The reduction of oxidized sulfur is essential in porphyry copper deposits whose mineralization predominantly comprises copper sulfides, whereas their source magmas are oxidized with most of their sulfur as SO₄²⁻ and with exsolved fluids having SO₂>>H₂S. To estimate the redox state of sulfur, we examined drill cores that intersect potassic and unaltered intrusive rocks in the deeper levels of the Grasberg porphyry copper-gold deposit. Magmatic oxybarometers such as the amphibole-titanite-magnetite-quartz assemblage, anhydrite, and amphibole consistently show that Grasberg ore-forming magmas were oxidized with fO₂ > FMQ+3. Initial hydrothermal events formed sulfide-free, anhydrite-rich K-feldspar, and biotite alteration, followed by successive vein stages of (1) magnetite, (2) biotite, (3) quartz, (4) anhydrite-chalcopyrite, (5) chalcopyrite ± sericite selvages, and (6) pyrite-chalcopyrite-quartz + sericite selvages. The δ³⁴S values of sulfide-sulfate mineral pairs indicate SO₂-derived SO₄²⁻ and H₂S in SO₄²⁻/H₂S molar proportions of ~ 4:1 to ~ 3:1 at > 550 °C. The hydrothermal fluid then likely followed a rock-buffered trajectory and became more reduced at < 550 °C. Hydrothermal biotite that replaces igneous amphibole and biotite has a phlogopitic composition, suggesting that Fe²⁺ was liberated from igneous mafic minerals and oxidized by reaction with SO₄²⁻ to form magnetite, resulting in sulfide formation by the simplified reaction 12FeO + SO₄²⁻ + 2H⁺ → 4Fe₃O₄ + H₂S.

斑岩型铜矿床的矿化主要包括硫化铜，而氧化硫的还原是必不可少的，而斑岩型铜矿床的源岩浆被其大部分的硫以SO ₄ ²⁻和溶解的SO ₂ >> H ₂ S流体氧化。在硫的氧化还原状态下，我们检查了在Grasberg斑岩型铜金矿深层中与钾质和未改变的侵入岩相交的钻芯。岩浆含氧气压计（如闪石－钛铁矿－磁铁矿－石英组合物，硬石膏和闪石）始终显示，Grasberg成矿岩浆被f O ₂氧化。 > FMQ + 3。最初的水热事件形成了无硫化物，富含硬石膏的钾长石和黑云母蚀变，随后依次是（1）磁铁矿，（2）黑云母，（3）石英，（4）硬石膏-黄铜矿，（5）黄铜矿±绢云母边，以及（6）黄铁矿-黄铜矿-石英+绢云母边。的δ ³⁴硫化物系无机硫酸盐对价值观表示SO ₂衍生的SO ₄ ^2-和H ₂在SO小号₄ ^2- / H ₂在> 550°C时S的摩尔比为〜4：1至〜3：1。然后，水热流体可能会遵循岩石缓冲的轨迹，并且在<550°C时会进一步减少。代替火成闪石和黑云母的热液黑云母具有金云母成分，表明Fe ²⁺从火成镁铁矿质矿物中释放出来，并通过与SO ₄ ^2-的反应被氧化形成磁铁矿，从而通过简化的反应12FeO + SO ₄ ²形成硫化物。^-  + 2H ⁺  →的4Fe ₃ Ò ₄  + H ₂ S.