The
Eocene-Oligocene porphyry belt of northern Chile contains
the world's largest accumulation of porphyry-related copper metal. Conflicting
models exist regarding the relative importance of strike-slip and reverse
faulting during the emplacement of the porphyry and epithermal systems, based on
regional studies and also from work at the Chuquicamata deposit. In contrast, at
the Collahuasi district, high sulfidation state copper-silver mineralisation was
superimposed into the core of the Rosario copper-molybdenum porphyry deposits
along normal faults during gravitational collapse of the Domeyko Cordillera.
Exhumation of the porphyry environment occurred rapidly during this event,
allowing near-surface epithermal mineralisation (<200 m paleodepth) to be>
juxtaposed into the potassic altered core of the porphyry deposit (estimated
depth of formation: 1300 m) in the space of approximately one million years.
Mass wasting after major episodes of tectonic uplift provides an effective
method of hypogene upgrading of porphyry ores by high sulfidation
mineralisation.