Investigating acid mine drainage in complex topography areas via semi-airborne and surface geophysical surveys: a case study in Fujian, China

Acid mine drainage (AMD) has emerged as a pressing global environmental challenge. It is produced from mining area and surrounding mining operation area, which has caused environmental degradation, contamination of soils and surface and groundwater, etc. This issue is particularly pronounced at an abandoned mining site named Yanshi Town, Fujian Province. The key to AMD pollution control is to find the contamination source and migration path. Many studies have shown that the underground goaf and water fissure in coal mine area provide favorable conditions for the generation and migration of AMD. We present a multidisciplinary approach to characterize an acid mine drainage contamination source and migration path of this abandoned coal deposit, which combines geophysical, geochemical, and statistical methods. A comprehensive contamination survey encompassing groundwater, surface water, and sediment was conducted and revealed weakly acidic conditions and elevated levels of sulfate (SO₄²⁻), manganese (Mn), and iron (Fe), all indicative of acid mine drainage contamination within this region. The complex topography makes it difficult to carry out a ground survey. Thus, we apply semi-airborne transient electromagnetic method and direct current electrical resistivity method in order to image subsurface goafs and identify potential acid mine drainage sources. By leveraging the resistivity contrast between water-rich areas and surrounding rock and integrating geological data, this study identified conductive areas within 300 m below the surface and analyzed the water content to map the geographical locations of these water-rich goafs. The integration of SATEM results, DC resistivity inversion profile, and geological information enabled the successful identification of four water-rich goaf areas, whose locations fit well with verified geological data.