The increasing demand for low carbon technology has increased the demand for some critical materials. Graphite is one of the strategic raw materials defined by the European Union as it is used in the production of for example batteries in electrical vehicles. Natural graphite is extracted through mining and the production is currently located outside the European Union. However, natural graphite deposits exist in for example Sweden. Mining activities can cause environmental issues, e.g. release of metals to the environment. By studying sediment in lakes, the historical element load can be investigated. In the Vittangi area (northern Sweden), a graphite deposit is located close to the natural lake Hosiojärvi. In the area, exploration has been conducted during the last 100 years. The latest exploration was conducted by the company Talga, who is also planning to extract the graphite. The aim of this master thesis is to determine the geochemical processes affecting the mobility of Co, Cu, Ni and Zn in Hosiojärvi, as well as their historical accumulation in the lake. Due to previous exploration in the area, the eventual impact from trace elements related to the bedrock and graphite deposit has also been studied. Based on previous elemental load to the sediment, the future impact until the mine starts have been discussed. The method used for answering the questions have been sampling of sediment, analysing metal concentrations in surface water, groundwater and sediment and dating of the sediment to determine sediment accumulation rate. The study shows that there has been an increase of Co, Ni and Zn to the lake, as the concentrations in the sediment has increased in the upper parts. By looking at those elements, the increase could be explained by the exploration during 1960 – 1970. The sediment is assumed to be in reduced conditions and the zone where redox processes can occur is assumed to be in the interface between the bottom water and the top sediment. In the sediment, framboidal pyrite is formed in the upper and lower parts of the sediment. Analysis on surface water shows that during the last four years, there is an increasing trend of  Co, Ni, Zn and SO4. The groundwater flows through the mineralisation and affects the water quality in Hosiojärvi, as the water quality of the lake has become more similar to the groundwater. The overall conclusion of the study is that the lake has been impacted by the previous exploration and is assumed to continue being affected until the planned mine is starting to operate.