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.
Several faults occur. Two faults cross the southwest part of the region and strike east and dip steeply south, but one splay of one fault dips north. The more northerly of these two faults, the Indiana fault, hosts the Blue Bell (092HSW020) and possibly the Indiana (092HSW022) and Summit occurrences. The southern fault, the Queen Bess fault, hosts the Queen Bess (092HSW021) occurrence. These two faults diverge to the west from the Treasure Mountain fault, and contain subparallel splays separated by shattered rock. The Queen Bess fault splits into two branches that diverge toward the west.
Mineral occurrences in the area are hosted in the Treasure Mountain fault and in and near subsidiary faults, and comprise one or more quartz-carbonate veins or stringers that branch and split and vary considerably in width and attitude (see Treasure Mountain, 092HSW016).
The Summit occurrence is underlain by Dewdney Creek Formation massive conglomerate, sandstone and argillite intruded by Late Cretaceous-Tertiary diorite-basalt-dacite dikes. The Indiana fault strikes through the area at 070 degrees and dips 70 degrees south. The fault continues to the east and passes through the Indiana occurrence area (092HSW022) onto the northern part of the Blue Bell occurrence (092HSW020).
A shaft explores the fault, where a 38 centimetre quartz vein stringer zone contains abundant galena and sphalerite with variable amounts of pyrite, pyrrhotite, arsenopyrite and chalcopyrite. Petrographic studies revealed proustite and tennantite as inclusions in pyrrhotite. Wallrock and gouge constitute a major portion of the fault zone. Sericite and epidote occur as disseminations in the quartz veins and along vein selvages. Quartz crystals are common. An opencut along the fault exposed a number of very narrow stringers of galena across a width of 1.8 metres of sparsely mineralized rock. Limonite (mainly goethite) occurs in fractures cutting the veins and sulphide mineralization.
To the west, the zone can be traced for 152 metres but consists of gouge and bleached wallrock. Ninety-one metres east of the shaft, widely separated quartz stringers form a zone 0.9 metre wide. Recent trenching of the fault structure starts 74 metres west of the shaft and extends east for a total distance of 315 metres. Channel sampling from the trenches across 1.37 metres of vein yielded a best assay of 0.19 per cent copper, 4.51 per cent lead, 5.87 per cent zinc, 396.61 grams per tonne silver and 2.70 grams per tonne gold (Assessment Report 18111). Grab samples at the Summit shaft yielded up to 0.5 per cent antimony (Dewonck, 1987).
Minor production took place in 1951.
