Lithium isotopic behaviour during high-temperature fluid-rock reactions of metapelites (>200 °C): A case study from the Baiyun orogenic gold deposit, Liaodong Peninsula, North China Craton

Liu，Shuaijie1,2; Chen，Bin1; Zheng，Jiahao1,3; Sun，Yang1; Bao，Chuang4; Zhao，Guochun2,5

2022-11-20

10.1016/j.chemgeo.2022.121121

CHEMICAL GEOLOGY   Impact Factor & Quartile

0009-2541

1872-6836

Mixing of low δLi sediment components (δLi(‰) = 1000 × [(Li/Li)/(Li /Li) − 1]) with high δLi altered oceanic crusts can explain the MORB-like Li isotopic signature of arc lavas. However, marine sediments with low δLi values have rarely been reported. The metasomatism of metasedimentary rocks in mélange zones may induce large Li isotopic fractionation; however, the Li isotopic behaviour of metasedimentary rocks during high-temperature fluid-rock reactions remains poorly understood. In this study, an integrated Li-O-Sr-Nd isotopic investigation was conducted on the Baiyun orogenic gold deposit, which represents a relatively simplified high-T hydrothermal system, to explore the Li isotopic behaviour during high-T metasomatism (>200 °C) of metapelites. The main host rocks in Baiyun are lithologically monotonous schists, with alterations including K-feldspathization, sericitization, and carbonation. The Nd isotopes identified host rock samples that could best represent the protolith of the altered schists in Baiyun. The Sr and O isotopic modelling yielded consistent water/rock ratios of 0.1–7.6 and 0.6–5.9, respectively, suggesting that relatively small volumes of fluids were infiltrated. There is no correlation among Li, Sr, and O isotopes; instead, a negative Li-KO correlation and a positive δLi-KO correlation of the altered schists are observed, suggesting that potassic metasomatism controlled Li concentrations and Li isotopes. The δLi values of altered schists in Baiyun can be classified into Group I, having lower Li concentrations (3.2–22.2 ppm) and δLi values (−3.8–0.4‰) than the protolith (31.6–47.9 ppm, 0.9–2.8‰), and Group II, having significantly lower Li concentrations (0.9–2.5 ppm) and overlapped or higher δLi values (1.0–4.5‰) than the protolith. Fluid leaching during high-T alteration removes Li and more Li than Li, which accounts for the lower Li concentrations and δLi values of Group I. When there is little Li remaining in rocks owing to progressive fluid leaching, the Li isotopes of the altered schists are equilibrated with heavy fluid Li (fluid buffering), which leads to higher δLi values observed in Group II. Based on a case study in Baiyun, this study proposes that similar high-T metasomatism of metasedimentary rocks in mélange zones could result in low δLi sediment inputs. Mixing of flux-modified isotopically light sediment inputs with isotopically heavy, altered oceanic crusts could account for the MORB-like Li isotopes of arc lavas.

Baiyun orogenic gold deposit Li isotopes Metapelites Metasomatism Mélange

SCI

English

First ; Corresponding

National Key Research and Development Program of China[2018YFC0603801];

Geochemistry & Geophysics

Geochemistry & Geophysics

WOS:000874240900001

ELSEVIER

GEOSCIENCES

2-s2.0-85138470133

Scopus

1.Department of Earth and Space Sciences,Southern University of Science and Technology,Shenzhen,Guangdong,518055,China
2.Department of Earth Sciences,The University of Hong Kong,Hong Kong
3.Zijin school of Geology and Mining,Fuzhou University,Fuzhou,350108,China
4.College of Ocean and Meteorology,Guangdong Ocean University,Zhanjiang,524088,China
5.State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an,710069,China

Liu，Shuaijie,Chen，Bin,Zheng，Jiahao,et al. Lithium isotopic behaviour during high-temperature fluid-rock reactions of metapelites (>200 °C): A case study from the Baiyun orogenic gold deposit, Liaodong Peninsula, North China Craton[J]. CHEMICAL GEOLOGY,2022,611.

Liu，Shuaijie,Chen，Bin,Zheng，Jiahao,Sun，Yang,Bao，Chuang,&Zhao，Guochun.(2022).Lithium isotopic behaviour during high-temperature fluid-rock reactions of metapelites (>200 °C): A case study from the Baiyun orogenic gold deposit, Liaodong Peninsula, North China Craton.CHEMICAL GEOLOGY,611.

Liu，Shuaijie,et al."Lithium isotopic behaviour during high-temperature fluid-rock reactions of metapelites (>200 °C): A case study from the Baiyun orogenic gold deposit, Liaodong Peninsula, North China Craton".CHEMICAL GEOLOGY 611(2022).