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=10

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=<p>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 gradual transitional lithofacies: porphyritic biotite monzogranite (mesophase facies), biotite monzogranite (transition facies) and topaz biotite monzogranite (central facies). All the three biotite monzogranite lithofacies are characterized by being rich in SiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub>, poor in TFe<sub>2</sub>O<sub>3</sub>, CaO, MgO, TiO<sub>2</sub>, MnO and P<sub>2</sub>O<sub>5</sub>, 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 Zr. The LREE/HREE decreases gradually from porphyritic biotite monzogranite, through biotite monzogranite to topaz biotite monzogranite, with increasing convex (“M-type”) lanthanide tetrad effect, which similar to the highly-fractionated granite. The high Th-U (Th<sub>avg.</sub> = 2051.56°ppm; U<sub>avg.</sub> = 1,498.23°ppm, respectively) and low Th-U (Th<sub>avg.</sub> = 708.14°ppm; U<sub>avg.</sub> = 441.57°ppm, respectively) zircon grains from porphyritic biotite monzogranite yielded weighted average <sup>206</sup>Pb<sup>/238</sup>U ages of 161.3 ± 1.6 Ma (MSWD = 1.3, <italic>n</italic> = 13) and 158.7 ± 2.0 Ma (MSWD = 1.7, <italic>n</italic> = 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 the causative magma was 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 topaz 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.</p>