There is a potential risk that geochemical cycles of critical metals (e.g Be and W) will be affected in the pristine environment, when mining of these metals increases to meet the demand in green technology. To understand their geochemical behavior and environmental impact are of high importance to ensure a sustainable development of mine waste and water management. Beryllium and W are identified as elements of potential concern that can have adverse impact on humans and ecosystems. The release of Be and W from two historical skarn tailings (Smaltjärnen and Morkulltjärnen repositories) from the same ore body (Yxsjöberg/Sweden), and the impact on epilithic water diatoms in downstream neutral surface water were studied. Dissolved Be had been released in high concentrations from danalite (Be3(Fe4.4Mn0.95Zn0.4)(SiO4)3.2S1.4) due to oxidation and acidifications in tailings stored open to the atmosphere (Smaltjärnen). Tungsten was released in low concentrations as an indirect consequence of sulfide oxidation. Thus, CO32- released from calcite buffering the acid produced had exchange with WO42- on scheelite (CaWO4) surfaces. High concentrations of dissolved W were present downstream the covered and water saturated tailings (Morkulltjärnen). Beryllium and W are considered as immobile elements, but both were transported in neutral mine drainage (NMD) >5 km downstream the mine site. The water quality from both repositories had negative impact on epilithic water diatoms >2 km from the site. This study shows the importance to understand the geochemistry and mineralogy before choosing remediation method for mine tailings enriched in critical metals, and the need to study NMD.