The Annaberg-Buchholz district is a classic occurrence of hydrothermal five-element (U-Ag-Bi-Co-Ni-As) veins in the Erzgebirge (Germany) with an historic production of ~8,700 metric tons (t) Co ore, 496 t U ore, and 26.9 t Ag. Multiple mineralization stages are recognized in polyphase veins hosted by Proterozoic paragneiss. Fluorite-barite-Pb-Zn mineralization occurs across the entire vertical profile of the district, whereas U and five-element stages are restricted to the upper 400 m below surface, coinciding with a graphite-rich gneiss lithology.Here, we present field and petrographic observations, electron probe microanalysis and fluid inclusion data, as well as thermodynamic calculations to characterize five-element and fluorite-barite-Pb-Zn associations, and to constrain the origin of the vertical zoning in the Annaberg-Buchholz district. Microthermometric analyses of fluid inclusions related to the fluorite-barite-Pb-Zn stage yield homogenization temperatures between 78° and 140°C and salinities between 21.9 and 27.7 equiv wt % (NaCl-CaCl₂). A correlation of fluid inclusion Na/ (Na + Ca) ratios with salinity suggests fluid mixing as a likely precipitation mechanism and relates ore formation tentatively to regional tectonics of the Mesozoic opening of the Atlantic.Thermodynamic calculations indicate that U is more sensitive to reduction than As, predicting that arsenide minerals are precipitated more distally relative to uraninite upon reduction along the fluid-flow path. This implies that the observed vertical zoning is not a primary feature but is the result of hydrothermal remobilization. The observations made in the Annaberg-Buchholz district have general importance to the understanding of U-rich five-element mineralization and may be relevant for exploration targeting in unconformity-related U deposits.

中文翻译：

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热液 U-Ag-Bi-Co-Ni-As 系统中的垂直分区：来自 Erzgebirge（德国）Annaberg-Buchholz 区的案例研究

Annaberg-Buchholz 区是 Erzgebirge（德国）的热液五元素 (U-Ag-Bi-Co-Ni-As) 矿脉的典型产地，历史产量约为 8,700 公吨 (t) Co 矿石，496吨铀矿石和 26.9 吨银。在元古界副片麻岩承载的多相矿脉中识别出多个矿化阶段。萤石-重晶石-Pb-Zn 矿化发生在该地区的整个垂直剖面上，而 U 和五元素阶段仅限于地表以下 400 m，与富含石墨的片麻岩岩性相吻合。岩相观察、电子探针微量分析和流体包裹体数据，以及热力学计算来表征五元素和萤石-重晶石-Pb-Zn 组合，并限制 Annaberg-Buchholz 区垂直分带的起源。₂）。流体包裹体 Na/ (Na + Ca) 比与盐度的相关性表明流体混合是一种可能的沉淀机制，并将矿石形成与大西洋中生代开口的区域构造暂时联系起来。 热力学计算表明 U 对还原更敏感因为，预测砷化物矿物在沿流体流动路径还原时相对于铀矿沉积在更远的地方。这意味着观察到的垂直分区不是主要特征，而是热液再动员的结果。在 Annaberg-Buchholz 区进行的观测对于了解富含 U 的五元素矿化具有普遍重要性，并且可能与不整合相关的 U 矿床的勘探目标有关。