn, 1.5 % Pb, 200 g/t Ag and 3.50 g/t Au were mined. A selective flotation process produced galena (Pb) and sphalerite (Zn) concentrates yielding a recuperation of 18-23% of Ag and 10-14% of Au.
2013- Joint venture between Maya Gold and Silver Inc (85%) and ONHYM (25%) to explore and develop the Boumadine property.
Remains of the mining installations are still visible at the mine site (Figure 6). They were probably dismantled shortly after the mine closure in 1992. Two dry stacked tailings are exposed on the site totaling approximately 240,000 t of material (Figure 7). These residues were generated upon the underground exploitation of the Boumadine deposit from 1988 to 1992. There are existing surface and underground mine workings which include at least 6 excavated shafts (638 m) and 6,036 m of underground adits, raises and stopes distributed in 5 main areas: Central Zone, Northern Zone, Southern Zone, Tizi Zone and Imariren Zone (Figure 2). Numerous pits and trenches are visible throughout the property. These can be small, a few square meters in area, but others extend for over 1,000m2.
Transmitted light photomicrograph showing mineralogical and textural variations in sphalerite+quartz veins in sample BOU2012-02. Low Fe-bearing sphalerite (yellow-brown) in a core of a diverging quartz vein that is cutting recristallized coarse-grained massive pyrite.