南非 Soutpansberg 煤田 6 号煤层中 REY-Ga-Se-Nb 富集分布的矿物学和地球化学控制因素

IF 3.2 2区 地球科学 Q1 GEOLOGY
Sanki Biswas, Ofentse M. Moroeng, Nicola J. Wagner
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引用次数: 0

摘要

煤炭被视为稀土元素(REY + Sc)的潜在替代来源,而稀土元素对现代技术的发展至关重要。以前的研究主要集中在评估南非煤炭中 REY + Sc 的浓度和分布。然而,这些元素在煤炭中的出现模式还有待研究。本研究对南非苏特潘斯贝格煤田 6 号煤层的矿物学和无机地球化学有了新的认识。目的是研究煤中 Ga、Se、Nb 和 REY + Sc 等关键元素的分布、富集和出现模式。6 号煤层是一种中等阶 B、中等玻璃光泽度(平均 41.5 vol%)的煤炭,含有高岭石、石英等主要矿物和麝香石、菱铁矿、白云石、黄铁矿、方解石等次要矿物。煤炭样本中的总 REY + Sc 浓度范围为 79.9 至 332.1 毫克/千克(平均值为 213.2 毫克/千克;全煤/岩石基),高于全球硬煤的平均值。煤的上部大陆地壳(UCC)归一化浓度系数(CC)显示出 La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy、Er、Yb 和 Y 的富集。在不同煤层中观察到不同的 REY + Sc 富集模式,分为两类:底层煤[底-上(BU)和底-下(BL)]富含轻型 REY(LREY)和中型 REY(MREY),而中层煤[中-上(MU)和中-下(ML)]富含中型 REY(MREY)和重型 REY(HREY)。与 MU 和 ML 样品相比,BU 和 BL 样品显示出更高的 REY + Sc 富集度。这些样品还含有较高浓度的镓(最高 106.1 毫克/千克)、硒(最高 50.9 毫克/千克)和铌(最高 14.8 毫克/千克),超过了中国煤炭报告的平均值。在考虑 REY + Sc 与主要氧化物元素、矿物和有机岩相组合之间的相关性时,REY + Sc 似乎与无机部分,特别是铝硅酸盐(如高岭石)和碳酸盐矿物(如白云石)的关系更为密切,而不是与有机部分的关系。高岭石和白云石分别代表了大部分的碎屑输入和外生成分。煤中的镓主要与氧化铝-氢氧化物有关,铌与粘土、金红石/金红石和锆石等矿物有关,而硒则与黄铁矿有关。Al2O3/TiO2和TiO2/Zr的氧化还原敏感元素比率表明,6号煤层煤炭的碎屑成分主要来自长英质-中英质岩石。这些物质很可能是林波波移动带被动大陆边缘构造框架中岩浆岩的风化产物。古气候条件推断为暖湿至炎热,泥炭沉积在亚缺氧至缺氧环境中。临界 REY 百分比(REYdef,rel%:29.85% 至 39.75%)的高值和展望系数≥ 0.7 表明,这些苏特潘斯贝格煤炭样本有望回收 REY + Sc 和镓。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Mineralogy and geochemical controls on the distribution of REY-Ga-Se-Nb enrichment in the No. 6 Coal Seam, Soutpansberg Coalfield, South Africa

Mineralogy and geochemical controls on the distribution of REY-Ga-Se-Nb enrichment in the No. 6 Coal Seam, Soutpansberg Coalfield, South Africa
Coal is being explored as a potential alternative source for rare earth elements (REY + Sc), which are critical for advancing modern technology. Previous research has mainly focused on assessing the concentration and distribution of REY + Sc in coals from South Africa. However, the modes occurrence of these elements in coal is yet to be investigated. This study offers new insights on the mineralogy and inorganic geochemistry of the No. 6 Seam coal from the Soutpansberg Coalfield (South Africa). The objective is to investigate the distribution, enrichment, and modes of occurrence of critical elements such as Ga, Se, Nb, and REY + Sc within this coal. The No. 6 Seam is a medium rank-B, moderate vitrinite (avg. 41.5 vol%) coal, and contains major minerals such as kaolinite, quartz, and minor minerals including muscovite, siderite, dolomite, pyrite, and calcite. The total REY + Sc concentrations in the coal samples range from 79.9 to 332.1 mg/kg (avg. 213.2 mg/kg; whole-coal/rock basis), higher than global averages for hard coal. The upper continental crust (UCC) normalized concentration coefficients (CC) of the coal shows enrichment of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, and Y. Distinct REY + Sc enrichment patterns are observed across different coal horizons, divided into two categories: light-REY (LREY) and medium-REY (MREY) in the bottom horizon coal [bottom-upper (BU) and bottom-lower (BL)], whereas the middle horizon coal [middle-upper (MU) and middle-lower (ML)] are enriched in medium-REY (MREY) and heavy-REY (HREY). The BU and BL samples show greater REY + Sc enrichment relative to the MU and ML samples. The samples also contain elevated concentrations of Ga (max. 106.1 mg/kg), Se (max. 50.9 mg/kg), and Nb (max. 14.8 mg/kg), exceeding the average values reported for Chinese coals.
When considering the correlations between REY + Sc and major oxide elements, minerals, and organic petrographic assemblages, REY + Sc appears to be more closely associated with inorganic fraction, particularly aluminosilicate (such as kaolinite) and carbonate minerals (like dolomite), rather than with the organic fraction. The kaolinite and dolomite represent mostly detrital input and epigenesis, respectively. Gallium in the coal is primarily associated with aluminium oxide-hydroxide, Nb with minerals such as clay, rutile/anatase, and zircon; and Se with pyrite. Redox-sensitive elemental ratios of Al2O3/TiO2 andTiO2/Zr suggest that the detrital components of the No. 6 Seam coals were predominantly derived from a source consisting of felsic-intermediate rocks. These materials likely represent the weathering products of magmatic rocks from the passive-continental margin tectonic framework of the Limpopo Mobile Belt. Paleoclimatic conditions are inferred to be warm-humid to hot, with the peat deposited under suboxic-to-oxic environments. High values of critical REY percentage (REYdef,rel%: 29.85 to 39.75 %) and an outlook coefficient ≥ 0.7 suggest these Soutpansberg coal samples to be promising for REY + Sc recovery along with Ga.
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来源期刊
Ore Geology Reviews
Ore Geology Reviews 地学-地质学
CiteScore
6.50
自引率
27.30%
发文量
546
审稿时长
22.9 weeks
期刊介绍: Ore Geology Reviews aims to familiarize all earth scientists with recent advances in a number of interconnected disciplines related to the study of, and search for, ore deposits. The reviews range from brief to longer contributions, but the journal preferentially publishes manuscripts that fill the niche between the commonly shorter journal articles and the comprehensive book coverages, and thus has a special appeal to many authors and readers.
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