Summary:
The Meliadine gold project is located in the Archean Rankin Inlet Greenstone Belt, in the Churchill Structural Province of the northern Canadian Shield. This belt consists of mafic volcanic rocks, felsic pyroclastic rocks, sedimentary rocks and gabbro sills of about 2.7 billion years old that have been polydeformed and metamorphosed. The Meliadine trend is defined by northwest-trending rock units as well as a major fault zone known as the Pyke Fault: a high-strain zone characterized by multiple foliations and regionally important shear zones.
The Meliadine gold district comprises a combination of orogenic greenstone- and banded iron formation (“BIF”) hosted gold mineralization. Gold in the district is associated with hydrothermally altered and sulphidized BIF (Lawley, et al., 2013).
The Pyke Fault appears to control gold mineralization on the Meliadine property. The seven deposits currently known on the Meliadine property are located in the thrusted/folded volcano-sedimentary rock sequence located adjacent to the north of the Pyke Fault. The deposits consist of multiple lodes of mesothermal quartz-vein stockworks, laminated veins and sulphidized iron formation mineralization with strike lengths of up to three kilometres. The Upper Oxide iron formation hosts the Tiriganiaq and Wolf North zones. The two Lower Lean iron formations contain the F-Zone, Pump, Wolf Main and Wesmeg deposits. The Normeg zone was discovered in 2011 on the eastern end of the Wesmeg zone, near Tiriganiaq. The Wolf (North and Main), F-Zone, Pump and Wesmeg/Normeg deposits are all within five kilometres of Tiriganiaq. The Discovery deposit is 17 kilometres east southeast of Tiriganiaq and is hosted by the Upper Oxide iron formation. Each of these deposits has mineralization within 120 metres of surface, making them potentially mineable by open pit methods. They also have deeper mineralized material that could potentially be mined with underground methods, and are currently being considered in various studies.
Seven gold deposits have been identified at the Meliadine project, of which Tiriganiaq is the most significant. The other deposits are the Discovery, F zone, Wesmeg, Normeg, Wolf and Pump. The Normeg deposit, discovered in 2012, is a southern expansion of the Tiriganiaq deposit, and extends as far as the Wesmeg deposit. Gold mineralization in these seven deposits is mostly mesothermal quartz-vein-dominated gold systems in strongly sheared and complexly folded host rocks of Archean turbidites, iron formation and volcanic rocks. Within each deposit are many gold-bearing lodes of quartz vein stockwork, laminated veins and sulphidized iron formation with strike lengths of up to 3 km. The stratigraphic units generally strike northwest-southeast, dip steeply to the north and are overturned, with the oldest units to the north. All seven deposits remain open at depth.
Mineralization
Mineralization in the Tiriganiaq gold deposit is strongly associated with shearing and quartz veining, which likely developed during the Proterozoic third deformation event. The most intense and consistent gold mineralization is present within both the Upper Oxide Iron Formation and proximal to the Lower Fault in the siltstones of the Tiriganiaq Formation, but minor amounts of mineralization have been reported in all rock types. Areas of intense shearing are ‘healed’ by quartz veining and there is generally little to no brittle deformation.
Gold mineralization is directly associated with syn- to post-deformational quartz veining. Vein appearance is highly variable from a several-metres-thick laminated vein along portions of the Lower Fault to wispy, apparently erratic quartz stringers and stockwork in the Tiriganiaq Formation. With some exceptions, quartz-only and quartz-ankerite veins tend to be mineralized with gold, while quartz-calcite veins are commonly barren in all lodes. This observation implies to multiple veining events.
Sulphide minerals in the Tiriganiaq gold deposit are of two distinct generations: primary and late sulphides.
Primary sulphides consist of wispy, discontinuous, bedding-parallel laminations of pyrrhotite, pyrite and chalcopyrite in oxide iron formations and black argillite. Fine-grained, web-textured sulphides in oxide iron formations close to quartz veins may represent remobilization of primary sulphides, but may alternatively signify sulphur introduced during mineralization. Gold values are generally low to absent in this sulphide assemblage, in the absence of quartz veining.
Late sulphides consist of coarse-grained (sub-centimetre-size) clots of arsenopyrite crystals and pyrrhotite associated with highly gold-bearing zones located in and close to quartz veining. The coarse arsenopyrite crystals rarely show signs of strain, having suffered little post-depositional deformation. Arsenopyrite of this type, in association with quartz veining, is a good visual indicator of elevated gold values.
Visible gold is common in all lodes in the deposit and is present in quartz veins, pyrrhotite, and along the margins and late fractures of arsenopyrite crystals.