Abstract

Concealed porphyry copper-molybdenum target. High-grade mineralization. Drilling to date has delineated >260 million metric tons of hypogene ore averaging a little more than 1 percent Cu equivalent. The deposit is associated with a partly unroofed stock of biotite dacite porphyry, which was emplaced into broadly cogenetic andesitic and dacitic volcanic rocks during the Jurassic. A composite batholith of intermediate composition is located only 1.7 km from the deposit but was emplaced 30 to 40 m.y. earlier. The cylindrical orebody contains chalcopyrite, molybdenite, and local traces of bornite. The orebody is largely overlain by an essentially barren quartz-sericite-pyrite lithocap up to several hundred meters thick. High-grade copper-molybdenum ore is hosted by multiple hydrothermal breccias. Although the Mocoa porphyry system is overlain by a jarositic zone of partial leaching up to 260 m thick, rapid erosion during the late Cenozoic precluded generation of a significant zone of supergene chalcocite enrichment. The high precipitation caused nearly complete removal of abundant hypogene anhydrite and supergene gypsum to depths of at least 900 m.--Modified journal abstract.

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