Metallogenic Provinces in Southeastern Pacific Region: ABSTRACT

Abstract

Mineral deposits of the southeastern Pacific region include: (1) hypogene, volcanogenic, and sedimentary deposits of the Andean region, (2) scattered copper deposits in the Antarctic Peninsula; and (3) metal-enriched sea-floor sediments and volcanic rocks. Andean metalliferous deposits are related spatially and genetically to calc-alkaline plutons and volcanic rocks emplaced during the Andean orogeny of Jurassic to Quaternary age. These deposits are components of a single metallogenic province, superimposed on two or more pre-Andean Paleozoic and Precambrian metallogenic provinces. Scattered copper deposits of the Antarctic Peninsula are similar in age and origin to deposits in the Andes and are considered to be in the Andean province. The sea-floor deposits include: (1) etal-enriched rocks and sediments that have formed at an accreting plate margin, such as the East Pacific Rise or near sea-floor volcanism; (2) sea-water precipitates; and (3) concentrations of heavy minerals in clastic sediments along the continental margin. End_Page 1435------------------------------ The Andean metallogenic province can be divided into dominant metal (or metals) subprovinces, each parallel with the Andes and the continental margin. The central Andes of Peru, northern Chile, and Bolivia contain the greatest concentration of exploitable deposits and greatest variety of ore types, and have five linear, partly overlapping, subprovinces. These subprovinces, from west to east, are characterized by deposits of: (1) iron; (2) copper, with or without gold; (3) polymetallic base metals (Zn, Pb, Cu), generally containing silver; (4) tin; and (5) gold. Iron deposits are near the coast from central Chile to southern Peru. The copper and polymetallic provinces are continuous throughout most of the central Andean region and extend south into Chile and north into Colombia. A disc ntinuous gold province, overlapping the copper and iron provinces, can be traced from central Chile to northwestern Colombia; another belt of gold deposits is in the eastern Andes from Bolivia to Ecuador. Tin deposits are restricted essentially to the eastern Andes of Bolivia. Magmas of the calc-alkaline rocks of the Andes are believed to have formed by melting of mantle, oceanic sediments, and oceanic crust at depths of 100 to 200 km along the Benioff zone. These igneous rocks generally decrease in age from west to east, though nonuniformly. Rocks of Jurassic and Cretaceous age are most abundant near the coast, whereas those of Tertiary and Quaternary age are dominant in the Andes; but locally, rocks and ore deposits of different ages are juxtaposed. These relations suggest variations in rates of subduction, in inclination of the subduction zone, and in position relative to the continental margin. Metals associated with the calc-alkaline rocks were supplied by the source rocks in the Benioff zone; some may have been enriched in metals, and from metal-rich ones in the overlying mantle and continental crust. The rising magmas probably assimilated or caused mobilization of previously formed ore deposits. End_of_Article - Last_Page 1436------------