The Central Andes in
Peru,
Chile,
Bolivia, and
Argentina
,
contain two contiguous terranes which were accreted to Gondwanaland between the
end of the Devonian and the end of the Triassic. These terranes,
Arequipa
in the north, and
Chilenia in the south, differ from each other in the timing and style of their
metallogenic development. However, they contain over 90% of the Central Andean
porphyry copper resource. The copper porphyries in the
Arequipa
terrane are
Paleocene to lower Oligocene in age, whereas the Chilenia deposits are mid-upper
Cretaceous and mid-upper Miocene. Porphyry copper deposits occur outside these
terranes, but are all Miocene in age. Miocene porphyry-style mineralisation also
exists in the
Arequipa
terrane, but is copper-deficient and
gold-rich. The accreted terranes may have favoured porphyry and other styles of
copper mineralisation because they possessed relatively thin continental crust
compared to adjacent parts of the
Andes.
Crustal thickening which commenced at about 30 Ma in the
Arequipa
terrane coincided
with a major change to polymetallic, precious metal mineralisation which
commonly displays high sulfidation characteristics.