期刊
MINERALS
卷 9, 期 7, 页码 -出版社
MDPI
DOI: 10.3390/min9070442
关键词
carbonatite; REE enrichment; Fe, C, and O isotopes; magmatic-hydrothermal
资金
- Nanotechnology Platform Program of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan
- Japan Society for the Promotion of Science (JSPS) KAKENHI [17H03502]
- Japan International Cooperation Agency (JICA)
- Joint Research Grant for the Environmental Isotope Study to the Research Institute for Humanity and Nature
- Grants-in-Aid for Scientific Research [17H03502] Funding Source: KAKEN
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 delta Fe-56 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 delta Fe-56 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 (similar to 200 mu m), 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.
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