The immediate Heffley Lake area is extensively covered with superficial glacio-fluvial deposits and is estimated to have less than 1 per cent rock exposure. Stratified rocks mainly comprise steeply dipping, northwest striking argillites and calcareous siltstones with lesser andesitic ash and lapilli tuff and some limestone belonging to the Devonian to Permian Harper Ranch and/or Upper Triassic Nicola groups. These rocks were intruded by the possible Late Triassic to Early Jurassic mafic-ultramafic Heffley Creek pluton and then folded and overprinted by lower to sub-greenschist metamorphism producing slaty and phyllitic fabrics. Bleached marbles and calcsilicate-rich metasediments are developed where hydrothermal or thermal alteration has occurred.

South of Heffley Lake are units of blue-grey crinoidal limestone and black argillite while north of the lake are coarsely clastic to conglomeratic limestone in the vicinity of the Heff skarn (092INE096) which lack crinoids and the argillites are less organic-rich. This and other lithological differences suggest that these rocks may be separated into northern and southern packages; these are tentatively believed to represent the Nicola and Harper Ranch groups respectively. The northwest trending contact between these packages is thought to pass under the Heffley lakes and continue southeastwards along Armour Creek. This original stratigraphic contact has been intruded by the Heffley Creek pluton and has subsequently been the locus of brittle movement along the Armour Creek fault (Fieldwork 1999).

Disseminated cumulate magnetite is common throughout the main Heffley Creek pluton but locally some pyrite +/- chalcopyrite +/- secondary copper oxides are also seen. Many of these sulphide-rich zones are characterized by silicification and plagioclase veining and they appear to be fault related. A new discovery, Shaw Hill, is a chalcopyrite-malachite-potassium feldspar occurrence found in a new roadcut and was discovered during the 1999 field season by the Geological Survey Branch. Hostrocks are mafic gabbro to diorite of the Heffley Creek pluton. Quartz-calcite veins occur nearby. A grab sample analysed 0.82 per cent copper and 14.4 grams per tonne silver (Fieldwork 1999).