This is a study of the variation in chemistry and inclusion mineralogy of
bedrock and placer gold from Fiji. It forms part of a large project,
undertaking gold characterisation from a wide range of geological
environments in Ecuador, Zimbabwe, Malaysia and Fiji. The work was
carried out under the Overseas Development AdministratiodBritish
Geological Survey Technology Development and Research programme
(Project R5549) as part of the British Government’s provision of technical
assistance to developing countries. For the Fijian component of the
project, samples were collected from river gravels, primary ore, and table
concentrates.
In total thirty-five samples from five localities were examined. Data
collected from these samples are represented by over 100 point analyses of
gold, identification of associated minerals, and microgeochemical maps of
gold-mineral intergrowths.
A framework for identifying possible sources of alluvial gold is given. This
was achieved by characterising bedrock gold mineralisation from a variety
of epithermal and porphyry environments. The environments studied
included alkali (the Emperor Gold Mine), high-sulphidation (the Mount
Kasi prospect) and telescoped (the Tuvatu prospect) systems.
A study of placer gold from the Waimanu alluvial deposit, the only alluvial
gold deposit in Fiji, showed two distinct sources of gold: one, a low-silver
type, associated with Cu-Fe sulphides, can be related to the nearby
Namosi porphyry copper deposit. The other source, a high-silver type with
abundant tellurides, indicates an alkali epithermal association, suggesting
a source similar in style to the mineralisation observed at Emperor Gold
Mine.
The identification of two bedrock sources for the Waimanu alluvials
clearly shows that there must be a, yet unknown, alkali epithermal
(Emperor) source within the Waimanu catchment. This demonstrates the
power of alluvial gold characterisation and its role in gold exploration.
An important implication of these results is that future exploration within
the area should be focussed on locating this “Emperor type” source
