Citizen participation should ideally occur as early as possible in a project, especially throughout the course of the Environmental Impact Assessment (EIA) study. In Chile, participation occurs after the EIA study has been completed and presented to authorities for evaluation. However, voluntary early participation has become an extended practice in large mining projects for financial and conflict-reduction reasons. The purpose of this study was to explore a variety of these early participation processes happening in large mining projects from 2001 to 2010 and analyze how well these practices measured up to standards and objectives defined in the EIA and participation literature. Beyond the legal implications of such practice, we sought to understand the role of this voluntary procedure within the EIA process and citizen engagement in projects. We found a wide range of objectives, approaches and results, primarily driven to facilitate approval and implementation of the ten projects analyzed. The underlying objective of voluntary participation processes analyzed (whether it seeks to inform, to note or to engage), determined the information presented, participants included, area of influence considered, time devoted to the process and influence of the information collected on EIA and project mitigation measures. Few of the principles for best practice in the literature were present in the ten projects examined. Moreover, given the voluntary and unregulated nature of these processes, purposes and outcomes were often mixed-up with the Indigenous Consultation required under ILO provision 169, or Corporate Social Responsibility programs. This finally revealed that contrary to expectations, an unregulated and early voluntary participation is not having a clear impact in the definition of projects mitigation measures, participants are at risk of being unsatisfied with the resulting agreements and moreover, it does not assure projects implementation or the avoidance of socio-environmental conflict.