The Cassiar asbestos mine is located approximately 4.5 kilometres north-northeast of the Cassiar townsite.

The area is underlain by four major thrust sheets, distinguished on McDame Mountain, of the Devonian to Triassic Sylvester Allochthon. These comprise greenstones, argillites, limestones, ultramafites and ultramafic bodies of variable size, shape and form. Bodies of antigorite-serpentinized harzburgites occur along at least three distinct horizons, which are probably major thrust fault surfaces. The lowest horizon occurs just above the Sylvester basal thrust fault, and contains a serpentinite thrust slice that hosts the Cassiar and McDame (MINFILE 104P 084) deposits. There were two episodes of faulting postulated, with asbestos forming during the change from normal to dextral motion on a north-trending fault that transects the serpentinite (45 degree shear).

The Cassiar pit occupies a zone of anomalous structure, with a north-trending, high-angle fault (Marble Creek fault) juxtaposing bedded chert (Sylvester) to the east and graptolitic Ordovician-Silurian Road River Group slate to the west. The latter is complexly imbricated with slivers of dolostone (Lower Devonian Tapioca sandstone or Middle to Upper Devonian McDame Group) below the Sylvester basal thrust.

The Cassiar orebody is roughly crescent-shaped with northeast- and southeast-trending horns. The orebody as a whole dips approximately 45 degrees east and measures approximately 600 by 150 by 150 metres. North-striking, east-dipping thrusts and shears slice the orebody into a number of massive blocks with well-developed systems of conjugate joints, most of which contain long, cross-fibre chrysotile. The orientation of joint systems within successive blocks varies widely, but tends to favour two directions, north-northwest to north-northeast, and east-southeast.

The orebody is a fibre-bearing zone containing upwards of 10 per cent cross-fibre chrysotile asbestos measuring up to 3 centimetres in length. Most veins are the two-fibre type, with a central parting. The short fibre component is also significant economically. There are two generations of asbestos veins with different orientations. Magnetite is abundant in partings and along vein walls. Pyrite and jade also occur within the serpentinite.

Post-vein shearing is most apparent in the footwall of the deposit. In country rocks near the orebody, there are many steeply dipping veins with quartz, tremolite, talc, zoisite and carbonates.

Work History

The area was originally staked in 1950 by four prospectors. The following year, the Conwest Exploration Company Ltd. formed the Cassiar Asbestos Corp. Ltd. (later Brinko Mining Ltd.) to develop the deposit. The first ore was mined in the fall of 1952 and continued through the early 1990s. In 1953, the area immediately east of the occurrence was prospected and mapped as the Par and Doreen claim group.

During 1978 through 1981, an adit was driven at the 1578-metre level, below the open pit mine, for a length of 1334 metres, from which a series of 37 diamond drill holes, totalling 12 092 metres, were initiated to increase the sampling density of the known ore reserves and to probe untested zones. In 1985, a further program of diamond drilling, totalling 622 metres, and an airborne magnetic survey was completed. Also at this time the lower (1415-metre) drift was driven 1081 metres and bulk sampling, totalling 875 tonnes, was carried out. In 1986 and 1987, 27 diamond drill holes, totalling 4960.6 metres, and at least 570.4 metres of underground development work was completed. An 846-tonne bulk sample was collected at this time. This work identified and developed the McDame (MINFILE 104P 084) underground deposit to the south of the Cassiar open pit mine.

Reserves at the Cassiar Asbestos mine were exhausted in June 1989, after 38 years of production. Stockpiled ore (1.4 million tonnes) from the pit supplied sufficient mill feed while the McDame deposit was prepared for production. The McDame deposit commenced production in February, 1991. Large, unknown quantities of jade were also produced over the years.

Reserves at the Cassiar mine are approximately 17 million tonnes grading 4.2 per cent asbestos and 23.5 per cent magnesium in a low-grade stockpile (waste from the former dry-milling operation) determined by drilling on 30-metre centres in the mid-1980s (P. Wojdak, personal communication, 1994 and Exploration and Mining in British Columbia 1998, page 25).

In 1998, Jedway Enterprises recovered 50 tonnes of jade from the old Cassiar Asbestos dumps. Cassiar Mining Inc., a wholly owned subsidiary of Minroc Mines Inc., expected to produce at a rate of 1000 tonnes of asbestos fibre per month from August to October 1998. A total of 20 000 tonnes was shipped. At this time, Minroc conducted a feasibility study to assess magnesium recovery in the tailings. In June 1999, Minroc changed its name to Cassiar Mines & Metals Inc.

In July 1999, Aluminum of Korea Ltd. (KORALU) entered into an agreement with Cassiar Mines & Metals Inc. to acquire 35 per cent of the magnesium metal project. The serpentine stockpile of 20 million tonnes contains 3630 million kilograms of magnesium metal and 700 million kilograms of chrysotile fibre (Cassiar Mines & Metals Inc., Press Release, December 27, 1999). In April 2000, Cassiar Mines & Metals Inc. changed its name to Cassiar Magnesium Inc. In 2000, Cassiar Magnesium Inc. dry milled surface stockpiles of chrysolite, with approximately 6 million tonnes of 7 per cent fibre outlined, to produce 60 to 70 tonnes per day of long and intermediate fibre. The dry mill facility was damaged by fire in December 2000 and production has been suspended.