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mineralizations, which upgraded the deposit significantly. The breccia-type U 4
mineralization accounts for the majority of the U in the Gunnar deposit.
3.5.2. Formation of breccia-type U deposits, the major U mineralization
Massive brecciation and formation of the breccia-type main U 4 -mineralizing event at
1850 Ma is linked to reactivation of the fault zones during the post-peak Thelon-Taltson
Orogen or, more likely, early stages of the Trans-Hudson Orogen (Dieng et al., 2011)
(Fig. 3.11D). δ 18 O, δ 13 C and δ 2 H values of syn-ore Chl 7 chlorite and Cal 8 calcite are
consistent with the ore-forming fluid as predominantly metamorphic in origin (Figs. 7 and
8). Syn-ore Chl 7 Chlorite crystal chemistry indicates that the fluid formed from Ca-Na-Fcontaining
metamorphic brine at ca. 330 o C also had relatively high Fe contents. These
fluids were likely derived from dehydration of hydrous minerals and ascended upward
along deep and large fracture systems and dilatant jogs that resulted from brittle
reactivation of early ductile shear zones, thus providing pathways for metamorphichydrothermal
mineralizing solutions (Fig. 3.11D). REE enrichment in U 4 uraninite,
abundant Cal 8 calcite in textural equilibrium with U 4 uraninite, and F in Chl 7 chlorite
indicate that U 4
uraninite transfer into the metasomatizing solutions was possibly as
uranyl-carbonate-fluoride complexes. Experimental results of Bilal and Koss (1980a)
demonstrate that both F - and CO 2- 3 can be effective ligands for complexing REE and U in
metasomatic fluids. The association of U 4 uraninite and Cal 8 calcite in the ore assemblage
(Fig. 3.4G) suggests that the fluids were likely alkaline (Cuney and Kyser, 2008). The
occurrence of both Br 1 brannerite and U 4 uraninite in the ore assemblage is similar to
others metamorphic-related U systems such as Valhalla (Polito et al., 2007) and the
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