* Says size of reserves at Mana mine up 125 pct
* Adds 961,000 oz of gold reserves at the mine
TORONTO, June 28 (Reuters) - Canadian gold miner Semafo (SMF.TO) said on Monday it is increasing the size of its reserves at its Mana mine in Burkina Faso by 125 percent following the completion of a pre-feasibility study.
The study resulted in the addition of 961,000 ounces of reserves at the mine in West Africa, Semafo said in a statement.
The Montreal-based gold junior, which produced almost 250,000 ounces of gold in 2009, begun operations from two open pits at Mana in 2008 -- much of the 90-kilometer strike length of the property has yet to be explored.
The positive pre-feasibility results, in conjunction with Mana's ongoing open pit operations and existing infrastructure, further confirm the economic viability of an underground mining operation at the site, the company said.
The company estimates that the underground mine has 688,000 recoverable ounces at a cash operating cost of $554 per ounce.
Shares of Semafo were down 7 Canadian cents at C$8.66 in midday trade on the Toronto Stock Exchange. (Reporting by Euan Rocha)