The Hewitt mine is situated on the north flank of Mount Twigg south of Silverton Creek, in the Slocan Mining Division. The underground workings include at least fourteen separate levels and straddle the north face of the mountain. The adits are located on the Hewitt and Lorna Doone Crown grants (Lots 4440 and 1401). The portal of the No. 10 or main working level is at 1495 metres elevation above sea level.
Adits were driven on the Lorna Doone claims in 1893 by owners Rathbourne and Culver, and on the Hewitt claim in 1896 by owners Tatlow, Yates and associates of Vancouver. The Lorna Doone was Crown-granted to Frank Culver in 1898 and the Hewitt to Robert Insinger in 1902. Development work to that date totalled about 1524 metres in 4 adit levels and 2 intermediate levels on the west (Hewitt) side of the hill. Lessees M.S. Davys, R. Sutherland and associates worked both claims from about 1903.
A New York syndicate acquired an option in 1907 and Hewitt Mining Company was incorporated in Delaware later that same year to operate the Hewitt and Lorna Doone. A 1524-metre long aerial tram was built from No. 3 adit to connect with the Wakefield mill. Ore shipments in 1908 were under the name Silver Cord Mining Company, Limited, which had been incorporated in March 1908 with head office at Sandon.
Silverton Mines, Limited was organized in about 1909 by M.S. Davys and G. Stillwell to lease and option the property. By 1911 three of the adits had been driven through the hill to the east (Lorna Doone) side. The camp was moved to the east side where No. 7 adit level was begun. An aerial tram was built from this adit to the Wakefield mill, which was leased. The mill, which was based on the water concentration principal, burned in 1912 and a new 150 ton per day flotation mill was installed, however due to metallurgical problems satisfactory operation was not achieved until 1915.
The property was acquired by C. Cunningham of Sandon in 1917 and intermittent mine and mill operations continued into 1920. Lessee M.S. Davys resumed work on the property in 1922. Hewitt Mines, Limited was incorporated in June 1925 with head office in Nelson. The property was acquired in 1925 or 1926 by The Victoria Syndicate, Limited and development work on Nos. 8 and 9 adit levels continued into 1928.
The Galena Farm Consolidated Mines Limited acquired the property in 1929. Plans were made to establish No. 10 level which was to be driven through the mountain for a total length of over 1828 metres. Development work began from both ends (No. 10 east and No. 10 west adits). An aerial tram was installed from No. 10 west portal to the Galena Farm mill, a distance of 2682 metres. Work ceased in January 1930 with some 228.6 metres remaining to make the connection between the two adit faces. Lessees worked intermittently during the period of 1935 to 1942. The Granby Consolidated Mining, Smelting and Power Company, Limited optioned the lease in 1946 and during 1947 drove a raise from No. 10 east adit to No. 9 level, the option was given up later that year.
Van Roi Mines (1947) Ltd. was re-organized in 1950 to consolidate the Hewitt and nearby Van Roi (082FNW064) properties under the name Van Roi Consolidated Mines Ltd.; control of the company was acquired by Transcontinental Resources Limited. A 100-ton per day mill was installed on Slocan Lake 1.6 kilometres south of Silverton in 1951 and stoping was carried out on No. 10 east level; operations ceased in July. The company name was changed in 1955 to Slocan Van Roi Mines Limited. The mine reopened in the latter half of the year and diamond drilling was done below No. 10 level. In 1956 a 198-metre winze was sunk in the hangingwall and a crosscut driven 30 metres south to the vein to establish No. 11 level. The ore shoot developed by this work was leased to J. Heichert and mined out by July 1957. The company name was changed in 1960 to Kopan Developments Limited. Lessees during 1962-64 deepened the internal winze to establish No. 12 level and stoping was carried out. In 1969 the property was leased to Frank Pho for a period of 10 years and the shaft was deepened to establish No. 13 level. Mr. Pho in 1970 assigned the lease to Surfside Explorations Ltd. No. 13 level was extended and stoping over a length of 18 metres was carried up to No. 12 level. Ground failure in stopes and the shaft area necessitated closing of operations in 1970 before all the known reserves were extracted. Indicated reserves were reported at 54,432 tonnes at 514.2 to 685.7 grams per tonne silver, 5.0 per cent lead and 7.0 per cent zinc (B.C. Published Reserves File). The company name (Kopan) was changed in 1972 to Jordesco Resources Limited.
Arjan Pacific Ltd. in April 1973 purchased the property and the 125-ton per day mill from Jordesco. Some rehabilitation work was done in No. 10 west adit.
Dungannon Explorations Ltd. and Sabina Industries Limited purchased the property early in 1977 under a joint venture agreement and subject to the prior lease by Pho. In May 1977 a new lease agreement for 3 years, with the option to renew for a further 5 years, was reached with Mr. Pho. During the year a new inclined shaft beneath No. 10 east level was sunk 27 metres, and 24 metres of drifting carried out.
Regionally, the area lies on the western margin of the Kootenay Arc, in allochthonous rocks of the Quesnel Terrane. In the vicinity of the occurrence, the Quesnel Terrane is dominated by very fine grained clastic sedimentary rocks of the Upper Triassic Slocan Group that include locally weakly metamorphosed argillite, quartzite, limestone and some tuffaceous rocks. These sedimentary rocks are intruded by dikes, sills and stocks of varied composition and origin. Permian and/or Triassic Kaslo Group metamorphosed volcanic rocks occur to the north of the Slocan Group rocks. Middle Jurassic Nelson intrusions are immediately south of the Slocan Group and are inferred to be the source of granitic to pegmatitic sills and dikes found in the area. The Nelson intrusions comprise at least six texturally and compositionally distinct phases ranging from diorite to lamprophyre. The most dominant phase is a medium to coarse grained potassium feldspar porphyritic granite (Paper 1989-5).
The Hewitt mine is hosted by quartzite, calcareous quartzite and argillite of the Slocan Group intruded by an apophysis of hornblende granodiorite to quartz diorite of the Nelson intrusions and thin felsic dikes. The felsic dikes are strongly altered in the vicinity of the mineralized veins and in places difficult to distinguish from the sedimentary rocks. The strata strike 077 degrees, dip 70 degrees northwest and have been affected by contact metamorphism from the emplacement of the nearby intrusion.
Mineralization is hosted within a brecciated shear zone striking east and dipping 70 degrees north. The shear consists of at least four separate fissures that have been explored for about 365 metres vertically. The maximum width of the shear zone, as developed in the upper workings, was 30 metres. The fissures are composed largely of crushed and brecciated wallrock and gouge cemented by quartz. Locally, ore minerals and vein material form an important constituent of the fissures. The main fissure or North vein marks the northern extend of the shear zone. It has been traced west as far as the Galena Farm property (082FNW067) and east as far as the Van Roi property (082FNW064), for a total strike length of about 4 kilometres. The North vein was the most persistent of all veins mined and has provided the bulk of the ore from the mine. Above the No. 4 level the North vein followed the intrusive contact on its footwall. Below the No. 4 level the vein was entirely hosted within the Slocan Group.
Other veins in the mine include the South or Main South, the West and the Main veins. The Main South vein marks the southern extent of the shear zone. It has been mostly worked above the No. 3 level and for a strike length of 75 metres. The vein strikes northeast, dips northwest and lies mostly along the intrusive contact. The West vein occurs between the Main South and Main veins. It is about 15 to 30 metres in length and strikes 010 degrees. The Main vein has been developed for about 135 metres on the second and third levels. The vein merges with the North vein to the east and west on the third level. Both the West and Main veins lie partly in the intrusion and partly in the sedimentary rocks.
Most of the ore came from two main ore shoots lying directly beneath the summit of the divide. The stopes on the North and Main veins have an aggregate length of 210 metres on the second level and average about 3 metres in width. Where the North and Main veins intersect the third level, the ore was 4.8 metres wide. The North vein extended to the No. 7 level about 135 metres vertically below and contained the highest zinc ore, assaying up to 20 per cent zinc (Geological Survey of Canada Memoir 184). The ore shoot plunged about 70 degrees to the west.
The second ore shoot is in the eastern section of the mine. This ore zone was mined, between levels 6 and 10, for a vertical distance of 350 metres and 60 metres along strike. The ore had a maximum width of 7.5 metres. This ore zone also had a westerly plunge of about 70 degrees. The lateral boundaries of the ore zones were determined by fault planes or narrow zones of bedding plane shears. Most of the movement along these faults is pre-mineral but slight left-lateral displacement of the veins was observed in a number of places. The richest parts of the ore shoots were mainly above the No. 3 level of the mine.
The vein filling consists of brecciated rock cemented by dense white quartz or a grey, sugary friable quartz with numerous vugs with fine clusters of crystals. A banded, ribbon, or agate structure also occurs and alternates with bands and streaks of galena and sphalerite. The ore minerals fill cavities, occur in specks, streaks and patches and form crusts on fragments of wallrock. In part, quartz is later than the sulphides. Siderite is subordinate to quartz and calcite is in very small amounts. Ore minerals consists of galena, sphalerite and tetrahedrite. Pyrite and pyrrhotite are abundant within the ore. Pyrargyrite and native silver occur in the high grade portions of the ore shoots and minor stibnite and a mineral resembling boulangerite have been observed in ore samples.
Production from the Hewitt between 1900 and 1983 yielded about 59 tonnes of silver, 2708 tonnes of zinc, 1770 tonnes of lead, 2 tonnes of cadmium and 3 kilograms of gold from 112,573 tonnes mined.
Klondike Gold Corp. acquired the Van Roi and Hewitt mines in December 1999. In 2009, Klondike Silver Corp. completed a program of prospecting, geological mapping, ground geophysical surveys, trenching and four diamond drill holes, totalling 480 metres on the area.