A combination of new radiometric age dates, local field
relationships and the regional tectonic history indicate that the
low sulphidation, fault breccia-hosted, epithermal gold-silver
mineralisation at Umuna is related to continental rifting processes
rather than subduction induced deformation and magmatism. K-Ar and Ar-Ar age dating of secondary sericite associated with
the gold-silver mineralisation indicates that the alteration
crystallised between 4.0 and 3.2 Ma, whereas relative age
relationships and SHRIMP II U-Pb dating of the abundant Boiou
porphyry intrusions on Misima confirm that the calc-alkaline
plutonism is significantly older (8.1 f 0.4 Ma) and related to a
different tectonothermal event. The Woodlark Basin sea floor spreading centre occurs to the north
of Misima and has continued to propagate westwards, into the
continental basement of the Papuan Peninsular, since the end of
the Miocene. The westernmost tip of sea floor spreading centre is
presently to the east of the D'Entrecasteaux Islands but would
have been to the east of Misima roughly 4 Ma. Many of the young
tectonothermal features in the D'Entrecasteaux Islands
(hydrothermal activity and associated epithermal mineralisation,
metamorphic core complex exhumation, detachment faulting,
peralkaline volcanism, half graben type basin formation) can be
attributed to major extensional deformation ahead of the
propagating rift system. Similar tectonothermal features on
Misima are temporally associated with the epithermal gold-silver
mineralisation at Umuna, suggesting that the D'Entrecasteaux
Islands are a modern day tectonic analogue for Misima at the
time of precious metal mobility and deposition. The rapid
exhumation of high grade metamorphic rocks and localised