Speaking at the Global Iron Ore & Steel Forecast Conference, Roy Hill CEO Barry Fitzgerald said while the mine had briefly hit an annualised run-rate of 55 million tonnes per annum, the past few months had seen shipments dip.
"There's no doubt that January and February were not our greatest moments," he said.
The mine was hit by wet weather and "breakdowns that cost us tonnes".
Fitzgerald believes March has brought a big improvement.
"We're back into the swing of things," he said.
"We need to now maintain it."
The new mine didn't quite make its "stretch target" of ramping up to 55Mtpa within 15 months, but Fitzgerald said the Roy Hill ore had been harder than expected.
"We've overcome a few challenges along the way," he said.
Fitzgerald noted there had been a lot of talk around C1 iron ore costs in the Pilbara, with Fortescue Metals Group (AU:FMG) setting its financial year 2018 guidance of US$11-12 per tonne.
"Clearly we need to compete with that," he said.
"We've got a lot of work to do."
Roy Hill has also applied to lift annual shipments to 60Mtpa.
While the Town of Port Hedland has recommended against it, Fitzgerald is confident that, like BHP (AU:BHP) recently, studies would find that Roy Hill ore was not contributing to the city's dust problem and approval would be granted.
"Certainly we believe we've got excess capacity in the plant, the car dumper and the shiploader to get to 60Mtpa," he said.