The Central Chile Porphyry Deposits in Compression with Iranian Porphyry Deposits
|Category||Economic geology & mineral exploration|
|Location||The 24 Symposium of Geosciences|
|Author||Ahmad Kazemimehrnia -Reza Zarinfar|
|Holding Date||13 August 2007|
Field trip to Central Chile porphyry deposits was started on 25th April 2005 and finished on 28th April 2005. We have visited three of the main porphyry systems in Central Chile (El Teniente, Rio Blanco-Los Bronces and Los Pelambres).
The Chilean Andes are the most richly endowed copper province on the Earth. A total resource (including production) of about 490 million tones of fine copper has been identified in more than 63 porphyry copper deposits and numerous prospects.
Andean porphyry deposits occur along five metallogenic belts that extend from central Chile to southern Peru and northwest Argentina. They formed between the Early-Late Cretaceous and Pliocene. Within these belts the deposits occur in clusters associated with multiphase plutonic complex. These relationships are particularly prevalent in the Late Eocene –Oligocene belt, the most prolific of all. The time span between the oldest and youngest belt corresponds to the period in which contractional tectonism of the Andean cycle was established and developed from late Cretaceous to Recent.
The five porphyry belts reflect Andean tectonomagmatic evolution, with progressive eastern migration of volcanism and plutonism with time .Arc migration correlates with discrete and transient periods of increased convergence velocity and convergence angle.
These periods coincide with the strongest deformation events that in turn correlated with the temporal development of each one of the five porphyry belts. These events resulted in regional uplift, shortening, and crustal thickening which in turn produced syn-orogenic erosion.
Porphyry copper emplacement occurs syn-tectonically and the resultant multiphase intrusive complexes have variable compositions ranging from granodiorite to tonalite,
Monzonite and quartz monzonite evolving in all case from intermediate composition pre-mineral phases to more felsic intra-mineral phases .A reversal to more mafic magmatism has been reported locally.
Alteration and mineralization processes evolved from early magmatic stage dominated by high-temperature fluids to late stage dominated by low or more moderate temperature hydrothermal fluids with magmatic and meteoric components.
Supergene modifications such as oxidation, leaching and secondary enrichment have been very important in developing the high-grade copper ore bodies that are presently
Being profitably mined in the Andes. Lateral migration of copper –bearing solutions has developed proximal exotic deposits.