Oilfield brines are emerging as unconventional lithium resources. Lithium concentrations in oilfield brines range widely, complicating exploration and valuation of these potential resources. We investigate the Devonian Leduc Formation, Alberta Basin lithium-enriched oilfield brine system documenting the utility of combining dissolved species concentrations with isotope signatures to elucidate brine origin and lithium sources and explain regional heterogeneities in brine chemistry.