Journal
CONTRIBUTIONS TO MINERALOGY AND PETROLOGY
Volume 176, Issue 10, Pages -Publisher
SPRINGER
DOI: 10.1007/s00410-021-01849-7
Keywords
Fluorapatite; Metasomatic alteration; REE remobilization; REE transport and enrichment; IOCG deposit
Categories
Funding
- Guang Dong Major Project of Basic and Applied Basic Research [2019B030302013]
- National Natural Science Foundation of China [42173065, 41725009]
- Strategic Priority Research Program of the Chinese Academy of Sciences [XDB42020404]
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The study demonstrates that the geochemical and textural features of altered fluorapatite from the Yinachang IOCG deposit were controlled by both sorption processes and the oxidation states of the hydrothermal fluids. The most salient feature in the Yinachang deposit is that REE remobilization associated with the alteration of fluorapatite by Neoproterozoic hydrothermal fluids is not strictly localized in extent, and REE in fluorapatite can also be transported in distance and precipitate as REE-rich minerals in independent mineralized veins.
Apatite-rich rocks from marine phosphorites, alkaline igneous complexes, and iron-oxide copper gold (IOCG) deposits commonly contain elevated but sub-economic contents of rare earth elements (REE). In this study, we selected fluorapatite from the Paleoproterozoic Yinachang IOCG deposit in Southwest China to evaluate the mechanisms of REE remobilization, transportation and precipitation during fluorapatite alteration. Four texturally and compositionally distinct types of fluorapatite were identified. Ap1, related to mantle-derived magmatic-hydrothermal fluid from dolerite intrusions, contains the highest (REE + Y) content (> 1 wt%). Ap2 was directly deposited from a magmatic-hydrothermal fluid related to Cu mineralization, rich in Cl and S but poor in REE + Y. Pervasive REE-rich mineral inclusions and micro-pores in the altered domains from Ap1 and Ap3-1 indicate that extensive metasomatic alteration occurred via a coupled dissolution-reprecipitation process, which was related to a late oxidizing hydrothermal fluid. After the end of the dissolution-reprecipitation process, Ap3-2 formed through regrowth of Ap3-1. Ap4 in late monazite-sulfide veins has extremely high positive Eu anomalies (24-32) and the highest Eu contents, which are related to a late reduced hydrothermal fluid. This study demonstrates that the geochemical and textural features of altered fluorapatite from the Yinachang IOCG deposit were controlled by both a sorption processes and the oxidation states of the hydrothermal fluids. The most salient feature in the Yinachang deposit is that REE remobilization associated with the alteration of fluorapatite by Neoproterozoic hydrothermal fluids is not strictly localized in extent, and REE in fluorapatite can also be transported in distance and precipitate as REE-rich minerals in independent mineralized veins.
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