Geology of the Lyon Lake ore deposits, Noranda Mines Limited, Sturgeon Lake area, Ontario

CIM Bulletin, Vol. 74, No. 833, 1981

J.D. HARVEY and J.B. HINZER, Mattagami Lake Exploration Limited, Toronto, Ontario

Noranda's Lyon Lake property in the Sturgeon Lake area of Northwestern Ontario was staked by Mattagami Lake Mines Limited in May 1969 to cover airborne Input anomalies. Subsequent ground geophysical and diamond drilling programs resulted in the discovery of the Boundary Extension, Lake and Creek ore zones. As of December 31, 1978, ore reserves were estimated at 3,945,000 tons assaying 6.53 per cent Zn, 1.24 per cent Cu, 0.63 per cent Pb, 3.42 oz/ton Ag and 0.010 oz/ton Au. These deposits are hosted within the South Sturgeon Lake volcanic pile of Archean age, which consists of several cycles of basic intermediate and felsic volcanic materials overlain by a sedimentary iron formation and built upon a plutonic base (Franklin, 1975). The top 50 m of the second felsic cycle, according to mine terminology, contains the mineralization within quartz-phenocryst-bearing felsic lapilli tuff and underlying thin discontinuous graphitic sediments and altered coarse pyroclastics. The basal andesitic member of the overlying cycle forms the hanging wall to the ore deposits.Although there is no alteration pipe below the deposits, the coarse footwall rocks are permeated by chlorite, garnet, carbonate, iron sulphide and magnetitie-bearing veins intensifying from west to east.Immediate host rocks are alkali depleted and MnO, FeO, Zn and Cu enriched compared to Goodwin's (1972) average Archean rhyolites. Bedded pyrite-pyrrhotite-chalcopyrite lenses with sphalerite-rich tops are underlain by weakly developed stringer mineralization.Traversing eastward from the Lake Zone to the Creek Zone and toward the Sturgeon Lake Mine deposit, more rapid fades changes, more pronounced chloritic and carbonate alteration, the presence of garnets, greater MnO, FeO, CaO and A g abundances, and increasing Zn/Cu and MnO/FeO ratios are apparent.
Keywords: Lyon Lake deposits, Sturgeon Lake area, Zinc, Copper, Exploration, Geophysical exploration, Alteration, Ore deposits.