The Highway Deposit Lower Showing is one of many micaceous pegmatite dyke and sill occurrences in an area covering both slopes of Fred Laing Ridge including the northerly flowing tributaries of Potlatch Creek, the southerly flowing tributaries of Mica Creek and portions of the valley bottom of the main Mica Creek (Newmarch, 1942). Pegmatites, as large semi-concordant bodies, are abundant along the contact between the Semipelite and Pelite units of the Hadrynian Horsethief Creek Group. Distribution within the northern Semipelite unit is sporadic. A common association with marble was noticed along a southeast trending ridge 3 kilometres south-southwest of Warsaw Mountain.

At least two generations of pegmatites occur in this area. Earlier generation pegmatites are concordant and boudinaged within enclosing semipelite units. Younger generation pegmatites crosscut layering and schistosity. Pegmatite dykes and sills in the area range from 0.90 to 9.0 metres in width, with thick pegmatites usually discordant. Orientations are also highly variable.

All pegmatites are plagioclase-rich, typically consisting of 70 per cent plagioclase, 20 per cent muscovite and 10 per cent quartz. Plagioclase is often strained and well twinned (Mitchell, 1976). Mica within these dykes and sills range from 5 to 20 per cent by rock volume and in size from 0.32 to 8.9 centimetres diameter and 5.0 centimetres thick. Mica booklets often show evidence of internal strain. Minerals associated with mica are almandine garnet and black tourmaline (Newmarch, 1942). For a detailed description of the regional geology refer to the Warsaw Mountain showing (083D 041).

At the Highway Deposit Lower Showing, mica booklets 7.62 by 7.62 centimetres, appear to be concentrated in an area of about 120 square centimetres in a 1.22-metre wide pegmatite dyke. This zone consists of 20 per cent muscovite by rock volume. This mica-bearing pegmatite dyke strikes 065 degrees and dips vertically.

A 0.635-centimetre band of kyanite is found in the enclosing schists. In the lower reaches of Mica Creek kyanite forms bands within schists. At the headwaters of the first and second tributaries of Mica Creek kyanite is present in localized pelitic horizons near the base of the Semipelite-Amphibolite division (Geological Society of America Memoir 153), the Aluminous Pelite unit (Open File 1988-26) or Lower Pelite unit (Geological Survey of Canada Open File 2324) of the Horsethief Creek Group. Kyanite porphyroblasts in these horizons are up to 5 centimetres in length.