Iron ore miner Sable agrees $1.3 bln export deal

* Agreement offers lifeline to London-listed firm

* Exploitation of Guinea mine previously too costly

* Sable flags announcement; shares soar 300 percent (Adds deal signing, updated stock price, quotes)

MONROVIA, Jan 23 (Reuters) - Sable Mining signed a $1.3 billion deal to export iron ore via Liberia on Friday, offering the London-listed firm the transport link it has so far lacked to exploit the site in Guinea where the ore is mined.

The agreement was signed by the head of the Liberia National Investment Commission George Wisner and Sable non-executive director Aboubacar Sampil in the nation's capital Monrovia.

The 25-year deal, which mandates the firm to expand rail links between the two countries, should allow it to begin transshipping ore from the Mount Nimba mine later this year, Wisner said.

Shares (Frankfurt: DI6.F - news) in AIM (SES: E1:A54.SI - news) -listed Sable soared more than 300 percent on Friday before closing up 156 percent.

Wisner said the agreement still needs parliamentary approval.

The Guinean government had been reluctant in the past to allow transshipment, insisting mining firms operating in Guinea ship their ore through the port of Conakry, which would have made Mount Nimba too costly for Sable to exploit.

But in October 2013 it granted permission for Sable to export via Liberia.

Wisner said Sable would invest $300 million in the first five years of the project and $1 billion in the remaining 20, and would ship its ore via the Liberian port of Buchanan.

Sable is expected to rehabilitate and expand an existing rail link from Yekepa in northern Liberia to Buchanan in accordance with third-party access rights between the Liberian government and ArcelorMittal (Other OTC: AMSYF - news) , the world's largest steelmaker, which operates the line.

Wisner said the Liberian government was taking the lead in facilitating the negotiations over third-party access.

"Under our constitution, the rail is owned by Liberia. The ground is owned by the republic of Liberia. I do not want to pre-empt the negotiation, but I do not foresee any hurdle in the third-party negotiation," he told Reuters.

ArcelorMittal has previously said that companies in Guinea would have to wait years to make use of the existing rail link through Liberia because there was no spare capacity.

But the LNIC said Sable was also mandated to construct a new line from Guinea via Tokadeh in northern Liberia to link with the existing line at Yekepa. (Reporting by James Harding Giahyue and Alphonso Toweh; Writing by Bate Felix and Daniel Flynn; Editing by Joe Bavier, John Stonestreet and David Evans)