The Mesozoic Laiziling granitic pluton comprises monzogranite and albite granite. It is associated with tin mineralization, and is situated within the central Nanling metallogenic belt. Magmatic and hydrothermal micas occur respectively in the pluton and greisen, unidirectional solidification texture (UST) and layered skarn (green and grey). The mica composition ranges from magmatic protolithionite (MPln) in monzogranite to zinnwaldite (MZnw) in albite granite. Their increasing Si/Al ratio and F-Li-Rb-Mn-Zn-Be contents, alongside decreasing Nb-Ta-Ti-Ga contents, reflect progressive peraluminous magma evolution. Hydrothermal zinnwaldite collected from the greisen (HZnw1) and from the UST (HZnw2) have similar Fe-F-Li-Rb-Cs-Zn-Mn-Sn-Pb-W enrichment, and much lower Nb-Ta-Ti contents than MZnw. This indicates distinct element partitioning during fluid exsolution. Residual zinnwaldite (HPh1) in the green layered skarn has significantly higher Sn-W-Rb, but similar Li-Cs-Zn-Mn-Pb-Nb-Ta contents relative to HZnw1 and HZnw2. Together, these data indicate two distinct fluid exsolution stages from the evolving magma: (1) early Sn-W-Li-Rb-Cs-Zn-Mn-Pb-rich fluid responsible for Sn-polymetallic mineralization in the country rocks; (2) late Li-Rb-Cs-Zn-Mn-Pb-rich but Sn-W-depleted fluid associated with Zn-Pb mineralization in greisen and UST. Hydrothermal phlogopite (HPh3) from grey layered skarn displays higher Fe-Li-Na-Mn-Zn-Ga but lower Rb-Cs contents than the primary phlogopite (HPh2) in green layered skarn, signifying variable element abundances during different alteration stages. Increasing δ7Li value from MPln (− 1.83 to + 0.21‰) to MZnw (− 0.19 to + 0.28‰) records measurable Li isotope fractionation during magmatic differentiation. The overlapping δ⁷Li range of HZnw1 (− 0.01 to + 0.40‰) and HZnw2 (+ 0.49 to + 0.60‰) with MZnw suggests minimal Li isotope fractionation during fluid exsolution. The distinctly higher δ⁷Li value of HPh3 (+ 6.09‰) indicates that water-rock interaction may have generated a Mg-rich, high-δ⁷Li fluid. Slightly higher δ⁷Li value in HPh1 (+ 0.68 to + 1.40‰) relative to HZnw2 may reflect diffusion-driven isotopic fractionation under disequilibrium conditions between the primary zinnwaldite and an early Mg-rich fluid at the skarn reaction front. This may have marginally increased the δ⁷Li value in the altered phlogopite (HPh1), while reducing the δ⁷Li in the coexisting Mg-rich fluid (inferred δ⁷Li = + 2.14‰, based on HPh2).

Geochemistry and Li isotopes of micas: implications for granitic magma evolution and fluid exsolution at the Laiziling Sn-polymetallic deposit in southern Hunan Province (South China)

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发表日期：

2026年1月5日

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Kaixuan Li,
Sheng Huang,
Cheng-Biao Leng,
Ruyi Zhao,
Dazhao Wang,
Xianping Luo

摘要

The Mesozoic Laiziling granitic pluton comprises monzogranite and albite granite. It is associated with tin mineralization, and is situated within the central Nanling metallogenic belt. Magmatic and hydrothermal micas occur respectively in the pluton and greisen, unidirectional solidification texture (UST) and layered skarn (green and grey). The mica composition ranges from magmatic protolithionite (M_Pln) in monzogranite to zinnwaldite (M_Znw) in albite granite. Their increasing Si/Al ratio and F-Li-Rb-Mn-Zn-Be contents, alongside decreasing Nb-Ta-Ti-Ga contents, reflect progressive peraluminous magma evolution. Hydrothermal zinnwaldite collected from the greisen (H_Znw1) and from the UST (H_Znw2) have similar Fe-F-Li-Rb-Cs-Zn-Mn-Sn-Pb-W enrichment, and much lower Nb-Ta-Ti contents than M_Znw. This indicates distinct element partitioning during fluid exsolution. Residual zinnwaldite (H_Ph1) in the green layered skarn has significantly higher Sn-W-Rb, but similar Li-Cs-Zn-Mn-Pb-Nb-Ta contents relative to H_Znw1 and H_Znw2. Together, these data indicate two distinct fluid exsolution stages from the evolving magma: (1) early Sn-W-Li-Rb-Cs-Zn-Mn-Pb-rich fluid responsible for Sn-polymetallic mineralization in the country rocks; (2) late Li-Rb-Cs-Zn-Mn-Pb-rich but Sn-W-depleted fluid associated with Zn-Pb mineralization in greisen and UST. Hydrothermal phlogopite (H_Ph3) from grey layered skarn displays higher Fe-Li-Na-Mn-Zn-Ga but lower Rb-Cs contents than the primary phlogopite (H_Ph2) in green layered skarn, signifying variable element abundances during different alteration stages. Increasing δ⁷Li value from M_Pln (− 1.83 to + 0.21‰) to M_Znw (− 0.19 to + 0.28‰) records measurable Li isotope fractionation during magmatic differentiation. The overlapping δ⁷Li range of H_Znw1 (− 0.01 to + 0.40‰) and H_Znw2 (+ 0.49 to + 0.60‰) with M_Znw suggests minimal Li isotope fractionation during fluid exsolution. The distinctly higher δ⁷Li value of H_Ph3 (+ 6.09‰) indicates that water-rock interaction may have generated a Mg-rich, high-δ⁷Li fluid. Slightly higher δ⁷Li value in H_Ph1 (+ 0.68 to + 1.40‰) relative to H_Znw2 may reflect diffusion-driven isotopic fractionation under disequilibrium conditions between the primary zinnwaldite and an early Mg-rich fluid at the skarn reaction front. This may have marginally increased the δ⁷Li value in the altered phlogopite (H_Ph1), while reducing the δ⁷Li in the coexisting Mg-rich fluid (inferred δ⁷Li = + 2.14‰, based on H_Ph2).