Carbon-Sulfur-Metal-Rich Graphitic Pelitic Gneisses from the Fraser Lakes Zone B Deposit Area, Saskatchewan, Canada: Implications for Metal Source(s) - 2013

Uranium (Nuclear Minerals) / Exploration, Mining, Marketing, & Acquisitions

Annesley and four co-authors reported in 2013 that the U-Th-REE mineralization at Fraser Lakes Zone B is hosted by ~1800 Ma granitic pegmatite /leucogranite sheets intruding the tectonic decollement between basal Paleoproterozoic Wollaston Group pelitic (+/- graphitic, +/-sulfides) gneisses and underlying Archean granitoid orthogneisses. These carbon-sulfur-metal-rich pelitic gneisses are inferred to be metamorphosed (in part highly metalliferous) black shales deposited in a continental margin marine environment. Major, trace element, and REE geochemistry of these gneisses is highly variable, but still reflects original sedimentary facies variations of metal content and constrains original paleoredox conditions.

Besides their structural role in the location of the mineralization, they are probably also the source of many of the elements present in unconformity-type
deposits (e.g. U, Ni, Cu, Mo, and V) and of the possible reductants.

The authors indicated that after assessing element mobility, they concluded that the wide range of chemical variation in the fresh graphitic pelitic gneisses reflects original sedimentary facies variations of metal content and constrains original paleoredox conditions. The authors opined further that pre-Athabasca basal Wollaston Group graphitic pelitic gneisses have not only a strong structural control on the localization of the uranium deposits (Thomas et al. 2000, Annesley et al. 2005, Jefferson et al. 2007), but also their large metal enrichments represent the most likely metal source for many of the metals found within the U/C-type uranium deposits and they may also represent a source of reductants (carbon and sulfur species, NH4+ liberated from the alteration of the K-micas (Pascal et al. 2015).

These gneisses also contain significant amounts of U, Th, and REE. Low-batch melting of these gneisses can explain quite well the metal endowment of the magmatic U-Th-REE deposit at Fraser Lakes Zone B; making this zone both potential economic ore (i.e. Hudsonian-age mineralization) and potential source rock for the Mesoproterozoic U/C-type uranium deposits of the Athabasca Basin.