The Golden Cross Mine is located within the Waitekauri Valley near the
southern end of the Coromandel Ranges, eight kilometres north-west of
Waihi, North Island, New Zealand. The mine is owned and operated in a
joint venture by Coeur Gold NZ Ltd (80 per cent) and Viking Mining Ltd
(20 per cent). The underground mine produces gold and silver from low
sulphidation epithermal quartz veins which developed in the shallow parts
of a meteoric water dominated system during the Upper Miocene (7.36 - 6.67 Ma). The Empire Vein System is hosted within a dilational structural
environment which developed at the lithological contact between acid
intrusives, rhyolitic-dacitic tuffs and reworked pyroclastics, and
undifferentiated andesites. The formation of the Empire Vein System was
controlled by the rheological properties of the host rocks and variable
displacement along a series of normal, right lateral, easterly-dipping
faults. These faults represent sub-parallel zones of master shearing within
a Riedel shear model. Underground mining extracts ore from the steeply dipping hangingwall
and the complex footwall veins of the Empire Vein System. Initially sills
are driven along the hangingwall vein on ten to fifteen metre sublevel
intervals. In the footwall zones where significant mineralisation adjacent
to the hangingwall sill drives has been identified, a series of cross-cuts
and footwall drives (sub-parallel to the hangingwall sill) are also
developed. Where continuity of mineralisation and ground conditions
permit a combination of post pillar flatbacking and AVOCA longhole
benching methods are used. Detailed underground mapping of lithology, quartz veining and major
structures provides the information for designing ground support and
footwall pillars, planning mine development and ore extraction
sequencing. Sectional interpretation displays the vertical extent of faults,
fractures and the vein system. The mining methods used underground at
the mine have evolved through a thorough understanding of the structural
complexity and the systematic geological mapping of the Empire Vein
System.