Petrology and Geochemistry at the Contact of the Round Lake Batholith in Robillard Township, Northeastern Ontario

Abstract

The Round Lake Batholith is a composite granitic intrusion into the Archean metavolcanics of the Abitibi Greenstone Belt, Superior Province. The mafic metavolcanics are mainly high iron tholeiitic basalts of ocean floor origin. The intrusion of the batholith has metamorphosed the metavolcanics to amphibolite grade. Moving towards the contact there is no change in the metavolcanics grain size, but mineralogy changes quickly from the actinolite zone with relict pumpellyite to the hornblende zone. Field evidence as well as thin section and chemical analyses have shown that the dioritic appearing hybrid rock, near the contact, is a product of the mafic meta volcanics assimilation into the batholith.