Tracing past migrations of uranium in Paleoproterozoic basins: New insights from radiation-induced defects in clay minerals

Abstract

Radiation-induced defects were identifi ed in kaolinite, illite, and sudoite by electron paramagnetic resonance spectroscopy of the alteration halo surrounding the uranium orebodies in the Athabasca Basin (Saskatchewan, Canada). Clay minerals are assumed to behave similarly under irradiation. In all samples, defects are similar in nature, but their concentrations can vary widely over several orders of magnitude. The maximum fl uctuations in defect concentrations are observed along the regional Paleoproterozoic unconformity between the lower sandstones and the metamorphic basement rocks and close to crosscutting brittle structures, both of which appear to be the main vectors of uranium-bearing fl uid transfer in the basin. In the basement, some Hudsonian faults connected to this unconformity also show high defect concentrations, attesting that uranium-bearing fl uids may have circulated in the fracture network. The proximity of mineralization can be revealed through defects that record the past presence of uranium in altered rocks at signifi cant distances from the mineralized bodies. The absence of correlation between defect concentrations and present dose rates indicates that migrations of uranium-bearing fl uids took place after the formation of clay minerals.

The thermal stability of radiation-induced defects in illite

“…They are very similar to the so-called A center in kaolinite, although their spectrum was described as being significantly broader, which may indicate a higher disorder in the defect environment (Morichon 2008;Allard et al 2012). Using defects in illite, it was also possible to suggest the past and transitory occurrence of uranium in some regions of the deposit (Morichon et al 2010). With this aim in view, the knowledge of stability of defects is essential for a reliable evidence of past migrations of uranium, especially when old and long-lived open geological systems, such as Meso-to Paleoproterozoic unconformity-related uranium deposits in Canada or Australia, are considered.…”

Intensive evaluation of radiation stability of phlogopite single crystals under high doses of γ-ray irradiation

“…Under these conditions, the radiation effect could be close to the radiation damage within the matrix of clay used in practice as their radiation defects are similar. 26 Taking these factors into consideration, phlogopite single crystals are the ideal material to investigate the mechanism of radiation damage within the clay matrix. It should be noted that even though the content of H 2 O in phlogopite crystals is small, its radiolysis cannot be avoided; generally, there is marginal H 2 O lying in the interlayers, edges, or on the surface, 1 as well as environmental condition.…”

Radioactivity recorded by clay minerals in the Shea Creek area, Athabasca Basin (Canada): Implications for uranium transfers and exploration

“…In the Athabasca Basin, temporary past radioactivity was revealed by the analysis of RID's in quartz and clay minerals up to 400 m and 1000 m away from the mineralization levels, respectively. The finding of one significant paleo-occurrence of radioelements at around 1000 m and one at 500 m vertical distances from unconformity by the study of clay minerals (Morichon et al, 2010b) may have important consequence on specifying the genetic model of ore deposits in the Athabasca Basin and this should be verified on other sites. Moreover, scattered data of [RID's] versus dose rate, instead of a single dosimetry curve, indicated anomalies related to past accumulations or losses of radioelements recorded since the formation of the clay minerals (Allard and Muller, 1998;Morichon et al, 2010b).…”

“…To improve the knowledge of the uranium migration processes, several studies, besides geochemical investigations, have considered the mineralogy, size fraction, and morphology of clay minerals as pathfinders (see, e.g., Hoeve and Quirt, 1984;Laverret et al, 2006;Kister et al, 2006). In order to reveal radioelement transfers, one can also take advantage of the record of the ambient cumulative dose of radioactivity by radiation-induced defects (RIDs) in quartz (Chatagnon, 1986;Botis et al, 2006;Hu et al, 2008;Cerin et al, 2017) or clay minerals (Clozel et al, 1994;Morichon et al, 2008Morichon et al, , 2010aMorichon et al, , 2010bAllard et al, 2012;Riegler et al, 2016) as evidenced by electron paramagnetic resonance spectroscopy (EPR). In the Athabasca Basin, temporary past radioactivity was revealed by the analysis of RID's in quartz and clay minerals up to 400 m and 1000 m away from the mineralization levels, respectively.…”