The Lake 21 occurrence is located approximately 8.5 kilometres west-northwest of the Kemess South occurrence (094E 094), 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. T
The Lake 21 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. The area hosts fault and/or skarn-controlled copper, lead, zinc and silver occurrences throughout.
The Lake 21 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 composed 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.
The Lake 21 showing consists of chalcopyrite, pyrite and galena within a vein hosted in skarn near a marble-andesite contact. The steeply dipping vein strikes northwesterly and can be traced for 15 metres. VLF electromagnetic results confirm a small conductor covering the area of the Lake 21 showing.
In 1984, sampling over a 1.5-metre width yielded 6.8 per cent copper, 88.2 grams per tonne silver with minor lead and zinc (Assessment Report 18241). In 1988, one of two 1-metre chip samples taken from the vein assayed 4.86 per cent copper, 89.9 grams per tonne silver, 1.04 per cent zinc with minor lead and gold (Assessment Report 18241).
Extensive exploration, including diamond drilling, was conducted on the ground around the Lake 21 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. 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. This work is summarized in the British Columbia government assessment report files, and targeted skarn mineralization in the area. 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.
Prospecting of the known showings revealed both the Cairn and Lake 21 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.
See Lake 22 (094E 108) for details of the Duncan Ridge area and work done in 1997 and 1998.
