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 Argentum occurrence is underlain by north-northwest striking (340-350 degrees), west dipping (60 degrees) volcanic sediments consisting of sandstone, conglomerate, agglomerate, tuff and argillaceous tuff intruded by dioritic sills and dikes. Shearing along dike contacts is sometimes accompanied by a narrow zone of quartz veinlets. The hostrocks belong to the Dewdney Creek Formation. Pyrrhotite and lesser pyrite are commonly disseminated throughout these lithologies. The tuffs and argillaceous tuffs are distinctive units in that they contain limonite coatings along fracture planes and have a higher percentage of pyrrhotite and pyrite. A fault is evidenced by offsets of some rock units.

Some minor shears occur in the volcanic sandstone, tuffaceous argillite and argillite units. The shears are highly fractured and oxidized and contain sparse pyrite, sphalerite and galena. Locally, unmineralized quartz veins to 25 centimetres wide also occur. Rock chip samples from the mineralized shear zones assayed up to 70.95 grams per tonne silver (Assessment Report 14714).