A magnitude-4.3 seismic event late on 31 July triggered a major collapse in the Andesita expansion of Codelco’s El Teniente mine near Rancagua, the world’s largest underground copper deposit. The company said one contract worker was killed, nine others were treated for non-life-threatening injuries and contact has been lost with five miners believed to be about 900 metres below the surface. Roughly 100 specialised rescuers, including veterans of the 2010 San José operation, are working around the clock as Codelco describes the next 48 hours as decisive. GPS tags indicate the likely location of the trapped group, but access tunnels remain blocked by rockfalls. Authorities have declared a Yellow Alert for the municipality of Machalí and deployed additional emergency teams and equipment. President Gabriel Boric ordered Mining Minister Aurora Williams to supervise the operation on site and announced a provisional halt to all underground activity at El Teniente. The O’Higgins regional prosecutor has opened a criminal probe for possible ‘cuasidelito de homicidio’ (negligent manslaughter), while the National Geology and Mining Service (Sernageomin) investigates whether the collapse was purely seismic or linked to operational practices. The accident comes as Codelco struggles to recover output after several project delays. El Teniente produced about 356,000 tonnes of copper in 2024—almost 7 % of national supply—and the Andesita expansion is central to meeting the state miner’s growth goals amid rising global demand. Prolonged closures or safety upgrades could further tighten the copper market.