Exploration significance of the emplacement and genesis of massive sulphides in the Main Zone at the Norita Mine, Matagami, Quebec

CIM Bulletin, Vol. 74, No. 828, 1981

PJ. MacGEEHAN and W.H. MacLEAN Department of Geological Sciences, McGill University, Montreal, Quebec, A.J. BONENFANT, Mines Noranda Ltée, Division Matagami, Mine Orchan Matagami, Quebec

The Norita deposit is an Archean volcanogenic-exhalative Fe-Zn-Cu sulphide accumulation of the distal type, consisting of six overlapping stratiform massive sulphide lenses, interbed-ded with exhalative cherts and thin pillow basalt flows, which formed down-topographic-slope from a mineralized hydrothermal discharge zone in the Norita rhyolite. The sulphide lenses are of two main types: channel-fill deposits such as the Main Zone and Main Zone West, composed of intricately layered pyrite-sphalerite-chert, which formed by the dynamic down-slope transport and re-deposition of sulphide exhaled from the vent zone; and stratiform lenses such as the Cu-rich A-Zone and A-Zone West, which formed even farther down-slope, in basinal depressions flanking the dome. Although rotated into a vertical position by folding, the sulphide lenses are otherwise essentially undeformed and contain a wide range of preserved primary sedimentary structures.Of prime importance in exploration has been the recognition that the formation of the distal sulphide lenses was controlled by submarine paleotopography, and that it is possible to approximate the sea-floor paleotopography using variations in the thickness and strike extent of the interbedded volcanic rocks. This has proved to be a major and successful exploration tool in the search for further sulphide mineralization in the mine, and offers prospects for use elsewhere in the district.
Keywords: Exploration, Sulphide deposits, Massive sulphides, Ore genesis, Norita Mine, Matagami district, Zinc, Copper, Volcanic stratigraphy, Hydrothermal alteration.