TORONTO — Shares in Kinross Gold Corp. were down nearly 20 per cent Tuesday morning after the gold miner said soaring costs at the Tasiast mine in Africa will require months of delay and a writedown related to its purchase of Red Back Mining.

Kinross fell $2.48 to trade for $10.72 on the Toronto Stock Exchange.

The Toronto-based miner said late Monday that it will take an additional six to nine months of analysis and planning to determine the optimal processing mix to reduce operating costs at Tasiast.

Kinross said it’s still working to determine the extent of a writedown that will be required under international financial reporting standards, but noted more half of the book value of Tasiast was goodwill at the end of the 2011 third quarter.

Goodwill is an intangible asset that reflects the long-term value of an acquired business. If the estimated value is eroded by changed circumstances, a company is required to take a charge.