The Yellowhead showing is located on the north side of Sleeper Mountain, 3.5 kilometres due south of Grant Brook on the Canadian National Railway between Tete Jaune and Jasper.
The geology of the area has received considerable attention in recent years. Detailed mapping has been primarily conducted by E.W. Mountjoy in the Rainbow Range from 1964 to 1968. M.R. McDonough, more recently conducted detailed mapping in the northernmost Selwyn Range.
Three informal map units have been recognized within the Hadrynian Miette Group of the northernmost Selwyn Range. The lowermost consists of a pelite and quartzite succession assigned to lower Miette status. This strata underlies a thick sequence of massive conglomeratic sandstones (grits) and green pelites belonging to the middle Miette. The upper Miette consists of a sequence of dark calcareous pelites and black limestone with minor sandstone.
The structure of the area is dominated by a series of large, upright F2 folds that form an anticlinorium in the Moose Lake Thrust, which truncates in the west limb of the Mount Robson synclinorium. Pelites of the lower and upper Miette are thickened primarily by folding and foliation development. Middle Miette strata are thickened by folding and thrust faulting. Pre F2 folding, bedding parallel thrusts also thickened middle Miette strata. This was first recognized by McDonough and Simony in 1988 (Geological Survey of Canada Paper 88-1D, pp. 105-113).
The metamorphic grade, in the area, decreases to the north and northeast into the biotite zone with scattered chloritoid of greenschist grade. At about 1844 metres, the massive conglomeratic sandstone beds of the middle Miette unit, striking east-west, develop quartz veins which strike in almost every direction. These vary in width from 2.5 to 90 centimetres. The widest veins appear to be conformable with bedding and are barren. Veins which are more or less vertical, varying in width from 15 to 45 centimetres wide show slight galena and chalcopyrite. A sample from one of these mineralized veins assayed trace gold, 75.4 grams per tonne silver and 5 per cent lead (Minister of Mines Annual Report 1927).
