Geochemical and mineralogical characterization of weathered granite hosting secondary uranium mineralization: A case study from the eastern part of the Reguibat shield, Northern Mauritania

IF 3.4 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Brahim Salem-Vall , Akinade Shadrach Olatunji , Ahmed Hamoud
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Abstract

The eastern part of the Reguibat shield hosts significant uranium deposits in Northern Mauritania. Weathered granite identified as the uranium host rock. The study area located at the extreme eastern part of the Requibat shield hosts uraniferous granites form part of neobirimian ensemble belonging to yetti complex. The present investigation concerns the petrographic, geochemical and mineralogical characterization and secondary uranium mineralization genesis. Analyses were conducted using EPMA-EDS and ICP-MS. The study area is made up of two uraniferous granites, coarse-grained porphyritic pink with a mylonitic texture and medium-grained grey granite. Paragenesis consists mainly of Qtz + K-F + Pl + Bt + Ap + Sph + Zr + Amp + Cal + Cls ± granet ± Barite ± Ilmenite. Both granites represent monzogranite weakly peraluminous and shoshonitic. REE signature illustrates a negative anomaly of Eu (Eu/Eu* = 0.1 and 0.18 average), and slight fractionation of LREE from HREE remarkable particularly for grey granite ((La/Yb)N = 5.37–10.27). Multielement spectra show significant enrichments in U, Ta, and Pb, depletions in Ba, Nd, and Eu of pink granite. However, grey granite highlights significant enrichments in U, and Pb, while showing depletions in Nb, Eu, Zr, and Ba.
Geochemistry of the rocks highlights the emergence of the processes of fractional crystallization. Petrogenetic indicator K/Rb ratio suggests rock moderately evolved derived from fractionated magma with potential involvement of crustal material. Rock generated in deep sources of the lower crust or the upper mantle by partial melting. Grey granite similar to A-type however pink granite is S-I-type fractionated to nofractionated granite. Tectonic diagrams placed confirm syn-collisional pink granite and grey granite as within plate granite setting.
Both granites exhibit low CIA and PIA indicting low to moderate weathered rocks. Uranium bearing minerals (Carnotite and Tyuyamunite) occur as small grains size (∼ 10 μm) associated with weathering products filling voids and fractures of the granitoids. The presence of calcite, Celestine, fluorite are the indictors of uranium mineralization formation within evaporitic context in dry and low-temperature conditions.
风化花岗岩含次生铀矿化地球化学和矿物学特征:以毛里塔尼亚北部Reguibat盾体东部为例
毛里塔尼亚北部的瑞吉巴地盾东部蕴藏着重要的铀矿床。风化花岗岩被确定为含铀岩。研究区位于requbat盾构的最东端,含铀花岗岩是叶氏杂岩中新brimian系的一部分。本文对该区的岩石学、地球化学和矿物学特征及次生铀矿成因进行了研究。采用EPMA-EDS和ICP-MS进行分析。研究区由两种含铀花岗岩组成,一种是粗粒带糜棱质的粉红色斑岩花岗岩,另一种是中粒灰色花岗岩。共生主要由Qtz + K-F + Pl + Bt + Ap + Sph + Zr + Amp + Cal + Cls±花岗岩±重晶石±钛铁矿组成。这两种花岗岩均为二长花岗岩,弱过铝质和松玄质。稀土特征为Eu负异常(Eu/Eu* = 0.1,平均值为0.18),重、重稀土分异明显,特别是灰色花岗岩((La/Yb)N = 5.37 ~ 10.27)。多元素光谱显示,粉红色花岗岩中U、Ta、Pb富集,Ba、Nd、Eu缺失。然而,灰色花岗岩突出U和Pb的显著富集,同时显示Nb, Eu, Zr和Ba的耗尽。岩石的地球化学特征突出了分馏结晶过程的出现。岩石成因指标K/Rb表明,岩石演化中等,源自分馏岩浆,可能有地壳物质参与。由下地壳或上地幔的部分熔融而形成的深部岩石。灰色花岗岩与a型相似,而粉红色花岗岩为s - i型分选—非分选花岗岩。放置的构造图证实了同碰撞的粉红色花岗岩和灰色花岗岩位于板块花岗岩背景内。两种花岗岩均表现出较低的CIA和PIA,表明为低至中等风化岩石。含铀矿物(卡诺铁矿和tyuyamunt)以小颗粒(~ 10 μm)的形式出现,与花岗岩类孔隙和裂缝中的风化产物有关。方解石、天青石、萤石的存在是在干燥和低温条件下蒸发环境下形成铀矿化的标志。
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来源期刊
Journal of Geochemical Exploration
Journal of Geochemical Exploration 地学-地球化学与地球物理
CiteScore
7.40
自引率
7.70%
发文量
148
审稿时长
8.1 months
期刊介绍: Journal of Geochemical Exploration is mostly dedicated to publication of original studies in exploration and environmental geochemistry and related topics. Contributions considered of prevalent interest for the journal include researches based on the application of innovative methods to: define the genesis and the evolution of mineral deposits including transfer of elements in large-scale mineralized areas. analyze complex systems at the boundaries between bio-geochemistry, metal transport and mineral accumulation. evaluate effects of historical mining activities on the surface environment. trace pollutant sources and define their fate and transport models in the near-surface and surface environments involving solid, fluid and aerial matrices. assess and quantify natural and technogenic radioactivity in the environment. determine geochemical anomalies and set baseline reference values using compositional data analysis, multivariate statistics and geo-spatial analysis. assess the impacts of anthropogenic contamination on ecosystems and human health at local and regional scale to prioritize and classify risks through deterministic and stochastic approaches. Papers dedicated to the presentation of newly developed methods in analytical geochemistry to be applied in the field or in laboratory are also within the topics of interest for the journal.
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