Intraplate orogenesis as a driver of multistage karst-hosted mineralization: the Imini manganese case (Atlas, Morocco)

IF 4.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Mineralium Deposita Pub Date : 2023-10-06 DOI:10.1007/s00126-023-01212-9
Augustin Dekoninck, Jocelyn Barbarand, Gilles Ruffet, Yves Missenard, Nadine Mattielli, Rémi Leprêtre, Abdellah Mouttaqi, Michèle Verhaert, Omar Saddiqi, Johan Yans
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Abstract

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.

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板内造山作用作为多阶段岩溶成矿作用的驱动因素:Imini锰案例(Atlas,摩洛哥)
伊米尼矿区(摩洛哥板内阿特拉带的南部前陆)拥有北非最大的锰资源,包括两个横向广泛的富含高品位软锰矿的锰矿体和第三个在~ 10 - 15米厚的塞诺曼-土伦系白云岩单元中含有的富含冕状锰矿的不连续中品位锰矿。到目前为止,锰矿石的起源和时间还没有得到很好的限制。新的铅同位素比值表明,三叠系(玄武岩和含铁砂岩)可能是金属的来源。K-Mn氧化物40Ar/39Ar测年表明,富锰矿体至少形成于晚白垩世至晚古新世(> 58 Ma)、晚始新世(约36.3 Ma)和早burdigian至早serravian三个时期,可能形成于约19-20 Ma和约13 Ma两个脉冲。这些时期与已知的晚白垩世、晚始新世和早中新世-中中新世三个亚特拉斯地貌建造阶段相吻合。因此,我们认为大西洋构造是锰成矿的一级控制。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,以维持(1)贫氧酸性流体与三叠系之间的流体-岩石相互作用,(2)富金属流体的运移,以及(3)Imini沉积部位的超压流体。Imini背斜前三叠系厚度的减小,迫使这些低温(< 100℃)流体与岩溶系统中的含氧和碱性地下水混合,沉淀Mn氧化物。北70°向的大西洋构造构造控制了锰矿床的走向。晚始新世-早中新世/中中新世隆升产生了晚白垩世初级中品位矿石的补充和/或原位再活化,形成高品位富软锰矿矿
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来源期刊
Mineralium Deposita
Mineralium Deposita 地学-地球化学与地球物理
CiteScore
11.00
自引率
6.20%
发文量
61
审稿时长
6 months
期刊介绍: The journal Mineralium Deposita introduces new observations, principles, and interpretations from the field of economic geology, including nonmetallic mineral deposits, experimental and applied geochemistry, with emphasis on mineral deposits. It offers short and comprehensive articles, review papers, brief original papers, scientific discussions and news, as well as reports on meetings of importance to mineral research. The emphasis is on high-quality content and form for all articles and on international coverage of subject matter.
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