Bulletin 055

Bulletin 055

BUL 055

Geology of the basement beneath the Athabasca Basin in Alberta

Author(s) Wilson, J.A. Date 1986-01-01

The unconformity beneath the Athabasca Basin in Alberta lies within 600 m of the surface for over 6000 sq. km, or 75 percent of the basin area. The basement beneath the unconformity can be subdivided into four granitoid rock types recognized as part of the Wylie Lake pluton, and two mylonitic rock types derived partly from the granitoids and partly from a metasedimentary or metavolcanic parent.

A zoned saprolite is present regional on the basement immediately eneath the unconformity. It represents a period of Helikian surficial weathering preserved by deposition of the Athabasca Group. The saprolite is crosscut by two types of widespread hydrothermal alteration, a thin bleached zone at the unconformity and a more widespread alteration associated with fracturing. Geochemical probes of the saprolite and hydrothermal alteration types indicate that they are products of leaching processes and would not be good mechanisms for concentrating economic minerals.

Locally, a fourth type of alteration, which may be associated with mylonitic rocks, shows enrichment in several potentially economic minerals (including uranium, nickel, zinc, lead and gold) and has a geochemical signature similar to the halos around some uranium ore deposits in Saskatchewan. This alteration is present beneath a onsiderable thickness of Athabasca Group sediments, but similar rock types and many of the conditions necessary for ore concentration are also present beneath the southern portion of the Athabasca Basin In Alberta, where the cover is thin.

Exploration in Alberta has utilized the Key Lake model for uranium re concentration. However, there are many similarities to the geology at Cluff Lake, suggesting that a model incorporating these features may be more appropriate.

Wilson, J.A. (1986): Geology of the basement beneath the Athabasca Basin in Alberta; Alberta Research Council, ARC/AGS Bulletin 55, 66 p.