The Cairn occurrence is located approximately 5.2 kilometres due west of the Kemess North deposit (094E 021), about 280 kilometres north of the community of Smithers. The occurrence lies within the Omineca-Cassiar mountains at the southern end of the Toodoggone Gold Camp.
The prospect 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 property is underlain by several bodies of recrystallized limestone belonging to the Asitka Group. Lesser 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 porphyritic monzonite, quartz monzonite, and granodiorite of the Early Jurassic Kemess pluton crop out surrounding the limestone lenses.
Extensive mineralization occurs in a fracture controlled replacement zone approximately 6.1 metres wide near the contact between Asitka Group limestone and the Kemess pluton. The zone consists of two main fractures in limestone, which intersect each other at 035 degrees. While the fractures host mineralization, the intersection of these fractures hosts the most intense mineralization with up to 6.1 metres of sulphides. Chalcopyrite with lesser galena and sphalerite comprise mineralization in a gangue of specularite, rhodochrosite, and altered limestone and quartz. Preliminary prospecting indicates ore over 121.9 metres and possibly up to 213.4 metres strike length.
The best material, from chip samples, assayed 125.14 grams per tonne silver and 7 per cent copper over a width of 6.86 metres. Low-grade material assayed 33.9 grams per tonne silver and 2.13 per cent copper (Energy, Mines and Resources Canada Corporation File - Annual Report and Statements (1931), The Consolidated Mining and Smelting Company of Canada). A picked (select high grade) sample assayed 1.37 grams per tonne gold, 2070.9 grams per tonne silver, 19.7 per cent copper, and 12.1 per cent lead (Energy, Mines and Resources Canada Corporation File - Annual Report and Statements (1932), The Consolidated Mining and Smelting Company of Canada).
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 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.
