Gypsum was discovered on Windermere Creek in 1947. Production, beginning in 1950, has been continuous to the present day totalling in excess of 6.8 million tonnes. Gypsum was mined from the four Windermere quarries until 1981 and, since 1982, from the Elkhorn quarry (Elkhorn 1 deposit, 082JSW021) 800 metres to the south.
Gypsum, in Devonian age rocks, occurs along a northwesterly trend which has a strike length of 5 kilometres north and south of Windermere Creek. The area is underlain by a sequence of evaporites and associated carbonate rocks of the Burnais Formation with an overlying limestone and shale sequence of the Harrogate Formation. More recent work proposed the term "Cedared Formation" for a sequence of dolomites, sandstones and limestones that is, in part, stratigraphically equivalent to the Burnais Formation. Much of the carbonate strata previously included in the Burnais Formation are now tentatively assigned to either the Cedared or Harrogate formations. The Harrogate Formation is the youngest Devonian unit in the Stanford Range.
Thin-bedded or laminated gypsum of the Burnais Formation is assumed to be in fault contact with the underlying Ordovician to Silurian Beaverfoot-Brisco Formation or in conformable contact with the Cedared Formation and overlain conformably by the black to dark grey limestone of the Harrogate Formation. The Beaverfoot-Brisco Formation is comprised of thin to medium-bedded light grey dolomite and limestone with characteristic ovular chert nodules and lenses in a carbonate matrix. The gypsum is of good quality ranging between 83 and 93 per cent gypsum. It varies in color from pale grey to grey, brownish grey and dark grey to black. Cream-colored laminae are also present.
The evaporite sequence has been folded into a series of northwest-plunging, 18 to 40 degrees, folds. Small scale faulting with minimal displacement is present. Two gypsum horizons are interpreted, separated by dolomite and limestone. The lower gypsum bed is 50 metres wide and 50 to 100 metres thick. The upper bed is structurally complex and the thickness is difficult to determine.
At the Windermere quarries, the Windermere Nos. 2 to 4 deposits are hosted by the main gypsum unit (upper bed) of the Burnais Formation and the Windermere No. 1 is hosted by a separate lens of gypsum which may represent a folded or faulted repetition of the main gypsum unit. Anhydrite is present in a breccia zone that is 30 metres wide. The breccia consists of angular anhydrite and gypsum fragments in an anhydrite matrix. The anhydrite tends to be more massive than the surrounding gypsum.
Minor production of mixed gypsum and anhydrite continues, as required by the cement industry. Exact production figures are not available.
Westroc Industries holds the property.