Textural Features and Chemical Evolution in Ta-Nb Oxides: Implications for Deuteric Rare-Metal Mineralization in the Yichun Granite-Marginal Pegmatite, Southeastern China

Research Article| June 01, 2018 Textural Features and Chemical Evolution in Ta-Nb Oxides: Implications for Deuteric Rare-Metal Mineralization in the Yichun Granite-Marginal Pegmatite, Southeastern China Mingqian Wu; Mingqian Wu 1 State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China2 Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4 Search for other works by this author on: GSW Google Scholar Iain M. Samson; Iain M. Samson 2 Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4 Search for other works by this author on: GSW Google Scholar Dehui Zhang Dehui Zhang 1 State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China † Corresponding author: e-mail, zhdehui@cugb.edu.cn Search for other works by this author on: GSW Google Scholar Author and Article Information Mingqian Wu 1 State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China2 Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4 Iain M. Samson 2 Department of Earth and Environmental Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4 Dehui Zhang 1 State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences (Beijing), Beijing 100083, China † Corresponding author: e-mail, zhdehui@cugb.edu.cn Publisher: Society of Economic Geologists Accepted: 23 Apr 2018 First Online: 18 May 2018 Online Issn: 1554-0774 Print Issn: 0361-0128 © 2018 Economic GeologyEconomic Geology Economic Geology (2018) 113 (4): 937–960. https://doi.org/10.5382/econgeo.2018.4577 Article history Accepted: 23 Apr 2018 First Online: 18 May 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mingqian Wu, Iain M. Samson, Dehui Zhang; Textural Features and Chemical Evolution in Ta-Nb Oxides: Implications for Deuteric Rare-Metal Mineralization in the Yichun Granite-Marginal Pegmatite, Southeastern China. Economic Geology 2018;; 113 (4): 937–960. doi: https://doi.org/10.5382/econgeo.2018.4577 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract The genesis of Ta-Nb oxides in granitoid environments and, in particular, the role of deuteric fluids in Ta-Nb ore formation remain controversial. Ta-Nb oxides in the Yichun deposit occur disseminated in a topaz lepidolite granite and in the intermediate zone of a zoned marginal pegmatite. Columbite-group minerals and microlite are the principal ore minerals in this topaz lepidolite granite. The principal Ta-Nb oxides in aplite of the marginal pegmatite are columbite-(Mn), tantalite-(Mn), and wodginite-group minerals. Ta-Nb oxides in the topaz lepidolite granite and aplite are mostly prismatic crystals or aggregates associated with lepidolite and albite, whereas in the pegmatitic intermediate zone, they occur in triplite-dominated nodules as aggregates of acicular columbite-(Mn) in association with fibrous molybdenite, zircon, and native bismuth. Most columbite-group minerals in the topaz lepidolite granite and aplite have a columbite-(Mn) core (stage I), overgrown and resorbed by a later stage II columbite-group mineral overgrowth that is distinctly richer in Ta than the stage I crystals. Textural and chemical features of the stage I crystals are consistent with a magmatic origin. Where stage I crystals are enclosed by snowball quartz, there is no overgrowth, and these crystals are richer in Nb, Sc, Fe, Ti, Y, Zr, U, Th, and W, and thus are more primitive in composition than those outside the snowball quartz. Stage II overgrowths have two to five times higher Ta/(Nb + Ta) values than stage I cores, such that is there is a large compositional gap between core and overgrowth, although the Mn/(Mn + Fe) values of the two stages are similar. Subsequent to formation of the stage II overgrowths in aplite, but not in the topaz lepidolite granite, the columbite-group minerals were altered and overgrown by wodginite-group minerals (stage III), with concomitant precipitation of cassiterite, zircon, and uraninite, requiring interaction of the stage II crystals with a liquid that contained high field strength elements and Sn. The textural relationships and the chemical features suggest that lepidolite, albite, and the snowball quartz at Yichun are all metasomatic.The chemical features of the columbite-group minerals and the low solubility of Ta in aqueous fluids, combined with the evidence for metasomatism at Yichun, suggest that the media from which the stage II crystals precipitated were hydrosilicate liquids, which have high concentrations of Si and Na, and approximately equimolar SiO2 and H2O concentrations. Distinct chemical differences between columbite-group minerals in the topaz lepidolite granite and aplite indicate that a single hydrosilicate liquid did not pervade the entire system; instead, distinct liquids were present in the various units. The triplite-dominant nodules most likely represent residual volatile-rich melts of the marginal pegmatite. The Nb-Ta-Mo-Bi mineral assemblages in these nodules were precipitated during hydrothermal alteration of triplite to fluorapatite from the same aqueous fluid. The chemistry of columbite-group minerals, as well as the published chronological data, suggest that aplite was not derived directly from the topaz lepidolite granite melt; rather, it represents a different magma that originated from the same magma chamber at depth from which the topaz lepidolite granite melt was derived. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.