MacDonald Island is underlain by Lower Jurassic Telkwa Formation (Hazelton Group) volcanics comprised of green to purple waterlain andesite tuffs and breccias with minor intercalated chert pebble conglomerates in the central and eastern part of the island. These rocks strike northerly and dip at moderate angles to the west and are overlain in the western part of the island by massive and amygdaloidal andesitic flows and thin bedded shales.
Copper mineralization at the Granisle mine is associated with a series of Eocene Babine Plutonic suite which occur in the central part of the island. The oldest is an elliptical plug of dark grey quartz diorite approximately 300 by 500 metres in plan. The most important intrusions are biotite-feldspar porphyries of several distinct phases which overlap the period of mineralization. The largest and oldest is a wide northeasterly trending dike which is intrusive into the western edge of the quartz diorite pluton. The contact is near vertical and several small porphyry dikes radiate from the main dike. Several of the phases of the porphyry intrusions are recognized within the pit area. Potassium-argon age determinations on four biotite samples collected in and near the Granisle ore body yielded the mean age of 51.2 Ma plus or minus 2 Ma (Minister of Mines Annual Report 1971).
The wide porphyry dike which strikes northeast is bounded by two parallel northwest striking block faults. The westernmost crosses the island south of the mine and the eastern fault extends along the channel separating the island from the east shore of Babine Lake.
An oval zone of potassic alteration is coincident with the ore zone. The main alteration product is secondary biotite. This potassic alteration zone is gradational outward to a quartz-sericite- carbonate-pyrite zone which is roughly coaxial with the ore zone. Within this zone, the intrusive and volcanic rocks are weathered to a uniform buff colour with abundant fine-grained quartz. Mafic minerals are altered to sericite and carbonate with plagioclase clouded by sericite. Pyrite occurs as disseminations or as fracture-fillings. Beyond the pyrite halo, varying degrees of propylitic alteration occurs in the volcanics with chlorite, carbonate and epidote in the matrix and carbonate-pyrite in fractured zones. Clay mineral alteration is confined to narrow gouge in the fault zones.
The principal minerals within the ore zone are chalcopyrite, bornite and pyrite. Coarse-grained chalcopyrite is widespread, occurring principally in quartz-filled fractures with preferred orientations of 035 to 060 degrees and 300 to 330 degrees with near vertical dips. Bornite is widespread in the southern half of the ore zone with veins up to 0.3 metres wide hosting coarse-grained bornite, chalcopyrite, quartz, biotite and apatite.
Gold and silver are recovered from the copper concentrates. Molybdenite occurs within the ore zone, most commonly in drusy quartz veinlets which appear to be later than the main stage of mineralization. Magnetite and specularite are common in the north half of the ore zone where they occur in fractures with chalcopyrite and pyrite. Pyrite occurs in greatest concentrations peripheral to the orebody as blebs, stringers and disseminations.
Mining at Granisle was suspended in mid-1982. Production from 1966 to 1982 totalled 52,273,151 tonnes yielding 69,752,525 grams of silver, 6,832,716 grams of gold, 214,299,455 kilograms of copper and 6,582 kilograms molybdenum.
Unclassified reserves are 14,163,459 tonnes grading 0.442 per cent copper (Noranda Mines Ltd. Annual Report 1984).
Remaining in situ reserves, as modelled in 1992 using a 0.30 per cent copper cu-toff, are estimated to be 119 million tonnes grading 0.41 per cent copper and 0.15 gram per tonne gold (CIM Special Volume 46, page 254).
HISTORY (source, Assessment Report 21012)
The earliest record of work on McDonald Island is reported in the BC Minister of Mines Annual Report for 1913. Chas. Newman and H.J. McDonald are credited with the property discovery and by the time of the report, two short tunnels, several open cuts and a shaft had been put in. Little information is available until 1927, when Douglas Lay visited the property and described the showings in his 1927 Minister of Mines Annual Report. On his recommendation the property was bonded by the Canadian Mining and Smelter Co. (Cominco) the following year.
In 1928 and 1929, Cominco’s work on the property included 18 open cuts, totalling 93 metres, and 5 diamond drill holes, totalling 1224 meters. Reserves of 7.26 million tonnes grading 0.8 per cent copper with low gold and silver values were indicated, however the option was allowed to lapse.
The property was examined by Dr. Victor Dolmage in 1943. Work had been done at that time by E.E. Campbell and the prospect was referred to as the Newman property (see 093L 145). Dolmage recommended work on the property, based on favorable geology and mineralology. Soon after Dolmage's report, in 1945, American Metals drilled four holes totaling 675 metres, but the results were poor and the property was dropped.
In 1955 the principal claims were purchased by Granby Mining Co., and their subsidiary, Granisle Copper Co. Ltd. was organized soon after. In 1955 and 1956, forty-eight vertical drill holes totalling 4079 metres, were drilled on a 61 metres square grid pattern. In 1959, a further 30 drill holes which totalled 3436 meters were drilled on a closer spacing and with some inclined drill holes. Three holes, totalling 502 metres, were drilled in 1962 to provide material for milling tests. In addition, 32 drill holes, totalling 1161 metres, were drilled outside the ore zone between 1956 and 1962.
In 1963 planning had advanced to the stage of mill testing and surveys for suitable mill sites. A feasibility study was completed in April 1964. Arrangements were made for financing and a production decision was made in February, 1965. Construction was carried out during 1965 and 1966, and in mid-November, 1966, production began at 4500 tonnes per day. Ore reserves were 20 million tonnes of 0.53 per cent copper. In 1969, a diamond drill program of 10,000 meters in 50 holes increased reserves to 81 million tonnes proven of 0.43 per cent copper. The mill facilities were expanded and by the end of 1972, 12,000 tonnes per day was being processed
Further drilling was conducted in the years 1970 to 1973. During this period, 38,050.2 metres were drilled in a total of 242 holes, including 7 percussion drill holes totalling 670 feet (204.3 meters).
In April of 1980, Noranda Minerals Inc. bought the assets of the Zapata Granby Mining Co., which included the Granisle Mine. Noranda operated the mine until June 30, 1982, when low metal prices forced the mine to close.
From 1962 to 1982 (inclusive) commodities recovered from 52,273,151 tonnes of ore mined at the Gransile mine were: silver, 69,752; 525 grams; gold, 6,832,716 grams; copper 214,299,455 kilograms; and molybdenum, 6,582 kilograms (from BC Ministry of Mines).
In 1990, 9632 metres of NQ diamond drilling was conducted in the Granisle open pit by Noranda. A total of 38 holes were drilled. The footage is divided among 38 inclined holes, drilled from ramps and benches within the pit. The intent of the program was to verify tonnage and grades calculated from previous drilling and determine the size and location of waste blocks within the ore body. In addition, a few exploration holes were drilled to test the potential for ore in the north wall of the pit. The drilling indicates these blocks continue and possibly flare somewhat with increasing depth. Values were reported to be erratic.
In 2012, ten seismic refraction lines totalling 10.7 kilometres were completed on behalf of operator Xstrata Copper Canada (owner Astorius Resources Ltd.) in the Bell Mine Area, the Hagan Area and the Granisle Mine Area. Resistivity surveying totalling 5 kilometres was carried out in line RL-2 in the Bell Mine site area and on lines RL-4 and RL-5 in the Hagan area, across Hagan arm from the Bell mine area. Surveying in this area consisted of a single seismic refraction line SL-10, located in the southern part of the island. The results of the interpretation of line SL-10 indicate the subsurface is comprised of four distinct velocity layers (Assessment Report 33965).