UPDATE 1-Kazakhmys rejects $13.8 bln offer from ENRC

(Adds more detail, comment, background)

LONDON, May 9 (Reuters) - Copper miner Kazakhmys (KAZ.L: Quote, Profile, Research) said it had rejected a 7.05 billion pounds ($13.8 billion) approach from Kazakh mining group Eurasian Natural Resources Corp (ENRC.L: Quote, Profile, Research), which has a May 16 deadline to make an offer.

Kazakhmys said on Friday ENRC had proposed paying 1,022 pence cash and 0.413 ENRC share per Kazakhmys share, adding the equity element represents Kazakhmys's current holding in ENRC.

"The board of Kazakhmys has considered and unanimously rejected the proposal from ENRC" it said in a statement.

Both are former state firms that have been privatised.

Kazakhmys shares closed 3.0 percent lower at 1,856 pence on Friday, to value the company at 8.44 billion pounds.

ENRC, the world's biggest producer of ferrochrome and the sixth-largest iron ore exporter by volume, first said on March 12 it was interested in Kazakhmys. Britain's Takeover Panel has since has since set it a May 16 deadline to decide on a bid.

Kazakhmys, the world's 10th-biggest copper producer, is owned 45.8 percent by its Chairman Kim Vladimir while Chief Executive Novachuk Oleg has a 7.7 percent stake. (Reporting by Dan Lalor; Editing by David Cowell)