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<p>Groundwater in abandoned mine catchments can remain impacted by acid mine drainage (AMD) long after closure, yet seasonal plume behaviour especially during snowmelt remains poorly constrained. This study investigated seasonal groundwater and surface-water hydrochemistry at an abandoned volcanogenic massive sulphide (VMS) mine in northern Japan (2023–2025) using integrated hydrogeochemical interpretation and multivariate statistics. Groundwater was persistently more acidic and mineralised than surface water (pH 3.07–5.02 compared with 3.30–7.79) and was dominated by SO₄<sup>2</sup>⁻‑rich facies (Ca<sup>2</sup>⁺–SO₄<sup>2</sup>⁻ to Ca<sup>2</sup>⁺–Mg<sup>2</sup>⁺–SO₄<sup>2</sup>⁻) across dry, wet, and snowmelt periods, confirming a sustained AMD solute source. Snowmelt reduced ionic strength (lower EC) but did not eliminate sulphate loading, whereas wet season recharge enhanced flushing of stored oxidation products and increased some trace metals mobilisation. Under persistently acidic conditions with near-zero groundwater HCO₃⁻, SO₄<sup>2</sup>⁻ reached ~ 381&#xa0;mg/L. Three hydrochemical water types (endmember-like groups) were identified from facies classification and qualitative mixing trends, spanning acidic sulphate-rich AMD waters in source and plume zones, partially modified Ca–SO₄ waters along plume margins, and relatively dilute bicarbonate-bearing surface waters influenced by episodic AMD inputs. Across seasons, PCA showed that the first two components explain 58.6–64.7% of the variance and separate an AMD-related mineralisation gradient from a pH–HCO₃⁻ buffering gradient, with secondary contrasts linked to redox conditions and recharge. Cross-sectional profiles indicate an approximately 450–600&#xa0;m southward-oriented AMD influence zone that is constrained by subsurface heterogeneity and seasonally attenuated by snowmelt dilution, providing a basis for targeted monitoring design and reactive-barrier placement.</p>

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Unravelling hydrogeochemical dynamics of seasonal acid mine drainage water quality in an abandoned mine site, Japan

  • 期刊论文

  • 发表日期：

    2026年3月20日

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  • Abel Abebe Ersulo,
  • Takahiko Arima,
  • Haruki Aotsuka,
  • Taichi Matsusaki,
  • Thaw Dar Wunn,
  • Aeron Elvin Dela Cruz,
  • Xiaobo Niu,
  • Walubita Mufalo,
  • Takaya Hamai,
  • Masao Okumura,
  • Hisatoshi Furuya,
  • Shingo Tomiyama,
  • Naoki Hiroyoshi

摘要

Groundwater in abandoned mine catchments can remain impacted by acid mine drainage (AMD) long after closure, yet seasonal plume behaviour especially during snowmelt remains poorly constrained. This study investigated seasonal groundwater and surface-water hydrochemistry at an abandoned volcanogenic massive sulphide (VMS) mine in northern Japan (2023–2025) using integrated hydrogeochemical interpretation and multivariate statistics. Groundwater was persistently more acidic and mineralised than surface water (pH 3.07–5.02 compared with 3.30–7.79) and was dominated by SO₄2⁻‑rich facies (Ca2⁺–SO₄2⁻ to Ca2⁺–Mg2⁺–SO₄2⁻) across dry, wet, and snowmelt periods, confirming a sustained AMD solute source. Snowmelt reduced ionic strength (lower EC) but did not eliminate sulphate loading, whereas wet season recharge enhanced flushing of stored oxidation products and increased some trace metals mobilisation. Under persistently acidic conditions with near-zero groundwater HCO₃⁻, SO₄2⁻ reached ~ 381 mg/L. Three hydrochemical water types (endmember-like groups) were identified from facies classification and qualitative mixing trends, spanning acidic sulphate-rich AMD waters in source and plume zones, partially modified Ca–SO₄ waters along plume margins, and relatively dilute bicarbonate-bearing surface waters influenced by episodic AMD inputs. Across seasons, PCA showed that the first two components explain 58.6–64.7% of the variance and separate an AMD-related mineralisation gradient from a pH–HCO₃⁻ buffering gradient, with secondary contrasts linked to redox conditions and recharge. Cross-sectional profiles indicate an approximately 450–600 m southward-oriented AMD influence zone that is constrained by subsurface heterogeneity and seasonally attenuated by snowmelt dilution, providing a basis for targeted monitoring design and reactive-barrier placement.