The rise of brownfield mining is reshaping global mineral supply and intensifying social and environmental risk

Global mineral demand is rising faster than supply growth, driven by efforts to scale renewable energy, transport, digital, and defense infrastructure. Yet, new mine commissioning has slowed, with production growth sustained by "brownfield" mining—expanding and intensifying extraction at existing sites. Because mine expansion is considered routine industry practice, questions about the global scale and scope of brownfielding are not prominent in public discussion or scientific research, limiting our understanding of its socioecological risks. Here, we leverage global production, exploration, and capital-expenditure data from 1998 to 2024 to uncover a decade-long acceleration in brownfield mining. We identify 366 brownfield mines, with 20.5% in ecologically intact or mixed landscapes, 51.5% near biodiversity or protected areas, and 77.9% above multiple high-risk thresholds, with activity concentrated in copper, gold, and iron ore in Chile, the United States, and Australia. A greater dependency on brownfielding requires governance that accounts for cumulative impacts and intergenerational liabilities.