The True Fissure deposit is on the east slope of Great Northern Mountain. It is at 1750 metres elevation at the head of Fissure Creek, a minor tributary that flows to the east into Ferguson Creek. The True Fissure (L.1097) tenure is one of several crown-granted mineral claims that straddles the border between NTS Mapsheets 82K/11 and 82K/12. The tenure cluster includes the True Fissure [082KNW030], Blue Bell [082KNW060], Great Northern [082KNW061] and St. Elmo [82KNW062]. The Broadview [082KNW031] property is to the southeast, across Broadview Creek.
The first showing in the area was found on the Great Northern claim in 1890. Other discoveries soon followed, and the entire vein system appears to have been located before the turn of the century. The True Fissure, St. Elmo and Blue Bell crown-grants and four adjacent claims were bonded by G.F. Park and Associates of Cincinnati, Ohio, who incorporated the Ohio Mines Development Company, Limited in October 1906. The claims were later transferred to the True Fissure Mining and Milling Company, Limited which was incorporated by Park and Associates in September 1907. In 1925, the True Fissure operation was described as having 610 metres of drifts and 550 metres of crosscuts. The workings were distributed between four adits, covering a vertical range of 150 metres on the True Fissure claim and two tunnels, with 36 metres of separation, on the adjacent Blue Bell claim (EMPR PF: Starr Report, 1925).
Intermittent exploration and development work was carried out by the owners or lessees until around 1930 when Latonia Milling Company was formed by the Park interests to install a 91 tonnes per day mill at the level of the True Fissure C (No. 3) adit. The mill was completed under the terms of the G.F. Park's will; although at that time there was no ore ready to mine. True Fissure Mines Limited optioned 22 claims in 1936 but no work was reported. The following year, New True Fissure Mining & Milling Company, Limited was formed to develop the True Fissure property and the Great Northern [082KNW061], which was optioned later in the year. The mill operated during the winter of 1937-38 and produced and shipped 5510 tonnes of lead concentrate. It produced a smaller amount of zinc concentrate at the same time, but not all of it was shipped. Further development work was carried out in 1939, but the company ceased operations in 1940.
Codan Lead & Zinc Company Limited shipped ore from the dumps in 1943 and 1944, and the following year, Comara Mining & Milling Company Limited acquired 43 claims on Great Northern Mountain and completed 670 metres of surface diamond drilling on the True Fissure and St. Elmo claims. Four years later, in 1949, the company's holdings were transferred to Columbia Metals Corporation Limited, and Granby Consolidated Mining, Smelting and Power Company, Limited was engaged to carry out exploration work in 1952. It diamond drilled some 914 metres on the True Fissure No. 2 and 3 levels. By that time, the True Fissure mine included four adit levels and two raises connecting the Nos. 2 and 3 levels. The Blue Bell workings consisted of two adits and a connecting raise. The St. Elmo workings comprised two unconnected adits and a winze from the upper adit, and the Great Northern workings included six adits. No further development was undertaken until 1966, when an induced polarization survey revealed an anomaly which more or less coincides with the projection of the main True Fissure vein toward the Broadview. A program of drifting and diamond drilling was begun in the True Fissure No. 2 adit. This program was resumed late in 1967 and continued through 1968. A 115 tonnes per day mill was installed at the portal of the Morgan (True Fissure No. 4) adit and overburden was stripped from a portion of the True Fissure vein in preparation for open pitting. The mill only operated for a few days between June and September, 1971. It closed down due to poor mill installation and ecological problems related to tailings disposal. The plant was later destroyed by snowfall. Exploration work in 1972 included electromagnetic and self potential surveys covering the St. Elmo, Blue Bell, True Fissure and Great Northern claims, and 1102 metres of diamond drilling in 54 holes. It is not clear where the drilling was focused; however, Hudson's Bay Oil and Gas Limited came up with a resource figure for the True Fissue deposit. The property was held by Sibola Mines Limited in the mid-1980's.
The Trout Lake area is underlain by a thick succession of sedimentary and volcanic rocks of the Badshot Formation and Lardeau Group near the northern end of the Kootenay arc, an arcuate, north to northwest trending belt of Paleozoic and Mesozoic strata that is now classified as a distinct, pericratonic, terrane. The arc rocks are bordered by Precambrian quartzite in the east and they young to the west, where they are bounded by Jurassic-age intrusive complexes. They were deformed during the Antler orogeny in Devonian-Mississippian time and were refolded and faulted during the Columbian orogeny, in the Middle Jurassic. A large panel, the "Selkirk allochthon", was later offset to the northeast by dip-slip motion along the Columbia River Fault.
The Badshot Formation is composed of a thick Cambrian limestone that is a distinctive marker horizon in the Trout Lake area. It is underlain by Hamill Group quartzite and it is overlain by a younger assemblage of limestone, calcareous, graphitic and siliceous argillite and siltstone, sandstone, quartzite and conglomerate, and also mafic volcanic flows, tuffs and breccias, all of which belong to the Lardeau Group. The rocks are isoclinally folded and intensely deformed, but only weakly metamorphosed. They occur as intercalated beds of marble, quartzite and grey, green and black phyllite and schist. Fyles and Eastwood (EMPR BULL 45) subdivided the group into six formations (Index, Triune, Ajax, Sharon Creek, Jowett and Broadview) of which the lowermost (Index) and uppermost (Broadview) are the most widespread. The Triune (siliceous argillite), Ajax (quartzite) and Sharon Creek (siliceous argillite) are restricted to the Trout Lake area. The Jowett is a mafic volcanic unit.
The True fissure and related deposits are in grits and phyllites of the middle division of the Broadview Formation in the core of a major anticline that is believed to be a large drag feature on the southwest limb of the main Silver Cup Anticline. The mine area is on the southwest side of the Cup Creek Fault, near the axis of the drag fold anticline, which strikes and plunges to the northwest. The area has been subdivided into four structural blocks by later faults. It is cut by the Great Northern Fault, a sinuous, north striking and relatively shallow east dipping reverse fault that separates the mine geology into eastern and western blocks. Both sides of the fault are disrupted by movement on the Broadview Fault, a younger, northeast trending structure. Most of the mineralization is in graphitic schist in the footwall of the Great Northern Fault. The geology of the mine area is described by Fyles and Eastwood (EMPR BULL45). The Great Northern Fault is a gouge and breccia zone of variable width that has been more or less injected with quartz and carbonate and a lens-shaped vein of quartz and carbonate follows the footwall of the fault for 365 metres from Fissure Creek to the True Fissure No. 1 adit, and may continue south to the Great Northern mine workings. The hanging wall of the vein is sharp but the footwall is locally diffuse. The vein is defined as rock that contains in excess of 50 percent quartz and carbonate. In some places the vein splits into several strands that are separated by quartz vein stringers in crushed country rock. The vein consists of massive, crushed, quartz and coarse-grained, buff coloured, ankerite and siderite. In the True Fissure mine, the "vein" may average approximately 10 metres in width but the siliceous upper portion may be only half that. Vugs lined with quartz crystals occur but are not common. The sulphide minerals are pyrite, sphalerite, galena, chalcopyrite, argentiferous tetrahedrite and possibly bournonite. They appear to have been introduced after the gangue.
In the True Fissure - Blue Bell mine area, there is a broad mineralized zone in the hanging wall part of the vein. It has a maximum (but unproven) length, from the True Fissure No. 1 adit to Blue Bell No. 1 drift, of about 400 metres. This vein has been exposed at different levels in several workings in both mines. It is erratically mineralized and individual ore shoots vary in length, width and grade. The True Fissure part of the vein is similar to that at Blue Bell but contains less, and finer-grained, quartz and more feldspar and siderite. Fyles and Eastwood (EMPR BULL 45) show that the depth down dip ranges from nothing west of True Fissure No. 3 portal to 110 metres near the south end of True Fissure No. 2 level, and 137 metres at the Blue Bell raise.
On the True Fissure No. 3 level, the mineralized zone is split into two lenses, one on the hanging wall surface of the vein and the other within the vein, 1.52 to 3.65 metres down from the hanging wall. The upper lens is narrow (up to 0.1 metre wide) and consists of sparse sphalerite and galena. It pinches out to the north and becomes pyritic and thins to the south. The lower zone has been traced for 64 metres. It pinches and swells from a few centimetres up to 1.8 metres in width and consists of pockets, lenses, disseminations and veinlets of sulphide in a quartz-carbonate gangue. The lens may be associated with a tight, smooth-walled fissure that cuts the vein parallel to the main fault. On the True Fissure No. 2 level, there is a single zone between 1.82 and 4.27 metres wide between handing wall gouge and a tight fissure. Galena, sphalerite and pyrite occur as lenses, pockets, veinlets and disseminations in the vein. A sample across 1.37 metres of "better-looking" ore assayed 4.1 grams per tonne gold, 312 grams per tonne silver, 0.59 per cent copper, 4.75 per cent lead, 6.3 per cent zinc and 0.05 per cent tin. In 1925, Starr (EMPR PF: Starr Report, 1925) described and sampled higher-grade sections of the True Fissure vein in a number of crosscuts in the "B" and "C" adits. At the face of the tunnel in the former, he obtained an assay of 230 grams per tonne silver, 4.8 per cent lead and 11.2 per cent zinc over 1.3 metres and in a crosscut in the latter, he obtained four samples, representing a width of 4.3 metres, that assayed 175 grams per tonne silver, 4.1 per cent lead and 8.9 per cent zinc. Similar but more erratic values were obtained when Goldfever Resources Limited sampled the dumps in the late 1980s. At that time, the company was particularly interested in the gold values which ranged from 0.6 to 87.8 grams per tonne gold (Stockwatch June 16, 1987).
In 1925, Starr was unable to establish a resource. However, several have been made since then. In 1942, Sargent (EMPR PF: Sargent Report, 1942) estimated a resource of 63,500 tonnes of averaging 1.47 grams per tonne gold, 236.57 grams per tonne silver, 6.0 per cent lead and 6.7 per cent zinc, with a little copper and cadmium in a shallow, (40 to 45 degree east) dipping block 91 metres long, 2.25 metres wide and 79 metres in down dip extent. More recently, in 1971, Columbia Metals described the "probable" resource as 19,700 tonnes grading 332 grams per tonne silver, 6.76 per cent lead and 6.41 per cent zinc, and the "possible" resource as 52,225 tonnes grading 355 grams per tonne silver, 7.39 per cent lead and 7.07 per cent zinc (Stockwatch December 15, 1987). The following year, Hudson's Bay Oil and Gas reported a "proven" reserve of 33,560 tonnes of 308.6 grams per tonne silver, 6.3 per cent lead and 7.4 per cent zinc and a "probable" reserve of 51,700 tonnes of 325.7 grams per tonne silver, 6.0 per cent lead and 7.6 per cent zinc (Northern Miner June 21, 1973).
The mine shipped 341,774 tonnes of lead concentrate (from an undefined tonnage) between October 1937 and March, 1938. It returned an average grade of 13.43 grams per tonne gold, 1,766 grams per tonne silver, 44.8 per cent lead, 14.02 per cent zinc and 2.78 per cent copper (EMPR PF: Sargent Report, 1942). Production from 1908 to 1944 is reported to have totalled 4605 tonnes, yielding 1311 kilograms of silver, 6 kilograms of gold, 241,773 kilograms of lead and 129,986 kilograms of zinc.