Zircon crystallization and the lifetimes of ore-forming magmatic-hydrothermal systems

• Published in: Geology (Boulder) 2011-08, Vol.39 (8), p.731-734
• Main Authors: von Quadt, Albrecht, Erni, Michaela, Martinek, Klara, Moll, Melanie, Peytcheva, Irena, Heinrich, Christoph A
• Format: Article
• Language: English
• Subjects: absolute age; Alumbrera Mine; Argentina; Bingham mining district; Bingham Utah; case studies; Catamarca Argentina; Copper; copper ores; crystal growth; Crystallization; Economic geology; Geochronology; Geology; gold ores; hydrothermal conditions; igneous rocks; intrusions; Magma; magma chambers; magmas; magmatism; metal ores; metallogeny; mineral deposits, genesis; mineralization; nesosilicates; ore-forming fluids; orthosilicates; porphyry; porphyry copper; porphyry gold; Salt Lake County Utah; silicates; South America; Studies; U/Pb; United States; Utah; volcanic rocks; zircon; zircon group
• ISSN: 0091-7613; 1943-2682
• DOI: 10.1130/G31966.1

Magmatic-hydrothermal copper ore formation involves multiple pulses of subvolcanic porphyry intrusion, vein opening, and hydrothermal ore deposition. It is driven by larger subjacent magma reservoirs, acting as the source of fluid and ore-forming components. High-precision U-Pb ages of individual zircon crystals from porphyries immediately predating and postdating Cu-Au mineralization at Bingham Canyon (Utah, United States) and Bajo de la Alumbrera (northwestern Argentina) show a significant spread of reliably concordant ages. This demonstrates zircon crystal formation over a protracted period of ∼1 m.y., which is interpreted to record the lifetime of the magma reservoir from which porphyries and ore fluids were extracted. The youngest zircons in all pre-ore and post-ore intrusions overlap within a much shorter time interval of 0.32 m.y. at Bingham Canyon and 0.090 m.y. at Alumbrera; these youngest zircons of each intrusion are interpreted to bracket the maximum duration of porphyry emplacement and ore formation to short periods, consistent with thermal constraints. This study illustrates that age brackets based on individual magmatic zircon grains are geologically more informative than the calculation of means and standard deviations based on apparently normal age distributions in zircon populations.