The McDame deposit is located approximately 1 kilometre from the Cassiar deposit (MINFILE 104P 005), north-northeast of the Cassiar town site and 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. Bodies of serpentinized peridotites occur along at least three distinct horizons that 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 (MINFILE 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 crossfibre chrysotile ore that 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 (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 averaged 9.2 per cent asbestos fibre, suggesting a higher overall grade than expected (Northern Miner - February 11, 1991).

In 1989, high quality asbestos underground reserves in the McDame deposit were estimated at 16 million tonnes (10 years of production; P. Wojdak, personal communication, 1994).

Work History

The area has been explored in conjunction with the adjacent Cassiar Asbestos Mine (MINFILE 104P 005) and a complete exploration history can be found there.