Alluvial gold is an ideal exploration tracer to bedrock source and indicator
of bedrock mineralisation style because:
(i) gold occurs in a wide range of deposit types,
(ii) primary composition is sensitive to style of mineralisation, and
(iii) it is a heavy resistate mineral that is readily preserved and easily
sampled.
In regional exploration of the Central Ranges of Irian Jaya, alluvial gold
mineralogy has been applied to maximise the information return from panned
concentrate sampling and to focus exploration effort. Primary gold is a solid
solution of Au+AgCuHg, trace Pd, Te, and Sb. In general AgHg increase and
Cu decreases with inferred decreasing temperature of formation, and gold from
particular mineralisation styles has signature compositions that can be used as
indicators of bedrock mineralisation type. Furthermore, the abundance of
alluvial gold is an indicator of the economic potential of a catchment. The
convergent continental-oceanic plate geology of the Central Ranges is conducive
to a wide range of mineralisation styles. Mineralogy of gold in ophiolite,
skarn, porphyry, mesothermal vein and possible VHMS environments is
characterised from alluvial and bedrock samples, and the use of gold mineralogy
in prospecting at regional scale through prospect definition to drilling is
demonstrated.