Generación de informes de estado

The Kaminak dyke swarm (Fig. 2.24) is made up of hundreds of north-northeast trending dykes which crop out over an area of 20,000 km² in southern Nunavut, approximately 100 km west of Hudson Bay (Buchan and Ernst 2004).

The Kaminak dykes are Fe-rich quartz tholeiites and are predominantly composed of plagioclase and clinopyroxene with minor amounts of olivine and Fe-Ti oxides (Christie et al. 1975; Sandeman and Ryan 2008). The dykes range in texture from aphyric to plagioclase porphyritic and locally, the dykes can contain abundant megacrysts (~10 cm wide) of plagioclase (Bleeker 2004). the dykes are highly variable in their extent of alteration, with unaltered dykes preserving ophitic textures, while more pervasive alteration in the dykes is characterised by saussuritization of feldspar, uralitisation of pyroxene replacement of olivine to serpentine (Christie et al.

1975; Sandeman and Ryan 2008).

The metamorphic mineral assemblages of epidote, sericite, amphibole and chlorite observed in the Kaminak dykes suggest that metamorphism of the bulk of the Kaminak dyke swarm reached a maximum of lower greenschist facies. However, metamorphic grade of the Kaminak dykes increases towards the north, where at maximum, the Kaminak dykes have been metamorphosed to large boudins of amphibolite within country rocks of migmatitic gneiss (Christie et al. 1975).

The Kaminak dykes are generally vertical and vary from ~1-40 m in thickness. The dykes tend to form resistant ridges which can be traced over tens of kilometres before being truncated by younger faults (Christie et al. 1975; Sandeman and Ryan 2008). The N-NE trend of the dykes bisects the dominant tectonic boundaries between the Archean supracrustal and granitoid rocks which make up the hosting Ennadai-Rankin greenstone belt (Aspler et al. 2000). The trends of the Kaminak dykes have been described as radiating, with an arc angle of ~40° by Ernst and Bleeker (2010) and as a linear array (Sandeman and Ryan 2008).

45

Fig. 2.24. Geological map showing locations of the Kaminak dykes. Modified from Sandeman and Ryan (2008).

Based on observed field relationships and geochemical similarities, the Kaminak dyke swarms have been interpreted to be feeders to the continental tholeiitic basalts of the Spi Group which crop out in the core of a syncline, preserved in the modern day Spi basin (Sandeman and Ryan 2008).

2.2.6.2. Age

The most widely cited age of the Kaminak dyke swarm is a U-Pb date from magmatic baddeleyite of 2450 ± 2 Ma (Heaman 1994). This age supersedes previous variable K-Ar whole-rock ages which have errors on the magnitude of ±100 million years (see summary in Christie et al. (1975)). A second Kaminak dyke dated by U-Pb analysis of magmatic baddeleyite yielded an age of 2498 ±2 Ma (Heaman 2004).

These two ages led Ernst and Bleeker (2010) to suggest that the Kaminak dyke swarm is a composite swarm made up of two pulses of magmatism, which were emplaced approximately 50 million years apart.

Heaman’s (1994; 2004) two widely cited U-Pb ages (Aspler et al. 2002; Sandeman and Ryan 2008; Ernst and Bleeker 2010) are reported in single page conference

46 abstracts and not in a more extensive work. Hence, it is difficult to fully determine the context of the reported dates or understand any potentially associated caveats with the analysis.

2.2.6.3. Tectonic Setting

Buchan and Ernst (2004) and Ernst and Bleeker (2010) propose that the trend of the Kaminak dykes define a radiating pattern with an arc angle of 40°, which indicates a focal point just to the south of Chesterfield Inlet. Further to this, Bleeker (2003) and Ernst and Bleeker (2010) suggest a genetic link between the Kaminak dyke swarm and the Matachewan dyke swarm on the Superior craton based on overlapping U-Pb ages and existing palaeomagnetic data from the dyke swarms which allow the Superior and Hearne cratons to be adjacent at ~2.5 Ga. The interpretation of the Kaminak dykes as a radiating swarm in its own right or as a now dismembered part of a much larger swarm including the Matachewan dykes, has led previous authors to interpret the Kaminak dyke swarm as a product of mantle-plume induced magmatism during rifting of an Archaean supercontinent (Fig. 2.25) (Bleeker and Ernst 2006;

Ernst and Bleeker 2010; Söderlund et al. 2010).

Fig. 2.25. Mantle plume model for the formation of the Matachewan and Kaminak dykes swarms and Huron and Hurwitz Supergroups. Modified from Bleeker (2004).

Sandeman and Ryan (2008) carried out the only geochemical study of the Kaminak dykes aimed at understanding the swarm in terms of its mantle source and tectonic setting. In their study, Sandeman and Ryan (2008) argue that the trace element

47 chemistry of the Kaminak dykes (characterised by enrichments in the large ion lithophile and light rare earth elements relative to the heavy rare earth elements and significant depletions in the high field strength elements) show that the parent magmas of the Kaminak dykes are the result of mixtures between subduction-modified sub-continental lithospheric mantle and depleted MORB mantle. Sandeman and Ryan (2008) contend that while the geochemistry of the Kaminak dykes does not indicate any material input from a mantle plume, this may be explained by the Kaminak dyke swarm having occupied a distal position relative to the plume head at

~2.45 Ga.

2.2.6.4. Ni-Cu-PGE Mineralisation

Ni-Cu-PGE sulphide mineralisation has not been observed in the Kaminak dyke swarm and the swarm is not the subject the of any past or present exploration projects. No layered intrusions coeval with the Kaminak dyke swarm have been identified on the Hearne craton.

2.2.7. Viianki Dyke Swarm