* Govt says would be "recovery", not nationalization
* Unions proposing mines return to state control (Updates with details on mines, output)
LA PAZ, April 14 (Reuters) - Bolivia's leftist government may rescind concessions on four mines run by Glencore [GLEN.UL] affiliates and Canada's Pan American Silver PAA.TO(PAAS.O), the Andean country's mining minister said on Thursday.
Mining unions are asking the state to "recover" the silver, zinc, lead and tin mines currently operated by private firms, minister Jose Pimentel told a news conference.
He said state-run Bolivia Mining Corp would assume control over the mines if the concessions were rescinded, adding this would affect top commodity trader Glencore's Porco, Colquiri and Bolivar mines as well as Pan American's San Vicente mine.
"The (unions') concrete proposal is to recover state companies that passed into the hands of the private sector one way or another. We will consider these cases when the unions working at each of the companies request this," Pimentel said.
San Vicente, located in the center of the silver-rich Potosi region, boosted output to some 2.6 million ounces of silver in 2009 from 875,000 in 2008. [ID:nN20173238]
For a factbox on Bolivia's top mines, see [ID:nN30167493] (Reporting by Claudia Soruco; Writing by Hilary Burke; Editing by Dale Hudson and David Gregorio)