Canadian Shield, Manitoba

Figure 19. Plot of Li isotopic composition vs. inverse Li concentration for lakes and basinal/oilfield brines. Lakes open circle = major global lakes (Chan and Edmond 1988 Falkner et al. 1997) semi-open circle = western U.S. closed basin lakes (Tomascak et al. 2003). Oilfield brines inverted triangle = Williston basin, Saskatchewan (Bottomley et al. 2003) diamond = Israeli oilfields (Chan et al. 2002d). Mine waters (Canadian Shield basinal brines) square = Yellowknife, NWT (Bottomley et al. 1999) triangle = Sudbury, Ontario, area (Bottomley et al. 2003) star = Thompson, Manitoba, area (Bottomley et al. 2003). Average composition of seawater is included for reference.

Continental-scale hydrologic forces can control the flow of basinal brines and are another major potential external source of saline fluids that may enter crystalline rock environments. Studies by Bottomley et al. (1999) suggest that hydraulic gradients in northwestern Alberta are such that brines are forced from Devonian strata into the underlying Canadian Shield. Similarly, it appears that western Canadian sedimentary basin brines have entered the Canadian Shield in some parts of the Lac du Bonnet batholith, Manitoba (Gascoyne et al., 1987). 

The Lac du Bonnet batholith is a 2.6-Gyr-old granite on the western edge of the Canadian Shield, —100 km east of Winnipeg, Manitoba. It has been studied in detail because it is the location of Canada s URL and is a research facihty of the Canadian program for disposal of high-level nuclear waste. 

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