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 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, along with temperature estimations for magnetite crystallization, are consistent with the manto magnetite belonging to an iron oxide-apatite (IOA) style mineralization that was overprinted by a younger, structurally controlled IOCG event that formed the hydrothermal unit orebody. Altogether, the stable isotopic data fingerprint a magmatic-hydrothermal source for the ore fluids carrying the Fe and Cu at Mina Justa and preclude significant input from meteoric water and basinal brines.

中文翻译：

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秘鲁 Mina Justa 氧化铁铜金 (IOCG) 矿床：对金属和矿石流体来源的限制

氧化铁铜金 (IOCG) 矿床是铜的主要来源，含有丰富的铁氧化物，并且在某些矿床中可能含有金、银、钴、稀土元素 (REE)、U 和其他金属作为经济上重要的副产品。它们由热液过程形成，但金属和矿液的来源仍有争议。我们研究了秘鲁 Mina Justa IOCG 矿床的热液单元和 Manto 矿体中磁铁矿的地球化学，以评估铁氧化物的来源及其与经济铜矿化的关系。我们确定了三种类型的磁铁矿：具有包裹体的磁铁矿（I型）仅在曼陀中发现，微量元素含量最丰富，结晶温度在459°至707°C之间；深色 (D) 型没有可见的夹杂物，在 543°C 左右形成；Bright (B) 型没有夹杂物，Fe 含量最高，形成于 443°C 左右。使用磁铁矿中的镁含量估算温度。Mina Justa 的磁铁矿样品产生的平均 δ⁵⁶ Fe ± 2σ 值为 0.28 ± 0.05‰ (n = 9)，平均 δ ¹⁸ O ± 2σ 值为 2.19 ± 0.45‰ (n = 9)，Δ ^'17 O 值介于 –0.075 和 –0.047‰ 之间. 硫化物分离产生 δ ⁶⁵Cu 值范围为 –0.32 至 –0.09‰。磁铁矿的微量元素组成和质地，以及磁铁矿结晶的温度估计，与属于氧化铁-磷灰石 (IOA) 型矿化的曼托磁铁矿一致，该矿化被更年轻的、结构受控的 IOCG 事件所覆盖，该事件形成了热液单位矿体。总而言之，稳定同位素数据为 Mina Justa 携带 Fe 和 Cu 的矿石流体提供了岩浆热液来源，并排除了大气水和盆地盐水的大量输入。