Environmental and social risks in mining regions often juxtapose promises of local economic growth. Brazil, a major global mineral supplier and conservation leader, has pursued resource-led development despite mining’s threat to its forests. Yet, the efficacy of this development strategy is uncertain. In this study, we examine mining’s contribution to deforestation and regional economic growth in Brazil. For garimpo mining concessions – originally small-scale and less rigorously regulated forms of informal mining – we identify substantial associations with elevated deforestation rates, highlighting the environmental risks of insufficient oversight. The economic benefits of mining are limited. Particularly for industrial mining, they are tied to fluctuations in global mineral prices. These findings challenge the perception that mining inherently drives sustained regional economic development. As global demand for minerals rises – particularly to support the energy transition – strategic mining investments must be revised to prioritise sustained local progress, nature conservation and community well-being.