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TitleGeneration of high-pH groundwaters and H2 gas by groundwater-kimberlite interaction, northeastern Ontario, Canada
AuthorSader, J A; Harrison, A L; McClenaghan, M BORCID logo; Hamilton, S M; Clark, I D; Sherwood Lollar, B; Leybourne, M I
SourceCanadian Mineralogist vol. 59, issue 5, 2021 p. 1261-1276,
Alt SeriesNatural Resources Canada, Contribution Series 20210302
PublisherMineralogical Association of Canada
Mediapaper; on-line; digital
File formatpdf; html
NTS32D/03; 32D/04; 32D/05; 32D/06; 32D/11; 32D/12
AreaKirkland Lake
Lat/Long WENS -80.0000 -79.3333 48.5833 48.0000
Subjectshydrogeology; geochemistry; Science and Technology; Nature and Environment; Economics and Industry; groundwater; groundwater geochemistry; hydrogen; alkalinity; hydroxides; bedrock geology; lithology; igneous rocks; intrusive rocks; kimberlites; isotopic studies; hydrogen isotopes; carbon isotopes; strontium strontium ratios; methane; magnesium geochemistry; potassium geochemistry; geothermometry; serpentinization; modelling; mining; tailings; Kirkland Lake Kimberlite Field; Phanerozoic; Mesozoic; Jurassic
Illustrationslocation maps; geoscientific sketch maps; tables; plots
ProgramTargeted Geoscience Initiative (TGI-5) Intrusion/Porphyry ore systems
Released2021 10 07
AbstractWe report new isotopic data for H2 and CH4 gases and Sr for groundwater collected from Jurassic Kirkland Lake kimberlites in northern Ontario, Canada. Groundwaters interacting with kimberlites have elevated pH (up to 12.4), are reducing (Eh as low as the H2-H2O couple), are dominated by OH- alkalinity, and have non-radiogenic (mantle) 87Sr/86Sr values (~0.706-0.707). Most significantly, the highest pH groundwaters have low Mg, high K/Mg, and are associated with abundant reduced gases (H2 ± CH4). Open system conditions favor higher dissolved inorganic carbon and CH4 production, whereas under closed system conditions low DIC, elevated OH- alkalinity, and H2 production are enhanced. Hydrogen gas is isotopically depleted (delta-2HH2 = -771 to -801 permille), which, combined with delta-2HH2O, yields geothermometry temperatures of serpentinization of 5-25 °C. Deviation of H2-rich groundwaters (by up to 10 permille) from the meteoric water line is consistent with Rayleigh fractionation during reduction of water to H2. Methane is characterized by delta-13CCH4 = -35.8 to -68 permille and delta-2HCH4 = -434 permille. The origin of CH4 is inconclusive and there is evidence to support both biogenic and abiogenic origins. The modeled groundwater-kimberlite reactions and production of elevated concentrations of H2 gas suggest uses for diamond-production tailings, as a source of H2 for fuel cells and as a carbon sink.
Summary(Plain Language Summary, not published)
This paper summarizes the results of a detailed study of the groundwater signatures of kimberlites in northeastern Ontario. This study was carried out as part of the Geological Survey of Canada's Targeted Geoscience Initiative.

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