Rankin Inlet - Meliadine, Tiriganiaq, Wesmeg

Nunavut, Canada

Main commodities: Au
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The Meliadine area of the Neoarchaean Rankin Inlet greenstone belt is located on the western shore of Hudson Bay in Canada, and hosts several significant orogenic or mesothermal gold deposits. The largest deposits are at Tiriganiaq in the Wesmeg area, where a resource of some 20.7 million tonnes @ 7.05 g/t Au has been established.

The area lies within the Hearne domain of the western Churchill structural province. The Hearne domain consists of Neoarchaean (2700 to 2660 Ma.) supracrustal and granitoid rocks unconformably and locally structurally overlain by the deformed 2450 to 1900 Ma sedimentary rocks of the Hurwitz Group and the undeformed, 1850 Ma sedimentary-volcanic basins of the Baker Lake Group. The mineralised area falls within the northwestern subdomain of the Hearne domain, characterised by abundant 2600 Ma granitoids and by tectonothermal events at 2500 Ma and 1900 Ma.

Rocks within the western Churchill province (and Hearne domain) have also been deformed by Palaeoproterozoic reworking due to interaction with the adjacent Thelon and Trans-Hudson orogens. The geometry of the province and the orientation and shear sense of its largest Palaeoproterozoic faults suggest crustal shortening perpendicular to the northeast strike of the orogens, resulting in the development of accommodation structures along a system of east- to northeast-trending shear zones active from 1900 to 1800 Ma. The overall geodynamic setting of the western Churchill province hinterland at 1850 to 1830 Ma involved regional shortening in response to marginal orogenic zones, regional metamorphism, and granitic and lampro-phyric magmatism, all of which were broadly contemporaneous with orogenic gold mineralisation. Field and geochronological evidence imply a close temporal and genetic relationship between gold and metamorphism and deformation. Lamprophyric and granitic intrusions were emplaced relatively late in the history of regional tectonothermal overprint and therefore are slightly younger than the gold deposits.

Supracrustal rocks of the Rankin Inlet belt comprise a polydeformed and metamorphosed sequence of Neoarchean (~2663 Ma) massive and pillowed mafic volcanic, felsic pyroclastic, associated sedimentary rocks and gabbro sills. Two volcanic cycles have been recognized, i). The lower volcanic cycle of mafic volcanic rocks interbedded with graded clastic sedimentary rocks, banded iron formation and volcanic-derived sedimentary rocks, separated from the overlying upper volcanic cycle by a clastic sedimentary unit including conglomerate and greywacke. ii). The upper volcanic cycle of predomiantly pillowed mafic volcanic rocks, minor sedimentary rocks and rare ultramafic sills, overlain by an assemblage of mixed siliciclastic and carbonate rocks intruded by diabase dykes of unknown age . The Rankin Inlet belt is in turn unconformably overlain by mature orthoquartzite of the Paleoproterozoic Hurwitz Group and intruded by 1830 Ma lamprophyre dykes.

The Wesmeg deposits occur within an area of greenschist to amphibolite facies Neoarchaean supracrustal rocks of the lower volcanic cycle. Lithologies comprise alternating east-southeast trending and moderately north-dipping panels of mafic volcanic (typically pillow basalt) and sedimentary rocks (greywacke-mudstone beds), partially bounded by Neoarchaean and Palaeoproterozoic granitoids. Banded iron formation (BIF) is interbedded in the mafic volcanic and greywacke units. Gold mineralisation occurs in all of these rock types.

The gold deposits are spatially associated with the structural hanging wall of a regional-scale deformation zone known as the Pyke Break, a lineament that is several kilometres wide and defined by multiple foliations and regionally important high strain zones. Four deformation events are recognised, although, gold mineralisation is only significantly developed in association with D2 and D3.

Gold mineralisation is associated with second order D3 shear zones and is accompanied by increased quantities of quartz and iron carbonate veining, iron sulphides (arsenopyrite and pyrrhotite) and silicate alteration minerals (predominantly chlorite and sericite) overprinting the dominantly greenschist facies hosts. The largest deposits are at Tiriganiaq, comprising two east-west trending subparallel zones, the Upper Contact zone and Lower Fault zone. Gold in the Upper Contact zone occurs in narrow (<1 to 20 cm), discontinuous extension veins crosscutting BIF and less abundant pelitic host rocks. These veins are predominantly quartz and carbonates (iron carbonate and calcite) with variable hydrothermal chlorite, iron sulphides, and lesser biotite, magnetite, and monazite. Arsenopyrite and pyrrhotite are mostly found in sulphidation haloes adjacent to the veins but are also disseminated in the veins. Gold occurs in veins and as discrete grains spatially associated with arsenopyrite. In contrast, gold in the Lower Fault zone is related to quartz veins occupying faults and associated quartz stockwork veins localised at contacts between mafic volcanic and sedimentary rocks. Fault-filling quartz veins are up to 4 m wide and commonly show laminations defined by spaced, white mica-rich septae parallel to vein margins. The sulphide content is typically only a few percent and includes arsenopyrite, pyrite, galena, and sphalerite. Native gold is normally associated with micaceous septae.

The most recent source geological information used to prepare this summary was dated: 2005.    
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.

  References & Additional Information
   Selected References:
Carpenter R L, Duke N A, Sandeman H A and Stern R  2005 - Relative and Absolute Timing of Gold Mineralization Along the Meliadine Trend, Nunavut, Canada: Evidence for Paleoproterozoic Gold Hosted in an Archean Greenstone Belt: in    Econ. Geol.   v100 pp 567-576
Gourcerol, B., Kontak, D.J., Thurston, P.C. and Petrus, J. A.,  2018 - Results of LA-ICP-MS sulfide mapping from Algoma-type BIF gold systems with implications for the nature of mineralizing fluids, metal sources, and deposit models: in    Mineralium Deposita   v.53, pp. 871-894.

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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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