The Sphinx occurrence is located on the north side of Gray Creek in its eastern headwaters, at an elevation of approximately 2050 metres.
The area is predominantly underlain by a north trending sequence of argillite and quartzite units of the Middle Proterozoic Mount Nelson Formation (Purcell Supergroup). This assemblage abuts the older conglomerate unit of the Upper Proterozoic Toby Formation (Windermere Supergroup) to the west and sedimentary rocks of the Dutch Creek Formation (Purcell Supergroup) to the east.
Locally, a 30-centimetre wide quartz veined shear hosts sphalerite, galena and pyrite. A short distance northwest, a 1-metre wide band of quartzite bound by phyllitic sediments hosts quartz veins with galena, chalcopyrite, pyrite and sphalerite. The zones both strike 8 degrees north and dip to the west.
In 2004, a sample (S-14) from the quartz shear assayed 112 grams per tonne silver and 1.23 per cent lead, while a samples (S-17 and S-16) from the quartzite band assayed up to 14.8 grams per tonne silver, 1.28 per cent copper and 0.25 per cent lead (Assessment Report 27819).
Another area of mineralization, located approximately 700 metres to the north-northwest at an elevation of 2280 metres, consists of narrow quartz veins with limonite in a weakly calcitic quartzite. In 2004, a sample (S-20) assayed 15.8 grams per tonne silver and 0.037 per cent antimony (Assessment Report 27819).
During 2002 through 2009, Eagle Plains Resources completed programs of rock, silt and soil sampling, and 135.0 line-kilometres of airborne geophysical surveys on the area as the Sphinx property.