ALONG CONVERGENT AND COLLISIONAL PLATE BOUNDARY ENVIRONMENTS
Deposits at Convergent Boundaries:
convergent plate boundary environments mineralization takes place in the
principal arcs as well as in the inner side of the principal arc.
arcs are linear belts of volcanoplutonic rocks that occur above subducting
particularly of Cu, Fe, Mo, Au and Ag are closely associated with
calc-alkaline magmatism in such zones.
the Circum-Pacific Belt major metallic deposits occur in western North and
South America, Japan, Philippines, New Zealand and Indonesia.
than half of the world's supply of copper comes from the Porphyry Copper
Deposits of this region.
deposits associated with present and former convergent margins are:
Base metals (Cu, Pb, Zn, Mo).
Precious metals (Pt, Au, Ag).
Other metals (Sn, W, Sb, Hg).
Bed uranium deposits are also associated with convergent boundaries Eg SW United
is also noted on the inner side of the principal arcs.
of these are the contact metasomatic (skarn) deposits of Zn, Pb, Ag in
eastern Peru, and on the eastern side of the Sierra Madre ranges in Mexico.
deposits are related to subduction in the western United States during
Cretaceous to mid-Tertiary.
tin-tungsten belts of Bolivia, East Indian Archipelago and South China are
thought to be located along similar tectonic settings.
of mineral deposits forming at convergent margins is apparent, Eg in the
from west to east, the various zones encountered are:
a) contact metasomatic Fe-deposits
b) Cu-Ag and Ag veins
c) Porphypy Cu-Mo deposits
d) Pb-Zn-Ag veins and contact metasomatic deposits; and
e) Sn deposits.
These zones are caused due to progressive liberation of metals from the
descending slab, with Sn coming from a depth of 300 Km.
The metals are derived from some combination of the descending slab and the
overlying mantle wedge.
arcs' represented by the Japanese arc-system are thought to be suitable for
the deposition of Kuroko-type deposits (skarn deposits are also common
occurs in the back-arc basins in arc convergent margins where organic matter
is trapped and there is a lack of free circulation so that its oxidation is
heat facilitates conversion of organic matter to petroleum, and accompanying
deformation forms traps for accumulation of petroleum.
Fig. 2 shows an extensional arc system and related metallogeny.
Deposits at Collision Boundaries:
the collisional settings, important tectonic zones are the hinterland
margins, suture zones, foreland thrust belts and foreland basins.
the obducted ophiolites in the suture zone, stratiform exhalative Cu-Fe
sulfide deposits occur at Cyprus and Newfoundland, Canada (Ordovician), and
podiform chronite deposite at Semail, Oman (Cretaceous).
the foreland thrust belts, Sn-W mineralization occurrs in the S-type
granites in SW England and probably in the Central Himalaya.
the foreland molasse basins, uranium mineralization is reported from the
Siwaliks in India and Pakistan. Fig.
3 shows a collisional tectonic environment and related metallogeny.
of the deposits that occur in collisional zones may actually have formed in
diverse tectonic settings and have merely been transported to the collision
a variety of metallic deposits are abundant here:
generally related with oceanic ridges (ophiolites).
associated with convergent plate margins.
deposits associated with cratonic assemblages.
associated with continental rifts.
genetically related to collision zones are hydrocarbons which may
accumulate in foreland basins associated with such zones, Eg the Persian
Gulf SW of the Zagros Suture in Iran.