The High Grade occurrence is located near the headwaters of the south fork of the Marmot River, 15 kilometres southeast of Stewart. Various gold-bearing quartz veins were extensively explored by trenching and tunnelling in this area during the late 1920s.
The occurrence consists of three veins developed in volcanic breccia and lithic tuff of the Lower Jurassic Unuk River Formation (Hazelton Group) just east of the Eocene Hyder pluton (Coast Plutonic Complex). The Unuk River Formation rocks are dark green-red and purplish andesitic flows, tuffs and breccias where bedding is locally well developed in the fine grained tuff units. Middle-Upper Jurassic Salmon River Formation (Hazelton Group) rocks are fine grained, grey to black argillites, siltstones and sandstones. Bedding is often well developed, striking 290 to 320 degrees and dipping from 35 to 45 degrees northwest. Both formations are intruded by northwest trending, granodiorite to quartz diorite of the Hyder pluton, in addition to minor smaller bodies and dikes related to the pluton.
The upper vein strikes 119 to 134 degrees for at least 150 metres, dips 45 to 55 degrees northeast and is 0.6 to 2.7 metres wide. Mineralization consists of stringers and massive lenses of pyrite, galena and arsenopyrite in a quartz-carbonate gangue. A grab sample assayed 7.56 grams per tonne gold (Assessment Report 16652, page 11).
The middle vein, 150 metres southwest of the upper vein, strikes 125 degrees for 100 metres, dips 45 degrees northeast and is up to 2.1 metres wide. The quartz vein is mineralized with pyrite, minor chalcopyrite, sphalerite and trace galena. In 2009, a rock grab sample from the middle adit on the High Grade vein analysed 20.7 grams per tonne gold and 68.3 grams per tonne silver (Assessment Report 31530).
The lower vein, 300 metres south of the upper vein, strikes 085 to 089 degrees for 1000 metres, dips 45 to 50 degrees north and is up to 1.0 metre wide. It contains brecciated and silicified wallrock with numerous lenses and veinlets of quartz with pyrite and minor chalcopyrite. A sample of quartz with disseminated pyrite assayed 86.2 grams per tonne gold and 123.0 grams per tonne silver (Minister of Mines Annual Report 1926, page 89).
The High Grade veins were explored by trenching and three short adits during the 1920s. In 1987, Corning Resources Ltd. conducted geological mapping and collected 276 rock and 22 soil samples. In 1993, A. Kikauka established a 2.5 kilometre grid and collected 40 soils and 6 stream sediment samples and conducted a magnetic and VLF-EM survey. In 1995, A. Kikauka mapped the High-Grade Vein and collected 22 rock and 18 soil samples. In 1997(?), Navarre Resources Corp. drilled 13 BQ holes in the High-Grade Vein area. In 2006, Enterayon Inc. conducted detailed surface and underground sampling of the High-Grade Vein, prospecting at and around the known showings and completed a seven hole, 254 metre diamond drilling program. In 2009, Castle Resources Inc. entered into an option agreement with the registered claim holders, J. Wang and R. Kasum. In the same year, Castle Resources conducted a one day prospecting and sampling program and three rock grab samples were taken and analysed from the middle adit area on the High Grade vein.
Granby Gold Inc.'s Marmot property, containing the High Grade, underwent geological mapping throughout 2013 to 2015. In 2017 the geology was finer tuned by interpretation with regional airborne geophysics and again in 2018 with airborne geophysical survey data. There is no clear anomalous geophysical response to the High Grade Prospect (Assessment Report 38124).
