Investigating the characteristics of mine water in a subsea mine using groundwater geochemistry and stable isotopes

Abstract

Investigation were conducted in the Xinli subsea mine from 2006 to 2011, which is the largest subsea mine in China and threatened by the overlying Quaternary aquifer and seawater. Hydrochemical and stable isotopic (δ2H and δ18O) analyses were used to study the relationships between various waters. Hydrochemical results indicated that the seepage water in the mine tunnels had higher EC, TDS, and concentrations of most elements than the seawater and saline groundwater. Water analyses indicated the mine discharge was a mixture of the seawater, brine, and atmospheric precipitation. The proportions of the three different sources were calculated based on hydrochemical and isotopic analyses. The seepage water were more isotopically enriched than the seawater but less than the brine. In addition, the isotope mixing calculation indicated that the average proportions of mine water from seawater, brine and atmospheric precipitation were about 38.5, 46, and 15.5 % respectively for the entire mine in 2006. However, the concentrations of these analyses decreased and the proportion of the seawater increased 21.1 % after 5 years of exploitation in 2011. These changes demonstrated that the surrounding rock mass underwent a certain extent of deformation and failure because of the mining disturbance, which enhanced the permeability of the surrounding rock mass.