Preliminary Map 35 describes the geology of the Penticton Tertiary outlier, southwest of Penticton and north of Keremeos in southern British Columbia. The 1:50 000 scale geology map includes a legend and a cross section.
The basement rocks to the Tertiary sequence consists of pre-Tertiary sediments, including chert, metavolcanic and schistose units, and mainly granitic intrusions. Early Cenozoic rocks of the Kettle River Formation, Springbrook Formation, the Marron Formation, the Marama Formation, the White Lake Formation, and the Skaha Formation are exposed. The Kettle River Formation consists primarily of the Shingle Creek porphyry, and conglomerate, arkose, wacke and rhyolite breccia. The Springbrook Formation consists mainly of polymictic conglomerate and breccia.
The Marron Formation contains the Yellow Lake member, which has a lower sill-like body, the Clark Creek porphyry, a wacke, ash flow, sandstone and conglomerate unit, and a unit dominated by mafic phonolite, the Shatford Creek member, an andesitic flow and breccia unit, the Kitchley Lake member, which is made up of trachyandesite flows, the Kearns Creek member of pyroxene phyric basalt, the Nimpit Lake member with mainly trachyte and trachyandesite flows and minor breccia units, and the Park Rill member, which is andesitic lava. Marama Formation is represented by rhyolitic pyroclastic rocks, volcanic conglomerate, and dacite lava and breccia. The White Lake Formation consists of a unit with volcanic conglomerate, sandstone, and shale, and a unit with mostly volcanic breccias. Skaha Formation rocks consist of a unit with granite boulder conglomerate and breccia, and arkosic sandstone, and a unit with slide breccia with mainly chert and greenstone clasts, and fanglomerate deposits.
Block faults with mainly northeast, north and northwest trends dominate the Tertiary map pattern. Normal and reverse movement have tilted the Tertiary strata.
The Dusty Mac mine is hosted by dacites of the Marama Formation. The deposit comprises polymetallic veins with silver-lead-zinc-gold values. It is an epithermal silver-gold, low sulphidation deposit. Potential exists for similar deposits in the area.