The Goldbanks deposit, owned by Kinross Gold, has had 1176
holes drilled to outline a geologic resource of 166 million tonnes
with a grade of 0.48 g/t gold and 1.40 g/t silver. The deposit was
found while prospecting in an historic mercury camp by G.L.
Grauberger in 1988. Geologic work prior to 1988 had not shown any
encouragement in attempts to locate a gold resource, primarily
because the mineralization does not crop out, and is covered by a
cap of basaltic flows and weakly consolidated Tertiary sediments.
Kinross acquired the property from Mr Grauberger in May, 1995,
and has delineated two mineralized deposits: the Main Zone, and the
The oldest rocks in the area consist of the Pumpernickel and
Havallah Formations generally considered to range in age from
Early Pennsylvanian to Early Permian. These units are unconformably
overlain by the Triassic Koipato Group, a series of rhyolitic
tuffs and shallow intrusions. A large body of Triassic
leucogranite is exposed in the northern part of the property and is
thought to be associated with the Koipato Group in age and composition.
Tertiary rocks unconformably overlie both Havallah and
Koipato rocks and have been subdivided into six separate rock units
based on dominant lithologies: a basal lithic sandstone (litharenite)
overlain successively by a polylithic breccia, a mudstone, opaline
sinter, weakly cemented volcaniclastics and basalt flows.
Tertiary strata were deposited into a rapidly subsiding basin
which covers most of the Goldbanks area. The basin development
coincided with the onset of Basin and Range faulting approximately
17 m.y. ago. The best hosts for gold mineralization are the lithic sandstone
and the polylithic breccia. Fractured areas in the Paleozoic and
intrusive rocks also host minor amounts of gold mineralization. The
strongest mineralization seems to be associated with the originally
most permeable rocks at the base of the Tertiary sediments.
The pathfinder elements arsenic and mercury show a weak correlation.
Iron oxidation has been found to depths of 365 meters
below surface along faults. The epithermal mineralization is interpreted
to have been formed by gold and silica-rich solutions ascending
along steep fault structures until they encountered permeable
clastic sediments along which the solutions migrated outwards to
form a siliceous blanket-shaped deposit in the Main Zone measuring
2 km by 1 km and approximately 90 m thick.