The Rio occurrence is in the eastern head waters of the Rambler Creek basin, a tributary of McGuigan Creek, at an elevation of approximately 2200 metres. This is approximately 900 metres northeast of the former Antoine mine (MINFILE 082KSW011) and 11 kilometres north east of New Denver, BC.
The area is underlain by siliceous slaty argillites, quartzites and limestone of the Triassic Slocan Group that are crosscut by quartz porphyry dikes. The general strike of these lithologies is southeast and dips are 35 to 60 degrees southwest. These sediments are intruded by irregular quartz to feldspar porphyry bodies and lamprophyre dikes. Lamprophyre dikes are cut by the vein and both are displaced by faults.
Workings of the former Rio mine explored a vein-lode system, averaging 0.9 metres in width and striking 065 degrees with a dip of 45 degrees to the south east. In the upper adit a dry ore shoot was intersected near the portal. Farther in, a shoot of galena was discovered. The shoot was 6 metres long by 15 centimetres thick. A long drift from the lower adit also intersected two ore shoots corresponding roughly to those discovered in the upper adit but carrying more galena overall. The first of these two shoots was 15 metres long. This was roughly 152 metres from the lower portal. The principal ore minerals are galena, tetrahedrite, freibergite and minor sphalerite.
In 1968, reported ore reserves were 1858 tonnes of ‘proven’ ore averaging 287 grams per tonne silver above the 2198 metre level; 8674.5 tonnes of ‘proven’ ore averaging 479 grams per tonne silver between the 2198- and 2160- metre levels and a total of 17,848 tonnes of ore from all classes averaging 376 grams per tonne silver (Property File - Rio Resources Ltd. [1969-02-22]: Geological Report on the Rio Property).
The Rio Crown- granted claim was opened in 1902. Production records indicate the initial shipment ore occurred in 1903 and intermittent production and shipments followed through 1937. In total, 170 tonnes were produced from which 1,364,273 grams silver, 62 grams gold, 52,952 kilograms lead and 10,224 kilograms zinc were recovered.
Workings at the former Rio mine included a 63-metre upper adit, a 52.5-metre connecting raise or shaft, a 225-metre lower crosscut adit and a 123- metre drift. The lower crosscut adit was 54 vertical metres below the upper adit. The ore shoot was reportedly mined for a length of 12 to 15 metres above the lower level with an estimated 3855.5 tonnes being removed.
In the late 1960’s, Rio Resources Limited examined the underground workings.
