The Brett-Bird showing is located 7 kilometres east-northeast of Armstrong, near Sneesby Creek.

This area, east of the Okanagan Valley fault, is underlain by metamorphic rocks of unknown age, metasedimentary rocks of the Proterozoic Silver Creek Formation and volcanic and sedimentary rocks of the Cambro-Ordovician Tsalkom Formation. All these units are probably in low-angle fault contact with each other. Intruding these rocks are Middle Jurassic granitic plutons. Pegmatite bodies of Mesozoic or Cenozoic age intrude the Silver Creek. Eocene Kamloops Group volcanic rocks occur to the north.

Quartz biotite schist of the Silver Creek is intruded by irregular, sheet-like bodies of oligoclase, orthoclase, quartz and muscovite pegmatite. Fresh greenish-tinged muscovite occurs disseminated and in patches throughout the pegmatite, with the grain size of the mica varying with the grain size of the other minerals. Muscovite plates range in size from 1 millimetre to 15 by 25 centimetres in size. In a coarse-grained section of the pegmatite, patches of muscovite, 30 by 60 centimetres in size, cover up to 5 or 10 per cent of the exposure. A few grains of radioactive mineral, possibly uraninite, occur in the pegmatite.

The first record of exploration is from 1927 when an open cut exposed muscovite plates. By 1950, a 10-metre adit and the three main open cuts had been completed. Approximately 100 tonnes of mica were shipped between 1932 and 1950.