A Geochemical Characterization of Streams Surrounding the Tom and Jason SEDEX Deposits of the MacMillan Pass, Yukon, Canada: Implications for Mineral Exploration and Toxicology

This study presents a geochemical characterization of stream waters draining the sedimentary exhalative (SEDEX) Tom and Jason Pb-Zn deposits and surroundings in the MacMillan Pass, Yukon. Streams sampled have wide ranging pH values of 3 to 8.2. Dissolved metal concentrations vary widely with water source and pH. Of note, streams draining the Tom and Jason deposits are acidic and neutral respectively, which greatly affects metal solubility. The Tom Deposit drainage is extremely high in dissolved and fine sediment fraction lead, as well as dissolved zinc. Neutral streams draining the Jason deposit have less dramatic metal concentrations, but do show elevated dissolved zinc and fine sediment fraction lead concentrations. Modelling using the thermodynamic equilibrium program PHREEQC and XRD analysis indicate that ferricrete hardpans underlying acidic drainages are formed where drainage water is saturated with respect to schwertmannite. Ferrihydrite is formed where the rapid mixing of waters increases the pH rapidly. An aluminium oxy-hydroxide, likely gibbsite, precipitates where pH levels exceed 4.5, however it appears to dissolve with decreasing pH. This study looks at dissolved, suspended and fine fraction sediments to provide a more complete view of metal movement under various conditions which may be useful to both exploration and environmental fields