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Group 2020 copper production has been cut to 135,000-175,000 tonnes from 165,000-205,000t.
Rio expects C1 copper unit costs of $1.20-1.35 per pound.
The company experienced delays to the restart of the Kennecott smelter due to unexpected issues that appeared following planned maintenance.
Repairs to the flash converting furnace were aligned to the planned 45-day smelter shutdown.
In March, Kennecott was impacted by a 5.7 magnitude earthquake, which led to a $100 million charge in Rio's half-year results and a $12 million net loss for the asset.
Rio said it was working closely with its customers to limit any disruptions and expects to have the smelter fully operational in two months.