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of the Koolpin Formation, while deposition of ±U 1 -Au 1 -PGE occurred in fractured and
sheared quartz-feldspar porphyry at the Coronation Hill deposit. The U 1 -Gn 1 -Au 1 -Cpy 2 ore
assemblage formed at temperatures of ca. 250 o C, based on chlorite crystal chemistry (Table
4.4, Cathelineau, 1988). Mernagh et al. (1994) indicated a temperature of 140 o C based on a
microthermometry study of quartz veins at Coronation Hill. However, cross-cutting
relations indicate that these quartz veins formed earlier, during the pre-ore alteration stage
and therefore, pre-date the U mineralizing event. Chl 2
chlorites at Coronation Hill
paragenetically associated with the Qtz 2 quartz veins have formation temperatures near
160 o C (Table 4.4), similar to temperatures proposed by Mernagh et al. (1994).
The presence of small amounts of fluorine and chlorine in syn-ore Chl 2 chlorite
(Table 4.4) and phosphate in U 1 uraninite (Table 4.1) suggest that fluorine, chlorine, and
phosphate were important ore transporting complexes. Uranium is mobile under oxidizing
conditions (Cuney and Kyser, 2008) and in oxidized aqueous basinal brines between pH 4
and 7.5, uranyl-phosphate complexes are the important species (Cuney and Kyser, 2008),
while chlorine- and fluorine-complexes are dominant in fluids under acidic conditions at
temperatures up to 200°C (Romberger, 1984; Kojima et al., 1994). Interaction of oxidizing
mineralizing fluid with the reducing Fe-rich interlayered cherty ferruginous shale of the
Koolpin Formation may have led to deposition of the U-ore metals at El Sherana.
Petrographic observation indicates that early Py 1 pyrite (Fig. 4.6D) in the basement rock
was a reductant so that Fe 2+ or S in Py 1 pyrite would have acted as reductants for U 6+ .
In hydrothermal fluids, Au and PGE are soluble as chloride complexes (Mountain
and Wood, 1988a, 1988b), which are more important in oxidized, low-temperature, acidic,
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