阿拉伯-努比亚地盾中蛇绿岩超基性岩的碳化和硅化以及含金鳞片岩的形成:来自 Al-Barramiya 地区的案例研究

IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
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引用次数: 0

摘要

阿拉伯-努比亚地盾(ANS)西北角加巴尔-巴拉米耶地区的新近新生代晚期地幔断面含有不同程度的蛇纹岩化橄榄岩,这些橄榄岩沿剪切带和推覆面发生了强烈的蚀变,形成了含金的列表岩。它们可分为碳酸盐闪长岩、硅碳酸盐闪长岩和硅闪长岩(桦皮岩)。碳酸盐 listvenite 的特征是存在与寄主蛇绿岩类似的片理和变形构造,但在硅碳酸盐 listvenite 和硅质 listvenite 中却不存在此类构造,这表明它们出现在碳酸盐 listvenite 和蛇绿岩化之后。沿剪切带出现的列表岩以及蛇纹岩和铬尖晶石遗迹反映了它们是由沿推覆断层循环的热液对超基性岩进行变质作用而形成的。硅碳酸盐岩的特征是含有富长石,富含锌、铅、铜、银和金。稀土元素(REE)的含量在所研究的列表岩中有所不同。硅碳酸盐列表岩的稀土元素总量最低(∑₌0.98-2.56 ppm),而硅列表岩的稀土元素总量最高(∑₌15.70-21.42 ppm)。根据上述情况,碳酸盐橄岩最早是由原前弧橄榄岩板块蛇绿岩化过程中释放的含二氧化碳流体渗入形成的,其次是由蛇绿岩俯冲过程中释放的二氧化硅饱和及含二氧化碳流体活动形成的硅碳酸盐橄岩。由于蛇绿岩化橄榄岩的热液蚀变作用,富含Si和K的流体与Cr-闪锌矿发生元气反应,形成了硅碳酸盐鳞片岩中的富长石。在最后阶段,早期形成的二氧化硅-碳酸盐列表岩发生硅化作用而形成二氧化硅列表岩。巴拉米亚蛇绿岩地幔段的列表venit化导致了金、铅、锌、铜和银的富集。与碳酸盐闪长岩(119-191 ppb)和硅质闪长岩(156-233 ppb)相比,硅质-碳酸盐闪长岩含有更高浓度的金(899-2199 ppb)。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Carbonatization and silicification of ophiolitic ultramafic rocks and formation of gold-bearing listvenites in the Arabian-Nubian shield: A case study from the Al-Barramiya district

Late Neoproterozoic mantle section in the Gabal Al-Barramiya area, the northwestern corner of the Arabian-Nubian Shield (ANS), contains variably serpentinized peridotites that are highly altered along shear zones and thrust planes to form gold-bearing listvenites. They can be categorized into carbonate listvenite, silica-carbonate listvenite and silica listvenite (birbirite). Carbonate listvenite is characterized by the presence of schistosity and deformation fabrics similar to the host serpentinites, but such fabrics are absent in the silica-carbonate and silica listvenites, suggesting that they postdate carbonate listvenite and serpentinization. The presence of listvenites along shears zones and the presence of relics of serpentine and Cr-spinel reflects their formation through metasomatism of ultramafic rocks by hydrothermal fluids circulating along the thrust faults. Silica-carbonate listvenite is characterized by the presence of fuchsite and is enriched in Zn, Pb, Cu, Ag, and Au. Rare earth element (REE) contents differ between the studied listvenites. Silica -carbonate listvenite has the lowest total REE (∑₌0.98–2.56 ppm), whereas the silica listvenite contains the highest total of REE (∑ ₌ 15.70–21.42 ppm). Based on the above, carbonate listvenite is the earliest to form by the infiltration of CO2–bearing fluids released during serpentinization of the original fore-arc peridotite slab, followed by formation of silica-carbonate listvenite due to the activities of SiO2–saturation and CO2-bearing fluids released during ophiolite obduction. Fuchsite in silica-carbonate listvenite formed as a result of metasomatic reactions of Si- and K-rich fluids with Cr-spinel due to hydrothermal alteration of serpentinized peridotite. Silica listvenite formed at the final stage by the silicification of the early formed silica-carbonate listvenite. Listvenitization of the mantle section of the Al-Barramiya ophiolite led to concentration of Au, Pb, Zn, Cu and Ag. The silica-carbonate listvenite contains higher concentration of gold (899–2199 ppb) than the carbonate listvenite (119–191 ppb) and silica listvenite (156–233 ppb).

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来源期刊
Journal of African Earth Sciences
Journal of African Earth Sciences 地学-地球科学综合
CiteScore
4.70
自引率
4.30%
发文量
240
审稿时长
12 months
期刊介绍: The Journal of African Earth Sciences sees itself as the prime geological journal for all aspects of the Earth Sciences about the African plate. Papers dealing with peripheral areas are welcome if they demonstrate a tight link with Africa. The Journal publishes high quality, peer-reviewed scientific papers. It is devoted primarily to research papers but short communications relating to new developments of broad interest, reviews and book reviews will also be considered. Papers must have international appeal and should present work of more regional than local significance and dealing with well identified and justified scientific questions. Specialised technical papers, analytical or exploration reports must be avoided. Papers on applied geology should preferably be linked to such core disciplines and must be addressed to a more general geoscientific audience.
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