Black shale heaving at Sainte-Foy, Quebec, Canada

Abstract

Oxidation of pyrite and crystallization of sulphate minerals in rock fractures have locally produced ground heaving in excess of 10 cm in the foundations of a college at Sainte-Foy, near Québec (Quebec). Black shales of the Sainte-Foy Formation are involved; they contain about 2% disseminated framboidal pyrite and 3% calcite. Reaction products identified with a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray chemical analyser (EDXA) are iron hydroxides and numerous sulphate minerals containing calcium, iron, potassium, aluminum, magnesium, manganese, barium, and strontium. In Ontario, heaving of black shales has been observed in the Ottawa area in particular; rock expansion there was mainly attributed to crystallization of gypsum along the bedding plane cleavages of the shales. At Sainte-Foy, fibroferrite, a fibrous iron–aluminum sulphate mineral, probably also contributed significantly to heaving.