Geochemical evaluation of mud volcanic sediment and water in Northern Borneo: A baseline study

A comprehensive geochemical investigation was carried out to characterise the sediment and water seeping out from mud volcano in Kampung Meritam, Limbang, northern Borneo. Chemical analysis included major oxides, trace metals, rare earth elements, and major ions. Interpretation of results reveals that the geochemical composition of sediment samples is originated from sedimentary provenance particularly Setap Shale, which is the dominant formation present in this region. The concentration of trace elements and major oxides were used to identify the origin and weathering nature of sediment. SiO₂ is the dominant major oxide present in the sediment samples with an average concentration of 58.24%. Whereas for trace metals, Ba is dominating with an average concentration of 263 ppm. Environmental pollution indices such as contamination factor, geoaccumulation index, and enrichment factor were used to assess the contamination level of mud volcanic sediments. Hydrochemistry of mud volcano suggests that the water is derived from ionic enriched solute, indicated by Na-Cl water type. The average concentration of Na⁺ and Cl⁻ is 987 mg/L and 10457.50 mg/L. The ionic ratios suggest that water–rock interaction including carbonate mineral dissolution is the predominant process that controls the water chemistry. Gibbs diagram shows that the water is influenced by the dissolution of evaporite minerals. Thermodynamic stability and saturation index were used to evaluate the mineral stability and saturation condition during weathering. Ca²⁺ and Mg²⁺ were released into the water due to the reverse ion exchange process, which was supported by XRD results. Higher ionic strength and Log pCO₂ values suggest longer residence time of water in the aquifer matrix and therefore significant dissolution of enriched solute due to the intensive water–rock interaction. The outcome of this study would provide the basis for a better understanding on the geochemical characteristics of Meritam mud volcano in Northern Borneo.