埃及爱资哈尔大学课题组近日取得一项新成果。他们报道了埃及沙漠东南部Zabara-Wadi El Gemal地区铍矿化成因及地球化学特征。该项研究成果发表在2024年5月4日出版的《地球化学学报》上。

研究显示，该地区为北西—东南走向，包括6个绿柱石赋存区。绿柱石(祖母绿)的绿色宝石品种仅限于金云母片岩、伟晶岩和石英脉。棱柱形六角形祖母绿晶体在金云母片岩和伟晶岩中发育良好。研究所检测的宝石品种祖母绿是钠质的和以铬为主导。它含有高浓度的发色团过渡元素，顺序为Cr(高达1511ppm)＞V(高达242ppm)>Sc(高达245ppm)，呈现出鲜艳的绿色，反映了镁铁质—超镁铁质对其的贡献。在研究所调查的祖母绿中，Sikait地区的BeO值最高(av.10.76 wt.%)。祖母绿的成分变异性很可能是因为寄主岩石的贡献。

举例来说，这是由祖母绿矿化所揭示的，Abu Rthemheid地区(含稀有金属花岗岩类的最佳暴露区之一)的微量元素和稀土元素平均浓度最高。相比之下，Um Kabu祖母绿的Co(av.20ppm)含量最高，Ni (av.299ppm)，MgO (av.8.2wt.%)， Fe₂O₃ (av.3.12wt.%)，以及CaO(avg.3.4wt.%)，这可能与暴露在那里的超镁质岩石有关。研究提出的祖母绿成因机制是富含K、Na、Be、Li和B的长英质侵入岩与富含Cr、V、Mg、Fe和Ca的镁铁质—超镁铁质岩石之间的交代作用。这种交代作用以金云母片岩的形成，祖母绿晶体的生长和伟晶岩脱硅为标志。

据介绍，绿柱石是铍的商业来源，它的几个品种是珍贵的宝石。为了进一步了解绿柱石的成因机制，该课题组人员对Zabara-Wadi El Gemal (Z-WG)地区的绿柱石成矿点进行了详细的地质、岩石学和地球化学调查。

附：英文原文

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

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

Issue&Volume: 2024-05-04

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.

DOI: 10.1007/s11631-024-00698-y

Source: https://link.springer.com/article/10.1007/s11631-024-00698-y