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

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 δ⁵⁶Fe and δ¹⁸O pairs for early-stage magnetite and late-stage hematite that provide information on the source reservoir of the hydrothermal fluids. Magnetite δ⁵⁶Fe values range from 0.46 ± 0.04 to 0.58 ± 0.02‰ and average 0.51 ± 0.16‰ (n = 10; 2σ). Three hematite δ⁵⁶Fe values were measured to be 0.34 ± 0.10, 0.42 ± 0.09, and 0.46 ± 0.06. Magnetite δ¹⁸O values range from 0.69 ± 0.04 to 4.61 ± 0.05‰ and average 2.99 ± 2.70‰ (n = 9; 2σ). Hematite δ¹⁸O values range from − 1.36 ± 0.05 to 5.57 ± 0.05‰ and average 0.10 ± 5.38‰ (n = 6; 2σ). These new δ⁵⁶Fe and δ¹⁸O values fingerprint a magmatic-hydrothermal fluid as the predominant ore-forming fluid responsible for mineralization in the Mantoverde system.