Brothers volcano, located on the Kermadec arc north of New Zealand, hosts two geochemically distinct hydrothermal systems. The NW Caldera and Upper Cone hydrothermal fields exhibit distinct fluid compositions that are significantly influenced by seawater and magmatic volatiles, respectively. In this study, we present trace metal chemistry and sulfur isotope compositions of pyrite within hydrothermally altered volcanic rocks recovered from drill cores at depths of up to 429 m below the seafloor collected during the International Ocean Discovery Program’s Expedition 376. Magmatic volatile-influenced alteration resulting in pyrophyllite ± natroalunite assemblages occurs at the Upper Cone and at the NW Caldera below 189 m. At the NW Caldera, a later seawater-derived hydrothermal fluid overprints magmatic volatile alteration forming chlorite-rich alteration. Pyrite at the Upper Cone is fine-grained, euhedral and enriched in Cu, As, Sb, Pb and Pt and has an average δ³⁴S composition of − 5.5 ± 2.9‰ (1σ, n = 32). In contrast, pyrite associated with pyrophyllite-rich alteration at the older NW Caldera site is coarse-grained, subhedral and has higher Co, Se, Te, and Bi contents but a comparable average δ³⁴S value of -4.8 ± 5.5‰ (1σ, n = 26). The difference in trace metal content between pyrite from pyrophyllite ± natroalunite assemblages at the NW Caldera and Upper Cone site indicates a change in the trace metal enrichment signature of pyrite with the age of the hydrothermal system. Pyrite from chlorite-rich alteration (NW Caldera) is depleted in Cu, Te and Bi relative to all magmatic volatile-influenced pyrite but has a similar average δ³⁴S composition of − 4.6 ± 3.5‰ (1σ, n = 20). The similarity in trace metal enrichment signature and average δ³⁴S composition of pyrite, regardless of associated alteration mineral assemblage shows that the initial magmatic volatile trace metal signature and sulfur isotope composition of pyrite is preserved during fluid overprinting. The lower content of Cu, Te, and Bi in pyrite from chlorite-rich alteration confirms the importance of seawater-derived hydrothermal fluids in metal mobilization and consequent formation of hydrothermal precipitates at the seafloor.

兄弟火山位于新西兰北部的克马德克弧上，拥有两个地球化学上截然不同的热液系统。NW Caldera 和 Upper Cone 热液场表现出不同的流体成分，分别受到海水和岩浆挥发物的显着影响。在这项研究中，我们展示了在国际海洋探索计划第 376 次远征期间收集的海底以下 429 m 深度的钻芯中回收的热液蚀变火山岩中黄铁矿的痕量金属化学和硫同位素组成。叶蜡石±钠铝石组合发生在上锥和 189 m 以下的 NW 火山口。在西北火山口，后来的海水衍生的热液覆盖了岩浆挥发性蚀变，形成了富含绿泥石的蚀变。上锥体的黄铁矿呈细晶、自面体，富含 Cu、As、Sb、Pb 和 Pt，平均 δ³⁴ S 成分为 − 5.5 ± 2.9‰ (1σ, n  = 32)。相比之下，在较老的 NW 破火山口地点与富含叶蜡石的蚀变相关的黄铁矿是粗粒的、半面体的，并且具有较高的 Co、Se、Te 和 Bi 含量，但可比较的平均 δ ³⁴ S 值为 -4.8 ± 5.5‰ (1σ , n  = 26)。在 NW Caldera 和 Upper Cone 地点，来自叶蜡石 ± natroalunite 组合的黄铁矿之间微量金属含量的差异表明随着热液系统年龄的增长，黄铁矿的微量金属富集特征发生了变化。与所有受岩浆挥发物影响的黄铁矿相比，来自富含绿泥石蚀变（NW Caldera）的黄铁矿的 Cu、Te 和 Bi 含量较低，但具有相似的平均 δ ³⁴ S 组成，为 − 4.6 ± 3.5‰ (1σ,n  =  20 )。无论相关的蚀变矿物组合如何，黄铁矿的痕量金属富集特征和平均 δ ³⁴ S 组成的相似性表明，在流体叠印过程中，黄铁矿的初始岩浆挥发性微量金属特征和硫同位素组成得以保留。富含绿泥石蚀变的黄铁矿中的 Cu、Te 和 Bi 含量较低，这证实了海水衍生的热液在金属流动和随后在海底形成热液沉淀物的重要性。