The Cousin Jack prospect outcrops along the northeast flank of Boulder Mountain, 2 to 3 kilometres north of Lockie (Boulder) Creek and 7 to 8 kilometres north-northwest of Tulameen.

The northeastern slopes of Boulder Mountain are underlain by andesitic to dacitic flows and pyroclastic volcanic rocks of the Upper Triassic Nicola Group. These rocks strike north, dip west and are regionally metamorphosed up to greenschist facies. A weak to moderately developed foliation dips 10 to 20 degrees west. The volcanics are flanked to the east by an elongate body of granodiorite of Late Triassic to Early Jurassic age outcropping along Otter Lake.

A zone of concordant to discordant quartz-carbonate veins occurs in andesite (greenstone) over a north-south distance of 1200 metres. Individual veins strike north for lengths of up to 380 metres and dip shallow to steeply west. They vary from 2 centimetres to 3 metres wide, but average less than 0.5 metre in width.

The andesite is sheared and hydrothermally altered in this zone of veining. The rock exhibits pervasive quartz-sericite-argillic alteration in the hangingwall and well-developed propylitic alteration in the footwall of steeply west dipping veins.

The veins and surrounding wallrock are variably mineralized with sphalerite, pyrite, galena and chalcopyrite. The veins are frequently pyritic and are sometimes mineralized with polymetallic massive sulphides. Such vein-hosted sulphides are massive to weakly interbanded with quartz. The locally convolute banding suggests an epithermal origin (Assessment Report 15315). Pyrite, galena and sphalerite are present in silicified wallrock as stringers and bands.

Surface sampling suggests the veins average 1 to 3 per cent combined lead and zinc, 0.2 per cent copper, 6.9 grams per tonne silver and 6.9 grams per tonne gold (Assessment Report 15315, page 21). A chip sample across a 1-metre wide vein with sphalerite and galena assayed 1.22 per cent lead, 12.49 per cent zinc, 0.09 per cent copper, 5.79 grams per tonne gold, and 20 grams per tonne silver (Assessment Report 13396, assay certificate, sample 6588). A chip sample taken across 0.9 metre of siliceous and pyritic andesite yielded 0.807 per cent lead, 7.666 per cent zinc, 0.186 per cent copper, 2 grams per tonne gold and 12.9 grams per tonne silver (Assessment Report 13396, assay certificate, sample 54287). Assays from diamond drilling ranged up to 1.1 grams per tonne gold, 26.4 grams per tonne silver, 1.90 per cent lead and 4.11 per cent zinc (Assessment Report 15993, page 7). The highest gold and silver values were found with highest lead and zinc values in siliceous andesite with minor carbonate.

This prospect was explored as early as 1901. Boulder Mining Company Ltd. conducted 98 metres of tunnelling in several adits between 1903 an 1905. The property was periodically assessed by several operators with minor development between 1922 and 1966. By 1971, Gold River Mines Ltd. had commenced a program of soil sampling and trenching, which culminated in the drilling of 33 diamond-drill holes totalling 1768 metres in 1972 and 1973. Since then, the deposit has been geophysically surveyed, trenched, mapped and sampled by various operators between 1980 and 1986. This work was followed with the drilling of 12 holes totalling 662 metres by Abermin Corporation in 1987.