Noble gases as tracers of aquitard integrity
Location: University of Ottawa
Advisors: Drs. Ian Clark (Ottawa) & Uli Mayer (UBC)
Low permeability argillaceous formations are key hydrostratigraphic barriers in regions being considered for activities that pose a risk to groundwaters and surface waters. Notable are international studies on such formations for the safe disposal of nuclear waste. Knowledge of the hydrogeology and hydrologic history of thick argillaceous formations is critical to establish that diffusional regimes exist (Al et al., 2015) and to predict their ability to act as effective barriers to contaminant migration (Hendry et al. 2015). Depending on the recharge history of groundwaters and porewaters, stable atmospheric noble gases can be useful tracers of groundwater and porewater origin. The ingrowth of geogenic noble gases including 4He, 21Ne, 40Ar and 136Xe can be used as measures of groundwater and porewater age (Clark et al., 2013). The age and spatial distribution of conservative solutes in aquitards can then be simulated by numerical methods to test hypotheses regarding barrier longevity and governing mass transport processes and to increase confidence in formation scale properties necessary to predict long-term fluid migration.
The objective of this project are (i) to develop methods for the analysis of noble gas concentrations and stable isotopes in porewaters from drill core of low-permeability argillaceous material, (ii) establish concentration and isotope profiles of selected noble gas isotopes through such argillaceous units, (iii) undertake numerical simulations of the data sets to establish the hydrogeological history of the profile, conservative diffusion rates and in-situ residence times for these conservative solutes.
Work will take place in the Advanced Research Complex at the University of Ottawa with Clark, developing core sample analysis protocols on a Helix multi-collector noble gas mass spectrometer. Suitable material exists from the Bruce DGR project that can be acquired. Other drill cores of opportunity will be considered. Numerical simulations of diffusion profiles will be undertaken with Mayer at the University of British Columbia.
Al, T.A., Clark, I.D., Kennell, L. Jensen, M. and K.G. Raven, 2015. Geochemical evolution and residence time of porewater in low-permeability rocks of the Michigan Basin, southwest Ontario. Chemical Geology, 404: 1-17.
Clark, I.D., Al, T., Jensen, M., Kennell, L., Mazurek, M., Mohapatra, R., and Raven, K.G., 2013. Paleozoic-aged brine and authigenic helium preserved in an Ordovician shale aquiclude. Geology, 41: 951-954.
Hendry, M.J., Solomon, D.K., Person, M., Wassenaar, L.I., Gardner, W.P., Clark, I.D., Mayer, K.U., Kunimaru, T., Nakata, K. and Hasegawa, T., 2015. Can argillaceous formations isolate nuclear waste? Insights from isotopic, noble gas, and geochemical profiles. Geofluids, doi: 10.1111/gfl.12132.
Origin, residence times and geochemical signatures of deep crustal fluids
Location: University of Toronto
Advisors: Drs. Barbara Sherwood Lollar (Toronto) and Dominique Weis (UBC)
Postdoctoral Fellow sought for project on the origin, residence times and geochemical signatures of organic carbon pools in deep crustal fluids in Precambrian cratons. Research on fracture fluids 1-3 km deep in Precambrian Shield rocks across Canada, Fennoscandian and South Africa has revealed that such fluids, like those at the hydrothermal vents, are rich in dissolved substrates such as hydrogen and methane (Sherwood Lollar et al., 2002 Nature; Sherwood Lollar et al., 2006 Chemical Geology). In 2006, in Science, Sherwood Lollar and colleagues in microbiology (Lin et al. 2006) demonstrated the role of such H2-rich fluids in sustaining chemolithotrophic microbial communities at 2.8 km below the surface in the deep gold mines of South Africa – one of the deepest microbial ecosystems yet discovered. Most recently, by incorporating conservative noble gas tracers, the extreme antiquity of these hydrogeologically ancient fracture waters has been demonstrated – with residence times ranging from tens of millions of years in the Witwatersrand basin (Lippmann-Pipke et al., 2011 Chemical Geology) to billions of years in the Timmins mine in Northern Ontario Canada (Holland et al., 2013 Nature). The carbon source driven both abiotic organic synthesis reactions and the deep biosphere in these isolated parts of the crust have yet to be resolved however and will be the focus of this postdoctoral project. Of particular interest to the MAGNET fellowship will be integration of CHONS stable isotope techniques at U of Toronto with novel developments in chromium isotopes at UBC that may allow determination of the provenance of fluids before and after oxygenation of the Precambrian atmosphere.