The Rainbow occurrence lies east of Summit Lake, on the Trojan Horse Ridge. Underlying rocks consist of volcanic breccia and andesite tuff, overlain by siltstone and argillite, of the Lower Jurassic Unuk River Formation (Hazelton Group). To the south of the Trojan Horse Ridge is an irregularly shaped body of andesite porphyry. The Lower Jurassic Summit Lake Stock, comprised of hornblende quartz monzonite and/or hornblende granodiorite, lies northwest of Summit Lake.
Mineralized east-trending, north dipping shear zones cut the volcanic breccia. The zones, which are up to 50 metres wide and 186 metres long, are mineralized with sphalerite, galena, pyrrhotite, chalcopyrite and arsenopyrite in zones usually less than 1.6 metres wide. Pyritization, silicification and quartz-carbonate stringers are common. Stringers and disseminations of pyrite and pyrrhotite occur along the contact between the volcanic breccia and the argillites, east of the ridge.
A 46 centimetre sample (#813) taken from a vein assayed 1.7 grams per tonne gold and 72 grams per tonne silver (Annual Report 1947). A mineralized zone was sampled within the Trojan Horse tunnel (675 metres from the south portal). This sample, located 300 metres west of the main Rainbow shear zone, assayed 5.6 grams per tonne gold over 2.7 metres (Assessment Report 12117).
Sampling of shear zone hosted sulphide-bearing quartz veins in the Rainbow vicinity in 2017 by Pretium Exploration yielded assays as high as 81.90 grams per tonne gold, 332 grams per tonne silver, and 2.59 per cent lead (sample B072087) and 5.03 grams per tonne gold (sample B072094) (Assessment Report 37435).
WORK HISTORY
The Trojan Horse tunnel was completed by Newmont Mining in 1967 in order to assess the mineralization; however the only significant gold mineralization encountered in the tunnel was 0.168 oz/ton over 2.7 metres (Assessment Report 12117). Serengeti Resources sampled the area in 2004, and found soils weakly anomalous in gold, silver, arsenic, lead, and antimony downslope of the known mineralization. The highest grade chip sample returned 11.65 grams per tonne gold across 3 metres in an old trench (Assessment Report 27876).
By at least 2017, Pretium Exploration held the showing as part of their extensive Bowser property which extended north to Brucejack Lake and farther. In 2017, Pretium Exploration conducted grass roots prospecting, sampling and mapping on their Bowser property, mostly southwest and south of Bowser Lake. They collected 2901 rock and 429 silt samples (Assessment Reports 37435, 37443). A number of samples were collected in the vicinity of the plotted location of the Rainbow occurrence.
In 2018, Pretium continued to evaluate their surrounding contiguous 1250 square kilometre mineral claims (the Bowser Property). The company completed an 8000 metres drilling program along with mapping and prospecting. Detailed results are pending.
As of September 2019, two drills were testing the high-priority A6 Zone VMS target, 14 kilometres northeast of Brucejack Mine, a third drill targeted a VMS system at the Canoe area, and a fourth drill targeted an intrusion related gold system at the Koopa area. Drilling earlier in the summer also focused on the Tuck and Lilliane areas, both epithermal gold system targets. To date, approximately 15,300 meters have been drilled, with drilling expected to continue through the end of September (Pretium Resoucres Inc., News Release, September 16, 2019). Detailed results are pending publication.
The best assay results came from the Rainbow showing, including 81.90 g/t Au, 332 g/t Ag, and 2.59% Pb (B072087) and 5.03 g/t Au (B072094). These samples were collected from narrow, shear zone hosted quartz veins and sheared mafic volcanic host rocks.
See Betty (104A 008) for details of relevant work that Pretium completed on its grassroots projects on their Bowser property, including significant property-wide geophysical surveys completed prior to to 2017.
