The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolution
The Lugiin Gol nepheline syenite intrusion, Mongolia, hosts a range of carbonatite dikes mineralized in rare-earth elements (REE). Both carbonatites and nepheline syenite-fluorite-calcite veinlets are host to a previously unreported macroscale texture involving pseudo-graphic intergrowths of fluorit...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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Elsevier
2019-03-01
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| Series: | Geoscience Frontiers |
| Online Access: | http://www.sciencedirect.com/science/article/pii/S1674987118300513 |
| _version_ | 1797719838257315840 |
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| author | Jindrich Kynicky Martin P. Smith Wenlei Song Anton R. Chakhmouradian Cheng Xu Antonin Kopriva Michaela Vasinova Galiova Martin Brtnicky |
| author_facet | Jindrich Kynicky Martin P. Smith Wenlei Song Anton R. Chakhmouradian Cheng Xu Antonin Kopriva Michaela Vasinova Galiova Martin Brtnicky |
| author_sort | Jindrich Kynicky |
| collection | DOAJ |
| description | The Lugiin Gol nepheline syenite intrusion, Mongolia, hosts a range of carbonatite dikes mineralized in rare-earth elements (REE). Both carbonatites and nepheline syenite-fluorite-calcite veinlets are host to a previously unreported macroscale texture involving pseudo-graphic intergrowths of fluorite and calcite. The inclusions within calcite occur as either pure fluorite, with associated REE minerals within the surrounding calcite, or as mixed calcite-fluorite inclusions, with associated zirconosilicate minerals. Consideration of the nature of the texture, and the proportions of fluorite and calcite present (∼29 and 71 mol%, respectively), indicates that these textures most likely formed either through the immiscible separation of carbonate and fluoride melts, or from cotectic crystallization of a carbonate-fluoride melt. Laser ablation ICP-MS analyses show the pure fluorite inclusions to be depleted in REE relative to the calcite. A model is proposed, in which a carbonate-fluoride melt phase enriched in Zr and the REE, separated from a phonolitic melt, and then either unmixed or underwent cotectic crystallization to generate an REE-rich carbonate melt and an REE-poor fluoride phase. The separation of the fluoride phase (either solid or melt) may have contributed to the enrichment of the carbonate melt in REE, and ultimately its saturation with REE minerals. Previous data have suggested that carbonate melts separated from silicate melts are relatively depleted in the REE, and thus melt immiscibility cannot result in the formation of REE-enriched carbonatites. The observations presented here provide a mechanism by which this could occur, as under either model the textures imply initial separation of a mixed carbonate-fluoride melt from a silicate magma. The separation of an REE-enriched carbonate-fluoride melt from phonolitic magma is a hitherto unrecognized mechanism for REE-enrichment in carbonatites, and may play an important role in the formation of shallow magmatic REE deposits. Keywords: Silicate-carbonate-fluoride melt immiscibility, Carbonatite, Alkaline syenite, Shallow REE deposit, Lugiin Gol, Mongolia |
| first_indexed | 2024-03-12T09:10:37Z |
| format | Article |
| id | doaj.art-2332df4028344ea5a7e5383c02793a85 |
| institution | Directory Open Access Journal |
| issn | 1674-9871 |
| language | English |
| last_indexed | 2024-03-12T09:10:37Z |
| publishDate | 2019-03-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Geoscience Frontiers |
| spelling | doaj.art-2332df4028344ea5a7e5383c02793a852023-09-02T14:59:23ZengElsevierGeoscience Frontiers1674-98712019-03-01102527537The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolutionJindrich Kynicky0Martin P. Smith1Wenlei Song2Anton R. Chakhmouradian3Cheng Xu4Antonin Kopriva5Michaela Vasinova Galiova6Martin Brtnicky7Mendel University in Brno, Zemedelska 1, 613 00 Brno, Czech Republic; Brno University of Technology, Technicka 3058/10, 616 00 Brno, Czech Republic; Corresponding author. Mendel University in Brno, Zemedelska 1, 613 00 Brno, Czech Republic.University of Brighton, Brighton BN2 4GJ, United KingdomBrno University of Technology, Technicka 3058/10, 616 00 Brno, Czech RepublicUniversity of Manitoba, Winnipeg, Manitoba, CanadaSchool of Earth and Space Sciences, Peking University, Beijing 100871, ChinaBrno University of Technology, Technicka 3058/10, 616 00 Brno, Czech RepublicBrno University of Technology, Technicka 3058/10, 616 00 Brno, Czech RepublicBrno University of Technology, Technicka 3058/10, 616 00 Brno, Czech RepublicThe Lugiin Gol nepheline syenite intrusion, Mongolia, hosts a range of carbonatite dikes mineralized in rare-earth elements (REE). Both carbonatites and nepheline syenite-fluorite-calcite veinlets are host to a previously unreported macroscale texture involving pseudo-graphic intergrowths of fluorite and calcite. The inclusions within calcite occur as either pure fluorite, with associated REE minerals within the surrounding calcite, or as mixed calcite-fluorite inclusions, with associated zirconosilicate minerals. Consideration of the nature of the texture, and the proportions of fluorite and calcite present (∼29 and 71 mol%, respectively), indicates that these textures most likely formed either through the immiscible separation of carbonate and fluoride melts, or from cotectic crystallization of a carbonate-fluoride melt. Laser ablation ICP-MS analyses show the pure fluorite inclusions to be depleted in REE relative to the calcite. A model is proposed, in which a carbonate-fluoride melt phase enriched in Zr and the REE, separated from a phonolitic melt, and then either unmixed or underwent cotectic crystallization to generate an REE-rich carbonate melt and an REE-poor fluoride phase. The separation of the fluoride phase (either solid or melt) may have contributed to the enrichment of the carbonate melt in REE, and ultimately its saturation with REE minerals. Previous data have suggested that carbonate melts separated from silicate melts are relatively depleted in the REE, and thus melt immiscibility cannot result in the formation of REE-enriched carbonatites. The observations presented here provide a mechanism by which this could occur, as under either model the textures imply initial separation of a mixed carbonate-fluoride melt from a silicate magma. The separation of an REE-enriched carbonate-fluoride melt from phonolitic magma is a hitherto unrecognized mechanism for REE-enrichment in carbonatites, and may play an important role in the formation of shallow magmatic REE deposits. Keywords: Silicate-carbonate-fluoride melt immiscibility, Carbonatite, Alkaline syenite, Shallow REE deposit, Lugiin Gol, Mongoliahttp://www.sciencedirect.com/science/article/pii/S1674987118300513 |
| spellingShingle | Jindrich Kynicky Martin P. Smith Wenlei Song Anton R. Chakhmouradian Cheng Xu Antonin Kopriva Michaela Vasinova Galiova Martin Brtnicky The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolution Geoscience Frontiers |
| title | The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolution |
| title_full | The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolution |
| title_fullStr | The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolution |
| title_full_unstemmed | The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolution |
| title_short | The role of carbonate-fluoride melt immiscibility in shallow REE deposit evolution |
| title_sort | role of carbonate fluoride melt immiscibility in shallow ree deposit evolution |
| url | http://www.sciencedirect.com/science/article/pii/S1674987118300513 |
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