Mesothermal quartz lodes in Paleozoic Greenland Group
metasediments of the Reefton area have produced 67 t of gold up to 1951, and
recent exploration has identified new gold resources in several deposits,
including the largest past producers, Blackwater and Globe Progress. The
metasediments consist of alternating sandstone and argillite, metamorphosed to
lower greenschist facies and hydrothermally altered near the quartz lodes. We
examined and sampled drill core from four prospects, Globe Progress, General
Gordon, Merrijigs and Blackwater, to determine the mineralogical and geochemical
characteristics of hydrothermal alteration in the sandstone units. The
sandstones are feldspathic litharenites averaging Q65, FlO and R25, with
detrital grains of quartz, feldspar, rock fragments, muscovite, biotite (mostly
altered to chlorite), and trace quantities of graphite, apatite, zircon,
tourmaline and titanite. Hydrothermal alteration has developed a secondary
mineral assemblage of K-mica (muscovite, sericite and illite), carbonate,
chlorite, pyrite, arsenopyrite and limonite. The abundance of secondary chlorite
is greater at Blackwater than at the other locations studied. Features in the
sediments associated with increasing hydrothermal alteration towards quartz
lodes include, the development and increasing intensity of colour bleaching and
carbonate spotting, increasing quantities of disseminated pyrite and
arsenopyrite, and the appearance and increasing quantity and size of thin
carbonate, quartz and sulphide veins. This is accompanied by increasing
concentrations of sulphur, arsenic and antimony as shown in assays, and of
volatiles (loss on ignition) and iron as seen in XRF analyses. We were unable to
identify consistent trends in the behaviour of potassium, sodium, and calcium
that are exhibited by similar mesothermal quartz lode deposits inVictoria,
Australia.