The Hidden Treasure occurrence is located on Grouse Mountain, north of North Lake.
Regionally, the area is underlain by a sequence of north west striking andesite flows and pyroclastics, with lesser rhyolite and basalts of the Lower Jurassic Telkwa Formation (Hazelton Group) and a north north-west trending sedimentary sequence comprised of marine black shale, argillite, siltstone and greywacke with intercalated tuffs and breccia of the Upper Jurassic Ashman Formation (Bowser Lake Group). The volcanic and sedimentary rocks are intruded by dikes and small stocks which strike north-northwest and dip west-southwest. These include feldspar porphyry, biotite feldspar porphyry, monzodioritic to gabbroic intrusives and aphanitic basic dikes of the Late Cretaceous Bulkley Plutonic Suite and Eocene Goosly Plutonic Suite. Alteration has affected mainly the feldspar and ferromagnesium minerals producing mica and clay minerals, chlorite, limonite, carbonates, and less commonly epidote.
The showing occurs in Lower Jurassic Hazelton Group rocks of the Telkwa Formation comprised of massive maroon to grey breccia and tuff deposits interbedded with green andesite to rhyolite flows. Tuff includes fine-grained crystal tuff, lapilli tuff, coarse-grained breccia and feldspathic epiclastics. The volcanics are intruded dikes and small stocks of monzonite porphyry. The dikes range between 10 to 60 metres in width and strike north northwest and dip moderately west southwest.
Mineralization consists of pyrite, chalcopyrite, sphalerite, and galena infilling a steeply dipping shear zone varying from 0.6 to 1.8 metres in width. The zone strikes 030 degrees, cutting a sequence of moderately folded argillite and tuffaceous rocks. Sulphides infill the shear, which diverges and is parallel to the bedding at the base of a thick pyroclastic deposit. Alteration minerals are mainly chlorite with clay products.
The best mineralization occurs in a schist crosscutting a westerly dipping felsite dike. In 1928, two sulphide rich samples assayed 171.4 grams per tonne silver, trace gold, 1.5 per cent copper, 24 per cent lead, 11 per cent zinc, and 54.9 grams per tonne silver, trace gold and 4.3 per cent copper, respectively (Minister of Mines Annual Report 1928, page 169).
Work History
The area has been explored in conjunction with the nearby Copper Crown (MINFILE 093L 026) occurrence and full regional geology and exploration history can be found there.
In 1928, a 13-metre long tunnel was driven below the surface exposure but failed to encounter significant mineralization. The following year, the adit was advance 15.8 metres along a 0.76-metre wide mineralized zone.
