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<p>Post-magmatic hydrothermal alteration in granite can significantly alter accessory minerals thereby mobilizing rare-earth elements (REEs). This study focuses on the effects of post-magmatic hydrothermal alteration in Mayong granite in northeast India. The whole rock total REE content of Mayong granite (A-type) ranges from 242 to 2067&#xa0;ppm (avg. 732&#xa0;ppm; median&#xa0;533.78&#xa0;ppm) which is significantly high compared to average granite. The presence of allanite, titanite, and bastnaesite in alteration textures suggests that there has been secondary alteration of the rock. These minerals are typically formed through processes such as hydrothermal alteration, indicating that the rock has been subjected to changes in its chemical composition. To assess the impact of post-magmatic fluid-induced alteration on accessory phases and possible REE remobilization, we evaluate REE distribution in alteration textures observed in Mayong granite in northeast India. We examine how hypogene alteration affected the Ce-enriched accessory minerals allanite, bastnaesite and titanite in Mayong granite. Allanite, bastnaesite and titanite display a LREE-enriched chondrite-normalized REE pattern. Textural features and mineral compositions suggest the alteration of Mn-poor allanites into bastnaesite and fluorapatite, mediated by a CO<sub>2</sub> and F-rich hydrothermal fluid. Precipitation of REE-poor but Ti-enriched titanite at the expense of REE-rich, Ti-poor titanite suggests REE mobilization from primary REE-enriched titanite. Mn-poor nature of allanite, whole-rock compositions and stable mafic mineral assemblage all suggest low to intermediate <i>f</i>O<sub>2</sub> conditions of crystallization having ilmenite series A-type affinity. These characteristics collectively demonstrate the impact of low-temperature hydrothermal alteration of the granite and highlight the significance of such processes for REE remobilization. </p> Graphical abstract <p>Alteration textures of subhedral to euhedral allanites, bastnaesite, titanite, fuorapatite and quartz phases</p> <p></p>

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Fluid-induced alteration and associated rare-earth elements (REEs) distribution in accessory minerals in Mayong granite, Shillong Plateau, northeast India

  • 期刊论文

  • 发表日期：

    2025年7月16日

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  • Dimple Doley,
  • Balen Bhagabaty,
  • Pritom Borah

摘要

Post-magmatic hydrothermal alteration in granite can significantly alter accessory minerals thereby mobilizing rare-earth elements (REEs). This study focuses on the effects of post-magmatic hydrothermal alteration in Mayong granite in northeast India. The whole rock total REE content of Mayong granite (A-type) ranges from 242 to 2067 ppm (avg. 732 ppm; median 533.78 ppm) which is significantly high compared to average granite. The presence of allanite, titanite, and bastnaesite in alteration textures suggests that there has been secondary alteration of the rock. These minerals are typically formed through processes such as hydrothermal alteration, indicating that the rock has been subjected to changes in its chemical composition. To assess the impact of post-magmatic fluid-induced alteration on accessory phases and possible REE remobilization, we evaluate REE distribution in alteration textures observed in Mayong granite in northeast India. We examine how hypogene alteration affected the Ce-enriched accessory minerals allanite, bastnaesite and titanite in Mayong granite. Allanite, bastnaesite and titanite display a LREE-enriched chondrite-normalized REE pattern. Textural features and mineral compositions suggest the alteration of Mn-poor allanites into bastnaesite and fluorapatite, mediated by a CO2 and F-rich hydrothermal fluid. Precipitation of REE-poor but Ti-enriched titanite at the expense of REE-rich, Ti-poor titanite suggests REE mobilization from primary REE-enriched titanite. Mn-poor nature of allanite, whole-rock compositions and stable mafic mineral assemblage all suggest low to intermediate fO2 conditions of crystallization having ilmenite series A-type affinity. These characteristics collectively demonstrate the impact of low-temperature hydrothermal alteration of the granite and highlight the significance of such processes for REE remobilization.

Graphical abstract

Alteration textures of subhedral to euhedral allanites, bastnaesite, titanite, fuorapatite and quartz phases