The Imini mining district (southern foreland of the intraplate Atlasic belt of Morocco) hosts the largest Mn resources of North Africa, consisting of two laterally extensive bodies of high-grade pyrolusite-rich manganese ore and a third discontinuous medium-grade coronadite-rich Mn ore in a ~ 10–15-m-thick Cenomanian–Turonian dolostone unit. Until now, the origin and timing of the Mn ore have been poorly constrained. New Pb isotopic ratios show that Triassic series (basalts and ferruginous sandstone) are likely the source of the metals. ⁴⁰Ar/³⁹Ar dating of K-Mn oxides shows that the Mn-rich orebodies formed during at least three periods: late Cretaceous to late Paleocene (> 58 Ma), late Eocene (ca. 36.3 Ma), and early Burdigalian to early Serravalian probably in two pulses at ca. 19–20 Ma and ca. 13 Ma. These periods coincide with three known building phases of the Atlasic relief during late Cretaceous, late Eocene, and the Early(?)-Middle Miocene. We therefore propose the Atlasic tectonics as the first-order control of the Mn mineralization. Periods with regionally high elevations modified the climate to wetter conditions that supplied meteoric water to feed temporary aquifers. Relief building created the required hydraulic head to sustain (1) fluid-rock interaction between O₂-poor acidic fluids and the Triassic series, (2) migration of the metal-rich fluid, and (3) to overpressure fluid in the Imini depositional site. The decreasing thickness of Triassic series in front of the Imini anticline forced these low-temperature (< 100 °C) fluids to mix with oxygenated and alkaline ground waters in the karst system and precipitate Mn oxides. The N70°-oriented Atlasic tectonic structure controls the orientation of the Mn deposits. The late Eocene–Early/Middle Miocene uplifts generated additional supplies and/or in situ remobilization of the primary late Cretaceous medium-grade ore to form the high-grade pyrolusite-rich ore.

Graphical Abstract

中文翻译：

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板内造山作用作为多阶段喀斯特矿化的驱动因素：伊米尼锰矿案例（摩洛哥阿特拉斯）

伊米尼矿区（摩洛哥板内阿特拉斯带的南前陆）拥有北非最大的锰资源，由两个横向广泛的高品位软锰矿富锰矿体和第三个不连续的中品位富绿锰矿矿体组成矿石产于约 10-15 米厚的塞诺曼阶-土伦阶白云岩单元中。到目前为止，锰矿石的来源和时间还没有得到很好的限制。新的铅同位素比表明三叠系（玄武岩和铁质砂岩）可能是这些金属的来源。⁴⁰氩气/ ³⁹K-Mn氧化物的Ar测年表明，富锰矿体至少在三个时期形成：白垩纪晚期到古新世晚期（> 58 Ma），始新世晚期（约36.3 Ma），以及布尔迪加期早期到塞拉瓦期早期可能在两个时期脉冲在约。19-20 Ma 和大约。13马。这些时期与晚白垩世、晚始新世和早（？）-中中新世这三个已知的阿特拉斯浮雕建筑阶段相吻合。因此，我们提出阿特拉斯构造作为锰矿化的一级控制。区域性高海拔时期使气候变得更加湿润，为临时含水层提供了大气水。救援建筑创造了所需的水头来维持 (1) O _{2之间的流体-岩石相互作用}-贫酸性流体和三叠系，(2)富金属流体的迁移，以及(3)Imini沉积地点的超压流体。伊米尼背斜前三叠系厚度的减小迫使这些低温（< 100 °C）流体与岩溶系统中的含氧和碱性地下水混合并沉淀出锰氧化物。N70°取向的阿特拉斯构造构造控制着锰矿床的走向。晚始新世 - 早/中中新世隆起产生了额外的供应和/或原位再活化晚白垩世中品位矿石，形成高品位富含软锰矿的矿石。

图形概要