Geochemical Characterization of Rock Samples from Selected Fiji Mine Sites to Evaluate On-Site Environmental Vulnerabilities

Although mining contributes to about 1.4% of Fiji's gross domestic product (GDP), the excavated rocks from mining may have detrimental effects on the environment. In this study, rock samples from five Fiji mine sites were selected to assess their geochemical characteristics from an environmental point of view. The mineralogical and chemical constituents, release and retention mechanisms of hazardous elements, and acid/neutralization potential of the rock samples were investigated to understand their environmental impacts on-site. The results showed that sulfide minerals typically found in the rock samples, such as pyrite, chalcopyrite, and sphalerite were responsible for the release of hazardous elements such as Cu, Pb, and Zn via oxidation. Leachates of rock samples from Mt Kasi, Nukudamu, and Wainivesi exceeded the World Health Organization (WHO) regulatory limit for Cu (2 mg/L), Pb (0.01 mg/L), and Zn (3 mg/L) in drinking water. In contrast, no hazardous elements were leached from the Tuvatu and Vatukoula rock samples, which could be attributed to the dissolution of calcite and dolomite that buffered the pH and limited heavy metal mobility. The acid-base accounting (ABA) and accelerated weathering test by hydrogen peroxide indicated that most of the rock samples containing sulfide minerals were likely to generate acidity. Furthermore, the results highlighted that once carbonate minerals are depleted in the rock samples, acid mine drainage (AMD) generation is inevitable. These findings reaffirm the need for committed effort in environmental management of the mine sites to prevent environmental issues associated with AMD.