JAKARTA, May 12 (Reuters) - Indonesia's PT Timah Tbk TINS.JK, the world's largest integrated tin miner, plans to acquire three coal mines with total reserves of 50 million tonnes, a senior company official said on Monday.

Timah has a mine in South Kalimantan which produces up to 1.4 million tonnes of coal a year, but the firm has been looking for new mines because of depleting reserves.

The company is aiming to sell 1.8 million tonnes in 2008. It exports thermal coal mainly to Japan, India and Korea.

Timah's commerce director, Gatot Hari Prasetio, said the company is working on a plan to acquire three coal mines in South Kalimantan and South Sumatra, but gave no details.

Timah's president director, Wachid Usman, told reporters the company could spend two trillion rupiah on acquiring coal mines and about 1.4 trillion rupiah on boosting output, exploration and business development.

Indonesia, the world's biggest archipelago with more than 17,000 islands, is rich in coal, copper, gold, tin and other minerals.

Indonesia is the world's largest exporter of thermal coal and is expected to export 170 million tonnes of coal this year and 190 million tonnes in 2009. ($1 = 9,235 rupiah) (Reporting by Nury Sybli, editing by Sugita Katyal)