Environmental and human health implications of the geochemical heritage of an abandoned Gold Mine: The case study from the Bonanza Gold Mine, Barberton Greenstone Belt, South Africa

Abandoned gold mines represent a persistent source of environmental contamination, posing significant risks to freshwater resources and agricultural land through the release of effluents enriched with potentially toxic elements (PTEs). This study investigated the physicochemical characteristics, major ions, and PTE concentrations in stream water and sediments collected upstream and downstream of the abandoned Bonanza gold mine in the Barberton Greenstone Belt, South Africa. The suitability of stream water for domestic use was assessed using the Water Quality Index (WQI) and the Environmental Water Quality Index (EWQI). Human health risks associated with drinking water consumption were evaluated using the non-carcinogenic hazard index (HI) and cancer risk (CR), while sediment contamination was assessed using the geo-accumulation index (GI). Multivariate statistical techniques, including Pearson correlation analysis, principal component analysis (PCA), and cluster analysis (CA), were applied to identify pollution sources and factors controlling PTE distribution. Results showed that downstream water samples exceeded World Health Organisation (WHO) and South African National Standards (SANS) guideline values for Fe, Ni, As, and Mn, indicating contamination from abandoned gold mine effluents. Multivariate analyses revealed common geochemical behaviour among As, Ni, Mn, and Fe, while Hg exhibited weak correlations with these elements, suggesting additional inputs from illegal gold mining activities. Stream sediments downstream were significantly enriched with As and Ni and classified as highly contaminated based on GI values. Water quality indices indicated that about 30% of stream water samples were unsuitable for human consumption. Health risk assessment revealed unacceptable non-carcinogenic risks for 80% of children and 50% of adults, while cancer risk values exceeded acceptable limits for all children and 80% of adults. Elevated PTE concentrations downstream highlight abandoned gold mining as the dominant contamination source. This study provides baseline data to support future monitoring and management, including assessments of seasonal variability.