Supplementary Cementitious Materials (SCMs) have been researched to improve properties of concrete, including environmental indicators. Copper Treated Tailings (TT) have shown a promissory use as SCM but need of mechanical and thermal treatment has an impact on their environmental performance. The impact of the use of SCMs on the mechanical properties mixtures and environmental indicators needs to be considered into the calculations, such as the mechanical performance decrease and the leaching of some potentially harmful elements from the mixture. This study calculates the environmental impacts of the use of TT as SCM. Three scenarios are evaluated: equivalent mechanical performance at the same water-to-cementitious (w/c) ratio, maximum mechanical performance, and maximum allowable replacement level (i.e. minimum allowable mechanical performance). To achieve each level of mechanical performance, different replacement levels were tested for mixtures with TT, and different w/c ratios were tested for mixtures without TT, at a constant water level to vary only the binder content. Results show that at higher mechanical performance TT mixtures show better environmental indicators than mixtures without TT. In the case of TT mixtures with lower mechanical performance, environmental benefits of the use of TT shows a decrease in environmental indicators of concrete with TT. It is concluded that considerations need to be made on the properties of the SCM for a proper comparison of concrete mixes. Avoided impacts and the relative contribution of cement depending on the performance and level of replacement are also important considerations to be made for a proper environmental comparison.