The Pha Lek Fe-polymetallic deposit in the southwest of the Truong Son orogenic belt records the evolution and metallogenesis of the southeastern Asia Tethys. Debates remain on the roles the Late Triassic volcanism played in the formation of the iron oxides of the deposit. Petrographic and SEM studies led to the recognition of two dominant iron oxides (magnetite and hematite) and three stages of mineralization (pre-ore, syn-ore, and post-ore stages). In situ LA–ICP–MS analyses for trace elements and Fe and O isotopic analyses were applied to understand the origin of the iron oxides. Generally, iron oxide of the syn-ore stage has higher total trace elements than post-ore stage, and magnetite has higher lithophile elements, whereas hematite has higher chalocophile elements. The trace-element abundance in magnetite is most comparable to porphyry-skarn-hydrothermal magnetite, and hematite is more comparable to supergene and secondary, non-magmatic hydrothermal chemistry. All δ56Fe values of the iron-oxide separates are above 0‰ and have an igneous signature, and syn-ore stage magnetite has relatively higher δ56Fe values than the post-ore stage hematite. All δ18O values of the iron-oxide separates are below 1‰ and plot within the non-igneous field, and show a similar decreasing trend from syn-ore stage magnetite to post-ore stage hematite. We propose that the Triassic volcanic activities played a limited role during the mineralization process; the deposit was formed because of the Late Carboniferous–Early Permian, porphyry-skarn-related, magmatic hydrothermal alteration; and the mixing of non-magmatic fluid and/or the supergene weathering caused the wide reprecipitation of Fe oxides. An evolutionary mineralization model related to the low-angle subduction for the deposit is also proposed.

中文翻译：

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老挝长山造山带西北部 Pha Lek Fe 矿床铁氧化物的原位地球化学和 Fe-O 同位素组成：对成矿过程的影响

长山造山带西南部的 Pha Lek Fe-多金属矿床记录了东南亚特提斯山脉的演化和成矿作用。关于晚三叠世火山作用在矿床铁氧化物形成中所起的作用仍存在争论。岩相学和 SEM 研究导致识别出两种主要的氧化铁（磁铁矿和赤铁矿）和三个矿化阶段（矿前、同矿和矿后阶段）。应用微量元素的原位 LA-ICP-MS 分析以及 Fe 和 O 同位素分析来了解氧化铁的来源。一般来说，同矿阶段的氧化铁总微量元素高于成矿阶段，磁铁矿的亲石元素含量较高，而赤铁矿的亲硫元素含量较高。磁铁矿中的微量元素丰度与斑岩-矽卡岩-热液磁铁矿最具有可比性，赤铁矿与表生和次生非岩浆热液化学更具可比性。氧化铁分离物的δ56Fe值均在0‰以上，具有火成岩特征，同矿阶段磁铁矿的δ56Fe值相对高于矿后阶段赤铁矿δ56Fe值。铁氧化物分离物的所有δ18O值均低于1‰并在非火成岩场内绘制，并且从同矿阶段磁铁矿到矿后阶段赤铁矿显示出类似的下降趋势。我们认为三叠纪火山活动在成矿过程中的作用有限；该矿床是由晚石炭世-早二叠世、斑岩-矽卡岩相关的岩浆热液蚀变形成的；非岩浆流体的混合和/或表生风化作用导致铁氧化物的广泛再沉淀。还提出了与该矿床低角度俯冲相关的演化成矿模型。