The Old No. 1 Slope and Vancouver workings of Canadian Collieries (Dunsmuir) Ltd. are located in the Extension field in the vicinity of the more recent Chambers mine. Historical production records for these operations during the turn of the century are not available. The coal is part of the Wellington seam which is part of the Upper Cretaceous Nanaimo Group, Extension Formation (Early Campanian Northfield Member). Refer to the Bebans mine (092GSW026) for further clarification of the Wellington Seam in the Nanaimo Coalfield.

The Chambers mine commenced operations in 1933 and underground mining consisted mainly of recovering pillars left by the former owners. Between 1933 and 1952, the mine produced over 50,000 tonnes of highly volatile, bituminous rank coal. In the latter part of 1952, a small strip pit was opened up within a section of the Wellington seam lying close to the surface in the vicinity of the old Vancouver Slope workings. The seam dipped gently west and the thickness of the overburden varied between 2.4 to 4.6 metres. The typical seam section on the property includes: 1.34 metres of top coal (partially eroded); 0.45 metre of carbonaceous shale; 0.43 metre of coal; 0.1 metres of rock; and 0.5 metre of coal. By the end of 1954, all available surface coal was depleted, and early in 1955 testing was started to determine the continuity of the seam underground. At the end of 1955, the slope reached a point about 122 metres from the portal where the coal varied from 1.8 to 2.4 metres in thickness. The coal was mined by picking out the middle band of carbonaceous shale with hand-picks. In 1961, this mine, formerly known as Chambers No. 5 mine, was operated by the Midan brothers. The Midan mine continued operations until the end of 1965.