Small iron-formations in Grenville metasediments have been examined as possible lateral stratigraphic equivalents of stratiform zinc deposits located along the western margin of the Mount Laurier Basin in the Maniwaki–Gracefleld area, Quebec. Similarities in carbonate and amphibolite units hosting the iron and zinc deposits tend to confirm this concept. Sphalerite sparsely disseminated along a dolomitic bed adjacent to the iron-formations, and the iron-formations themselves, are interpreted as the distal extremities of the massive sphalerite lenses found in the proximity of thick amphibolitic strata close to the (fault-bounded?) basin margin. A submarine exhalative model generating proximal zinc and distal iron deposits is proposed to explain this metal zoning. Originally the iron-formations probably consisted of sedimentary siderite that has been transformed under intense metamorphism to the present magnetite–graphite assemblage.

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