Summary:
Deposit Type
The Boumadine polymetallic deposit (Ag, Au, Pb, Cu, Zn) is located on the northwest side of the Ougnat Massif (or Boutonnière), at the eastern end of the Anti-Atlas Mountain Range. The geology of the Massif consists of a Neoproterozoic metasedimentary basement overlain unconformably by a Late Neoproterozoic volcano-sedimentary rock sequence and by Paleozoic lacustrine sedimentary and minor volcanic rocks. The basement consists of sandstone, pelites and greywackes that are intruded locally by granite, granodiorite, and diorite bodies. The volcano-sedimentary sequence consists of felsic and mafic volcanic rock units separated by volcano-sedimentary units.
The volcanic and volcano-sedimentary units have been grouped into three formations, from oldest to youngest:
• Tamerzaga-Timrachine Formation (“TTF”): ignimbrites, rhyodacites, and andesites;
• Isilf-Ouinou-Oufroukh Formation: tuffs, breccia, andesite flows, and fine- to coarse-grained sedimentary rocks;
• Aoujane-Aissa-Akchouf Formation: ignimbrites, dacite domes and flows, andesite flows.
These formations are intruded by dolerite, microdiorite and andesite dykes. At the Boumadine Mining License, only the andesite dykes are present and trend north-south. The TTF volcaniclastic sequence of felsic tuffs and mafic tuffs hosts the Boumadine Deposit. The felsic tuffs consist of angular to rounded cm-size felsic fragments, quartz eyes, plagioclase grains, and locally mafic fragments. This felsic sequence is homogeneous and massive, and sits unconformably on mafic tuffs. Mafic tuffs consist of amphibole and fragments/clasts of sedimentary rocks, interpreted as underwater-deposited volcaniclastic eruptives.
Boumadine mineralization traditionally was considered to be hosted only in felsic tuffs. However, drilling completed from 2017 to 2023 intercepted mineralized veins within mafic tuffs. Furthermore, the mineralized veins in the mafic tuffs appear to be more continuous, richer and thicker than in the felsic tuffs.
Many intrusions are observed on the Boumadine Property. The intrusions are divided into a pre-to synmineralization group and a post-mineralization group. The pre- to syn-mineralization intrusions are mainly felsic to intermediate in composition, show aphanitic to porphyritic textures, and form dykes and sills. Locally porphyritic mafic dykes, similar in composition to mafic tuffs, crosscut the felsic tuff sequence and synmineralization dykes, suggesting bimodal magmatism. The post-mineralization intrusions consist of rhyolite subvolcanic domes associated with normal faults and are interpreted as synchronous with a deformation episode that disrupted the Boumadine mineralized zones. Subsequently, a swarm of regionally extensive mafic dykes intruded every lithological unit on the property.
Aya Gold & Silver Inc. preferred interpretation is that the mineralizing system at Boumadine developed under shallow submarine conditions in a graben setting. In this model, magma-derived high-temperature acidic fluids/vapours containing Au and Ag ascend from the subvolcanic andesite/diorite intrusions and mix with circulating low-temperature, seawater-derived chlorinated fluids containing Fe, Zn and Pb. Mixing, cooling and wall rock reactions drive metal precipitation and deposition in volcaniclastic rocks below the seafloor.
Hydrothermal Alteration
Hydrothermal alteration at Boumadine resembles that found in high sulphidation (acid) epithermal systems. Aluminous alteration is more proximal to sulphide-rich mineralized zones and the propylitic alteration more distal. Propylitization is generally induced by the convection of surface fluids, whereas aluminous alteration results from the contribution of acidic magma-derived fluids during degassing of andesite/diorite subvolcanic intrusions.
Two events of hydrothermal alteration are observed on the Boumadine Mining License. The first alteration event affects the felsic tuff sequence as phyllic alteration (quartz-sericite-pyrite). Proximal to massive sulphide veins (1 to 5 m thick), there is an advanced clay alteration composed of kaolinite and pyrophyllite. The second sequence of alteration affects mainly the underlying mafic tuffs and consists of propylitic alteration (epidote and chlorite). Near the veins, the alteration minerals are black chlorite, pyrophyllite and pyrite. The transition between these two alteration events is relatively sharp and consistent with the change in tuff composition.
Due to the extensive weathering to clay minerals, the Boumadine Deposit has a very light colour that contrasts with the surrounding landscape. The mantos, “chapeau de fer” or “iron cap” alteration extends from 5 to 10 meters depth. The mantos consist principally of goethite and jarosite with sparse hematite and no lepidochrosite. This mineralogical assemblage indicates that the oxidation fluids were strongly acidic. In this case, Mn, Zn, Cd, Ni, Co, Pb are highly mobile in the acid and sulphur-rich fluids and are commonly leached at surface. However, Ag, Au, Ba, Sr and Pb are immobile and form stable sulphosalts. The hydroxide-rich “mantos” has been partially mined out by artisanal workers for ochre and precious metals.
Mineralization
The Boumadine mineralized zones generally consist of 1 to 4 m-wide massive sulphide lenses/veins oriented N20°W and dipping 70° east. The massive sulphide veins (>70% sulphide) are composed mainly of pyrite, sphalerite, galena, arsenopyrite and chalcopyrite, with subordinate amounts of cassiterite, silver-rich sulphosalts, stannite, enargite, bismuthinite, native copper and bismuth. The main mineralization zone is generally surrounded by a 1 to 10 m (locally up to 20 m) thick halo of 10 to 30% disseminated pyrite and two types of veinlets: 1) quartz-carbonate-galena-sphalerite veinlets; and 2) massive pyrite veinlets.
Within massive sulphide veins, zones of breccias with silicified angular fragments and round fragments have been completely replaced by pyrite. Those breccia zones underline the presence of syn-volcanic faults, which probably served as fluid pathways for the mineralization. In weathered felsic tuffs, breccia fragments can be replaced by pyrite which locally form large, mineralized sub-zones as much as 10 m thick. Those thick subzones are interpreted to be the upper part of the hydrothermal system. Geochemically, there is a strong positive correlation of gold with silver and copper and a weaker correlation of zinc with lead and molybdenum.
The Boumadine Deposit has been traced on surface and in drilling for approximately 5,400 meters along strike. Strike direction varies from mainly northwest to northerly and dips vary from steeply northeast to steeply southwest. The deposit consists of 45 mineralized domains grouped into five separate zones. The South and Central Zones consist of 13 stacked mineralized vein domains extending 4,800 meters along strike, 300–400 meters across strike, and up to 1,000 meters down-dip. The South Zone appears to be offset dextrally from the Central Zone by a northeast-trending fault; the Central Zone is offset senestrally from the North Zone. The North Zone includes eight closely spaced mineralized vein domains over 650 meters of strike length and 500 meters down-dip. It appears truncated by the Imariren Zone. The Imariren and Tizi Zones are sub-parallel mineralized veins, 200–500 meters apart, striking north and dipping vertically. Tizi extends 2.0 km, Imariren 1.0 km, both to 600 meters down-dip.
U/Pb single zircon dating from a “chonolithic” rhyolite intrusion cutting the mineralized veins yielded an age of 553 ± 16 Ma. This result is consistent with a late Neoproterozoic maximum age for the mineralization.