Sturgeon Narrows

Lying principally along the eastern shore of the narrows on Sturgeon Lake the alkaline complex is 13.7x1.3-4.5 km and appears to plunge to the southwest. Contacts are generally conformable against greenschist facies sediments and volcanics which have been slightly fenitized locally. The alkaline rocks are often banded with some compositional and textural layering. Three compositional zones can be distinguished with gradational contacts. The more northeasterly rocks vary from nepheline syenite to a rock with 5% quartz. They comprise alkali feldspars, nepheline or quartz, and mafics in excess of 25% including pyroxene, amphibole, biotite, garnet and opaques. An outer syenite is a variously equigranular or porphyritic nepheline syenite of alkali feldspars, nepheline, sodalite, zeolite and cancrinite, 10-25% mafics including aegirine-augite/augite, sodic amphibole, biotite, garnet and accessories. The inner leucosyenite contains 10-15% of aegirine-augite, biotite and garnet, with alkali feldspars, nepheline and zeolite. Lamprophyric, aplitic and pegmatitic dykes occur within the complex. Details of the mineralogy are not yet available but rock analyses are given in Trowell (1983b, p. 58).