We report detailed mineralogy and geochemistry of hydrothermal mounds and chimneys in the TA25 West vent field (TA25 WVF), a newly discovered magmatic–hydrothermal system in the Tonga (Tofua) arc. Chimney samples are classified as sulfate- or sulfide-rich, based on major sulfide, sulfosalt, and sulfate minerals. The former type represents a simple mineral assemblage of predominance of anhydrite/gypsum + barite + pyrite, whereas the sulfide-rich chimneys show three different stages of mineralization with decreasing fluid temperature: sphalerite–pyrite dominated stage I, sphalerite–sulfosalts dominated stage II, and stage III is dominated by seawater alteration. Mound samples are characterized by sulfide assemblages and paragenesis similar to those of sulfide-rich samples, but abundant chalcopyrite indicates a relatively high-temperature mineralization. The chimney and mound samples are enriched in Au (average 9.2 ppm), Ag (297 ppm), As (1897 ppm), Sb (689 ppm), Hg (157 ppm), and Se (34.6 ppm). LA–ICP–MS and FE–TEM studies indicate that most of these elements occur in sulfides or sulfosalts in solid solution, although some occur as nanoparticles. This is mainly controlled by the combined effects of fluid conditions (temperature and redox state) and influx of ambient seawater. Petrography and trace-element compositions of sulfides and/or sulfosalts suggest that most concentrations of Au and Ag in the TA25 WVF result from the precipitation and/or adsorption of Au–Ag-bearing nanoparticles on rapidly crystallized sulfides, the substitution of Au and Ag in sulfide and/or sulfosalt minerals, and the saturation of Ag in hydrothermal fluids during late, relatively low-temperature mineralization (< 150 °C). The maximum measured temperature (242 °C) of venting fluids and calculated formation temperatures of sphalerite (229–267 ℃) are below the boiling temperature of seawater at the depths (966–1096 m) of the TA25 WVF, suggesting fluid boiling had little effect on Au–Ag-rich mineralization in the TA25 WVF. The presence of enargite–tetrahedrite–tennantite assemblages, high concentrations of magma-derived elements (e.g., Au, Ag, As, Sb, Hg, and Se), low δ³⁴S values (2.1 to 4.3‰) of sulfide minerals relative to the host rocks, and the distribution of CO₂-rich hydrothermal plumes (500 to 1000 ppm) suggest that the TA25 WVF is a submarine hydrothermal system influenced by a magmatic contribution in an arc setting. Our results indicate that the magmatic contribution is most likely to play an important role in supplying various metals, including Au and Ag, to the TA25 WVF. Subsequently, the rapid crystallization of sulfides induced by abundant fluid-seawater mixing significantly contributes to the precipitation of Au–Ag-rich mineralization.

我们报告了 TA25 West vent field (TA25 WVF) 中热液丘和烟囱的详细矿物学和地球化学，这是汤加 (Tofua) 弧中新发现的岩浆-热液系统。根据主要的硫化物、硫盐和硫酸盐矿物，烟囱样品被分类为富含硫酸盐或富含硫化物。前一种类型代表一个简单的矿物组合，主要是硬石膏/石膏+重晶石+黄铁矿，而富含硫化物的烟囱随着流体温度的降低显示出三个不同的成矿阶段：闪锌矿-黄铁矿占主导地位的第一阶段，闪锌矿-硫盐占主导地位的第二阶段，第三阶段以海水蚀变为主。土丘样品的特征是硫化物组合和共生，类似于富含硫化物的样品，但丰富的黄铜矿表明矿化温度较高。烟囱和土堆样品富含金（平均 9.2 ppm）、银（297 ppm）、砷（1897 ppm）、锑（689 ppm）、汞（157 ppm）和硒（34.6 ppm）。LA-ICP-MS 和 FE-TEM 研究表明，这些元素大部分以硫化物或硫盐的形式存在于固溶体中，尽管有些以纳米颗粒的形式存在。这主要受流体条件（温度和氧化还原状态）和周围海水流入的综合影响控制。硫化物和/或磺胺盐的岩相学和微量元素组成表明，TA25 WVF 中大多数浓度的 Au 和 Ag 是由含金银纳米颗粒在快速结晶的硫化物上的沉淀和/或吸附、Au 和 Ag 的取代引起的在硫化物和/或硫盐矿物中，以及在晚期相对低温矿化（<150°C）期间热液流体中Ag的饱和度。在 TA25 WVF 深度（966-1096 m）处，泄放流体的最高测量温度（242 °C）和闪锌矿的计算形成温度（229-267 ℃）低于海水的沸腾温度，表明流体沸腾几乎没有对 TA25 WVF 中富金银矿化的影响。辉锰矿-四面体-钛锰矿组合的存在，高浓度的岩浆衍生元素（例如，Au、Ag、As、Sb、Hg 和 Se），低 δ 在 TA25 WVF 深度（966-1096 m）处，泄放流体的最高测量温度（242 °C）和闪锌矿的计算形成温度（229-267 ℃）低于海水的沸腾温度，表明流体沸腾几乎没有对 TA25 WVF 中富金银矿化的影响。辉锰矿-四面体-钛锰矿组合的存在，高浓度的岩浆衍生元素（例如，Au、Ag、As、Sb、Hg 和 Se），低 δ 在 TA25 WVF 深度（966-1096 m）处，泄放流体的最高测量温度（242 °C）和闪锌矿的计算形成温度（229-267 ℃）低于海水的沸腾温度，表明流体沸腾几乎没有对 TA25 WVF 中富金银矿化的影响。辉锰矿-四面体-钛锰矿组合的存在，高浓度的岩浆衍生元素（例如，Au、Ag、As、Sb、Hg 和 Se），低 δ^{硫化物矿物相对于主岩的34} S 值（2.1 至 4.3‰）和富含 CO ₂的热液羽流（500 至 1000 ppm）的分布表明 TA25 WVF 是受岩浆贡献影响的海底热液系统。弧设置。我们的研究结果表明，岩浆贡献最有可能在向 TA25 WVF 提供各种金属（包括 Au 和 Ag）方面发挥重要作用。随后，大量流体-海水混合引起的硫化物快速结晶显着促进了富金银矿化的沉淀。