Lake Kopiago is located some 71km
northwest of Tari in the Southern
Highlands Province and lies on the
northern edge of the Papuan Fold Belt.
The area is underlain by middle Miocene
carbonate and fine grained clastic
sediments intruded by late Miocene
hornblende gabbros.
Two mineral deposits occur to the
south of Lake Kopiago. These are the
Bisamu gold prospect and the Wunaki
zinc-lead gossan.
The Bisamu deposit consists of a
calcic skarn assemblage which is
geochemically anomalous in gold,
silver, copper, zinc, cobalt, bismuth
and tellurium. The prograde mineral
assemblage includes garnet, clino-
pyroxene and epidote whereas the
retrograde assemblage includes epidote,
quartz, actinolite and chlorite.
Pyrrhotite is the dominant sulphide
with minor pyrite and marcasite and
trace chalcopyrite and sphalerite.
Minor magnetite is also present. The
Bisamu skarn shows many of the features
typical of gold-skarn type mineral-
isation.