Mixing　of　low　δ7Li　sediment　components　(δ7Li(‰)　=　1000　×　[(7Li/6Li)sample/(7Li　/6Li)L-SVEC　−　1])　with　high　δ7Li　altered　oceanic　crusts　can　explain　the　MORB-like　Li　isotopic　signature　of　arc　lavas.　However,　marine　sediments　with　low　δ7Li　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-K2O　correlation　and　a　positive　δ7Li-K2O　correlation　of　the　altered　schists　are　observed,　suggesting　that　potassic　metasomatism　controlled　Li　concentrations　and　Li　isotopes.　The　δ7Li　values　of　altered　schists　in　Baiyun　can　be　classified　into　Group　I,　having　lower　Li　concentrations　(3.2–22.2　ppm)　and　δ7Li　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　δ7Li　values　(1.0–4.5‰)　than　the　protolith.　Fluid　leaching　during　high-T　alteration　removes　Li　and　more　7Li　than　6Li,　which　accounts　for　the　lower　Li　concentrations　and　δ7Li　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　δ7Li　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　δ7Li　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.　©　2022　Elsevier　B.V.