* Zimbabwe to sell 300,000 carats in Antwerp
* Diamond revenues have been source of conflict
* Marange firms say deposits depleting
HARARE, Dec 10 (Reuters) - Zimbabwe will this week auction its first ever diamonds in Belgium, nearly three months after the European Union (EU) removed sanctions on the country's state mining company, an Antwerp-based diamond sector representative said on Tuesday.
Belgium, centre of the global diamond trade, had pushed hard for the EU to lift sanctions on the state-owned Zimbabwe Mining Development Corporation (ZMDC), in line with an earlier agreement.
ZMDC operates seven joint-venture mines in the Marange diamond fields, producing eight million carats last year and generating $685 million in exports.
The Antwerp World Diamond Centre said in a statement that 300,000 carats of diamonds from Marange would be auctioned from Wednesday, a move which is expected to increase transparency over Zimbabwe's diamond sector.
"Antwerp is convinced that the combination of solid transparency, accountability and potentially increased mining revenues will contribute to a sustainable social and economic development of Zimbabwe," the AWDC said.
Belgium has said lifting EU sanctions on ZMDC would increase Zimbabwe's tax revenues by $400 million a year.
Diamond revenues were a source of conflict in the previous coalition government formed by President Robert Mugabe and long-time opponent Morgan Tsvangirai.
Mines Minister Walter Chidhakwa said on Monday that companies operating in Marange had reported that alluvial diamond deposits, which are nearer the surface and cheaper to extract, were fast depleting.
The companies are now asking the government for new mining concessions and say it is now becoming too expensive to mine deeper into the ground.
The Marange diamond fields, 400 km (240 miles) east of Harare, have been a focus of controversy since 20,000 small-scale miners invaded the area in 2008 and were then forcibly removed by soldiers and police.
Human rights groups say up to 200 people were killed during the process, charges denied by Mugabe's government. (Reporting by MacDonald Dzirutwe; Editing by Ed Stoddard and Angus MacSwan)