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Open AccessArticle

Magmatic-Hydrothermal Processes Associated with Rare Earth Element Enrichment in the Kangankunde Carbonatite Complex, Malawi

1
Graduate School of Engineering, Hokkaido University, N13W8, Kita-ku, Sapporo 060-8628, Japan
2
Faculty of Engineering, Hokkaido University, N13W8, Kita-ku, Sapporo 060-8628, Japan
3
Institute for Geo-Resources and Environment, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Central 7, 1-1-1 Higashi, Tsukuba 305-8567, Japan
*
Author to whom correspondence should be addressed.
Present affiliation: SA Business Unit, JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan.
Minerals 2019, 9(7), 442; https://doi.org/10.3390/min9070442
Received: 14 March 2019 / Revised: 5 July 2019 / Accepted: 14 July 2019 / Published: 18 July 2019
Carbonatites undergo various magmatic-hydrothermal processes during their evolution that are important for the enrichment of rare earth elements (REE). This geochemical, petrographic, and multi-isotope study on the Kangankunde carbonatite, the largest light REE resource in the Chilwa Alkaline Province in Malawi, clarifies the critical stages of REE mineralization in this deposit. The δ56Fe values of most of the carbonatite lies within the magmatic field despite variations in the proportions of monazite, ankerite, and ferroan dolomite. Exsolution of a hydrothermal fluid from the carbonatite melts is evident based on the higher δ56Fe of the fenites, as well as the textural and compositional zoning in monazite. Field and petrographic observations, combined with geochemical data (REE patterns, and Fe, C, and O isotopes), suggest that the key stage of REE mineralization in the Kangankunde carbonatite was the late magmatic stage with an influence of carbothermal fluids i.e. magmatic–hydrothermal stage, when large (~200 µm), well-developed monazite crystals grew. The C and O isotope compositions of the carbonatite suggest a post-magmatic alteration by hydrothermal fluids, probably after the main REE mineralization stage, as the alteration occurs throughout the carbonatite but particularly in the dark carbonatites. View Full-Text
Keywords: carbonatite; REE enrichment; Fe, C, and O isotopes; magmatic-hydrothermal carbonatite; REE enrichment; Fe, C, and O isotopes; magmatic-hydrothermal
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Chikanda, F.; Otake, T.; Ohtomo, Y.; Ito, A.; Yokoyama, T.D.; Sato, T. Magmatic-Hydrothermal Processes Associated with Rare Earth Element Enrichment in the Kangankunde Carbonatite Complex, Malawi. Minerals 2019, 9, 442.

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