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postgraduate thesis: The genesis of carbonate minerals in the Dong Pao REE deposit, northwest Vietnam

TitleThe genesis of carbonate minerals in the Dong Pao REE deposit, northwest Vietnam
Authors
Advisors
Advisor(s):Zhou, MF
Issue Date2018
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Chan, T. [陳廷宇]. (2018). The genesis of carbonate minerals in the Dong Pao REE deposit, northwest Vietnam. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.
AbstractThe Dong Pao REE deposit in northwest Vietnam contains REE-fluorocarbonates, barite and fluorite. It has been proposed that this deposit is carbonatite-related, but carbonatite has not yet been properly identified, described and analysed. In this study, a magmatic-hydrothermal assemblage comprising calcite-barite- celestine±tainiolite with an accessory amount of apatite and pyrochlore has been identified. Calcite has elevated SrO (2.50 wt. % on average), MnO (0.54 wt. % on average), and REE (1250 ppm on average) and displays enrichment of LREE over HREE. Calcite has δ13C values of -4.7–-2.7‰VPDB and δ18O values of +9.3–+12.5‰VSMOW, with half of the analyses falling within the field of primary igneous carbonatite. Apatite in the assemblage also has an elevated Sr/Mn ratio (>100:1), indicative of a carbonatitic origin. REE-fluorocarbonates in a hydrothermal assemblage contain calcite, synchysite, celestine and fluorite. The hydrothermal calcite was formed subsequent to synchysite, celestine and fluorite. It is typified by MnO>SrO, elevated REE concentrations (total REE ≥500 ppm) and a flat chondrite-normalized REE pattern. Geochemical signatures of apatite and calcite C- O isotopic compositions reflect a common signature with the magmatic-hydrothermal assemblage. This is interpreted as a product of the evolving carbonatitic fluid after sequestration of LREE by REE-fluorocarbonates. Calcite with such an enriched and flat REE signature could be a pathfinder of potential REE deposits in carbonatitic systems. Being 100- times enriched over chondrite, this hydrothermal calcite might have a potential to be exploited for HREE. In-situ LA-ICP-MS analyses on Sr isotope systematics reveal a high 87Sr/86Sr ratio, 0.7078–0.7081, for all carbonatitic and carbo-hydrothermal calcite and apatite. Enrichment of Li, as indicated by the presence of tainiolite (KLiMg2Si4O10F2), Ba, Sr and REE characterises the nature of the Dong Pao carbonatite. Such a nature is consistent with the REE-mineralizing carbonatites in the eastern Indo-Asian collision zone (EIACZ). These geochemical signatures suggest an involvement of enriched mantle component. Subduction of marine sediments could have fertilized the sub-continental lithospheric mantle at the edge of the South China Block and laid the foundation for regionwide REE mineralization in the EIACZ.
DegreeMaster of Philosophy
SubjectCarbonate minerals - Vietnam
Rare earth metals - Vietnam
Dept/ProgramEarth Sciences
Persistent Identifierhttp://hdl.handle.net/10722/267784

 

DC FieldValueLanguage
dc.contributor.advisorZhou, MF-
dc.contributor.authorChan, Ting-yu-
dc.contributor.author陳廷宇-
dc.date.accessioned2019-03-01T03:44:51Z-
dc.date.available2019-03-01T03:44:51Z-
dc.date.issued2018-
dc.identifier.citationChan, T. [陳廷宇]. (2018). The genesis of carbonate minerals in the Dong Pao REE deposit, northwest Vietnam. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.-
dc.identifier.urihttp://hdl.handle.net/10722/267784-
dc.description.abstractThe Dong Pao REE deposit in northwest Vietnam contains REE-fluorocarbonates, barite and fluorite. It has been proposed that this deposit is carbonatite-related, but carbonatite has not yet been properly identified, described and analysed. In this study, a magmatic-hydrothermal assemblage comprising calcite-barite- celestine±tainiolite with an accessory amount of apatite and pyrochlore has been identified. Calcite has elevated SrO (2.50 wt. % on average), MnO (0.54 wt. % on average), and REE (1250 ppm on average) and displays enrichment of LREE over HREE. Calcite has δ13C values of -4.7–-2.7‰VPDB and δ18O values of +9.3–+12.5‰VSMOW, with half of the analyses falling within the field of primary igneous carbonatite. Apatite in the assemblage also has an elevated Sr/Mn ratio (>100:1), indicative of a carbonatitic origin. REE-fluorocarbonates in a hydrothermal assemblage contain calcite, synchysite, celestine and fluorite. The hydrothermal calcite was formed subsequent to synchysite, celestine and fluorite. It is typified by MnO>SrO, elevated REE concentrations (total REE ≥500 ppm) and a flat chondrite-normalized REE pattern. Geochemical signatures of apatite and calcite C- O isotopic compositions reflect a common signature with the magmatic-hydrothermal assemblage. This is interpreted as a product of the evolving carbonatitic fluid after sequestration of LREE by REE-fluorocarbonates. Calcite with such an enriched and flat REE signature could be a pathfinder of potential REE deposits in carbonatitic systems. Being 100- times enriched over chondrite, this hydrothermal calcite might have a potential to be exploited for HREE. In-situ LA-ICP-MS analyses on Sr isotope systematics reveal a high 87Sr/86Sr ratio, 0.7078–0.7081, for all carbonatitic and carbo-hydrothermal calcite and apatite. Enrichment of Li, as indicated by the presence of tainiolite (KLiMg2Si4O10F2), Ba, Sr and REE characterises the nature of the Dong Pao carbonatite. Such a nature is consistent with the REE-mineralizing carbonatites in the eastern Indo-Asian collision zone (EIACZ). These geochemical signatures suggest an involvement of enriched mantle component. Subduction of marine sediments could have fertilized the sub-continental lithospheric mantle at the edge of the South China Block and laid the foundation for regionwide REE mineralization in the EIACZ.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subject.lcshCarbonate minerals - Vietnam-
dc.subject.lcshRare earth metals - Vietnam-
dc.titleThe genesis of carbonate minerals in the Dong Pao REE deposit, northwest Vietnam-
dc.typePG_Thesis-
dc.description.thesisnameMaster of Philosophy-
dc.description.thesislevelMaster-
dc.description.thesisdisciplineEarth Sciences-
dc.description.naturepublished_or_final_version-
dc.date.hkucongregation2019-
dc.identifier.mmsid991044081526703414-

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