The Prosperity and Porter Idaho mines are located on the south slope of Mount Rainey, 5.5 kilometres southeast of Stewart. These two mines were in operation between 1922 and 1950. The deposit is hosted in andesitic to felsic volcanics of the Lower Jurassic Betty Creek Formation (Hazelton Group), which are intruded to the west and north by Eocene granodiorite of the Hyder pluton (Coast Plutonic Complex). These are overlain to the east by clastic sediments of the Middle-Upper Jurassic Salmon River Formation (Hazelton Group).

Mineralization is contained within dacitic crystal to welded tuffs with minor andesitic lapilli tuff and dacitic waterlain tuff within a thick sequence of epiclastic conglomerate, andesitic and dacitic ash tuff, lapilli tuff, crystal tuff, welded tuff and tuff breccia.

The Prosperity and Porter Idaho deposit comprises six major subparallel shear zones, spaced roughly 150 to 175 metres apart, striking 160 to 180 degrees and dipping 45 to 65 degrees west. These occur in volcanics that strike 020 to 040 degrees, and dip steeply west. The shear zones have been traced on surface for between 200 metres (Prosperity West vein) and 1000 metres (D vein) and downdip for a vertical distance of up to 425 metres (D vein). Widths vary from between 2 and 13 metres. The shear zones terminate to the south against the Big Rig fault which strikes approximately 084 degrees and dips 50 degrees north. In the vicinity of the fault, the shears are dragged westward with reduced dips of 40 degrees. The shear zones show some minor lateral displacement by other west striking faults and are cut by several lamprophyre dikes.

The shear zones contain discontinuous, well mineralized lenses and shoots up to 13 metres wide, 250 metres long and at least 200 metres downdip. High-grade mineralization occurs as individual sinuous massive sulphide veins usually between 0.2 and 0.6 metre wide and sometimes coalescing into veins up to 2 metres wide. The veins typically follow the footwall and hangingwall of the shear zones within sheared, altered and mineralized wallrock. Mineralization consists of galena, sphalerite, pyrite, tetrahedrite and minor chalcopyrite, pyrrhotite, argentite, pyrargyrite, polybasite, native silver, arsenopyrite and trace electrum. Adjacent to the veins, disseminations, blebs and veinlets of quartz, ankeritic carbonate, manganese oxide and similar sulphides occur in variably silicified country rock for up to 5 to 6 metres outward from the veins.

In 1989, underground geological reserves were 826,400 tonnes grading 668.5 grams per tonne silver, 5 per cent lead and 5 per cent zinc (D. Alldrick, Ph.D. Thesis, University of British Columbia, 1991).

Between 1922 and 1950, 27,268 tonnes of ore were periodically mined from the underground workings of the Prosperity and Porter Idaho mines. The production came from the D, Prosperity and Blind veins, and averaged 0.986 gram per tonne gold, 2692.1 grams per tonne silver, 5.08 per cent lead, 3.853 per cent zinc and 0.101 per cent copper. Sorted ore was shipped via an aerial tramway to tidewater and barged from there to the smelter at Tacoma, Washington. The mine workings cover a vertical interval from 1287 to 1707 metres. Most of the underground workings are located on Lot 4730 (Nettie L.), Lot 1858 (Prosperity), Lot 1857 (Tea Pot Dome), Lot 1866 (Gargoyle Fraction), Lot 4731 (Sunday), Lot 4729 (Lucille) and Lot 4737 (Prickly Heat Fraction).

Apart from sporadic examinations between 1947 and 1970, little definitive work had been performed since mine closure. In 1975, Seaforth Mines Ltd. drilled three holes to test the vertical extension of one ore shoot with mixed results. In 1980-81, Pacific Cassiar Limited commenced a program of rehabilitation to permit evaluation of the vein systems in light of re-interpretation of old data, and enhanced silver prices. During 1982, Pacific Cassiar Limited carried out a program of reconnaissance and detailed geological mapping including limited trenching, and rock and soil sampling.

In 2008, Raimont Energy Inc. reported an indicated mineral resource of 394,700 tonnes grading 868 grams per tonne silver, 3.37 per cent lead and 1.41 per cent zinc with an inferred mineral resource of 88,900 tonnes grading 595 grams per tonne silver for the D and Prosperity veins (Carter, N.C. (2008-03-10): Technical Report on the Prosperity - Porter Idaho - Silverado Silver Property).

In 2016, Skeena Resources announced plans to acquire private company Mount Rainey Silver for its Porter Idaho silver property. The 5.9 square kilometre property hosts two shear hosted and silver-rich vein systems named the Silverado (103P 088) and Prosperity-Porter Idaho. Both showings are spaced 2 kilometres apart, located on opposite sides of a mountain that overlooks the town of Stewart.