Iron oxide copper-gold (IOCG) deposits are major sources of Cu, contain abundant Fe oxides, and may contain Au, Ag, Co, rare earth elements (REEs), U, and other metals as economically important byproducts in some deposits. They form by hydrothermal processes, but the source of the metals and ore fluid(s) is still debated. We investigated the geochemistry of magnetite from the hydrothermal unit and manto orebodies at the Mina Justa IOCG deposit in Peru to assess the source of the iron oxides and their relationship with the economic Cu mineralization. We identified three types of magnetite: magnetite with inclusions (type I) is only found in the manto, is the richest in trace elements, and crystallized between 459° and 707°C; type Dark (D) has no visible inclusions and formed at around 543°C; and type Bright (B) has no inclusions, has the highest Fe content, and formed at around 443°C. Temperatures were estimated using the Mg content in magnetite. Magnetite samples from Mina Justa yielded an average δ56Fe ± 2σ value of 0.28 ± 0.05‰ (n = 9), an average δ18O ± 2σ value of 2.19 ± 0.45‰ (n = 9), and D’17O values that range between –0.075 and –0.047‰. Sulfide separates yieldedmore »
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.
- Award ID(s):
- 1924142
- Publication Date:
- NSF-PAR ID:
- 10294839
- Journal Name:
- Mineralium deposita
- ISSN:
- 0026-4598
- Sponsoring Org:
- National Science Foundation
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Iron oxide-copper-gold (IOCG) deposits are major sources of Cu, contain abundant Fe-oxides and may contain Au, Ag, Co, rare earth elements (REE), U and other metals as economically important byproducts in some deposits. They form by hydrothermal processes, but the source of the metals and ore fluid(s) is still debated. We investigated the geochemistry of magnetite from the manto and breccia ore bodies at the Mina Justa IOCG deposit in Peru to assess the source of the iron oxides and their relationship with the economic Cu mineralization. We identified three magnetite types: Type Inclusion (I) is only found in the manto, is the richest in trace elements, and crystallized between 459 - 707 °C; Type Dark (D) has no visible inclusions and formed at around 543 °C; and Type Bright (B) has no inclusions, has the highest Fe content, and formed at around 443 °C. Magnetite samples from Mina Justa yielded an average δ56Fe ± 2σ value of 0.28 ± 0.05‰ (n=9), an average δ18O ± 2σ value 2.19 ± 0.45‰ (n=9), and Δ’17O values that range between -0.075‰ and -0.047‰. Sulfide separates yielded δ65Cu values that range from -0.32‰ to -0.09‰. The trace element compositions and textures of magnetite,more »
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Iron oxide-copper-gold (IOCG) deposits are major sources of Cu, contain abundant Fe-oxides and may contain Au, Ag, Co, rare earth elements (REE), U and other metals as economically important byproducts in some deposits. They form by hydrothermal processes, but the source of the metals and ore fluid(s) is still debated. We investigated the geochemistry of magnetite from the manto and breccia ore bodies at the Mina Justa IOCG deposit in Peru to assess the source of the iron oxides and their relationship with the economic Cu mineralization. We identified three magnetite types: Type Inclusion (I) is only found in the manto, is the richest in trace elements, and crystallized between 459 - 707 °C; Type Dark (D) has no visible inclusions and formed at around 543 °C; and Type Bright (B) has no inclusions, has the highest Fe content, and formed at around 443 °C. Magnetite samples from Mina Justa yielded an average δ56Fe ± 2σ value of 0.28 ± 0.05‰ (n=9), an average δ18O ± 2σ value 2.19 ± 0.45‰ (n=9), and Δ’17O values that range between -0.075‰ and -0.047‰. Sulfide separates yielded δ65Cu values that range from -0.32‰ to -0.09‰. The trace element compositions and textures of magnetite,more »
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Accepted Manuscript1.0
- Publisher's Version of Record
- https://doi.org/10.1007/s00126-019-00936-x
