Abstract

Zinc and iron deposits in the Grenville Supergroup metasedimentary rocks of the Maniwaki-Gracefield district, Quebec, exhibit close similarities to the economically important Balmat-Edwards district of New York State. The mineralization is stratiform, it is consistently associated with dolomitic marble units, and it has ages similar to the New York deposits ( approximately 1,200-1,300 m.y.). At least two phases of intense Grenvillian deformation affected the host rocks, and regional metamorphism reached the granulite facies. Lateral and vertical zoning of major and trace elements observed within the zinc deposits indicate that they probably had a submarine exhalative origin.Small magnetite-rich iron-formations related to Mg-rich carbonates, and minor amounts of base metal sulfides including sphalerite, occur within metasediments closely resembling those which host the zinc deposits. The iron deposits are interpreted to occur at stratigraphic positions which are laterally equivalent to the zinc mineralization, and consequently the iron-formations form an important stratigraphic guide to zinc mineralization within the complexly deformed and strongly metamorphosed strata of the Grenville Supergroup.At the regional scale, the Grenville zinc deposits of Quebec, Ontario, and New York are located along two major structural lineaments which border the Central Metasedimentary belt and define a first-order basin hosting the metasedimentary rocks of the Grenville Super-group. These basin-margin lineaments also delineate two regional metallogenic zones characterized principally by zinc and iron deposits: a western zone which encompasses the Maniwaki-Gracefield showings as well as several minor to medium-sized stratiform base metal deposits in Ontario and adjacent portions of Quebec, and an eastern zone which includes the Balmat-Edwards and East Pierrepont deposits of New York as well as the stratiform gold-zinc deposits of Montauban, Quebec. These regional aspects are consistent with current models for the origin of sediment-hosted submarine-exhalative base metal mineralization.

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