The Crystal Peak Garnet deposit is centred on Mount Riordan, 26 kilometres west-southwest of Princeton.
The deposit is located on the eastern edge of the Hedley Mascot and Nickel Plate mining camp. The general area has been extensively prospected.
The deposit is hosted in a roof pendant of carbonate-rich sediments (limestone) of the Upper Triassic French Mine Formation, Nicola Group that has been almost completely replaced by garnet-rich skarn. The roof pendant is intruded from the north and east by hornblende porphyritic granodiorite of the Middle Jurassic Bromley batholith (locally known as Mount Riordan stock), part of the Middle Jurassic Nelson intrusions (Bulletin 101).
An elongate mass of garnetite trending north-northwest for up to 900 metres lies centred on Mount Riordan. The deposit contains three major, high grade zones (60 to 100 per cent garnet) outcropping over a total area of 3.35 hectares. Remnant bodies of microdiorite up to 30 metres in diameter are scattered about a broad zone lying in the centre of the skarn.
The skarn consists of massive and coarsely crystalline garnetite comprised of approximately 90 per cent andradite and 10 per cent grossularite. Garnet crystals typically contain andradite-rich cores and grossularite-rich margins. The garnet is usually brown and green, with minor black, red-brown, pink and yellow-green varieties. Diopside, quartz, calcite, epidote, actinolite, hedenbergite, clinopyroxene and magnetite occur in relatively low quantities. Traces of chlorite, wollastonite, scheelite and various sulphides are also present. Total impurities amount to 5 to 15 per cent of the skarn. Calcite occurs as rare flat lying or gently dipping marble layers, as interstitial blebs 1 to 3 millimetres in diameter, and as small veins developed near the summit of Mount Riordan.
Scheelite mineralization tends to occur as small crystals less than 1 millimetre in diameter sparsely disseminated or clustered throughout the skarn, and as blebs, coarse crystalline masses and veinlets up to 5 centimetres in width and 3 metres in length near the summit of Mount Riordan. A grab sample of scheelite-rich mineralization taken near the summit contained in excess of 5 per cent tungsten (Fieldwork, 1987). Some scheelite-rich sections also contain coarse axinite.
Pockets, irregular veinlets and blebs of magnetite intergrown with variable amounts of pyrrhotite, pyrite, chalcopyrite and traces of bornite are also present in the skarn. This mineralization is best developed in a series of gossanous zones found along a west trending linear structure in the northern half of the deposit. A grab sample of magnetite-rich mineralization assayed 1.69 grams per tonne gold, 19 grams per tonne silver, 0.74 per cent copper and 0.11 per cent zinc (Fieldwork, 1987).
Indicated reserves at the North zone are 17,955,000 tonnes grading 80 per cent garnet; indicated reserves at the West Zone are 11,848,200 tonnes grading 78 per cent garnet; indicated reserves at the South zone are 10,663,380 tonnes grading 77 per cent garnet (Mineral Development Assessment Process - Crystal Peak Garnet, Stage 1 Report, March 1991).