Indonesia's biggest coal miner, PT Bumi Resources Tbk (BUMI.JK), said on Wednesday it has agreed to buy a 44 percent stake, worth $218 million, in PT Darma Henwa Tbk. (DEWA.JK), a mining operator which has contracts with Bumi.

Indonesia's Bakrie & Brothers (BNBR.JK), which was the main shareholder in Bumi, said last month it had reduced its stake in the firm as part of its debt restructuring. The Bakrie group had borrowed heavily to expand its coal, telecoms, property and plantations interests.

Bumi said it would pay 10 percent of the value of the deal up front, and a further 10 percent during the first year, with the remainder due to be paid at the end of the third year.

The acquisition is one more major step in realising Bumi's coal expansion and mining-related diversification plans, Bumi's president director, Ari Hudaya, said in a statement.

Bumi said it used a coal SPV, or special purpose vehicle, to buy an 80 percent stakes in Zurich Assets International Ltd., which owns the 44 percent stake.

Earlier this week, Bumi announced it had bought 98.5 percent of PT Fajar Bumi Sakti, a local mining firm, for around 2.5 trillion rupiah ($234 million).

Bumi shares ended down 9.4 percent on Wednesday, at 770 rupiah, while shares of Darma Henwa fell 10 percent to 55 rupiah, whereas the index .JKSE fell 0.98 percent. ($1=10,700 Rupiah) (Reporting by Dicky Kristanto and Andreas Ismar, editing by Sara Webb) © Thomson Reuters 2009 All rights reserved