The
Sovereign, Jubilee, Scotia and Jasper Creek prospects occur in an area of ~3.0
km by 2.5 km (~7.5 km2) in the Hauraki goldfield. The prospects are
hosted by andesitic to dacitic flows, autoclastic breccias and localised
pyroclastic and air fall deposits. Jubilee and Sovereign prospects lie along the
northern and southern parts of the Waitekauri Fault, respectively, whereas
Scotia is located ~1 km to the E, and Jasper
Creek a further ~1.2 km to the ENE. Wall rocks are typically intensely altered,
although the degree of alteration becomes more variable east of Scotia and at Jasper Creek. Alteration minerals include
quartz, adularia, albite, chlorite, pyrite, illite, interstratified
illite-smectite, smectite and calcite. Several of these minerals have
distributions that show distinct zonation with adularia most abundant at
Sovereign and Jasper Creek, but restricted to shallow levels at Scotia. Illite occurs throughout Sovereign and Jubilee
plus the western margin of Scotia where it
grades into interstratified illite-smectite; smectite predominates at Jasper
Creek. Veins are uncommon and typically narrow, but show distinct zonations.
Quartz veins are more abundant at Sovereign and Jubilee, whereas calcite veins
are more abundant at Scotia and Jasper Creek.
Laumontite veins occur at Scotia, and rare
clinoptilolite, mordenite and stilbite veinlets with calcite occur at Jasper
Creek. Fluid inclusion in quartz and calcite homogenised between 141 to 272C
and trapped a dilute solution with an apparent salinity of less than 2.6 weight
percent NaCl equivalent. Homogenisation temperatures are hottest at Sovereign
(average 241C) and Jubilee (average 239C), cooler at Scotia (average 204C) and coolest at Jasper Creek
(average 162C). Calculated paleowater table elevations suggest the water table
was 680 m to 750 m above sea level at Sovereign and Jubilee, 450 m at Scotia and 225 m at Jasper Creek. The current data suggest
three scenarios that can explain why Sovereign and Jubilee are deep and hot,
whereas Jasper Creek is cool, shallow and marginal;
1. some or all of the prospects may
represent separate overlapping hydrothermal system,
2. a high-relief hydrothermal system
on the side of volcano with an inclined water table and outflow towards Jasper
Creek, and
3.
a low-relief hydrothermal system
that has been either tilted or block faulted with greatest uplift and erosion to
the west.