IOCG deposits are major host for Cu, rare earth elements (REEs), U and other metals, and whose source(s) of ore-forming fluids are highly debated. Particularly, whether or not external fluid was involved during Cu-mineralization stage is of great interest and intense debate. In this contribution, we investigate this topic using triple sulfur isotope geochemistry of Cu-mineralization stage sulfides in the Mina Justa deposit. The results show that the chalcopyrite that intensely replaced early-stage pyrite has similar triple sulfur isotopic composition to early-stage pyrite, which largely in the range of magmatic sulfur (Δ³³S = 0 ± 0.05 ‰, Δ³³S = δ³³S − 1000 × [(1 + δ³⁴S/1000)^0.515 – 1]). However, chalcopyrite that occurs alone or with only minimal replacement of coexisting pyrite shows triple isotope (Δ³³S = 0.05 to 0.20 ‰) that deviates from magmatic sulfur. This indicates that the sulfur of chalcopyrite with intense replacement of early-stage pyrite mainly inherits sulfur from early-stage pyrite, while the sulfur of chalcopyrite that exist alone or with minimal replacement of pyrite obtained their sulfur from a non-magmatic source. Collectively, the triple sulfur isotope data indicates that external fluid is present in the Cu-mineralization stage.

IOCG 矿床是 Cu、稀土元素 (REE)、U 和其他金属的主要宿主，其成矿流体的来源备受争议。特别是在铜矿化阶段是否涉及外部流体引起了极大的兴趣和激烈的争论。在这篇文章中，我们使用 Mina Justa 矿床中铜矿化阶段硫化物的三硫同位素地球化学研究了这个主题。结果表明，强烈替代早期黄铁矿的黄铜矿具有与早期黄铁矿相似的三重硫同位素组成，主要在岩浆硫范围内（Δ ³³ S = 0 ± 0.05 ‰，Δ ³³ S =  δ ³³ S − 1000 × [(1 +  δ ³⁴ S/1000) ^0.515– 1]）。然而，单独出现或仅与共存的黄铁矿发生少量置换的黄铜矿显示出偏离岩浆硫的三重同位素（Δ ^{33 S = 0.05 至 0.20 ‰）。}这表明早期黄铁矿置换强烈的黄铜矿硫主要从早期黄铁矿中继承硫，而单独存在或黄铁置换极少的黄铜矿硫从非岩浆来源获得。总的来说，三重硫同位素数据表明在铜矿化阶段存在外部流体。