The Cos occurrence is located on the north bank of the Scud River approximately 11 kilometres east of the confluence with the Stikine River.
The Cos showing is marked by a large and easily visible gossan which occurs at the faulted contact between Lower Jurassic quartz monzonite and Permian or older Stikine Assemblage sedimentary rocks. The quartz monzonite is medium-grained, potassium feldspar megacrystic and has 15 to 20 per cent mafic minerals with hornblende greater than biotite. The intrusion forms a roughly circular plug 10 kilometres in diameter that has been dated at 204 +/- 7 Ma (Fieldwork 1988). The quartz monzonite becomes highly altered (rusty, chloritic) around the fault zone. The sediments are also altered (rusty, silicified) around the fault zone and comprise light to medium grey, variably foliated sandstone and siltstone. Thin discontinuous horizons of highly recrystallized limestone occur within the metasediments. A well dated (Fieldwork 1988). Late-Early Permian sequence of limestone over 1000 metres thick overlies the foliated sedimentary rocks and lies further to the east. Only a few kilometres to the north, Middle Jurassic granodiorite intrudes both the quartz monzonite plug and the Paleozoic sediments.
Mineralization is poorly documented and comprises narrow quartz veinlets mineralized with bornite and chalcopyrite. The veinlets strike north parallel to the fault zone which can be traced tens of kilometres to the south.
In 1989 and 1990 the Cos showing was tracked up Bailey Creek. Veinlets and disseminations of chalcopyrite occur in narrow silicified limestone and argillite beds. Both associated silver and gold values were insignificant.
Work History
In 1964, Skeena Silver Mines held sixteen claims in the area now covered by the Jameson 5 claims (BCDM, 1965). The claims covered a copper occurrence, named the COS showing, in which bornite and chalcopyrite stringers occur within a large skarn zone situated along a limestone-monzonite contact. No work was recorded on the claims and they were allowed to lapse.
During September of 1989, Sundial Resources Ltd. carried out two days of geological mapping, prospecting and stream sediment sampling on the Jameson claims, taking 20 stream sediment samples and 11 rock samples. Grab samples of float assayed 0.05 gram per tonne gold, 1.4 grams per tonne silver, 0.0691 per cent copper, and 0.6830 per cent zinc (Assessment Report 19791).
During September and October of 1990, Sundial Resources Ltd. carried out two days of reconnaissance exploration on the Jameson claims, consisting of geological mapping, prospecting and stream sediment sampling. This program was directed towards locating and sampling the COS copper showing and continuing property-wide exploration coverage. During the course of this program, 3 silt samples and 12 rock samples were taken.
