MERN - Québec Mines Diamonds in the Apple Formation?

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June 2004

Diamonds in the Apple Formation?

Claude Dion and Jean Goutier
Direction de Géologie Québec

Apple Formation and alluvial diamonds – A comparison

Given the similarity between these different paleoplacer-type Archean deposits, the possibility of finding diamonds in conglomerates of the Apple Formation is certainly worth considering. A few factors support this possibility:

  • Sedimentary rocks of the Apple Formation were deposited on a basement that represents a Mesoarchean craton. This setting suggests a relatively early lithospheric root for this part of the Superior craton, which is considered a favourable criterion for the formation and preservation of diamonds in the mantle.
  • Although no Archean kimberlites have yet been recognized in the Lac Yasinski area, the fertile nature of the underlying Archean mantle is indicated by the presence of diamonds in Wawa-type heterolithic mafic to ultramafic dykes sampled by Dianor Resources in the same area (PEM 1404 in map sheet 33F/06 and Lac de l’Astrée in map sheet 33F/05; Ryder, 2002). These Archean dykes are cross-cut by Proterozoic gabbro sills, and are interpreted as late to post-tectonic.

Paquette (1998) conducted a detailed study of uraniferous conglomerates of the Apple Formation, which did not reveal the presence of diamonds. However, a petrographic study of thin sections would probably not be sufficient to test this hypothesis given the restricted size of the samples and the low diamond count. A study based on a heavy mineral concentrate from a larger sample (a few tens of kilograms) should be conducted. The area around the Apple deposit is a good target area of course, but several other lenses of weakly uraniferous conglomerate are known elsewhere in the Apple Formation, in map sheets 33F/03 and 33F/06. The same exercise could also be undertaken in conglomerates and quartz arenites of the Proterozoic Sakami Formation, which are locally uraniferous as well.

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