The Spokane polymetallic vein prospect, located at the headwaters of Holbrook Creek, 4.5 kilometers southeast of Rex Peak, is within granodiorite of the Eocene Mission Ridge pluton and Tertiary hornblende feldspar porphyry (porphyritic dacite), known as the Rexmount Porphyry. These rocks intrude serpentinite melange of the Permian and older Shulaps Ultramafic Complex and phyllite of the Mississippian to Jurassic Bridge River Complex (Group).
The principal vein is predominantly massive white quartz, but is locally ribboned to vuggy. The ribbons are partings of chlorite and some wallrock blebs and disseminations of pyrite, chalcopyrite and pyrrhotite. Rare tellurides, molybdenite, arsenopyrite, bornite and native gold constitute 1 to 3 per cent of the vein material. Sulphide distribution is erratic. The distribution of gold closely follows that of copper and is commonly accompanied by anomalous silver, tungsten and bismuth. The vein is approximately 2 metres thick and is traceable for at least 700 metres, over 250 metres elevation. Sericite and chloritic alteration haloes are common adjacent to vein margins, sometimes a few metres thick. In places, granodiorite that is distant from veins is weakly mineralized with chalcopyrite, pyrrhotite, pyrite and molybdenite, and suggests a porphyry copper-molybdenum environment. Host granodiorite is foliated adjacent to the vein, whereas porphyritic dacite is fresh and in places cuts both vein and foliated granodiorite. This indicates that the vein is younger than the granodiorite but older than the porphyritic dacite.
In 1983, a 1.8-metre chip sample taken across a quartz vein assayed 6.97 grams per tonne gold and 42.20 grams per tonne silver (Assessment Report 11502). In 1988, a drill hole intersection with true of 6.3 metres assayed 13.714 grams per tonne gold (Assessment Report 19041).
The main mineralized zone consists of a copper-gold quartz vein system which is continuous over a strike length of about 700 metres and tested to an average depth of about 75 metres. A resource estimate of 190,000 tonnes containing 8.57 grams per tonne gold and 0.92 per cent copper has been defined within the main mineralized zone (George Cross News Letter No.28 (February 8), 1996).
Work done in 1995 by Spokane Resources Ltd., with support from the Explore B.C. Program, consisted of geological and geochemical surveys and 2531 metres of diamond drilling in 20 holes which further defined East and West zone mineralization. This work also allowed a combined resource estimate of 189,453 tonnes grading 8.57 grams per tonne gold and 0.92 per cent copper, evenly split between the two zones. The East zone averages 7.95 grams per tonne gold and 1.06 per cent copper; the West zone averages 9.18 grams per tonne gold and 0.77 per cent copper (Explore B.C. Program 95/96 - M23).
