Petrography and Geochemistry of the Gabbro Lake Sill, Superior Province, Northwest Ontario

Abstract

<p> A gabbroic intrusion within the Wabigoon Greenstone Belt, southeast of Dryden Ontario, was studied and mapped. Petrographic examination of the sill was carried out and geochemical whole rock data was obtained using X.R.F. methods. </p> The Gabbro Lake Sill was injected into a mafic pile and subsequently underwent fractional crystallization and differentiation. The sill exhibits good phase layering resulting in its division into six basic units: Chilled Margin Gabbro Diabasic Gabbro Leucocratic Gabbro Pyroxenitic Gabbro Pegmatitic Gabbro Sheared Gabbro </p> <p> These units are evident in thin section and are distinguishable both modally and textUrally. In most cases, variations in the chemistry and norms reflect the units mapped in the field. </p> <p> Many features of the sill are analogous to other intrusions, and comparisons have been drawn and theories incorporated to explain these features in the Gabbro Lake Sill. </p>