TRACE ELEMENT GEOCHEMISTRY AND METAL MOBILITY OF OXIDE MINERALIZATION AT THE PRAIRIE CREEK ZINC-LEAD-SILVER DEPOSIT, NWT

Prairie Creek is an unmined high grade Zn-Pb-Ag deposit in the southern Mackenzie Mountains of the Northwest Territories, confined within the boundaries of the Nahanni National Park. The upper portion of the primary quartz-carbonate-sulphide vein mineralization have undergone extensive oxidation, forming high grade zones rich in smithsonite (ZnCO₃) and cerussite (PbCO₃). This weathered zone represents a significant resource and a potential component of mine waste material. This research is focused on the characterization of the geochemical and mineralogical controls on metal mobility at Prairie Creek, with particular attention to the metal carbonates as a host for trace elements under mine waste conditions. Analyses were conducted using a combination of SEM, EMP, MLA, LA-ICP-MS, and synchrotron-based µXRD and µXRF techniques.

Results include the identification of previously unknown minor phases, including cinnabar (HgS), acanthite (Ag₂S), bindheimite (Pb₂Sb₂O₆(O,OH)), and multiple metal arsenate minerals. Anglesite (PbSO₄) may also be present in greater proportions than is suggested by previous work. Smithsonite consistently contains elevated concentrations of Pb, Cd, Cu, Fe, and Mn, while cerussite (expected to be removed as Pb concentrate) regularly hosts Zn, Cu and Cd. Variable concentrations of Fe, As, Sb, Hg, Ag, and Se are present in both, in approximately decreasing order. A significant proportion of the trace metals may also be attenuated by other secondary minerals. Processing into tailings will remove significant sources for these elements; however, smithsonite will subsequently remain as the major source for most of them. Significant Hg and Ag could remain in tailings from cinnabar and acanthite that is trapped within smithsonite grains.

In a mine waste setting, near-neutral pH will encourage precipitation and attenuation of trace metals. Regardless, oxidation, dissolution and mobilization is expected to continue at a slow rate, which may be slowed by saturated conditions, or accelerated by localized flow paths and acidification of isolated, sulphide-rich pore spaces.