Geothermal anomalies of different types occur within distinct
geological/structural settings in Papua New Guinea. According
to R.F. Herring, geothermal occurrences in Papua New Guinea
can be classified into two types, those related to vulcanism (Lihir,
Rabaul and other series of islands along the volcanic arc) and
those resulting from a regional heat flow probably caused by
radiogenic sources, for instance those in the Wau/Bulolo area.
The manifestation of this potential source of energy generally
coincides with either converging or diverging tectonic plate
boundaries. Previous inventories on thermal waters were carried
out by vulcanologists from the Rabaul Observatory in the early
1960s. However, these studies rarely included chemical analyses
of water and gas emissions and the investigations were carried
out in an ad hoc manner, generally as a secondary activity. The most recent investigation on thermal waters was conducted
on Lihir Island in connection with the development of the open
pit gold mine. These studies included detailed exploratory drilling
to a maximum depth of 730 m, and a water chemistry isotopic
sampling and analysis programme. The hydrothermal waters were
not considered as an energy source but as a hazard during the
development stage of the mine. Nevertheless, the geothermal
anomaly observed at Lihir includes hot springs emerging along
the coastal zones with temperatures that approach 100C, steam,
and thermal borehole waters with temperatures that exceed 200C. Chemical analysis results of thermal fluids from Rabaul, Talasea
and other areas in Papua New Guinea generally show high total
dissolved solids and low pH. In contrast, recent results from the
deepest and hottest thermal source at Lihir shows a neutral pH, a
Na-CI-SO4 composition and temperatures above 200C. Despite
the concentration of chloride being similar to that of sea water,
other chemical results and stable hydrogen and oxygen isotopic
compositions of thermal fluids imply the source to be mixture of
local meteoric water and deep thermal water rather than sea water.
Results of geothermal modelling suggests that the total geothermal
uptlow is equivalent to 54 MW.