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The Andean Cordillera, in the area of the Volcan project, is
characterized by a series of volcanic-plutonic arcs of Mesozoic-Cenozoic
age associated with the subduction of Pacific Plate beneath the western
edge of the South American Plate. During the Oligocene-Miocene (23-14
Ma) age, in conjunction with the formation of a large volcanic caldera
complex, several important hydrothermal systems developed leading to the
formation of the La Coipa silver-mercury-gold-sulphur deposit, the La
Pepa gold deposit and the Marte / Lobo deposits.
Ignimbritic flows covered and truncated hydrothermally
altered rocks in many localities, including La Pepa, and form a
volcanic plateau east of the mine. Some of the craters and
caldera-like circular structures on the Southern Claim Block
appear to be related to this phase of explosive volcanism.
Hydrothermal and solfataric activity led to the formation of
sulphur deposits above many strongly argillised and silicified
alteration zones. Cinnabar, vuggy quartz and enriched levels of
arsenic and other elements generally associated with gold, are
present in one hydrothermal explosion vent in Quebrada Azufre
Sur, possibly indicating that gold might have been concentrated
at depth.
Resurgence of the caldera floor may have elevated some of the older
volcanic strata, and magmatism culminated with the formation of the
6,052 meter high Volcán Copiapo summit, probably as late as 5 Ma or 4 Ma
ago. Late, dark coloured andesitic lavas covered much of the altered
zones, including some of the sulphur accumulations. Erosion has incised
abrupt ravines into the volcano flanks exposing alteration zones and
sulphur deposits.
Mineralization Gold-copper mineralization at Volcan is related to the intensely
developed hydrothermal alteration that gave rise to the native sulphur
deposits which occur throughout the property. The hydrothermal system
was a consequence of the sub-volcanic intrusion of dacitic to
microdioritic porphyry into a complex of domes and lava flows of dacitic
composition and the development of hydrothermal breccias is synchronous
with the widespread acid leaching of the host rocks. The known gold
mineralization often occurs in banded quartz veinlets within
transitional potassic-argillic altered volcanic flows. The style of
mineralization and associated alteration is consistent with gold
mineralization at other precious metal enriched, high sulphur epithermal
systems in the area.
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