Codelco is a Chilean public company that is the largest copper producer in the world and it has developed multiple initiatives to implement Lean Management in its operations. This article evaluates the impacts of the implementation of Lean production methods on an underground mining development project. The effects of Lean methods, such as The Last Planner (R) System (LPS), on an appropriate case study and the analysis of these results produced statistical research findings and qualitative observations that suggest a broader implementation of Lean in the mining industry. Among these observations are: a) improvement of the mean for all indicators studied; b) reduction in the variance of some indicators, suggesting more stable processes; c) correlation between the percent plan complete (PPC) from the LPS and its coefficient of variation (CV); d) reduction in the time wasted in delays; and, e) improvement in key organizational attributes. Additionally, all variables associated with positive performance improved during the research, suggesting that the implementation of Lean methodologies improved overall performance throughout the organization.