Petrology and Geochemistry of the Heron Bay Area Granites, Superior Province, Northwestern Ontario.

Abstract

The Heron Bay area, located in the Wawa Belt of the Superior Province in northwestern Ontario, contains portions of three granitoid batholiths. Petrographic and chemical analysis revealed that nine different phases existed among the three batholiths: PIC BATHOLITH 1. Porphyritic quartz monzodiorite (most northerly 2. Biotite hornblende quartz monzodiorite batholith) 3. Biotite hornblende granodiorite HERON BAY 1. Porphyritic (K-feldspar) granodiorite BATHOLITH 2. Hornblende biotite granodiorite PUKASKWA GNEISS COMPLEX (most southerly 1. Porphyritic trondhjemite batholith) 2. Granite 3. Porphyritic granodiorite 4. Hornblende biotite granodiorite Each phase is distinctive through its mineralogy and texture. Chemical variation diagrams suggest that the batholiths were formed from at least two different magmas though perhaps phases present within the individual batholiths are a result of magmatic differentiation from a single magma. The high K/Rb ratios in the more mafic phases suggest that they were produced from a magma that was derived from partial melting of the upper mantle/lower crust rocks.