The Silverado occurrence is located on the northwest slope of Mount Rainey, 3 kilometres southeast of Stewart. Several shipments of high-grade ore were made from this occurrence, discovered in 1920, between 1921 and 1932.
The occurrence is hosted in volcanic breccias, conglomerates, sandstones and crystal tuffs of the Lower Jurassic Unuk River Formation (Hazelton Group). These are intruded, to the west, by Eocene granodiorite of the Hyder pluton (Coast Plutonic Complex) and are unconformably overlain, to the east, by clastic sediments of the Middle Jurassic Salmon River Formation (Hazelton Group).
Four major, subparallel shear zones are developed in northwest striking, gently east dipping andesitic tuff breccias. The tuff breccias are cut by a few northwest striking, steeply west dipping porphyritic granodiorite and lamprophyre dikes. The shear zones, generally striking 130 degrees and dipping between 63 and 76 degrees southwest, vary in width from a few centimetres to 4.6 metres. The zones have been traced vertically for up to 300 metres (Number 3 zone), along surface for between 100 metres (Number 4 zone) and 490 metres (Number 3 zone) and southeastward up to the terminus of the Silverado Glacier. These zones may extend underneath the glacier through Mount Rainey for 2 kilometres southeastward, to the Prosperity and Porter Idaho mine (103P 089). The Numbers 1, 2 and 3 shear zones may correlate with the Blind, Prosperity and D veins, respectively, of the mine.
Mineralization occurs as discontinuous quartz lenses, up to 1.8 metres wide and 60 metres long, hosted within shear zones. The lenses contain massive galena, sphalerite, and pyrite with minor chalcopyrite, tetrahedrite, pyrargyrite, argentite and native silver. The wallrocks are variably silicified and weakly pyritized and epidotized. A 0.381 metre chip sample from the number 1 shear zone assayed 0.69 gram per tonne gold, 2866 grams per tonne silver, 8.9 per cent lead, 6.3 per cent zinc, 0.20 per cent copper and 0.09 per cent cadmium; a second 0.102 metre chip sample across the same shear zone assayed trace gold, 7870.7 grams per tonne silver, 29.8 per cent lead, 12.8 per cent zinc, 0.47 per cent copper and 0.14 per cent cadmium (Minister of Mines Annual Report 1946, page 78).
Various quartz veins occur in this vicinity. These are gently dipping, up to 2 metres wide and mineralized with abundant tetrahedrite and pyrite. The veins have averaged 4285 grams per tonne silver; samples of pure tetrahedrite have assayed up to 34,000 grams per tonne silver (Minister of Mines Annual Report 1927, page 86).
Tungsten is reported to occur in quartz veins to the west on the lower slopes of Mount Rainey. The veins, 1 to 1.8 metres wide, occur in a shear zone up to 1.8 metres wide. A chip sample across 0.189 metre, assayed 0.22 per cent tungstic oxide (WO3) (0.17 per cent tungsten) (Bulletin 10, page 56).
Between 1921 and 1932, 167.8 tonnes of sorted high-grade ore were produced. A 12.7-tonne shipment in 1927 averaged 3400 grams per tonne silver equivalent for silver combined with minor gold and lead values (Minister of Mines Annual Report 1927, page 86).
Work History
In 1920, the Silverado group of claims was staked and prospected intermittently until 1928, when the Premier Gold Mining Company undertook a programme of underground work designed to develop at depth, showings of high-grade silver ore found under the toe of the Silverado Glacier. The result of about 1219 metres of crosscutting, drifting and raising was disappointing, and development ceased in 1930. Subsequently, a drift beneath the surface showings, known as Zero level, was extended by leasers, and from this and surface workings small shipments of hand-sorted silver ore were made. Differential recession of the glacier of 183 to 305 metres from its position in 1923, by revealing continuations of structures in which the high-grade silver ore was found, has renewed interest in the property (ca. 1946). During the summer of 1946, a crew of variable size, averaging about twenty, was employed, mainly in surface construction. Two men were engaged in sampling surface and underground exposures and two others advanced Zero level 16.7 metres. Raises from the lower levels are being re-timbered so that men can reach Zero level. A Pioneer-drive tram line 1341 metres long was erected, connecting this point with the portal of the lowest mine workings, at an elevation of 900 metres. A new bunkhouse for sixteen men was built near the lowest mine workings. Seven days were spent examining the main surface showings and underground workings on the Silverado group, and a reconnaissance was made over the saddle of Mount Rainey.
In 1981, Domody Resources Ltd. prospected the area Contact, Red Reef and Sky claims. During 1984 through 1987, Teuton Resources Corp. completed programs of prospecting, geochemical (rock, soil and stream sediment) sampling and a 24 line-kilometre airborne geophysical survey on the area. In 1985, An undescribed sample (9419) taken several hundred metres east of the plotted location of the Silverado occurrence yielded 1.31 grams per tonne silver and 2177 grams per tonne silver (Assessment Report 14341). In 1987, six select samples (2152, 2154, 2155, 2158, 2161 and 2179) from the same area are reported to have yielded from 0.22 to 0.94 per cent copper, 0.56 to 15.92 per cent lead, 0.18 to 2.16 per cent zinc, 180.1 to 1179.8 grams per tonne silver and 0.25 to 0.72 gram per tonne gold (Assessment Report 15574).
In 1990, Amphora Resources completed an 8.1 line-kilometre airborne magnetic and electromagnetic (VLF) survey on the area. In 1991 and 1994, Teuton Resources Corp. completed a program of prospecting and rock sampling on the area as the Sky and Red Reef claims.
In 2011, Teuton Resources Corp. prospected and sampled the area as the Silver Mountain property. A grab sample (SM-26) from the Silverado occurrence area yielded 409.0 grams per tonne silver, 0.723 gram per tonne gold, 4.00 per cent lead and 2.33 per cent zinc (Assessment Report 32668).
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 and Prosperity-Porter Idaho (103P 089). Both showings are spaced 2 kilometres apart, located on opposite sides of a mountain that overlooks the town of Stewart.
In 2018, Granby Gold Inc. completed an 88.25 line-kilometre airborne magnetic and gamma-ray spectrometry survey on the area.
