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Updated: Sep 6, 2026

Preparation of Authigenic Pyrite from Methane-bearing Sediments for In Situ Sulfur Isotope Analysis Using SIMS
Published on: August 31, 2017
Variable redox states of sulfur in porphyry copper-fertile arc magmas
Xuyang Meng1, Adam C Simon2, Jingwen Mao3
1State Key Laboratory of Geological Processes and Mineral Resources/Ministry of Natural Resources Key Laboratory for Exploration Theory and Technology of Critical Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China.
Abstract:
Porphyry copper systems formed in magmatic arcs represent the largest concentrations of copper and most massive anomalies of sulfur worldwide. Whether the ore-fluid-source magmas were dominated by oxidized or reduced sulfur remains the subject of intense debate. Here, we quantitatively measured in situ the relative abundances of S6+, S4+, and S2- in sulfur-bearing primary apatite grains hosted in zircon, amphibole, and biotite in igneous rocks related to porphyry and skarn copper-gold deposits in the Middle-Lower Yangtze River metallogenic belt, Eastern China. Calculated S6+/ΣS ratios of the sulfur-bearing apatite grains vary from 0.18 to 0.97 and are independent of the crystallization pressure and temperature of their host minerals. The data reveal two distinct groups of ore-fluid-source magmas: (i) highly oxidized, dominantly sulfate (anhydrite)-saturated and (ii) relatively reduced, dominantly sulfide-saturated. The results demonstrate that economic porphyry copper systems can form from intermediate-felsic magmas over a broad range of S6+/ΣS ratios and oxygen fugacities (fO2), possibly throughout Earth history including the Proterozoic and Archean.
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