The Rio Tinto showing is located at 975 metres elevation above sea level between Poplar and Cascade creeks, in the Slocan Mining Division.

Regionally, the area lies within the Selkirk Mountains of southeastern British Columbia. The occurrence is within the Kootenay Arc, a curving belt of highly deformed metasedimentary and metavolcanic rocks which includes the Upper Proterozoic Horsethief Creek Group, the Upper Proterozoic to Lower Cambrian Hamill Group, the Lower Cambrian Badshot Formation, and the Paleozoic Lardeau and Milford groups. The volcano-sedimentary sequence is intruded by numerous Paleozoic to Mesozoic granitoid plutons.

The Lardeau River area of the Selkirk Mountains is mainly underlain by massive pillow lavas, volcanic breccia and green phyllitic rocks of the Index Formation and by grey-green mica schist of the Broadview Formation. Grey phyllitic rocks and marble of the Milford Group are exposed near the edges of the Mesozoic Mobbs Creek, Rapid Creek and Poplar Creek stocks. All rocks have undergone regional metamorphism to middle or upper greenschist facies. Rocks of the Milford Group have also been affected by thermal metamorphism (Geological Survey of Canada Bulletin 193).

The showing consists of a quartz vein containing ankerite, pyrite, galena and sphalerite. The mineralization has been exposed in three short adits and in an incline shaft. The underground workings follow a 30 to 60 centimetre wide silicified fault gouge filled with talc. A grab sample of the talcose fault gouge assayed 68 grams per tonne silver (Minister of Mines Annual Report 1919).