The company outlined a 29% production drop in the March quarter due to higher rainfall and lower evaporation rates.
It said although production in the June quarter was expected to be significantly higher, its full year production would be about 10% lower than expected.
In London, diversified miner Anglo American (LN:AAL) fell 3.17%. Reports have emerged it will be fined BRL125.6 million (US$37.7 million) by Brazil authorities for the first of two pipeline leaks last month at its Minas-Rio operations.
Anglo has suspended Minas-Rio for 90 days to conduct a full pipeline inspection after a second rupture occurred last week, "in close proximity" to the earlier, repaired leak.
In a translated statement, the company said it was analysing the notice of infraction and said it took all measures to minimise the effects of the March 12 and 29 incidents.
Elsewhere, trade war tensions had weighed on markets and metals prices.
The S&P/TSX Composite Index metals and mining sector closed down 0.98% yesterday, pulled lower by the copper stocks' combined drop of 2.32%.
Lundin Mining (CN:LUN) posting the biggest drop in the sub-group of 2.75%.
In the US, copper miner Freeport-McMoRan (US:FCX) lost 0.23% while in the UK, the FTSE100 metals and mining sector had closed down 2.69%.