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y the abundance of Ap 1 apatite and Mnz 2 monazite intergrown with U 5 uraninite in the
ore assemblage, suggesting that U 5 uraninite was probably transported in its oxidized state
as U 6+ primarily as uranyl-phosphate complexes (e.g. UO 2 (HPO 4 ) -2 2 ). Therefore, changes
in the pH or Eh state of the mineralizing solution through interaction between the
oxidizing hydrothermal brine and the reduced metamorphic host rocks was likely the key
process leading to U 5 uranium deposition. Destabilization of the aqueous uranyl-phosphate
complexes have resulted in the phosphate-bearing minerals intergrown with U 5 uraninite.
During the late Paleoproterozoic, the Athabasca Basin formed at ca. 1750 Ma
(Kyser et al., 2000) following exhumation of the Martin Lake Basin rocks. Tectonic
reactivation along fault zones during the Mesoproterozoic Mazatzal Orogen (Labrenze and
Karlstrom, 1991; Eisele and Isachsen, 2001) caused minor fracturing, deformation of the
basin and deposition of the 1620 Ma Athabasca-type U 6 mineralization observed in the
Ace-Fay and Martin Lake deposits (Dieng et al., 2011). Syn-ore Chl 9 chlorites formed
from fluids with δ 18 O and δ 2 H values (Fig. 3.8) identical to those of the unconformityrelated
U-deposits in the Athabasca Basin (e.g. Fayek and Kyser, 1997; Cuney and Kyser,
2008). The crystal chemistry of syn-ore Chl 9 chlorite indicates that fluids related to U 6
uraninite formed at ca. 235°C also identical to those of the Athabasca brines. U 6 uraninites
have total REE contents intermediate to those of U 4 and U 5 uraninites and are LREE
enriched, suggesting that these uraninites may have originated from an environment where
both U 4 and U 5 uraninites were remobilized. These observations suggest that this event
may be related in part to remobilization of pre-existing U mineralization into late fractures
from fluids that formed the unconformity-type U-mineralization in the Athabasca Basin
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