Alteration Related to Uranium Deposits in the Kiggavik-Andrew Lake Structural Trend, Nunavut, Canada: New Insights From Petrography and Clay Mineralogy

Abstract

International audienceThe Kiggavik project, located 70 km west of Baker Lake (Nunavut), is a major uranium exploration project in the Canadian arctic, with three significant basement-hosted uranium deposits (Kiggavik, End, and Andrew) which spread along a NE SW trend a few kilometers from the south-eastern border of the Thelon Basin. These deposits are closely associated with alteration zones in which clay minerals are abundant. At the scale of the whole structural trend, the alteration paragenesis is composed of illite +/- sudoite +/- hematite +/- aluminum phosphate sulfate minerals (APS). Alteration petrography and mineral paragenesis are similar to those identified in basement-hosted uranium deposits related to Paleoproterozoic unconfornaities in the Athabasca Basin (Canada) or Alligator River (Australia). The alteration haloes are characterized by two similar types of phyllosilicate assemblages (dioctahedral micas or illite and chlorites) corresponding to a regional retrograde metamorphic stage that was overprinted by hydrothermal alteration during the mineralization event. These two assemblages can be distinguished on the basis of crystallographic and chemical properties and mapping of structural parameters, such as the variation of crystallinity along the c-axis or the polytypes of phyllosilicates, which can be used as a vector to mineralization. The crystal chemistry of the hydrothermal phyllosilicates replacing the previous metamorphic minerals indicates a release of iron. This last point is fundamental to the occurrence of hematite in alteration zones and points out the potential effects of the iron redox state in the control of uranium precipitation during the hydrothermal even

The thermal stability of radiation-induced defects in illite

“…The crystal chemistry properties of these illites ( Fig. 1; Table 1) are representative of those already described in the Kiggavik area (Riegler et al 2014). In addition, the whole-rock chemistry indicates the presence of uranium in the illitized rocks (Table 1).…”

“…A selection of four pure illite specimens has been made in a larger data set of about 60 samples from illite-and sudoiterich alteration zones developed in the Woodburn Lake Group, an Archean volcano-sedimentary sequence hosting unconformity-related uranium mineralization, in the Kiggavik area, Nunavut, Canada (Riegler 2013;Riegler et al 2014), and in the Athabasca sandstones of the Shea Creek mining prospect, Saskatchewan, Canada (Laverret et al 2006). The age of alteration related to the ore formations is constrained within 1.2-1.4 Ga in both uranium deposits according to illite K/Ar geochronological data (Miller et al 1989;Laverret et al 2010).…”

Nanoscale relationships between uranium and carbonaceous material in alteration halos around unconformity-related uranium deposits of the Kiggavik camp, Paleoproterozoic Thelon Basin, Nunavut, Canada

“…During the alteration at Kiggavik, quartz was dissolved and all primary metamorphic silicate minerals (feldspars, muscovite, biotite, chlorite) were replaced by mainly illite and sudoite (Al-Mg di-trioctahedral chlorite) in various proportions. This alteration paragenesis is similar to that of many other Proterozoic unconformity-associated U deposits in Canada and Australia (Beaufort et al 2005;Laverret et al 2006;Hoeve and Quirt 1984;Polito et al 2004;Riegler et al 2014). …”

“…The main goal of the present study is to identify the origin of the CM associated with U minerals in the Kiggavik exploration camp located at the southeastern margin of the Paleo-to Mesoproterozoic Thelon Basin, building on the paragenetic context developed by (Riegler 2013;Riegler et al 2014;Riegler et al 2015;Sharpe 2013;Sharpe et al 2015). The second focus is on the solid properties of the CM to better understand their very unusual spatial and textural associations with U oxide minerals.…”

“…the main U minerals are uraninite and coffinite, are surrounded by decametre-scale clay alteration envelopes mainly developed in lower amphibolite to upper greenschist facies Neoarchean metagreywacke of the Woodburn Lake group (Riegler et al 2014;Lewry and Sibbald 1980). Unlike the basement-hosted deposits of the Athabasca Basin , deposits in the Kiggavik Project area are not located along graphitic conductors although reactivated intersecting faults are important in both camps Fuchs and Hilger, 1989;Miller and LeCheminant, 1985;Jefferson et al, 2007;Tschirhart et al, 2014).…”