A review of historic mining information and geological literature pertaining
to the Alpine Mine, Lyell Goldfield has been completed. As a result of this work
the Alpine reef is inferred to be associated with an upright anticline with a
sub-horizontal axis. Structural profiles prepared from limited underground data
indicate that the reef is subparallel to the eastern limb of the anticline and
cuts across the western limb.
Reassessment of structural mapping completed by the New Zealand Geological
Survey indicates that Greenland Group metasediments within the Lyell Goldfield
are folded into a series of opposed assymetic folds with sub-horizontal axes. It
is suggested that the anticline which harbours the Alpine Reef is located on the
axis of a synclinorium. Along the western limb of the synclinorium the
subsidiary folds have steep west dipping limbs and shallow east dipping limbs
(western sense of assymmetry) whereas shallow west dips and steep east dips are
typical of the eastern limb. The notion of quartz mineralisation occupying the
axis of a synclinorium is contrary to the situation in the Reefton Goldfield
where quartz mineralisation is affiliated with folds associated with an
anticlinorium.
Historic mine data reveals that below No.4 Level the quartz-gold
mineralisation, in the Alpine Mine, occupied a steeply dipping ore channel. The
strike of the channel was to the northwest and within this structure the are
shoots plunged to the north at approximately 40. Archival mine plans show that
two quartz bodies, the North and South Blocks, were present at No. 4 Level.
Although the North Block was followed down to No 14 Level (530 m vertically
below the surface outcrop) the South Block was only mined as far as No 7 Level.
Sampling on No 7 Level together with the results of trial mining suggest that
the grade of quartz underfoot in South Block is low.
Information from the Mines Statements and mapping undertaken by the Gold
Prospecting Scheme reveals that faulting had a profound influence on the
intregity and extent of the Alpine Reef. The reef occupies a Inajor shear zone
but little is known about it. It is also apparent that below No 7 Level the reef
was progressively shattered by faulting and this may be the chief reason for the
decrease in grade in the lower levels of the mine.
No substantive facts are available about wall rock alteration effects
adjacent to the Alpine Reef Still this is not surprising considering that
comments on the mineralised pug envelope and breccias adjacent to the mined
quartz shoots at the Globe - Progress Prospect were omitted from contemporary
publications. In spite of this the existance of sulphide bearing reef casing
lithologies cannot be completely dismissed since 9.15 m of 'reef track' has been
reported in Reids No 2 Level.