The Reefton Goldfield has produced 67 t of gold from
mesothermal vein gold deposits in metasedimentary rocks of the Greenland Group
(Cambrian-Ordovician). The Globe-Progress deposit contributed 13.2 t (418,000
oz) of this total, predominantly from quartz veins. Recently a resource of 14 Mt
at 1.96 g/t Au (27.5 t or 882,300 oz of contained gold) has been
delineated at Globe-Progress in quartz vein remnants and disseminated within
adjacent sedimentary rock, much of which has been locally
brecciated.
The breccias consist of quartz vein and sedimentary wall
rock fragments set in a matrix of clay rock flour' and sulphide (arsenopyrite
plus minor pyrite and stibnite). Gold, closely associated with sulphide, is
disseminated within the breccia.
Disseminated gold also occurs in massive siltstone and
sandstone adjacent to the quartz veins and breccias. Exploration drilling at
Globe-Pogress, and several other Reefton prospects (e.g. Capleston, Merrijigs,
Big River and Alexander River), has intersected zones of
disseminated arsenopyrite carrying up to 20 g/t more gold. These mineralised
sediments commonly have little or no megascopic quartz and or carbonate veining.
There is little visible indication of former primary or secondary permeability
for the passage of hydrothermal fluid and deposition of gold. However, porosity
and permeability were formerly present in inter-granular pore spaces and
microveinlets now filled with quartz, carbonate and
K-mica.
The Fosterville gold deposit in Victoria bears many
similarities to the Globe-Progress deposit at Reefton, in terms of age, host
rocks, hydrothermal alteration and mineralisation style. Many ofthe disseminated
deposits in Nova Scotia, including deposits at
North Brookfield and Moose River (Touquoy
Zone), have similar characteristics to the Reefton disseminated mineralisation,
but commonly have abundant pyrrhotite and some deposits have disseminated metal
alloy grains of complex metallurgy.