AUTHOR=Ze-Yi Chen , Yong-Jun Shao , Han-Tao Wei , Cheng Wang 

TITLE=Relationship Between Nb-Ta Enrichments and Highly-Fractionated Granitic Magma Evolution in South China: Geochronological, Zircon Hf Isotopic and Geochemical Evidence From Jianfengling Granite

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2022.886849

DOI=10.3389/feart.2022.886849

ISSN=2296-6463

ABSTRACT=The Jianfengling granite is an important ore-forming rock unit in the Xianghualing orefield in Nanling region (South China), and its magmatic evolution is vital to understand the regional niobium (Nb)-tantalum (Ta) mineralization. The Jianfengling granite comprises three lithofacies: porphyritic biotite monzogranite (mesophase facies), medium-fine-grained biotite monzogranite (transition facies) and medium-grained biotite monzogranite (central facies). All the three biotite monzogranite lithofacies are characterized by being rich in SiO2 and Al2O3, poor in TFe2O3, CaO, MgO, TiO2, MnO and P2O5, and are peraluminous high-K calc-alkaline. These rocks are remarkably enriched in Rb, Th, U, Nb and Ta, strongly depleted in Ba and Sr, and slightly depleted in La, Zr and Sm. The LREE/HREE decreases gradually from porphyritic biotite monzogranite, through fine-medium-grained to medium-grained biotite monzogranite, with increasing negative Eu anomaly (Eu/Eu*) and convex (“M-type”) lanthanide tetrad effect. The high Th-U (Thavg. = 2051.56 ppm; Uavg. = 1498.23 ppm, respectively) and low Th-U (Thavg. = 708.14 ppm; Uavg. = 441.57 ppm, respectively) zircon grains from porphyritic biotite monzogranite yielded weighted average 206Pb/238U ages of 161.3 ± 1.6 Ma (MSWD =1.3, n = 13) and 158.7 ± 2.0 Ma (MSWD = 1.7, n = 13), respectively, consistent with the large-scale magmatic-mineralization event in the Nanling region (ca. 160–150 Ma). The εHf(t) values of the high Th-U (-6.48 to -2.51) and low Th-U (-6.58 to -1.12) zircon grains from the porphyritic biotite monzogranite indicate that their causative magma were formed from partial melting of the Mesoproterozoic Cathaysian basement rocks in a lithospheric extension setting. The Nb and Ta contents increase with fluorine from the porphyritic to medium-grained biotite monzogranite, indicating that the Nb-Ta enrichment may have caused by the gradual increase of fluxing content (fluorine) during the fractionation of the Jianfengling granitic magma.