The area is underlain by northeast striking, moderately northwest dipping felsic to intermediate metavolcanics and minor interlayered metasediments of the Lower Cambrian and older(?) to Mississippian Eagle Bay Formation. The rocks hosting the Rexspar uranium deposits consist of a deformed and metamorphosed pile of alkali feldspar porphyry, porphyry breccia, lithic tuff and breccia of trachytic composition, with occasional pyritic schist of rhyolitic composition. Rocks of this "trachyte" unit are light grey in colour and stained rusty brown or yellow due to widespread pyrite. They may be massive, brecciated, or markedly schistose and lineated. Fractured and sheared crystals of potassium feldspar and albitic plagioclase, and rock chips of trachytic composition occur in a fine-grained groundmass of feldspar and sericite. The trachyte unit, which is 15 to 120 metres thick, is apparently a mixture of intrusive porphyry and its extrusive equivalent tuffs and tuff breccias. It is likely related to a volcanic centre or vent active during the Middle Devonian. The above unit is structurally underlain by quartz-sericite schist, chlorite schist and dacitic and andesitic volcanic breccia, with interlayers of grey phyllite, slate, chert and sericitic quartzite.

The prominent schistosity, which is parallel to the compositional layering and was probably produced during the first phase deformation, is deformed by tight, recumbent, east trending second-phase folds. These structures are refolded by upright third-phase, northerly to northeasterly trending structures. Subsequent late kinks and prominent north trending tension fractures are commonly followed by post-tectonic felsic and mafic dykes of Cretaceous or later age. High-angle, northerly trending faults sharply control the distribution of the trachyte unit.

Uranium and thorium mineralization occur exclusively in the trachyte unit and mainly in the dark-coloured, upper part of the unit, which shows extensive replacement by silver-grey fluorphlogopite and pyrite, with lesser fluorite and calcite. The replacement zones, a few centimetres to several metres in size, generally occur as coarse-grained segregations, which show conformable and crosscutting relationships and deformation similar to the surrounding rocks. The best grade material occurs in a series of discontinuous, conformable tabular masses or lenses, generally less than 20 metres thick and up to 140 metres long.

The principal radioactive minerals include uraninite, uranothorite, torbenite, metatorbenite, thorianite and uranium thorite. They occur as tiny discrete grains within fluorphlogopite flakes, and cause pleochloric haloes, or are scattered in the pyrite-fluorphlogopite matrix. Uranium and thorium also occur in monazite and niobium ilmenorutile. Rare earths, mainly cerium and lanthanium, occur in bastnaesite and monazite. Other minerals include celestite, galena, sphalerite, chalcopyrite, molybdenite, scheelite, siderite, dolomite, barite and quartz.

The geological setting and mineralogy suggest that the mineralized zones were formed by deuteric, volatile rich fluids during a late-stage in the formation of the trachyte unit. The considerable amount of thorium and widespread rare earths associated with the uranium support its origin as primary rather than secondary.

A potassium/argon age of 236 Ma +/- 8 Ma for fluorphlogopite from one of the mineralized zones is considered a minimum age and used cautiously because of some analytical problems. This Middle Triassic age suggests the mineralization is syngenetic with the host rocks, that is in no way related to the nearby Cretaceous Baldy batholith.

Three main tabular zones of radioactivity occur parallel to the surfaces of the alkali feldspar porphyry and have irregular terminations above and below.

The BD or Black Diamond zone is a flat-dipping lens with a strike length of 140 metres, dip-slope length of 90 metres and an average thickness of 15 metres. A 1.8 metre sample across part of the zone assayed 0.09 per cent uranium, 0.14 per cent thorium oxide, 0.025 per cent niobium and trace yttrium and lanthanum (Minister of Mines Annual Report 1954). The zone lies along the upper surface of the porphyry and the radioactivity appears to be mainly associated with uranothorite, associated with rutile.

The A zone, 600 metres east-northeast of the BD zone, is a shallow dipping (12 degrees) irregular lens averaging 15 metres thick which has been traced along strike for about 60 metres. It pinches out at a slope depth of about 60 metres and appears to occur at a lower horizon in the porphyry mass. A 1.8 metre sample across the zone assayed 0.07 per cent uranium, 0.06 per cent thorium oxide, 0.015 per cent niobium and trace yttrium, lanthanum and cerium (Minister of Mines Annual Report 1954). The principal radioactive mineral is uraninite associated with rutile.

The B zone, 360 metres north-northeast of the BD zone, averages 8 metres wide, strikes about 60 metres and has a dip-slope length of about 75 metres.

Ore reserves for the three zones outlined by polygons within the proposed pit limits as defined by a cutoff grade of 0.021 per cent uranium are 1,114,385 tonnes grading 0.066 per cent uranium with an overall stripping ratio of 12:1 (Property File - Kilborn Engineering, 1977). The ore zones also grade 5 to 10 per cent fluorite (Property File - Wright Engineers, 1975).

Smaller zones occurring in relation to the BD zone include the F zone, 450 metres to the west, the H zone, 600 metres to the north- northeast, and the G zone (082M 022), 1420 metres to the northeast.

The Fluorite zone (082M 007) lies about 550 metres northeast of the BD zone and contains no uranium reserves.

In 1926 Smuggler Hill Development Company was formed to explore and develop silver and lead deposits (Smuggler, 082M 023 and Foghorn, 082M 029), which were originally staked in 1918 by A.G. McDonald. The results of this early exploration activity were reported by H.G. Nicol, 1926 and D.B. Starrett, 1930. A manganese occurrence was examined by W. Elliot and N.C. Stines in 1929 (Smuggler Manganese, 082M 158). Further geological examinations of fluorite occurrences were reported on by D.B. Starrett, R.P.D. Graham and M.R. Wilson in the early 1940's (Spar, 082M 007). The ground was relocated in 1942 by Ole Johnson and the B.C. Fluospar Syndicate developed the fluorite deposit in 1943. The property was leased by A.E. Sjoquist and optioned in 1951 by Technical Mine Consultants who conducted an extensive exploration and development program for Rexspar Uranium and Metals Mining Co. Ltd.

The presence of uranium mineralization became known in late 1949. Dr. F.R. Joubin studied and reported on the mineral occurrences during 1950 and 1951. Rexspar Uranium, later reorganized as Consolidated Rexspar Minerals and Chemicals Ltd., acquired the rights to mineral claims incorporating the uranium bearing zones and delineated three uranium deposits in the late 1950's. However, the deposits were not brought into production. Denison Mines Ltd. resampled and undertook an economic feasibility study in 1969. Exploration programs and geological reviews were conducted in 1969-1972, directed mainly at determining fluorite reserves. Additional diamond drilling of the uranium bearing zones was carried out in 1976 and the drill core was used in a metallurgical test program undertaken to establish process flowsheets.

The Fluorite deposit and the three uranium deposits have been outlined by fairly close spaced diamond drilling and by surface sampling. A total of 368 surface and underground holes have been drilled from 1943 to 1976, for a total of approximately 17,280 metres. Of these, 121 holes were on the "A" deposit, 81 on the "B" deposit, 125 on the "BD" deposit and most of the others on the fluorite deposit. Drifts, cross cuts and raises for a total of 664 metres were driven in the "A" and "BD" uranium zones. The property has been prospected several times over the years. Geological mapping, radiometric surveying, soil sampling and metallurgical testing have also been performed. Work conducted by Placer Development Ltd. during October, 1981, included ground magnetometer and VLF - EM surveys.

In 1987, Consolidated Rexspar changed its name to Conrex Corporation and sold the property in 1988 to Gold Ventures Limited. American Bullion Minerals Ltd. attempted to get a permit to do exploration on the main fluorite zone in the early 1990's.

In 2007, International Ranger Resources Inc. held the property as the Foghorn Polymetallic Project, and commissioned a technical report to summarize the geology, mineralization and exploration potential.