Rt€@lll

Figure): Diagramsof
Massive sulphide
(cul
-'
I
I
MID. oCEAN RI D GE
- llt
subduction and collision, with environrnents of mineralization
'cotLtsoN'
Thick crust sntsrs and chokes
tho Subduction System
Nodules
(Cu,CoI
High-level Au,
PorphyryS skarnlCu,Au,
\-- -.\
MANTLE luttramafic) -\
(Ni.Co, Cr)
sulphide
(Cu, P_b, Zn)
SUBDUCTION SYSTEM
Certain mineral deposits ere essociated with volcsnic processes, notebly the exhalative
bese-metal ruphide deposits of the rifte and +reading ridges, and the porphyry end sksrn
copper and gold and high-level gold and silver of the volcanic islands (Figure )). Tlese ere
the types of mineralization found in volcanic terrein.
In collision terrain, which by its natur€ mugt include volcenic terrain, the sarne types
of minerelization are found, but to thege are added the onee of nelals associated with mantle
rock8, notebly nickel, cobelt and chromium.
Examplee of volcanie terrain are the iglends of the Fiji and Western Samoa groups,
while the claseic exarnple of a collision terrein is New Caledonia (Figure l). In southwestern
Pryua New Guinea a third type of ternain, epi-cretonic, lrray be recognized where retatively
thin eediments ovarlie a northerly extension of the Ar.ntralian craton.