Evolution of Li-enriched oilfield brines in Devonian carbonates of the south-central Alberta Basin, Canada

Abstract

There is a long and extensive history of study regarding the origins and characteristics of brines within the Alberta Basin of Canada. This study focuses on the origins of Li-enriched (>50 mg/kg) brines of the late Devonian Swan Hills, Nisku and Leduc Formations of the southwestern Alberta Basin. Available data show that two Li-enriched brines having distinctly different geochemical characteristics, and thus distinct evolutionary histories, exist within the late Devonian carbonates of the southwestern Alberta Basin. Li-enriched brine of the Swan Hills Formation appears to have been formed by dissolution of halite and mixing with Li-enriched fluids expelled from Precambrian crystalline basement. The degree of mixing between Swan Hills brines and meteoric water is unknown. Formation of Li-enriched brines in the Nisku and Leduc Formations could be explained by preferential dissolution of Li-enriched late-stage evaporite minerals, likely from the middle Devonian Prairie Evaporite Formation, into evapoconcentrated late Devonian seawater. Dense Li-enriched brine migrated downward into the underlying early Devonian Winnipegosis Formation and then westward in response to westward tilting beginning in Jurassic time. Li-enriched brine was then diluted by mixing with meteoric water driven into the Devonian of the southwestern Alberta Basin in response to hydraulic gradients created by the effects of Laramide tectonics.