Epithermal Silver-Gold Veins at Palmarejo, Guadalupe and La Patria, Chihuahua, Mexico

摘要

The Palmarejo, Guadalupe and La Patria Silver-Gold epithermal vein deposits occur in south-western Chihuahua state, Mexico (Figure 1). The veins are hosted in a volcano-sedimentary sequence that comprises andesitic to basaltic resedimented volcaniclastic rocks, together with less abundant coherent and pyroclastic facies and minor red-beds. The host sequence is part of the Lower Volcanic Series, and formed in a magmatic arc environment during the Late Cretaceous to Early Tertiary Laramide Orogeny. The Lower Volcanic Series is overlain unconformably by an extensive sequence of Miocene rhyolitic ignimbrites, known as the Upper Volcanic Series. At this time, it is uncertain whether epithermal mineralisation was related to andesitic intrusions (85 Ma) and/or Oligocene rhyolitic dykes (25 Ma). Epithermal Ag-Au orebodies at Palmarejo, Guadalupe and La Patria are hosted in fault-hosted vein breccias (interpreted here to be hydrothermal-tectonic breccias), with mineralisation related to several brecciation events defined by different ore and gangue assemblages.