The Big Ledge deposit is located 60 kilometres south of Revelstoke and approximately 8 kilometres west of Upper Arrow Lake between North Fork Creek and Ledge Creek.
The area is underlain by rocks of the Thor-Odin gneiss dome of the Proterozoic Monashee Complex and metamorphic rocks of the Proterozoic to Paleozoic Kootenay Assemblage. The Thor-Odin is one of a series of gneiss domes spaced approximately 80 kilometres apart along the eastern edge of the Shuswap Complex. A central core zone in the dome consists of gneissic and migmatitic rocks. This zone is surrounded by a heterogeneous assemblage of metasedimentary rocks of the Mantling zone and Fringe zone, the latter containing abundant pegmatite and lineated quartz monzonite. The Supracrustal zone, consisting of quartzite, marble, phyllite, schist and metavolcanic rocks, forms a cover to the gneisses.
The Big Ledge deposit is located south of the Core zone in an east-west trending succession of metasedimentary rocks of the Mantling zone. The rusty weathering succession consists of a heterogeneous mixture of schist and gneiss, calcareous quartzite, calc-silicate gneiss, marble and amphibolite. The structure is dominated by a series of east-west trending, open to tight folds. These are inclined to the south, overturned to the north and plunge variably to the east and west. The mineralized horizon is in the core of a fold which is a tight antiform, inclined to the south and overturned to the north.
Showings of pyrrhotite, pyrite, sphalerite, galena, chalcopyrite and marcasite occur along a layer known as the Ledge for a distance of over 10 kilometres. The Ledge consists of fine- grained, dark graphitic-sericitic schist, dark quartz-rich schist, calc-silicate gneiss and minor siliceous marble layers. Pyrite and pyrrhotite are disseminated throughout these units resulting in a characteristic rusty weathering. Drilling indicates that there are at least four massive sulphide layers within the Ledge. It is not known if these are individual layers or fold repetitions of one or more layers. The massive sulphide layers consist of medium to coarse-grained pyrrhotite or pyrite with varying amounts of dark sphalerite. Quartz-eyes are common in the massive sulphide layers and sphalerite is commonly aligned parallel to layering in the adjacent schists.
The Ledge averages 30 metres in thickness and is conformable to bedding. Pyrrhotite is the most abundant sulphide and pyrite, usually in nodular masses, is locally abundant. Sphalerite is erratically distributed with the pyrrhotite. Galena is occasionally present in minor amounts along with the other sulphides but the only notable concentrations are small occurrences in calcareous beds adjacent to the main mineralized sections. In general, the sulphides are coarsely crystallized; a small amount of the ore minerals are intergrown with pyrrhotite. Iron sulphides are usually accompanied by scattered graphite flakes.
A zone of heavier mineralization occurs in the upper portion of the rock series. This zone ranges from 61 centimetres to greater than 6 metres in thickness (old drill records indicate up to 18 metres). This zone is conformable with bedding but the sulphides are erratically distributed in irregular massive and disseminated bodies. There is a large amount of granitic and pegmatitic material in this zone. Sphalerite appears to be most abundant in disseminated sulphide sections but small, irregular, high-grade patches occur with both the massive and disseminated sulphides.
Indicated ore reserves are 6.5 million tonnes grading less than 6 per cent combined lead and zinc (CIM Bulletin Vol. 75, No. 840, page 119).
The deposit was originally staked as a gossanous exposure in 1892. Subsequent staking occurred in two main groups, the Monarch and Adventurer. By 1925, 210 metres of underground work in four adits had been completed on the Bonanza, Sunshine (Lot 2477), Skyline and Adventurer (Lot 1067) claims. In 1927, 16 holes were drilled on the property. Between 1947 and 1953, Consolidated Mining and Smelting Company of Canada Ltd. drilled 6100 metres on the property and completed programs of geological mapping, soil sampling and a ground geophysical survey. In 1960, the ground was restaked as the BL group (Lots 16071-16114). From 1964 to 1966, approximately 3960 metres of drilling, geological mapping and geochemical and magnetometer surveys were carried out. During 1979 through 1981, Esperanza Explorations Limited completed programs of geochemical sampling, geophysical surveys and geological mapping. In 1990, a program of geological mapping, geochemical sampling and a ground magnetic survey were conducted on the area immediately south as the AMF claims. During 2006 through 2012, programs of prospecting, rock sampling and a ground magnetic survey were completed on the area.
