Bedrock in the area can be classified into four major groups: (I) a quartzo–feldspathic gneiss complex, (II) anorthosite, (III) a porphyritic silicic igneous complex, and (IV) granitic and alaskitic veins.The gneiss complex forms a pre-Grenville basement which acted as the host for the intrusions of anorthosite and silicic rocks. The intrusive rocks follow dominant north–south trends, whereas structures in the basement gneisses are varied.The anorthosite and its associated silicic rocks overlie the basement gneisses and underlie typical Grenville group lithologies. The intrusion thereby occupies a major stratigraphic boundary. An unconformity may be such a boundary.

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