Formation of the Mantoverde iron oxide-copper-gold (IOCG) deposit, Chile: insights from Fe and O stable isotopes and comparisons with iron oxide-apatite (IOA) deposits

• Published in: Mineralium deposita 2020-10, Vol.55 (7), p.1489-1504
• Main Authors: Childress, Tristan M., Simon, Adam C., Reich, Martin, Barra, Fernando, Arce, Mauricio, Lundstrom, Craig C., Bindeman, Ilya N.
• Format: Article
• Language: English
• Subjects: Apatite; Copper; Copper ores; Copper sulfides; Earth and Environmental Science; Earth Sciences; Fluids; Geology; Gold; Haematite; Hematite; Iron oxides; Isotopes; Magnetite; Mineral Resources; Mineralization; Mineralogy; Stable isotopes; Sulfides; Sulphides
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s00126-019-00936-x

The Mantoverde iron oxide-copper-gold (IOCG) deposit, Chile, contains hundreds of millions of tonnes (Mt) of mineable iron oxide and copper sulfide ore. While there is an agreement that mineralization at Mantoverde was caused by hydrothermal fluid(s), there is a lack of consensus for the role(s) that non-magmatic vs. magmatic fluid(s) played during the evolution of the mineralized system. In order to overcome the hydrothermal overprint at Mantoverde, which is known to disturb most conventional stable isotope systems (e.g., oxygen), we report the first δ 56 Fe and δ 18 O pairs for early-stage magnetite and late-stage hematite that provide information on the source reservoir of the hydrothermal fluids. Magnetite δ 56 Fe values range from 0.46 ± 0.04 to 0.58 ± 0.02‰ and average 0.51 ± 0.16‰ ( n = 10; 2 σ ). Three hematite δ 56 Fe values were measured to be 0.34 ± 0.10, 0.42 ± 0.09, and 0.46 ± 0.06. Magnetite δ 18 O values range from 0.69 ± 0.04 to 4.61 ± 0.05‰ and average 2.99 ± 2.70‰ ( n = 9; 2 σ ). Hematite δ 18 O values range from − 1.36 ± 0.05 to 5.57 ± 0.05‰ and average 0.10 ± 5.38‰ ( n = 6; 2 σ ). These new δ 56 Fe and δ 18 O values fingerprint a magmatic-hydrothermal fluid as the predominant ore-forming fluid responsible for mineralization in the Mantoverde system.