This paper is concerned with the role of social impact assessment (SIA) in the resolution of an environmental conflict involving demands for the conservation of an ecologically significant area, a proposal to exploit mineral wealth, and the concerns of indigenous custodians who feared damage to sacred lands. This is a case in which the knowledge claims of key protagonists were deeply politicized and contested, and in which the process of decision-making was itself the subject of controversy and debate. The paper reviews the case, emphasizing the roles of western and indigenous epistemologies in decisionmaking. It presents an approach to SIA that addresses these epistemological issues and ensures the articulation of indigenous knowledge to governmental decision-makers.