On the genetic links between epithermal deposits and ash-flow calderas

摘要

Although spatial correlation between ash-flow calderas and epithermal ore deposits is well-documented, their temporal relationships are poorly understood. Thus, geochronological data indicate that mineralization can appear several millions years before or/and after the caldera formation. We present thermo-mechanical models of the upper crust before and afte caldera formation in order to add some large-scale overview for the devleopment of thermal and structural traps for epithermal deposits. Petrophysical properties have been incorporated into the models, which account for faulting initiation and caldera collapse mechanisms. The outer sides of the border faults are associated with both anomalous heat transfer and enhanced fracture density. Regional far-field extension favours conditions for porphyry-type deposits to form, at the expense of shallower ore deposits. When a hot silicic magma chamber settles in the shallow crust, the resulting overpressure can lead to pre-eruptive faulting, allowing for mineralization to predate the caldera formation.