The Burnais prospect is located north of the Windermere quarries (082JSW028) on the north side of Windermere Creek.

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 (082JSW021), 800 metres to the south of the Windermere deposits.

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, dark grey and 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, structurally complex, is exposed semi-continuously over a strike length of 4.2 kilometres from Windermere Creek to north of Burnais Creek. To the north, it thins and disappears under thick overburden and anhydrite and limestone of the Cedared Formation.

Gypsum at the Burnais showing is similar to that observed elsewhere in the area, grading 74 to 94 per cent and averaging better than 85 per cent gypsum. Drilling on the ridge north of Windermere Creek intersected gypsum to depths varying from 17 to 43 metres and underlain by anhydrite.