Volcanology of the felsic volcanic rocks of the Kidd-Munro assemblage in Prosser and Munro townships and preliminary correlations with the Kidd Creek deposit, Abitibi greenstone belt, Ontario

Abstract

The felsic volcanic rocks of the Kidd-Munro assemblage form an important stratigraphic unit that hosts the Kidd Creek volcanogenic massive-sulphide deposit; however, the rocks are poorly understood throughout the assemblage, due to poor exposure. Outcrops in Prosser and Munro townships were mapped in detail to determine volcanic facies and to correlate with the stratigraphy of the Kidd Creek mine. In Prosser Township, the upper part of the assemblage includes aphyric subaqueous coulees formed in a near-vent environment that are interfi ngered and in peperitic contact with massive brown and blockbearing tuff units. The aphyric rhyolite is overlain by a poorly sorted pumice- and spatter-rich tuff in which the fragments lack quenched margins, but have an apparent synvolcanic alteration preserved. The pumice-rich tuff is overlain by a distinctly quartz-phyric rhyolite. Munro Township hosts contrasting rocks including calc-alkaline rhyolite, tholeiitic lapilli tuff, and variolitic rhyolite. The calc-alkaline rhyolite consists of a massive to lobate unit. The lapilli tuff contains a large variety of clasts, including spatter, blocks, jigsaw-fi t breccia clasts, and fractured perlitic clasts, indicating a proximal vent source. The variolitic rhyolite could represent a spherulitic rhyolite, an air-fall bed, a spherulitic pyroclastic fl ow, or be the result of magma mingling. Texturally and geochemically, the rhyolite units of Prosser Township correlate with the mine stratigraphy at the Kidd Creek deposit. The quartz-phyric rhyolite shows a similar fl ow structure, phenocryst population, and geochemical signature. Thus, the stratigraphic sequence equivalent to that of Kidd Creek is found in Prosser Township.