Victor Maksaev

Associate Professor of Economic Geology
Departmento de Geologïa
Universidad de Chile
Plaza Ercilla #803
Casilla 13518 - Correo 21
Santiago - Chile
tel. 56-2-6784117
Fax 56-2-6963050

The geologic evolution of the Antofagasta segment of the Chilean Andes (21^o-26^oS) has been dominated by persistent subduction-migrated subsequent to tectonic pulses that are recorded in the stratigraphy. Hydrothermal processes associated with over 300 Ma of virtually continuous igneous activity generated most of the metallic ore deposits. These include some of the world's largest porphyry copper deposits and significant concentrations of gold, silver, copper, iron, and sulphur.

Field observations and new 40Ar-39Ar, K-Ar and fission track data indicate that the most important metallic mineral deposits of this Andean segment were formed during three discrete metallogneic epochs: (1) Middle to Late Jurassic copper stratabound and vein copper deposits of the Coastal Cordillera Metallogenic Belt (2) Paleocene epithermal silver and gold vein deposits, and sub-economic porphyry copper type, and breccia pipe deposits in the western section of the Domeyko Cordillera Metallogenic Belt; and (3) Late Eocene-Early Oligocene giant porphyry copper deposits along the Domeyko Cordillera Metallogenic Belt.

The metallogenic analysis suggests that geologic, tectonic, and geomorphic factors influenced arc-related magmatic activity, hydrothermal, and supergene processes. This accounts for the extraordinary specialization and recurrence of copper mineralization of the region. The thermochronological data are consistent with formation of major porphyry copper deposits following uplift. Geochemical and isotopic data support the hypothesis that porphyry copper mineralization resulted from a period of deep magma generation after a crustal thickening event. Characteristic magmas with restricted Sr, Nd, and Pb isotopic compositions and optimum proportions of volatiles extracted metals from their source, transported their loads to near-surface where late-magmatic/hydrothermal processes concentrated metals and sulphur. Limited regional denudation resulting from aridity since the Late Cretaceous contributed to the formation and preservation of rich supergene ores.

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Pages: 592
Supervisor: Marcos Zentilli