Abstract
The types of metallic ore deposits vary from porphyry copper to strata-bound deposit, which have been developed in many countries of the world. These economic ore deposits are especially concentrated in the convergent plate boundaries. However, the copper reserves are different from place to place, even in the Circum-Pacific subduction zone. The amount of copper reserves is excellent in the western coastal region of South America, and particularly the northern Chile (central Andes) is famous to occupy about 30% of world copper reserves. It is also noteworthy that the ages of N-S trending porphyry copper belts get younger to the East (inland Chile), indicating an inland migration of volcanic front. What factors control such process to concentrate copper? The original supplier of copper is a mid-oceanic ridge where metallic elements including copper, are fixed as massive sulfide ore deposits through the formation and sedimentation of chimneys. Later they move further from the midoceanic ridge through oceanic plate spreading and are fixed in a subduction zone. The mechanism to accumulate copper can be explained by “tectonic erosion”, which destroys the hanging wall of an older subduction complex or even the basement of the overriding continental plate. Accumulation of copper is driven by dehydration of subducting materials, consisting of both oceanic plate and eroded continental material, which could release metallic elements to forearc region with volatiles through hydrothermal circulation. This mechanism constrains subduction of metallic elements into deep mantle, resulting in storage of metallic elements within forearc region, since tectonic erosion emerged along the western coast of South America. In addition, ridge subduction causes partial melting of both oceanic plate and eroded continental material, resulting in formation of enormous porphyry copper deposits coupled with the inland migration of volcanic front. The tectonic erosion has been ongoing in the western coastal region of South America over 600 million years and will be a key mechanism to unravel the Andean metallogenesis through extensive future research. To emphasize the significance of this mechanism, we name it“ Metallogenic Copper Accumulation Mechanism (MCAM)”. And, the place to accumulate copper through tectonic erosion is named “Copper Bank”.
