Interpreting Mine Water Sources and Determining Mixing Ratios Based on the Spatial and Chemical Characteristics of Bedrock Brines in a Coastal Mine

Abstract

Water inrush caused by mining below the seafloor seriously affects the safety and production of mines. Identifying the end element of mine inrush and accurately calculating the mixing ratios of end elements are the basis for a reasonable evaluation of water inrush risk. Based on hydrogeochemical and stable isotope indexes, combined with the spatial distribution characteristics of brine, the classification of brine in the study area was preliminarily determined as follows: shallow brine, middle brine, and deep brine (while previous studies have only classified bedrock brine as one category). Hierarchical multi-index analysis was used to identify the inrush end elements in the different sublevels, and an end-element mixed model was determined according to the analysis results of the four pairs of evaluation indexes (Cl−–δ18 O, Cl−–Ca2+, Cl−–Mg2+, and Cl−–Na+). Through a comparison with the deviation analysis results of previous studies, it was shown that this method is suitable for mine-water-source identification when under complex hydrogeology conditions. According to the calculation results of the mixing ratio, the seawater ratio shows, within the mining process, a trend of first increasing, then decreasing, and finally stabilizing. This trend is controlled by disturbance stress, self-weight stress, and tectonic stress. The vertical zonation of the seawater proportions indicates that seawater mainly recharges mine water through vertical fractures. The difference in the proportion of seawater at the water inrush points of the −600 m sublevels indicates that the F3 fault and the northwest water-conducting fracture zone may be the preferred flow channels for seawater to recharge mine water. The research results are of great significance to promote the safe mining of coastal mines around the world.