Y.Q. Wei
Geochemistry and iron isotope systematics of coexisting Fe-bearing minerals in magmatic Fe-Ti deposits: A case study of the Damiao titanomagnetite ore deposits, North China Craton
Wei, Y.Q.; Niu, Yaoling; Gong, H.M.; Duan, M.; Chen, S.; Guo, P.Y.; Sun, P.
Authors
Yaoling Niu
H.M. Gong
M. Duan
S. Chen
P.Y. Guo
P. Sun
Abstract
Geochemical and iron isotopic compositions of magnetite, ilmenite and pyrite separates from the FeTi oxide ores hosted in the Damiao anorthosite-type FeTi ore deposit were analyzed to investigate sub-solidus cooling history of the titanomagnetite. The FeTi oxides form two series of solid solutions, namely, ulvöspinel-magnetite (Usp-Mtss) and hematite-ilmenite (Hem-Ilmss) solid solutions. The magnetite separates have 14–27 mol% ulvöspinel, while the ilmenite separates have 5–8 mol% hematite. Major element compositions of the mineral separates suggest that the ilmenites were mainly exsolved from the Usp-Mtss by oxidation of ulvöspinel in the temperature range of ~820–600 °C and experienced inter-oxide re-equilibration with the magnetites. Associated with the exsolution is the substantial inter-mineral iron isotope fractionation. The magnetite separates are characterized by high δ57Fe (+0.27 − +0.65‰), whereas the ilmenite separates have lower δ57Fe (−0.65 to −0.28‰). Two types of pyrite are petrographically observed, each of which has a distinctive iron isotope fingerprint. Type I pyrite (pyriteI) with higher δ57Fe (δ57Fe = +0.63 − +0.95‰) is consistent with magmatic origin, and type II pyrite (pyriteII) with lower δ57Fe (δ57Fe = −0.90 to −0.11‰) was likely to have precipitated from fluids. Iron isotopic fingerprints of the pyrite may result from fluid activities, whereas those of the pyriteII probably indicate variations of oxygen fugacity. The iron isotopic fractionation between the magnetite and ilmenite is the net result of sub-solidus processes (including ulvöspinel oxidation and inter-oxide re-equilibration) without needing varying oxygen fugacity albeit its presence. Although varying composition of magnetite-ilmenite pairs reflects variations of oxygen fugacity, inter-oxide iron isotopic fractionation does not.
Citation
Wei, Y., Niu, Y., Gong, H., Duan, M., Chen, S., Guo, P., & Sun, P. (2020). Geochemistry and iron isotope systematics of coexisting Fe-bearing minerals in magmatic Fe-Ti deposits: A case study of the Damiao titanomagnetite ore deposits, North China Craton. Gondwana Research, 81, 240-251. https://doi.org/10.1016/j.gr.2019.12.001
Journal Article Type | Article |
---|---|
Acceptance Date | Dec 15, 2019 |
Online Publication Date | Dec 27, 2019 |
Publication Date | May 27, 2020 |
Deposit Date | Dec 27, 2019 |
Publicly Available Date | Dec 27, 2020 |
Journal | Gondwana Research |
Print ISSN | 1342-937X |
Publisher | Elsevier |
Peer Reviewed | Peer Reviewed |
Volume | 81 |
Pages | 240-251 |
DOI | https://doi.org/10.1016/j.gr.2019.12.001 |
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Copyright Statement
© 2019 This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
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