δ98MO AS A POTENTIAL TRACER TO EVALUATE SOURCES AND PROCESSES CONTROLLING MO CONCENTRATIONS IN NATURAL AND PROCESS AFFECTED WATER IN THE ATHABASCA OIL SANDS REGION

There is concern that the extraction and processing of bitumen from the Athabasca Oil Sands Region (AOSR) may result in increases in metal loading to aquatic ecosystems through atmospheric deposition, leaking tailings ponds, or mining activities. Tracers capable of identifying sources and or processes controlling the fate and transport of metals are of particular interest. Previous preliminary studies have identified molybdenum concentrations and isotopic ratios as potential tracers of anthropogenic sources of atmospheric sources of Mo. To further investigate the potential use of Mo concentrations and isotopic compositions to identify various sources of Mo in the AOSR we analyzed oil sands tailings process affected waters (OSPW) (e.g. tailings ponds and coarse tailings), Athabasca River water and Quaternary, Cretaceous and Devonian waters in the region for δ⁹⁸Mo values to identify the range of isotopic labelling present in natural and anthropogenic waters in the area. Mo concentrations are higher in OSPW than in any of the other waters sampled. Differences between the Mo concentration and isotopic labelling in coarse tailings and tailings pond waters suggest that biogeochemical processes (e.g. adsorption, co-precipitation, microbial utilization) are occurring. The δ⁹⁸Mo values for the three tailings pond waters analyzed were very similar and were 1.5 ‰ lower than the coarse tailings samples, consistent with removal of Mo during formation of iron or manganese oxides or biological processes that favour assimilation of the lighter isotopes of Mo. The Mo concentrations in the Athabasca River at Fort McMurray are lower than those measured downstream of mining operations.