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TitlePreliminary results of coupled Fe and Mg isotopes plus Fe speciation investigations at the Bong uranium deposit, Thelon Basin Canada
AuthorPotter, E GORCID logo; Sharpe, R W; Girard, IORCID logo; Fayek, M; Gammon, P; Quirt, D; Robbins, J
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 37, 2014 p. 225-226 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20130509
PublisherGeological Association of Canada - Mineralogical Association of Canada
MeetingGAC-MAC 2014; Joint annual meeting of Geological Association of Canada and Mineralogical Association of Canada; Fredericton; CA; May 21-23, 2014
File formatpdf
NTS66A/05; 66A/06
Lat/Long WENS-98.0000 -97.0000 64.5000 64.2500
Subjectseconomic geology; geochronology; isotope ratios; isotopes; iron; magnesium; uranium; uranium deposits; Thelon Basin; Bong uranium deposit
ProgramTargeted Geoscience Initiative (TGI-4) Uranium Ore Systems
AbstractThe precipitation of significant amounts of Fe - and Mg - bearing minerals ( e.g. hydrothermal Fe - oxides/hydroxides and chlorite) is often genetically linked with formation of Proterozoic unconformity - related U deposits. The proposed mechanism is that the formation of these alteration minerals during host - rock alteration reactions released Fe 2+ whose oxidation to Fe 3+ facilitated reduction of U 6+ to immobile U 4+ through a coupled redox reaction, and the precipit ation of uraninite, the dominant ore mineral. Located on the southern margin of the northeast Thelon sub - basin, U at the Bong deposit is associated with a broad alteration halo characterized by intense illitization ± chloritization of the host Woodburn La ke Group metasedimentary rocks. Uranium precipitated in two generations, in veins associated with graphite (Stage A) and in miniature roll - fronts (Stage B) around 1120 Ma and 1040 Ma. Iron and Mg isotope compositions (d 57 Fe and d 26 Mg) were determined by M C - ICP - MS for whole - rock and clay - sized fractions after a four acid digestion of powdered core samples from a mineralized drill hole. Both whole - rock and clay - size fraction data exhibit downhole zones with significant positive isotopic shifts. Whole - rock s amples produced the widest range in d 57 Fe IRMM - 14 values (+0.48 to +1.30permil), whereas the clay - sized fraction yielded the greatest range in d 26 Mg DSM - 3 values (+0.73 to +1.02permil). A zone with elevated d 57 Fe and d 26 Mg values is associated with the alteration zon e of the Bong deposit and a hematitic alteration zone, located at the top of the drill hole, that is often ascribed to 'paleoweathering' in the literature. These isotopic values correlate with relatively low molar Fe 2+ concentrations in the altered zones (0.47 mol.% Fe 2+ ) whereas the molar concentration of Fe 2+ in unaltered zones is 2.30 mol.%. Concentrations of Fe 3+ remain relatively constant in both altered (0.47 mol.% Fe 3+ ) and unaltered (0.51 mol.% Fe 3+ ) zones. Therefore, host - rock alteration processe s, that formed both the U - bearing alteration and the red hematitic so - called 'paleoweathering', mobilized Fe 2+ while enriching the fluids in the lighter isotopes of Fe and Mg. The association of similar elevated isotopic values with both the host - rock alt eration and the red hematitic material suggests that this latter material is unlikely to have formed through paleoweathering processes.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. These studies are exploring potential new exploration vectors that may also lead to refinements of the ore deposit model through examination of Fe and Mg isotope signatures and shifts in Fe oxidation state (Fe2+ vs. Fe3+) at the Bong U deposit and nearby 'paleoweathered' horizons. The preliminary results of this study highlight significant isotopic shifts coupled with changes Fe2+/Fe3+ ratios in the ore zones and paleoweathered horizons, suggesting both the U-bearing alteration and paleoweathered zones formed by a similar process that mobilized Fe2+ while enriching the fluids in the lighter isotopes of Fe and Mg.

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