Virtual Museum ID: 19-AME144
Serpentine Asbestos - 3cm long fibres
Once hailed as a “wonder mineral” for its fire, sound and heatproof properties, asbestos has become notorious for the terrible effects it can have on those who are exposed to it. Its long, flexible fibres can be woven into matting, mixed in with cement to make insulating boards, or teased into soft fluffy insulation. It was widely used throughout the late 19th century and most of the 20th century.
Even today, asbestos still poses a threat to health because it was used in many homes and public buildings. Fortunately, people are now aware of the risks and can use personal protective equipment when doing work like renovating and removing asbestos to avoid breathing in and touching the fibres.
Asbestos refers to a group of fibrous minerals, including “white asbestos” (chrysotile), “blue asbestos” (crocidolite) and “brown asbestos” (amosite). This sample is chrysolite, which forms in environments were ancient oceanic crust is metamorphosed and deformed. Although often much shorter, asbestos fibres can easily grow up to 3 cm long, like the ones in this specimen.
This sample of chrysotile asbestos comes from the Cassiar Asbestos mine on McDame Mountain, just north of Cassiar in northwestern BC. The mine produced asbestos from 1951 to 1989, when ore reserves were depleted. Ore from mine stockpiles continued to be processed into the early 1990s. In total, over 60 million tonnes of ore were produced there over its 40-year lifespan. More recently, there has been interest in re-opening the mine to extract magnesium, but to date this hasn’t been successful.
The Cassiar townsite is now considered a ghost town, with most houses abandoned and pulled or burned down. At its peak in the 1950s to 1970s, the population was as high as 2,500, served by local newspapers like the Asbestos Sheet.
Jade, used for jewellery and other decorative objects, was also produced at the mine.
The information listed below relates to the current holding location or collection that the sample is from, and whether the item is viewable at that location or is part of a private collection. Coordinates are given as guides, and we remind you that collecting specimens from these locations is not allowed. Caution is advised visiting such sites and Below BC assumes no responsibility for any injuries or trespassing charges that may occur as a result of the viewer entering these sites.
Original Collection:Association for Mineral Exploration (AME)
Virtual Museum ID:19-AME144
Date Added to VM:2017-11-02
Sample Origin:Mt. McDame, Cassiar, BC
Specific Site:Cassiar Asbestos Mine
Datum:09 (NAD 83)
Primary Mineral Formula:Mg3Si2O5(OH)4
Advanced Geological Information
The following section provides geological data relating to the specimen or the site it was collected from, when available. Information has been obtained from various sources including private and government datasets but may not be up to date. Any geological time periods or ages listed often relate to the primary geology of the area, and may not be the actual date of an event such as mineral formation.
Geological Formation:Sylvester Allochthon
Geological Period:Devonian to Triassic
Geological Terrane:Slide Mountain
Minfile ID:104P 084
The McDame deposit is located about 1 kilometre from the Cassiar deposit (104P 005), north-northeast of the Cassiar town site, 100 kilometres north of the community of Dease Lake.
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. These bodies of serpentinized peridotites 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 (104P 005) and McDame deposits. The ultramafite sheet dips 32 to 50 degrees east under McDame Mountain where it attains a thickness of 300 metres. There are two episodes of faulting postulated with asbestos thought to have formed during the change from normal to dextral motion on a north-trending fault that transects the serpentinite (45 degree shear).
The hangingwall of the McDame ultramafite is marked by shearing, serpentinization, chloritization, pods of schistose tremolite, talc soapstone, zoisite, epidote and clay. The footwall is characterized by sheared carbonaceous argillite and gouge. Pyrite and magnetite are disseminated throughout.
Chrysotile veining is controlled primarily by the joint system. Joint sets in the serpentinite strike east-northeast and south-southeast. Normal faulting is prominent in an east and northeast direction. The McDame deposit is the downward extension of the Cassiar deposit.
Drilling has outlined an east-dipping body of cross-fibre chrysotile ore which thickens towards the east. Reserves have been calculated for a deposit having the approximate dimensions of 540 metres dip length (east-west), 320 metres width (north-south), and 15 to 150 metres thickness. Measured geological reserves are 19.94 million tonnes with a 6.21 per cent mill yield of asbestos; proven reserves with a 6.21 per cent mill yield of asbestos (Princeton Mining Corp. Annual Report 1990).
Production at the McDame deposit began in February 1991 after three years of underground development, prompted by declining reserves from open-pit operations at the adjoining Cassiar asbestos mine. Production up to October 1991 totalled 40,000 tonnes (George Cross News Letter No.200, 1991). The ore has averaged 9.2 per cent asbestos fibre, suggesting overall grade is higher than expected (Northern Miner - February 11, 1991).
High quality asbestos underground reserves in the McDame deposit were estimated at 16 million tonnes (10 years of production) in 1989 (P. Wojdak, personal communication, 1994).