Freeport-McMoRan's Grasberg mine in Indonesia — the world's second-largest copper mine — suffered a major operational disruption in September 2025 when the main Grasberg Block Cave experienced an ingress of wet material that killed seven workers and forced the immediate closure of the affected operation. (FACT: INN, May 19, 2026) The accident removed approximately 40% of Grasberg's copper output from the global market, contributing to the concentrate tightness that drove TC/RCs to zero and then negative in 2026.
Freeport has executed a phased restart plan. Unaffected portions of the Grasberg complex reopened by the end of 2025, and the Block Cave itself began a phased restart in Q2 2026. (FACT: INN, May 19, 2026) Freeport targets 65% capacity in the second half of 2026, 80% by mid-2027, and near-full capacity by the end of 2027. (FACT: Mining.com, May 4, 2026) The slow recovery timeline reflects the complexity of remediating a cave mining operation where material ingress compromised the structural integrity of underground workings.
Grasberg's reduced output has been one of the primary drivers of global copper concentrate tightness. The mine produces approximately 700,000 tonnes of copper annually at full capacity, accounting for roughly 3% of global mined copper supply. (FACT: INN, May 19, 2026) A 40% reduction for 12 months removes approximately 280,000 tonnes from the concentrate market — equivalent to the entire ICSG-projected 2026 surplus of 96,000 tonnes, and then some. The Grasberg shortfall, combined with the permanent closure of Cobre Panama, underperformance at Kamoa-Kakula, and TC/RC compression, has created the tightest copper concentrate market in history.
The restart timeline is critical for the global copper balance. H2 2026 at 65% capacity means Grasberg contributes approximately 230,000 tonnes in the second half — about 120,000 tonnes below full potential. (FACT: Freeport-McMoRan, H1 2026 guidance) Mid-2027 at 80% restores approximately 560,000 tonnes annualized, and end-2027 at near-full capacity returns the mine to its pre-accident output. (FACT: Mining.com, May 4, 2026) The recovery, when complete, will be one of the largest single additions to global copper supply in 2027-2028.
The number that matters for your business: The Grasberg accident removed approximately 280,000 tonnes of copper concentrate from the global market over 12 months — enough to supply a medium-size Chinese smelter for an entire year. A cathode buyer purchasing 5,000 tonnes/year of copper that is ultimately sourced from Grasberg concentrate has faced indirect supply pressure through elevated TC/RC premiums and the concentrate-to-cathode bottleneck. With the phased restart underway, concentrate availability should improve gradually from H2 2026 onward. Full normalization — with Grasberg back at pre-accident output — does not occur before end-2027.
Action: For copper concentrate buyers and smelters, the Grasberg restart is the single most important supply-side event for 2027 concentrate negotiations. The mine's return to 65% capacity in H2 2026 adds approximately 230,000 tonnes to the H2 concentrate pool — enough to modestly ease spot TC/RCs but not enough to lift them back to positive territory. TC/RC negotiations for 2027 should incorporate the mid-2027 ramp to 80% capacity. For cathode buyers, the Grasberg restart flows through to refined supply with a 3-6 month lag as concentrate is smelted and refined — expect the refined copper market to begin feeling the supply improvement by Q1 2027.
Horizon: Concentrate tightness begins easing H2 2026, but does not normalize until mid-2027. Cathode availability improves 3-6 months behind concentrate. Full Grasberg normalization by end-2027 is the timeline for a return to pre-accident copper supply conditions from this mine.
Trigger: Watch Freeport's quarterly production reports — if H2 2026 output exceeds 65% of capacity, the ramp is ahead of schedule and concentrate tightness eases sooner. Conversely, any operational setback at the Block Cave restart would extend the tightness into 2028.