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Wasamac |
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Quebec, Canada |
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Au
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Super Porphyry Cu and Au
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The Wasamac gold deposit is located within the southern Archaean Abitibi Greenstone Belt of the Superior Province in the Canadian Shield, ~15 km WSW of the city of Rouyn-Noranda, In Quebec, Canada,
(#Location: 48° 12' 57"N, 79° 11' 10"W).
Regionally the deposit is located at the boundary between the orogenic gold district of Noranda and the Kirkland Lake gold district dominated by intrusion-related gold systems. It is underlain by the Blake River Group in the southern section of the Abitibi Greenstone Belt, the southern boundary of which lies along the Cadillac–Larder Lake Fault Zone, a major structural break marking the contact with younger metasedimentary rocks of the Pontiac Subprovince.
The Wasamac, Consolidated Francoeur, and Western Buff mineralised blocks lie along the Francoeur-Wasa Shear Zone, a second order fault that is parallel to, and 2.5 km north of the Cadillac–Larder Lake fault zone. This shear zone has strong structural similarities with the Cadillac–Larder Lake fault zone, representing a thick zone of intense ductile shearing of the volcanic units, with associated strong metasomatic alteration. In the vicinity of the Wasamac deposit, the shear zone crosscuts the meta-volcanic units of the Blake River Group, which have been tilted to ~55°N and follow the same east-west, ~260°, trend.
Near the Wasamac deposit, the Blake River metavolcanic units are composed of three lithologies, all intermediate to felsic in composition:
• Massive andesite is the most common lithology, and is the principal host to the Francoeur-Wasa Shear Zone from surface to depth. It locally
includes a variety of volcanic textures including aphanitic, porphyritic, amygdaloidal, pillowed and brecciated. Andesitic volcanic breccia layers are >100 m thick, with clasts of andesite-rhyodacite and intermediate to felsic tuff blocks in a massive or lapilli-crystal tuff matrix.
• Rhyolitic units are mostly aphanitic and locally porphyritic with mm-scale quartz and feldspar phenocrysts. A few volcanogenic textures are locally evident, such as flow banding and breccia. They range from greyish to pinkish beige reflecting local pervasive albitic and sericitic alteration spatially associated with micron-scale fractures that increase in abundance towards the shear zone. This rhyolite occurs in the hanging wall of the Francoeur-Wasa Shear Zone and has undergone brittle deformation in contrast to the ductile deformation of the andesitic units.
• Intrusive units of two generations cross-cut the metavolcanic units at Wasamac. These are gabbro and syenite, both of which are locally deformed by the shear zone. The gabbros have a calc-alkaline affinity and occur as either coarse-grained stocks with fine-grained contacts, or as metre-scale aphanitic to fine-grained dykes and sills. The grey syenite dykes are generally metre-scale, rarely as thick as 10 cm or
more. Their contact with the host rock is sharp and straight.
The Francoeur-Wasa Shear Zone is found close to the contact between the andesite and rhyolite units, but is mostly within andesite. Both contacts of the shear zone are gradational over a few metres, marked by increasing concentrations of barren carbonate veinlets that become progressively sheared towards the deformation zone. The shear zone thickness varies from several metres to >100 m, and generally widens with depth.
Gold mineralisation at Wasamac is typically associated with finely disseminated pyrite and a stockwork of pyrite-rich micro-veinlets that are hosted in albite-sericite-ankerite alteration zones confined to the shear zone. This alteration where related to gold mineralisation, is typically beige-brown, making the mineralised zone visually distinguishable from the surrounding sheared rocks. Quartz veins are not common and do not significantly contribute to the gold endowment.
The resource at Wasamac deposit is continuous over 900 m vertically and 2.7 km along strike, remaining open at depth and along strike. It is composed of five mineralised areas, from west to east: Main Area, Area 1-2, Area 3-4, Wildcat Zone and the MacWin Zone. Areas 1-2, 3-4, MacWin Zone, and most of the Main Area fall within the Francoeur-Wasa Shear Zone. The Wildcat Zone is found within a separate structure.
The Main Area occurs in the western section of the deposit where it is constrained to the west by the Horne Creek Fault. Its upper part was mined during historic underground operations between 1965 and 1971. Gold mineralisation occurs within several discrete sub-parallel zones that are generally 5 to 15 m and locally up to 25 m in true thickness. They include the Main Zone, Main Zone 2, Main Zone 3, Stockwork Zone, Footwall Zone, and Footwall Zone 2. The Main Zone, Main Zone 2, Main Zone 3 are confined to the Francoeur-Wasa Shear Zone and are accompanied by disseminated pyrite and stockworks of pyrite-rich micro-veinlets hosted in albite-sericite-ankerite alteration zones. The Stockwork Zone, Footwall Zone, and Footwall Zone 2 occur in the structural footwall the Francoeur-Wasa Shear Zone and are principally associated with relatively undeformed pyrite stockwork mineralisation with minor albite alteration, and locally contain higher
gold grades.
The Areas 1-2 and 3-4 both include one single mineralised zone that is characterised by albite-sericite-ankerite-pyrite alteration. It is composed of a continuous structure interpreted as the eastern extension of the Main Zone. Area 3-4 is slightly offset relative to Area 1-2, which is interpreted to be related to a cross-cutting structure that offset the shear zone and stratigraphy. Historically, the zone in Area 1-2 and Area 3-4 has been separated into four zones (Zone 1, Zone 2, Zone 3, and Zone 4). A small section of Area 1-2 was mined during the last phase of historic production, although, only a limited tonnage, ~0.1 Mt of ore was mined.
The MacWin Zone, formerly known as the Wingate Zone, was discovered in 1945 along the Francoeur-Wasa Shear Zone, ~300 m east of Zone 3. Gold mineralisation is found both within the shear zone and in the hanging wall rhyolite. A small shaft was sunk on this zone, and although it has been included in the mineral resources, it is excluded from the ore reserves.
In the albitic alteration assemblage documented in the Main Zone and Zone 3, >98% of gold occurs in the native state, principally as disseminated free grains. The average size of these free gold grains is 5.7 µm, although some are >10 µm. SEM results show native gold contains an average of 8% silver. Gold is spatially associated with pyrite-rich zones where the sulphide content is frequently >5%. Pyrite has a non-porous texture and rarely contains inclusions of gold. It is locally brecciated, characterised by micron-scale cataclasis zones in a matrix of carbonates, albite, sericite, quartz and chlorite, within which native gold occurs as free grains or as fracture fillings in pyrite (Mériaud and Jébrak, 2017).
In the dominant potassic alteration sections of Zones 1 and 2, ~50% of the gold is found as the tellurides petzite (Ag3AuTe) and calaverite (AuTe2). More than 80% of telluride minerals are found along the contacts of pyrite grains that are <100 µm in size and <5% in abundance. Gold tellurides occur as very fine grains, averaging 3.5 µm
in diameter, whilst other tellurides (Ag, Bi, Pb and Ni) occur in trace amounts. Gold tellurides are mostly found as inclusions in pyrite and fillings related to localised pyrite porosity. Rarely, they are found as free grains disseminated within the alteration assemblage, or occasionally they are trapped in microcline, titanite, hematite or sericite. Gold tellurides also commonly fill pyrite fracture planes less than 5 µm wide, whilst native gold is found in wider >5 µm fractures (Mériaud and Jébrak, 2017).
Mériaud and Jébrak (2017) concluded that the Wasamac deposit is a replacement-type gold deposit located along a second-order ductile fault zone. It is the result of two successive alkaline hydrothermal events, potassic then albitic. Each alteration facies is marked by crystallisation of pyrite and gold concentration. Four features characterise gold mineralisation at the Wasamac deposit: i). it is disseminated within the Francoeur-Wasa Shear Zone
mylonitic schist, without any lode systems, ii). Arsenic-free pyrite is the only sulphide spatially associated with gold mineralisation, iii). pyrite zonation supports metal inheritance from one hydrothermal event to the other, and iv). gold mineralogy is specific to each alteration facies.
Gold mineralisation was first discovered at Wasamac in 1936 by Mine d'Or Champlain via trenching work. Subsequent diamond drilling intersected encouraging gold values although geological continuity was erratic. The 60 m Wildcat shaft was sunk, and one underground level was developed. D Sporadic exploration took place between 1936 band 1965 by Mine d'Or Champlain, Wasa Lake Gold Mines, and Wasamac Mines Ltd. Between 1965 and 1971, exploration and production at the Wasamac mine by Wasamac Mines Ltd produced ~1.9 Mt @ 4.16 g/t Au. Lac Minerals continued exploration, including drilling and ground geophysics from 1971 to 1986, including dewatering of the old Wasamac mine. From 1986 to 2016, further exploration took place while rehabilitation and reclamation was undertaken at the old Wasamac mine site by Richmont Mines Ltd. A pre-feasibility study report released in 2012 with updated resources. In 2017, the project was acquired by Monarch Mining who conducted another feasibility study in 2018 that yielded a new strategy for the Wasamac project’s development to circumvent major social acceptability issues faced by Richmont. In early 2021, Yamana Gold acquired the Wasamac project, consolidating it with neighbouring properties held by other parties and began the first phase of its exploration program. These included the Consolidated Francoeur-, Wasamac NE-, Arntfield-, Lac Fortune-, Western Buff-, R.M. Nickel- and the Teck JV-blocks, which cumulatively cover an area of ~102.68 km2. After optimisation of its feasibility study, Yamana Gold confirmed its intention to begin operations after obtaining government authorisations which remained outstanding in late 2022.
Reserves and Resources
NI 43-101 compliant Ore Reserves and Mineral Resources as at 31 December, 2021 were (Yamana Gold Mineral Reserve and Mineral Resource Estimates, 2021):
Probable Reserves - 23.168 Mt @ 2.56 g/t Au for 59.3 tonnes of contained gold;
Indicated Resource - 5.769 Mt @ 1.76 g/t Au, for 10.15 tonnes of contained gold;
Inferred Resource - 3.984 Mt @ 2.01 g/t Au, for 8.00 tonnes of contained gold.
NOTE: Resources are exclusive of reserves.
The information in this summary is largely drawn from: Raponi, T.R., Carrier, A., Gourde, D., Palkovits, F., Piciacchia, L., Verreault, M., Gagnon, C., Hooshiar, A., Weston, S., Tanguay, S. and Nadeau-Benoit, V., 2021 - Technical Report on the Wasamac Feasibility Study Update; an NI 43-101 Technical Report. prepared by Ausenco Engineering Canada Inc. for Yamana Gold Inc., 386p.
The most recent source geological information used to prepare this decription was dated: 2021.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Wasamac
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Selected References:
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Meriaud, N. and Jebrak, M., 1027 - From intrusion-related to orogenic mineralization: The Wasamac deposit, Abitibi Greenstone Belt, Canada: in Ore Geology Reviews v.84, pp. 289-308. doi.org/10.1016/j.oregeorev.2017.01.021.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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