Shareholders of mining group Xstrata Plc approved a $5.9 billion rights issue on Monday so the firm could pay off debt and also voted for the acquisition of a coal mine in Colombia.

Xstrata, the world's fifth biggest diversified mining group by market value, announced plans to issue heavily-discounted new shares on Jan. 29 that will triple its shares in issue.

An extraordinary general meeting in Switzerland gave approval for Xstrata to issue 1.96 billion new shares at 210 pence a share, a statement said.

The issue price was a 66 percent discount to the closing price of the shares on the day before the initial announcement.

Xstrata shares fell 7.98 percent to 640 pence by 1237 GMT, compared with a 4.6 percent decline in the UK mining index.

The shares will become ex-rights on Tuesday and the theoretical ex-rights price will be 348 pence, Xstrata said.

The meeting also gave approval to the $2 billion purchase of the Prodeco coal mine in Colombia from Xstrata's biggest shareholder, Swiss commodities trader Glencore.

Some shareholders had expressed unhappiness about the Prodeco deal, which was arranged so that Glencore could use an asset instead of cash to participate in the fund raising and maintain its 35 percent shareholding.

The resolution about Prodeco was approved by 80.3 percent of shareholders voting while three other resolutions about the rights issue got 95 percent approval.

Xstrata and Glencore could not agree on a price for Prodeco so Xstrata granted an option to Glencore allowing it to buy back the mine after a year.

Following the fund raising, Xstrata's net debt is due to fall to around $12.6 billion from $16.3 billion at the end of 2008, while gearing would decline to less than 30 percent from 40 percent.

The rights issue is fully underwritten by Glencore and investment banks Deutsche Bank and JP Morgan. (Reporting by Eric Onstad; editing by Simon Jessop)

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