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Gneiss: Brookville


Colour image of gray rock with black, green and pink spots and streaking
Gneiss: Brookville. Precambrian. Saint John, New Brunswick. Collector: R. Miller, 1987. New Brunswick Museum (NBMR 1802). Specimen width 16 cm. The gneiss forms a narrow belt, 37 km long and about 1 km wide from Green Head, near the mouth of the St. John River to Hammond River in Kings County. The Brookville Gneiss and Green Head Group are both intruded by Cambrian granitoid plutons of the Golden Grove Plutonic Suite, but the original relationship between these units remains uncertain. Recent evidence suggests that the Brookville Gneiss is younger than the Green Head Group. U-Pb zircon ages indicate that the Brookville Gneiss is more than 600 million years old. Previous studies had suggested that the gneiss might have been as old as about 1.6 billion years old.