The Treasure Mountain region is underlain by northwest striking, moderate to steeply southwest dipping volcanic and sedimentary rocks of the Lower-Middle Jurassic Dewdney Creek Formation (Ladner Group) and Lower-Upper Cretaceous Pasayten Group, intruded by numerous dikes and sills. The Dewdney Creek Formation comprises volcanic rocks and a minor amount of sediments and consists of tuff, breccia and agglomerate with interbedded argillite and conglomerate. The Dewdney Creek Formation is considerably altered; pyrite is commonly present and many outcrops are rusty. The Pasayten Group includes predominantly arkose, argillite and conglomerate. Locally, the two sequences are separated by a northwest striking, northeast dipping fault but in large part are conformable.

The John occurrence is underlain by faulted, brecciated and slightly altered sediments of the Pasayten Group consisting of graphitic argillite, conglomerate and arkose with various dikes and some andesite also occurring. Diamond drilling intersected a quartz-calcite vein with graphitic gouge and graphitic fragments near a dike contact. A sample of the vein assayed 41.47 grams per tonne silver, 2.86 per cent lead and 0.47 per cent zinc (Assessment Report 10276).

Rotary drilling in 1989 intersected a quartz-carbonate vein mainly hosted in arkose and containing pyrite, galena, sphalerite and possibly chalcopyrite and tetrahedrite. A 1.5-metre interval, part of a 6-metre intersection of the vein, yielded 2800 grams per tonne silver, 36.5 per cent lead and 0.02 per cent zinc (Assessment Report 20373, drillhole RH#3). Trenching in 1990 revealed the existence of two parallel veins.