Water quality in the Lisungwi and Kaphamtengo Rivers in Manondo, Central Malawi: Assessment of the impact of artisanal small scale gold mining

Water quality assessment for river systems is important for tracing any changes in quality caused by, among other things, mining  activities. Mining activities can be one of the most impactful sources of water contamination. In Malawi, gold deposits occur in the  basement rocks of the Lisungwi-Manondo region. As a result, a boom in small scale artisanal mining has occurred as residents have  settled in the area. Despite the development of artisanal small scale mining activities, few studies have investigated the water quality of  the main rivers in the region (i.e., the Lisungwi and Kaphamtengo Rivers), upon which local residents are highly dependent for daily use.  This study provides baseline data for water quality in the region. On-site and laboratory measurements were carried out on the river  water samples, to obtain the physio characteristics (e.g. pH, turbidity, electric conductivity) and the major and minor element  concentrations of the river water. The data was compared to the regional geology to establish anthropogenic and/or geological impacts  on the water quality. The river water has a moderate buffering capacity due to its high alkalinity, along with high Ca, Si, Mg, and Cl  concentrations sourced from the gneiss and calcsilicate rocks in the region. Further analysis of the water quality based on the physiochemical parameters, major and trace element concentrations, showed that the river waters were in accordance with guidelines  set by the Malawi Bureau of Standards (MBS) and the World Health Organization (WHO) for river water quality, with all analyzed  parameters being below the stipulated standards. Our results indicated that the regional geology exerts a significant control on water  chemistry, but the mining activities on and along the river water leaves the water in an uncontaminated state

The formation of Fe colloids and layered double hydroxides as sequestration agents in the natural remediation of mine drainage

The increasing need to treat wastewater from mine effluents has drawn attention to passive treatment systems. Colloids are common in mine waters and are highly reactive, so their formation, characteristics, behavior, and the critical factors that affect them need to be understood for designing efficient treatment systems. An investigation was conducted at the abandoned Ainai mine drainage, Japan, where aeration is utilized to remove Fe, As, and Zn from circumneutral wastewater drainage, during rainy and dry seasons of 2016 and 2018 respectively, based on observations of physiochemical characteristics, elemental concentrations in dissolved and colloidal fractions, transmission electron microscopy, and synthetic experiments. In this circumneutral Fe-rich mine drainage, Fe2+ is oxidized to Fe3+, resulting in the formation of Fe colloids that incorporate As during their formation. Colloid formation increases turbidity, and, in the rainy season, increased colloidal interaction enhances their aggregation and higher flow rates lead to greater mobilization of the colloids. Zn-bearing colloids are rare in Ainai mine drain-age because the Zn concentrations are low. However, Zn-Fe layered double hydroxide (LDH) was identified and confirmed by geochemical modelling and experiments. The Zn-Fe LDH was formed by isomorphous substitution of Zn into an Fe2+-Fe3+-CO32-LDH, at pH greater than 7.5, thereby achieving efficient natural remediation of Zn and As in the drainage

Magmatic-Hydrothermal Processes Associated with Rare Earth Element Enrichment in the Kangankunde Carbonatite Complex, Malawi

Carbonatites undergo various magmatic-hydrothermal processes during their evolution that are important for the enrichment of rare earth elements (REE). This geochemical, petrographic, and multi-isotope study on the Kangankunde carbonatite, the largest light REE resource in the Chilwa Alkaline Province in Malawi, clarifies the critical stages of REE mineralization in this deposit. The delta Fe-56 values of most of the carbonatite lies within the magmatic field despite variations in the proportions of monazite, ankerite, and ferroan dolomite. Exsolution of a hydrothermal fluid from the carbonatite melts is evident based on the higher delta Fe-56 of the fenites, as well as the textural and compositional zoning in monazite. Field and petrographic observations, combined with geochemical data (REE patterns, and Fe, C, and O isotopes), suggest that the key stage of REE mineralization in the Kangankunde carbonatite was the late magmatic stage with an influence of carbothermal fluids i.e. magmatic-hydrothermal stage, when large (similar to 200 mu m), well-developed monazite crystals grew. The C and O isotope compositions of the carbonatite suggest a post-magmatic alteration by hydrothermal fluids, probably after the main REE mineralization stage, as the alteration occurs throughout the carbonatite but particularly in the dark carbonatites