The rating agency sees iron ore prices supported in the next few months but expects declines later this year.
The country reported increases in iron ore pellet revenue and volumes in the first three months of the year.
The new rules, due to be enforced in December 2018, aim to capture 95% of smelter emissions.
Copper, gold, zinc, tin, iron ore and molybdenum exports all rose in February as companies increased shipments and benefitted from the ongoing price rally.
Will copper be at US$5,000/t or US$7,000/t in 2020? Expert opinions vary.
The uptick in copper and iron ore prices helped offset the decline in output as a result of the 43-day strike that affected BHP Billiton's Escondida mine.