The Dunsmuir occurrence is underlain by the Upper Cretaceous Nanaimo Group (Haslam Formation). The poorly-bedded shale is dark blue-grey when fresh, and weathers to a brown colour. It has a silty texture, and contains abundant pelecypods, ammonites and other fossils. The shale is brittle and shatters readily into 0.5 to 5.0 centimetre fragments.
Two samples of the shale were analyzed: sample 1 consisted of equal-sized chips picked at random from oxidized rock that formed the muck pile at the working face of the quarry; sample 2 consisted of equal-sized chips gathered at random from the freshest accessible exposures of the unweathered shale. The samples analyzed as follows (Geology, Exploration and Mining in British Columbia 1970, page 496):
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Sample 1 (values in per cent) Sample 2
SiO2 52.88 53.64
Al2O3 17.01 16.06
Fe2O3 8.14 3.02
FeO 2.51 7.33
TiO2 1.50 1.56
CaO 0.54 1.14
MgO 2.04 2.59
Na2O 2.81 2.65
K2O 1.99 2.20
H2O 3.88 (-105 degrees Celsius) 2.48
H2O 6.11 (+105 degrees Celsius) 6.69
The shale was quarried for use in cement manufacture and is presently being quarried by Dunsmuir Quarries Ltd. (Mineral Market Update, July, 1991).
