Details
Original language | English |
---|---|
Article number | 122021 |
Number of pages | 19 |
Journal | Chemical geology |
Volume | 652 |
Early online date | 6 Mar 2024 |
Publication status | Published - 5 May 2024 |
Abstract
This study presents a geochemical and Sm–Nd isotopic study on pyrochlore from the Ririwai alkaline complex in north-central Nigeria, aiming to reconstruct the magmatic-hydrothermal history and provide insights into the formation of niobium deposit hosted in alkaline igneous rocks. Three texturally and compositionally distinct types of pyrochlore (Pcl I, II, and III) are identified. Primary Pcl I grains are enriched in Nb2O5 (mean of 60.5 wt%) and other high field strength elements (HFSE), rare earth elements (mean of 17.2 wt% REE2O3), Ca, Na, and F, suggesting that they crystallized in a Nb-rich peralkaline magma. The occurrence of patchy zoning as well as the development of microfractures and pores within these pyrochlore grains indicate two stages of hydrothermal alteration responsible for the formation of Pcl II and Pcl III. The first stage of alteration from Pcl I to Pcl II was induced by high-temperature, alkali-rich, and F-moderate fluids, leading to the removal of Na, Ca, and F while filling the vacant A- and Y-sites with K, Rb, Y, and Zn. The Nb and REE contents in Pcl III (mean of 41.3 wt% and 9.4 wt%, respectively) are lower than those in Pcl I and Pcl II (mean of 58.1 wt% and 17.3 wt%, respectively). Thereby, the second stage of alteration from Pcl II to Pcl III was related to low-temperature, Si- and Al-rich alkaline fluids, which resulted in the leaching of Nb, Ti, Th, U, and REE (mainly LREE) from the A- and B-sites, compensated by the incorporation of Si, Pb, K, Al, Fe, and Mn. The leached elements either precipitated into Nb-bearing minerals such as rutile, thorite, and zircon in alteration assemblages as an in-situ replacement of Pcl II or remobilized locally to form hydrothermal veins of Si, Al, Nb, and CO2-bearing oxides. The comparable εNd(t) values between hydrothermal Pcl II and III (−1.9 to −2.8 and − 1.5 to −3.2, respectively) and magmatic Pcl I (−2.0 to −2.6) indicate that there was only a minimal external contribution to Nd (and by analogy Nb as well) from fluids. Two-stage hydrothermal fluids in the Ririwai alkaline complex have limited effects on Nb mobilization, without significantly enhancing or reducing the Nb grade.
Keywords
- Hydrothermal alteration, Nb mineralization, Peralkaline granite, Pyrochlore, Ririwai complex
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Chemical geology, Vol. 652, 122021, 05.05.2024.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Pyrochlore composition and Sm–Nd isotope signature as indicators of magmatic-hydrothermal processes
T2 - The case of Ririwai complex, north-Central Nigeria
AU - Zhu, Yuxiang
AU - Wang, Lianxun
AU - Pan, Yuanming
AU - Zhang, Chao
AU - Almeev, Renat R.
AU - She, Zhenbing
AU - Holtz, François
N1 - Funding Information: This study was financially supported by the National Natural Science Foundation of China (No. 42072082) and the Hubei Province Natural Science Foundation of China (2022CFB116). The authors are grateful to Dr. Dachuan Wang, Victor Ikechukwu Vincent, Hafizullah Abba Ahmed, and Minbo Yang for their help in the field and lab works. Yu-Xiang Zhu wish to thank the supports from the State Scholarship Fund of China Scholarship Council (202206415002) and the Fundamental Research Funds for National Universities, China University of Geosciences (Wuhan). F. Holtz acknowledges financial support from German Science Foundation (DFG, project HO 1337-50). We greatly appreciate the valuable comments provided by Dr. Carl Spandler and another anonymous reviewer, as well as the editorial handling by Dr. Marco Fiorentini, all of which have enhanced this manuscript.
PY - 2024/5/5
Y1 - 2024/5/5
N2 - This study presents a geochemical and Sm–Nd isotopic study on pyrochlore from the Ririwai alkaline complex in north-central Nigeria, aiming to reconstruct the magmatic-hydrothermal history and provide insights into the formation of niobium deposit hosted in alkaline igneous rocks. Three texturally and compositionally distinct types of pyrochlore (Pcl I, II, and III) are identified. Primary Pcl I grains are enriched in Nb2O5 (mean of 60.5 wt%) and other high field strength elements (HFSE), rare earth elements (mean of 17.2 wt% REE2O3), Ca, Na, and F, suggesting that they crystallized in a Nb-rich peralkaline magma. The occurrence of patchy zoning as well as the development of microfractures and pores within these pyrochlore grains indicate two stages of hydrothermal alteration responsible for the formation of Pcl II and Pcl III. The first stage of alteration from Pcl I to Pcl II was induced by high-temperature, alkali-rich, and F-moderate fluids, leading to the removal of Na, Ca, and F while filling the vacant A- and Y-sites with K, Rb, Y, and Zn. The Nb and REE contents in Pcl III (mean of 41.3 wt% and 9.4 wt%, respectively) are lower than those in Pcl I and Pcl II (mean of 58.1 wt% and 17.3 wt%, respectively). Thereby, the second stage of alteration from Pcl II to Pcl III was related to low-temperature, Si- and Al-rich alkaline fluids, which resulted in the leaching of Nb, Ti, Th, U, and REE (mainly LREE) from the A- and B-sites, compensated by the incorporation of Si, Pb, K, Al, Fe, and Mn. The leached elements either precipitated into Nb-bearing minerals such as rutile, thorite, and zircon in alteration assemblages as an in-situ replacement of Pcl II or remobilized locally to form hydrothermal veins of Si, Al, Nb, and CO2-bearing oxides. The comparable εNd(t) values between hydrothermal Pcl II and III (−1.9 to −2.8 and − 1.5 to −3.2, respectively) and magmatic Pcl I (−2.0 to −2.6) indicate that there was only a minimal external contribution to Nd (and by analogy Nb as well) from fluids. Two-stage hydrothermal fluids in the Ririwai alkaline complex have limited effects on Nb mobilization, without significantly enhancing or reducing the Nb grade.
AB - This study presents a geochemical and Sm–Nd isotopic study on pyrochlore from the Ririwai alkaline complex in north-central Nigeria, aiming to reconstruct the magmatic-hydrothermal history and provide insights into the formation of niobium deposit hosted in alkaline igneous rocks. Three texturally and compositionally distinct types of pyrochlore (Pcl I, II, and III) are identified. Primary Pcl I grains are enriched in Nb2O5 (mean of 60.5 wt%) and other high field strength elements (HFSE), rare earth elements (mean of 17.2 wt% REE2O3), Ca, Na, and F, suggesting that they crystallized in a Nb-rich peralkaline magma. The occurrence of patchy zoning as well as the development of microfractures and pores within these pyrochlore grains indicate two stages of hydrothermal alteration responsible for the formation of Pcl II and Pcl III. The first stage of alteration from Pcl I to Pcl II was induced by high-temperature, alkali-rich, and F-moderate fluids, leading to the removal of Na, Ca, and F while filling the vacant A- and Y-sites with K, Rb, Y, and Zn. The Nb and REE contents in Pcl III (mean of 41.3 wt% and 9.4 wt%, respectively) are lower than those in Pcl I and Pcl II (mean of 58.1 wt% and 17.3 wt%, respectively). Thereby, the second stage of alteration from Pcl II to Pcl III was related to low-temperature, Si- and Al-rich alkaline fluids, which resulted in the leaching of Nb, Ti, Th, U, and REE (mainly LREE) from the A- and B-sites, compensated by the incorporation of Si, Pb, K, Al, Fe, and Mn. The leached elements either precipitated into Nb-bearing minerals such as rutile, thorite, and zircon in alteration assemblages as an in-situ replacement of Pcl II or remobilized locally to form hydrothermal veins of Si, Al, Nb, and CO2-bearing oxides. The comparable εNd(t) values between hydrothermal Pcl II and III (−1.9 to −2.8 and − 1.5 to −3.2, respectively) and magmatic Pcl I (−2.0 to −2.6) indicate that there was only a minimal external contribution to Nd (and by analogy Nb as well) from fluids. Two-stage hydrothermal fluids in the Ririwai alkaline complex have limited effects on Nb mobilization, without significantly enhancing or reducing the Nb grade.
KW - Hydrothermal alteration
KW - Nb mineralization
KW - Peralkaline granite
KW - Pyrochlore
KW - Ririwai complex
UR - http://www.scopus.com/inward/record.url?scp=85187208879&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2024.122021
DO - 10.1016/j.chemgeo.2024.122021
M3 - Article
AN - SCOPUS:85187208879
VL - 652
JO - Chemical geology
JF - Chemical geology
SN - 0009-2541
M1 - 122021
ER -