The Lake 22 occurrence is located approximately 8.5 kilometres west-northwest of the Kemess South occurrence (094E 094), about 260 kilometres north of the community of Smithers. The showing lies within the Omineca-Cassiar mountains at the southern end of the Toodoggone Gold Camp.
The Lake 22 showing is situated within a Mesozoic volcanic arc assemblage which lies along the eastern margin of the Intermontane Belt, a northwest-trending belt of Paleozoic to Tertiary sediments, volcanics and intrusions bounded to the east by the Omineca Belt and to the west and southwest by the Sustut and Bowser basins.
Permian Asitka Group crystalline limestones are the oldest rocks exposed in the region. They are commonly in thrust contact with Upper Triassic Stuhini Group andesite flows and pyroclastic rocks. Stuhini volcanics have been intruded by the granodiorite to quartz monzonite Black Lake Suite of Early Jurassic age and are in turn unconformably overlain by or faulted against Lower Jurassic calcalkaline volcanics of the Toodoggone Formation (Hazelton Group).
The dominant structures in the area are steeply dipping faults which define a prominent regional northwest structural fabric trending 140 to 170 degrees. In turn, high angle northeast-striking faults (approximately 060 degrees) appear to truncate and displace northwest-striking faults. Collectively these faults form a boundary for variably rotated and tilted blocks underlain by monoclinal strata.
The Thutade Lake area is largely underlain by andesite volcanics and related sediments of the Stuhini Group and small pockets of Asitka Group sediments. The major structures in the area are north-northwest striking faults, such as the Moose Valley fault and the Ingenika fault. Extensive exploration, including diamond drilling, was conducted on the ground around the Lake 22 showing from 1970 to 1984. Some nine mineral showings were found. The area hosts fault and/or skarn controlled copper, lead, zinc and silver occurrences throughout.
The Lake 22 showing is underlain by fine grained to coarse plagioclase and augite porphyritic, grey to greenish grey to maroon andesite, argillite, chert, quartzite, breccia and conglomerate of the Stuhini Group and the Early Jurassic Kemess pluton, a large intrusive body of porphyritic monzonite, quartz monzonite and granodiorite. Several bodies of marble have been mapped along the northeast corner of Thutade Lake belonging to the Asitka Group.
Skarn and quartz vein mineralization were discovered at the Lake 22 showing, 780 metres north of the Cairn showing (094E 012). A sample of skarn mineralized subcrop assayed 2.78 per cent zinc, 0.73 per cent lead, 0.064 per cent copper and 92.1 grams per tonne silver (Assessment Report 13022). In 1984, a sample of mineralized quartz vein assayed 2.34 per cent copper, 0.91 per cent zinc, 0.124 per cent lead and 73.9 grams per tonne silver (Assessment Reports 13022, 18241).
In 1998, Royal Oak Mines Inc., while prospecting for the Lake 22 showing, located 300 metres of skarn mineralization they called Duncan Ridge. In this area, float of both limestone and monzonite consisted of pervasive actinolite, epidote, quartz and with some garnets, variable sphalerite, pyrite, chalcopyrite, bornite, malachite and azurite. Select grab sampling of subcrop yielded up to 55.0 grams per tonne silver, 6.28 per cent zinc, 0.19 per cent copper, 0.80 per cent lead, and 0.06 per cent cadmium (Assessment Report 25812). The location coincides with two small resistivity low anomalies from a 1997 airborne survey; the western portion of the showing was thought to coincide with the Lake 22 showing. An airborne resistivity low anomaly occurs 200 metres directly south of the Duncan Ridge showing, and may represent a geophysical response to a conductive body downdip of the subcrop showing.
Extensive exploration, including diamond drilling, was conducted on the ground around the Lake 22 showing from 1970 to 1984. Some nine mineral showings were found. Modern exploration at Duncan Ridge began in 1983-85 with Pacific Ridge Resources Corp. completing geology, geochemistry, trenching and diamond drilling. Hermes Ventures Ltd. subsequently completed geology, geochemistry, geophysics, trenching and diamond drilling in 1987-88. The work yielded ore grade skarn mineralization in trenching and drilling, but was terminated.
In 1998, preliminary exploration work at Duncan Ridge was undertaken on behalf of Royal Oak Mines Inc. Prospecting was done over the sites of magnetic, radiometric and resistivity anomalies from the 1997 airborne geophysical survey, and known mineral showings: Cairn (094E 012), Lake 21 (094E 067) and Lake 22 (094E 108). The airborne survey was conducted over 327 line kilometres. In 1998, 365 soil and 43 rock samples were collected.
The 1997 and 1998 work showed the presence of massive, potassic altered and magnetic Duncan Lake monzonite which explained radiometric and magnetic highs at the northern end of the ridge. No field evidence was seen for the three resistivity lows in the centre portion of the ridge which were apparently covered by massive Asitka Group limestone. Prospecting of the known showings revealed both the Cairn and Lake 21 showings to be structurally controlled, narrow, vertical, quartz-calcite-sulphide veins hosted in Asitka Group limestone, interpreted to represent skarn veins. Both showings were exposed in old trenched outcrops located in steep ravines along the western side of Duncan Ridge, and contained significant sphalerite, chalcopyrite, galena and malachite. The Lake 22 showing could not be located at the time, but a small area of skarn mineralized subcrop was found just east of where Lake 22 was expected to be, and which is informally called the Duncan Ridge showing. The large, angular subcrop boulders contain zinc-lead skarn or polymetallic replacement- (Manto-) type mineralization consisting primarily of actinolite, with chlorite and epidote, and containing significant sulphide mineralization consisting of sphalerite, chalcopyrite and galena. Immediately south of the subgroup showing, an outcrop of Asitka limestone was found with bedding striking 050 degrees and dipping 10 degrees southeast, suggesting the source of the nearby skarn mineral subgroup is also flat dipping.
Two showings, Duncan Ridge (094E 108) and Metcalf (094E 313), are interpreted to be either zinc-lead skarns or polymetallic replacement- (Manto-) type mineralization in flat-lying limestone, and are located 2.5 kilometres apart.
In 1998, soil sampling in the Duncan Ridge area successfully established areas elevated in gold, copper, lead and/or zinc spatially associated with known showings and/or low resistivity airborne geophysical anomalies. The presence of elevated levels of gold, copper and other metals in soils combined with conductive geophysical anomalies and highly favourable geology suggest that economically significant porphyry copper skarn-related or copper skarn types of mineralization may be present at Duncan Ridge.
Refer to Kemess South (094E 094) for related details of the Lake 22 deposit of which the Lake 22 showing is part of.
