South32 Ltd (S32.AU) saw its stock price plummet by 8.92% during intraday trading on Thursday, marking a significant decline for the mining company.

The sharp drop follows the company's announcement of substantial delays and cost overruns at its Taylor deposit, part of the Hermosa project in Arizona. South32 now expects to spend approximately $3.30 billion to build the zinc, lead, and silver project, a dramatic increase from the initial estimate of about $2.16 billion. First production is anticipated in the second half of fiscal year 2028, a full year later than previously estimated, with full capacity now expected in fiscal 2031 instead of 2030.

Chief Executive Graham Kerr cited contractor underperformance, productivity challenges, scope changes, materially higher inflation, and U.S. tariffs as key factors driving the increased costs and timeline delays. The company also revised its forecast for average operating unit costs upward to $100 per metric ton from $86 previously, reflecting general inflation and higher assumed energy costs.