When a collapse in its services shaft caused rapid gas build up and its
premature closure in. 1951, the Blackwater Mine at Wiauta was in full production
with significant ore reserves yet to be mined. A total of nearly 23 tonnes of
gold was produced from the mine during its 44 year life. It was New Zealand's
deepest underground mine, producing gold from an extensive sub-vertical
mineralised quartz reef that averaged 0.6 m in width. Mining was by stoping
between adits and short shafts, latterly with the main mine access through the
840 m deep Prohibition shaft. Macraes Mining Company Ltd are presently
investigating the possibility of reopening the mine. This paper outlines a
preliminary assessment of the main geotechnical factors for achieving the
reopening, using recent exploration and old mine information. The greywacke host
rock mass in the vicinity of the quartz reef has been evaluated using both these
sources, and the paper discusses how the geological structure, intact and rock
mass strengths, the rock mass defects, in situ stresses, and groundwater inflows
may effect the reopening and support of the prohibition shaft, the excavation
methods and support for a new supplementary shaft, and the likely excavation and
support requirements for working adits and stopes in the rejuvenated
mine.