Origin and geochemical characteristics of beryllium mineralization in the Zabara-Wadi El Gemal region, South Eastern Desert, Egypt

IF 1.4 4区地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS

Acta Geochimica Pub Date : 2024-05-04 DOI:10.1007/s11631-024-00698-y

Gehad M. Saleh, Farrage M. Khaleal, Mohammed Z. El-Bialy, Mohamed S. Kamar, Mokhles K. Azer, Mohamed M. Omar, Mohamed N. El Dawy, Ahmed Abdelaal, El Saeed R. Lasheen

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Abstract

Beryl is the commercial source of beryllium and several varieties of it are valued as a gemstone. To contribute to understanding the mechanism of beryl formation, we carried out detailed geological, petrographical, and geochemical investigations on beryl mineralization occurrences in the Zabara-Wadi El Gemal (Z-WG) region. This region is an NW–SE trending tract that includes six beryl-hosting areas. The green gem variety of beryl (emerald) is restricted to phlogopite schist, pegmatite, and quartz veins. Prismatic hexagonal emerald crystals are well-developed in phlogopite schist and pegmatite. The gem variety emerald examined is sodic and Cr-dominant. It contains high concentrations of chromophore transition elements ordering Cr (up to 1511 ppm) > V (up to 242 ppm) > Sc (up to 245 ppm), giving rise to its vivid green color, reflecting mafic–ultramafic source contribution. Among the investigated emeralds, the Sikait area contains the highest BeO (av. 10.76wt.%) concentration. The compositional variability of emeralds is most likely attributed to the contribution from the host rocks. This is revealed by the examined emerald mineralization, for instance; the Abu Rusheid area (one of the best areas exposing rare metal-bearing granitoids) possesses the highest average of trace and REEs concentrations. In contrast, Um Kabu emerald has the highest contents of Co (av. 20 ppm), Ni (av. 299 ppm), MgO (av. 8.2wt.%), Fe₂O₃ (av. 3.12wt.%), and CaO (avg. 3.4wt.%) relative to other areas, which may be linked to contribution of ultramafic rocks exposed there. The proposed mechanism we suggest for emerald genesis is metasomatic interaction between felsic (intrusions, that are enriched with K, Na, Be, Li, and B, with mafic–ultramafic rocks that are enriched in Cr, V, Mg, Fe, and Ca. This interaction is marked by the formation of phlogopite schist, the growth of emerald crystals, and desilicated pegmatite.

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埃及东南沙漠 Zabara-Wadi El Gemal 地区铍矿化的起源和地球化学特征

绿柱石是铍的商业来源，有多个品种的绿柱石被珍视为宝石。为了帮助了解绿柱石的形成机制，我们对 Zabara-Wadi El Gemal（Z-WG）地区的绿柱石矿化现象进行了详细的地质、岩相和地球化学调查。该地区呈西北-东南走向，包括六个绿柱石矿床区。绿柱石的绿色宝石品种（祖母绿）仅限于辉绿岩片岩、伟晶岩和石英脉。棱柱状六角形祖母绿晶体在辉绿岩片岩和伟晶岩中非常发达。经检测，宝石品种祖母绿呈钠态且以铬为主。它含有高浓度的发色过渡元素，包括铬（高达百万分之 1511）、钒（高达百万分之 242）和钪（高达百万分之 245），从而形成了鲜艳的绿色，反映了黑云母-超黑云母来源的贡献。在所调查的祖母绿中，Sikait 地区的氧化铍（平均 10.76wt.%）含量最高。祖母绿成分的多变性很可能是由寄主岩造成的。例如，Abu Rusheid 地区（揭露含稀有金属花岗岩的最佳地区之一）的微量元素和稀土元素平均浓度最高。相比之下，Um Kabu 绿宝石的钴（平均百万分之 20）、镍（平均百万分之 299）、氧化镁（平均 8.2wt.%）、氧化铁（平均 3.12wt.%）和氧化钙（平均 3.4wt.%）的含量相对其他地区最高，这可能与该地区出露的超基性岩有关。我们提出的祖母绿成因机制是富含 K、Na、Be、Li 和 B 的长英质（侵入体）与富含 Cr、V、Mg、Fe 和 Ca 的黑云母-超黑云母岩之间的成岩作用。这种相互作用的标志是辉绿岩片岩的形成、绿宝石晶体的生长以及脱硅伟晶岩。

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来源期刊

Acta Geochimica GEOCHEMISTRY & GEOPHYSICS-

CiteScore

2.80

自引率

6.20%

发文量

1134

期刊介绍： Acta Geochimica serves as the international forum for essential research on geochemistry, the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth‘s crust, its oceans and the entire Solar System, as well as a number of processes including mantle convection, the formation of planets and the origins of granite and basalt. The journal focuses on, but is not limited to the following aspects: • Cosmochemistry • Mantle Geochemistry • Ore-deposit Geochemistry • Organic Geochemistry • Environmental Geochemistry • Computational Geochemistry • Isotope Geochemistry • NanoGeochemistry All research articles published in this journal have undergone rigorous peer review. In addition to original research articles, Acta Geochimica publishes reviews and short communications, aiming to rapidly disseminate the research results of timely interest, and comprehensive reviews of emerging topics in all the areas of geochemistry.