(Rewrites with stock price, analyst, Barrick executives' comment)
By Nicole Mordant
April 25 (Reuters) - Barrick Gold gave details on Tuesday of $500 million worth of improvements and expansions it is planning at its Veladero mine in Argentina over the next five years, on a day when its stock price sank 11 percent on disappointing earnings.
Shares in Barrick, the world's biggest gold miner, dropped the most in 21 months on a weaker gold price and after its earnings fell short of market expectations. That was partly caused by higher costs and lower-than-expected output at Veladero, which has had three cyanide solution spills in 18 months.
Improvements to Veladero's leach pad processing facility, where the spills occurred, would include adding containment barriers, strengthening and moving pipes, and installing new high-definition cameras to monitor the site, Barrick chief operating officer Richard Williams said.
The Canadian miner is also adding new valves to control the flow of processing solution, increasing management oversight and worker training at the facility, Williams told analysts on a conference call to discuss quarterly results out late Monday.
Earlier on Tuesday, Barrick President Kelvin Dushnisky told shareholders at the company's annual meeting in Toronto that the repeated spills were "completely unacceptable".
The latest spill, on March 28, resulted in Argentine authorities suspending the addition of cyanide to the leach pad pending repairs and improvements, and led Barrick to slash Veladero's 2017 output forecast and hike costs.
COO Williams said Barrick was confident the cyanide suspension would be lifted by June as repairs and discussions with authorities were going "pretty well".
The $500 million is not new money for Veladero but part of Barrick's five-year sustaining capital plan for the mine, he said.
The miner's aim is to first get the existing leach pad to a standard that it and authorities are happy with, and then to proceed to a second phase of getting permits to expand the processing facility, Williams said.
Despite Barrick's below-consensus earnings Jefferies analyst Christopher LaFemina said the company remained his "preferred" North American gold miner.
That was because of its ongoing debt reduction, strategic partnerships, quality of assets and low cost profile, he said.
Barrick's stock closed down 11 percent at C$22.89 on the Toronto Stock Exchange. (Reporting by Nicole Mordant in Vancouver, editing by G Crosse and Grant McCool)