The Benue Trough of Nigeria is an intracratonic rift basin hosting several vein-type base metal deposits. The Akiri Cu ± (Ag) deposit represents a distinct sub-class of sediment-hosted Pb-Zn-Cu-Ba mineralization found throughout the Benue Trough. The deposit is hosted in bleached red beds of the Keana Formation and in shale-siltstones and carbonates of the Ezeaku Formation in the Middle Benue Trough, North-Central Nigeria. Mineralization at the Akiri deposit occurs as vein in-fillings in a series of NE-SW and E-W trending faults and fractures in the Early- to Late-Turonian Keana and Eze-Aku sedimentary rocks. To better constrain the sources of ore minerals and structural controls on the formation of this sediment-hosted Cu ± (Ag) mineralization, we report combined geologic, geochemical, mineralogical, and stable isotopic data for the Akiri Cu ± (Ag) deposit. Major ore-stage sulfides at Akiri are chalcopyrite and pyrite, which were accompanied by several types of alteration, including silicification, hematization, limited pyritization, and bleaching of mineralized sandstone bodies. In-situ trace element and sulfur isotopic data distinguishes early-stage pyrite (Py1) from late-stage pyrite (Py2). The late-stage Py2 co-exists with chalcopyrite suggesting coeval precipitation. Early-stage pyrite (Py1) contains lower Ag (avg. 0.04 ppm) but higher Au (avg. 3.03 ppm) than the late-stage pyrite (Py2) (avg. Ag = 2.78 ppm; Au = 0.424 ppm). The δ³⁴S values of the early-stage sulfide (Py1) vary from 19.07‰ to 25.99‰ (avg. 22.20‰), suggesting that sulfur was largely derived from thermochemical reduction (TSR) of seawater sulfate. The δ³⁴S values for co-existing Py2 and chalcopyrite range from 9.83‰ to 11.24‰ (avg. 10.32‰) and from 7.37‰ to 10.69‰ (avg. 8.96‰), respectively, suggesting a derivation of sulfur from TSR of seawater sulfate with contributions from magmatic sulfur. Based on structural features and ore textures, we propose that sulfide precipitation at Akiri was facilitated by sulfur-rich fluids circulating through pre-existing structures (fractures and faults) under fairly high (>200 °C) to moderate (<170 °C) temperature conditions. Geological, mineralogical, geochemical and isotopic data from this study support the classification of the Akiri Cu (+Ag) deposit as an epigenetic sandstone-hosted copper deposit.

尼日利亚的贝努埃海槽是克拉通内裂谷盆地，拥有多个脉型贱金属矿床。Akiri Cu ± (Ag) 矿床代表了在整个 Benue 海槽中发现的一个独特的沉积物亚类 Pb-Zn-Cu-Ba 矿化。该矿床位于尼日利亚中北部贝努埃海槽中的 Keana 组的漂白红层和 Ezeaku 组的页岩粉砂岩和碳酸盐岩中。Akiri 矿床的矿化以一系列 N E 中的脉充填形式发生-早到晚Turonian Keana和Eze-Aku沉积岩中的SW和EW向断层和裂缝。为了更好地限制矿石矿物的来源和对这种沉积物承载的 Cu ± (Ag) 矿化形成的结构控制，我们报告了 Akiri Cu ± (Ag) 矿床的地质、地球化学、矿物学和稳定同位素数据的综合数据。Akiri 的主要成矿阶段硫化物是黄铜矿和黄铁矿，伴随着几种类型的蚀变，包括硅化、赤铁矿化、有限的黄铁矿化和矿化砂岩体的白化。原位微量元素和硫同位素数据将早期黄铁矿 (Py1) 与晚期黄铁矿 (Py2) 区分开来。后期的 Py2 与黄铜矿共存，表明存在同期降水。早期黄铁矿 (Py1) 包含较低的 Ag（平均 0. 04 ppm）但金（平均 3.03 ppm）高于后期黄铁矿 (Py2)（平均 Ag = 2.78 ppm；Au = 0.424 ppm）。δ早期硫化物 (Py1) 的³⁴ S 值从 19.07‰ 到 25.99‰（平均 22.20‰）不等，这表明硫主要来自海水硫酸盐的热化学还原（TSR）。δ ³⁴共存的 Py2 和黄铜矿的 S 值范围分别为 9.83‰ 到 11.24‰（平均 10.32‰）和 7.37‰ 到 10.69‰（平均 8.96‰），这表明硫从海水硫酸盐的 TSR 中衍生出来并有贡献来自岩浆硫。基于结构特征和矿石结构，我们认为在相当高（> 200 °C）到中等（<170 °C）条件下，富硫流体通过预先存在的结构（裂缝和断层）循环促进了 Akiri 的硫化物沉淀温度条件。本研究的地质、矿物学、地球化学和同位素数据支持将 Akiri Cu (+Ag) 矿床分类为表生砂岩铜矿床。