Release of toxic-metal acid brines related to slumping of Cretaceous mudstones—Smoking Hills (Ingniryuat), Arctic Canada

The Smoking Hills (Ingniryuat) is a polar desert of Arctic Canada that contains naturally occurring streams and ponds of hyperacidic (pH <−2) metal-rich brines (total dissolved solids up to 394,000 mg/L). Acid waters are formed though oxidation of pyrite and metal-rich mudstones of the Late Cretaceous Smoking Hills Formation. Water in contact with the mudstones rapidly changes chemistry, becoming acidic, metal-rich, and opaque orange due to precipitation of Fe-sulfates. Acid generation occurs through fluvial incision through bedrock strata and mass wasting of Smoking Hills Formation mudstones due to coastal erosion, stream undercutting, permafrost thaw, and ground-ice melt. These hyperacidic metal-rich waters discharge to larger river systems and are transported to the Arctic Ocean with uncertain impact. We suggest that climate warming may increase slumping and associated debris flows, impound more surface ponds and stream courses, generate more acid waters, amplify toxic-metal flux to the environment, and drive river “rusting.”