The lower Paleozoic Sicamous Formation (Mount Ida Group) comprised of calcareous phyllite and limestone is underlain by schist of the Hadrynian and/or Paleozoic Silver Creek Formation (Mount Ida Group). This sequence is intruded by altered Cretaceous? granites and capped by Eocene volcanics of the Kamloops Group.
The Bonnie Brae workings expose a reticulate system of quartz veins striking north to northeast in highly sheared and fractured mica schists cut by porphyritic felsic dikes, adjacent to a granitic intrusion. Mineralization occurs along sheeted fracture zones and milky quartz veins and lenses 0.3 to 1.8 metres wide, and comprises pyrite, sphalerite and argentiferous galena. Pyrrhotite occurs locally in lower workings. Silicification is prevalent.
A number of opencuts along a northeast trend exposes a series of the quartz lenses. A tunnel had been driven for 21 metres in a general southerly direction, following the course of a porphyry dike which lies on the west side of a zone of shearing. Between 1967 and 1969, seven trenches were completed totalling 548 metres, and 2 diamond-drill holes were drilled totalling 609 metres.