Preliminary Map 49 describes the geology of the Moyie Lake area (82G/W) in southeastern British Columbia.
Accompanying notes present results of a reconnaissance stream sediment sample survey of the Moyie Lake sheet.
The geology map is at 1:50 000 scale and includes a legend, 4 geological cross sections, descriptive notes, and references.
The Moyie lake area is underlain dominantly by clastic rocks of the Purcell Supergroup of Helikian and Hadrynian age. Two past producers, the Midway mine and the St. Eugene mine, numerous small silver-lead-zinc and copper vein occurrences, and placer gold on Moyie River make the area an attractive exploration target area. Virtually the entire area is below timberline with relief varying from approximately 929 metres (3,050 feet) near Moyie Lake to 2302 metres (7,554 feet) in the northwest corner. Exposure is generally poor, because many of the rounded hills and most valleys are covered by a veneer of Quaternary and Recent sand and gravel.
The oldest rocks within the map-area, rusty weathering siltstone and quartzite of the lower Aldridge Formation, occur in the hangingwall of the Moyie fault. They are sheared, tightly folded, and locally overturned adjacent to the fault. Moyie intrusive rocks (metadiorites) crosscut lower Aldridge rocks, although the general aspects of most are sill-like. Only the largest and most continuous are shown on the map, and these (as in the middle Aldridge) commonly consist of a number of separate intrusions with screens of sedimentary rocks. The boundary between the lower and middle Aldridge is gradational. It has been placed at the surface above which grey-weathering quartz-wacke beds predominate over siltite, although quartz wackes occur throughout the upper part of the lower Aldridge, and rusty weathering thin to medium-bedded graded siltite beds, typical of the lower Aldridge, occur in the basal part of the middle Aldridge.
Grey-weathering graded quartz-wacke beds interpreted to be turbidite deposits occur throughout the middle Aldridge. Basal scour marks indicate northerly-directed current transport. In general, in the middle Aldridge, quartz-wacke beds become thinner, less pure, and less volumetric up-section; the upper part comprises a number of distinct cycles of massive, grey quartzite-wacke beds capped by siltstone and argillite. The contact with the upper Aldridge is placed above the last bed of massive grey quartzite. Metadiorite sills are the most important markers within the thick middle Aldridge section and allow correlation across many of the faults. Some of the larger of these sills have been designated by letter symbols on the map.
The base of the Creston Formation is commonly marked by a thick, generally massive, grey quartzite unit. It is commonly overlain by dark argillite and siltstone that is distinguished from the upper Aldridge by the presence of thin green siltstone lenticles and occasional mud cracks. Green siltstone is characteristic of much of the Creston Formation, but may also be dominant in the basal unit of the overlying Kitchener Formation. The base of the Kitchener is placed beneath the first section containing prominent buff- weathering dolomitic siltstone. The contact between the Kitchener and the Van Creek Formation is gradational, from thin-bedded grey argillaceous limestone into grey siltstone with a few green and brown silty limestone layers in the basal part of the Van Creek Formation.