Proposed Title 1: - Queen's University

of the Arrowsmith Orogen at ca. 2.35 Ga (Berman et al., 2005, Dieng et al., 2011).
Metamorphic retrogression continued during exhumation to shallower crustal depths
resulting in greenschist facies conditions wherein retrograde Chl 1
chlorite replaced
regional metamorphic Bt 1 biotite down to ca. 200°C. Chl 1 chlorite reflects exhumation and
retrograde metamorphism to lower greenschist facies in the basement rocks during the late
stages of the Arrowsmith Orogen (Hartlaub et al., 2007; Berman et al., 2010).
Metamorphic-hydrothermal fluids associated with Chl 1
chlorite are relatively Ca-rich,
have high F and Mg contents and likely result from interaction with, or metamorphic
hydration of, Ca-Mg-F-rich rocks of the basement rocks.
Shear zones were reactivated at shallower levels resulting in overprinting of
mylonite by cataclasite and early tensional veins at ca. 2.29 Ga (Dieng et al., 2011).
Petrographic observations indicate that U 1
uranium mineralization occurs as fine
disseminations in the cataclasite matrix and is cut by early tensional Qtz 3 +Cal 3 -±U 2 veins
(Fig. 3.11B). Syn-ore Cal 4 calcite associated with U 2 uraninite at the Ace deposit has δ 13 C
and δ 18 O values that are consistent with fluids derived from retrograde metamorphic
processes. Syn-ore Chl 4 chlorite chemistry indicates that fluids associated with U 2
mineralization formed at ca. 310 o C and were Ca-F-Mg-rich. The compositional similarity
between syn-ore Chl 4 chlorite and retrograde Chl 1 chlorite indicates that U-bearing fluids
derived from retrograde metamorphic processes during exhumation and erosion during the
post-Arrowsmith Orogen may have been involved in the formation of U 2 mineralization.
Hydraulic fracturing in response to fluid generation via decompression and hydration was
probably the main mechanism of the early tensional vein formation. The high F and Ca
119