The Reserve mine is located southwest of Harmac, just east of South Wellington. The first sod was turned and sinking of the Reserve shafts began in July, 1910. The Douglas coal seam was intersected at a depth of 323 metres in May 1913, when labour troubles caused a suspension of operations. In 1914, operations resumed and the mine operated continuously until 1930. In February of 1934, the mine was dewatered and efforts concentrated on retreating with the pillars and recovering all available coal. The Reserve mine produced a substantial amount of coal between 1936 and 1939 before being exhausted.

The coal is part of the Douglas seam in the Early Campanian Newcastle Member which is part of the Upper Cretaceous Pender Formation, Nanaimo Group. The Douglas seam in the Reserve mine was reported to range between 0.3 to 6.1 metres in thickness and was described as lenticular in formation, or full of pinches and swells with abundant slickensides. The roof of the mine is friable and consists of carbonaceous shales. The coal produced is of high volatile bituminous rank.