Download The evolution of magmatic arcs in porphyry copper systems

The evolution of magmatic arcs in porphyry copper systems formation: Southern
Peru
Fernando Nuñez and Adolfo Manrique, Southern Peru Copper Corporation, Lima, Peru
The Andes range, the most important tectonic feature of South America, is the product
of tectonic-orogenic deformation processes, which are associated with the generation of
magmas in different geological epochs. These, in turn, are directly or indirectly related
to the formation of metal-bearing ore deposits, remarkable porphyry systems, among
other.
The geodynamics of tectonic-orogenic episodes are characterized by distension and
compression phases, which are associated with the formation of magmatic arcs such as
the so-called volcanic island arcs of the Jurassic-Lower Cretaceous, those of the
Cretaceous-Paleocene and those of the Lower Oligocene; all of them related to the
generation of mineralization systems of economic value in Peru and South America.
The evolution of magmatic arcs are related to the formation of economically exploitable
porphyry systems of Cu-Au, Cu-Mo, or Cu-Mo-Au. Research results show that the
magmatic arcs that evolved from the Jurassic-Lower Cretaceous to the CretaceousTertiary are also genetically related to economically minable copper-gold mineralization
in porphyry systems that were emplaced in the so-called coastal range, as was the case
of La Tapada and Tia Maria. These porphyry systems indicate that in the western edge
of the South American plate a volcanic island arc existed, with the presence of tholeitic
magmatism that evolved into calc-alkaline magmatism which, contrary to what was
previously assumed, are related to the occurrence of economically minable copper
mineralization with absence of molybdenum and presence of gold.
The Cretaceous-Paleocene magmatic arcs are related to typical porphyry systems
known as Andean porphyries such as Cerro Verde, Toquepala, Quellaveco, Cuajone,
among others, which are associated to intermediate calc-alkaline magmatism with
copper and molybdenum mineralization, which develop marked hypogene alteration
halos that have been widely known and researched; however, according to recent work
these systems show the presence of economic mineralization at depths exceeding
1,200 meters of mineralized column with alteration assemblages of higher temperature,
as is the case of Toquepala.
Regarding the Oligocene magmatic arc emplaced on the eastern part of the Western
Range, a number of porphyry systems have been recognized, mainly Las Bambas and
Los Chancas, which systems are related to calk-alkaline magmas rich in potassium
feldspar associated with economically minable mineralization of copper, molybdenum
and gold. The petrographic characteristics of the plutons associated with this type of
mineralization show deep emplacements, embedded in thick sedimentary strata with
developments in areas of alteration-mineralization, different from known systems with
individual assemblages; these peculiar features of the system may correspond to a new
sub-type among Andean porphyry systems.