The Extension No. 8 mine of Canadian Collieries (Dunsmuir) Ltd. opened in 1926. The mine is located on the south side of the Nanaimo River in the vicinity of McKay Lake. The presence of the Wellington seam in good thickness and quality was proved by boring and surface prospecting several years earlier. The slope, driven in excellent coal, struck a declivity after advancing on a steep dip and was eventually abandoned. The No. 1 slope was abandoned in 1928 and all work was concentrated on the No. 2 slope, the coal remaining in the No. 1 slope was eventually reached by the workings of the No. 2 slope.

The coal is part of the Wellington seam which occurs near the base of the Upper Cretaceous Extension Formation, Nanaimo Group in the Early Campanian Northfield Member. The coal seam averaged about 1.5 metres in thickness. The roof of the workings was in shale and the floor was generally sandstone. Refer to the Bebans mine (092GSW 026) for a description of the Wellington Seam and Nanaimo Coalfield operations.

The Extension No. 8 mine occurs within a structure known as the Extension Basin. The structure in the basin consists of a northwest trending syncline. The No. 8 mine is located on the west limb where the structure strikes generally northwest and dips approximately 65 degrees northeast.

In 1928, the No. 8 mine produced 35,206 tonnes of high volatile bituminous rank coal (production for 1926 and 1927 is included with the Extension mine (092GSW028). The mine ceased operations in October 1928. In 1945, the Timberlands Colliery reopened the old No. 8 mine workings and commenced production of excellent quality Wellington seam coal averaging 76 to 102 centimetres in thickness. Production of coal was continuous between 1945 and 1955. Prospecting in 1951 expanded this area into a second new mine, the Lewis mine. This extension of the old No. 8 mine, or the new Lewis mine, commenced production in 1951 and continued to 1966. The Wellington seam averaged about 1.8 metres in thickness, including two rock partings, and dipped about 08 degrees south. The coal outcrop was bounded to the west by a thrust fault that also formed the western boundary of the old No. 8 mine. The mine was abandoned in 1966.