Monteith Bay quarry, Vancouver Island, Alberni Mining Division, British Columbia, Canada
|Latitude & Longitude (WGS84):||50° 7' 52'' North , 127° 17' 52'' West|
|Latitude & Longitude (decimal):||50.13111,-127.29778|
The Monteith Bay geyserite deposit consists mainly of replacement silica in a concentration greater than 96 per cent SiO2. It is a paleo-hotsprings deposit of massive thickness, originally of gently dipping bedding, now somewhat faulted, bent and dipping to the south about 40 to 50 degrees.
The volcanic hostrocks in the Monteith Bay area consist of hornblende-plagioclase porphyritic andesite, amygdaloidal flows and flow breccias of the Lower Jurasssic Bonanza Group. Late intrusive rocks occur as fine grained porphyritic andesite dikes and sills.
The rocks are altered to various degrees, with silicic and advanced argillic zones present. The lack of structural control, of associated large intrusions and overall distribution of the alteration assemblages suggest that the silicification took place contemporaneously with volcanism before significant structural dislocation. The sericite-rich alteration in Monteith Bay appears to correlate directly with the emplacement and shearing of the later andesite dikes. The presence of chalcedonic silica, alunite and pyrophyllite indicate a probable near surface origin for the main phase of alteration.
8 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
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174.1 - 201.3 Ma
Age: Early Jurassic (174.1 - 201.3 Ma)
Stratigraphic Name: Bonanza Group
Description: Massive amygdaloidal and pillowed basalt to andesite flows, dacite to rhyolite massive or laminated lava, green and maroon tuff, feldspar crystal tuff, breccia, tuffaceous sandstone, argillite, pebble conglomerate and minor limestone (Sinemurian t
Comments: N.W.D. Massey, P.J. Desjardins, and E.C. Grunsky, 1994, Geological Compilation of Vancouver Island, OF 1994-6, BCGS
Lithology: Calc-alkaline volcanic rocks
Reference: B.C. Geological Survey. British Columbia Digital Geology.