Deposits of the Reefton
Goldfield, West Coast, New
Zealand, are hosted on N-NE striking, upright
folds of the Greenland Group. High-grade quartz lodes are hosted on axial planar
shears, typically have short strike lengths, and form shoots that pitch steeply
on the hosting shears. Deposits within the field area of a detailed structural
study share these characteristics. Field mapping and microstructural analysis
have demonstrated that the Greenland Group was affected by a multideformational
sequence. Gold mineralisation is hosted on shears axial planar to the
F2 folds, but occurred during a subsequent deformation event
(D4). Deformation during D4 resulted from N-NE directed
shortening, near parallel to the trend of the F2 folds. This
event produced F4 kink folds that were accommodated by layer parallel
slip on S2 parallel shears, gold mineralisation during D4
being confined to the dilational hinges of F4 kink folds. The
semi-brittle nature of D4 allowed the formation of stockwork veining
and disseminated mineralisation within the F4 hinge zones. Most
deposits within the goldfield are similar to those within the field area, and
are interpreted to have been mineralised during D4. The two largest
known deposits within the goldfield, however, are distinct. The Blackwater
Deposit, striking parallel to the hosting folds, has a combined strike length of
1 km. The Globe-Progress Deposit is hosted on an E-W striking discordant shear
in which a brittle zone of disseminated mineralisation encompasses high-grade
quartz lodes. The characteristics that distiguish the Globe and Blackwater
deposits may be due to formation before and after D4 respectively.
Detailed field mapping in the vicinity of known deposits throughout the
goldfield will further refine the relationships between the F2 folds,
later deformations and the localisation of ore deposits. Additional mapping may
also help constrain the position, orientation and extent of additional
orebodies.