CESC Ltd will lose its most important producing captive Sarshatali mine which has annual capacity of three million tonne per annum, company sources said.
The mine is operated through its subsidiary 'Intregated Coal Mining Ltd' located in Asansol and was operational since last seven years.
Captive coal accounts for 45 per cent of coal for generation of 1,225 MW of CESC.
West Bengal Power Development Corporation (WBPDCL) is set to lose six mines with total production of 4-5 million tonnes of coal.
He said the company will continue to mine till March 2015 as allowed by the Supreme Court.
The court had asked holders of 46 operational blocks to file reply within 6 months and said that government can auction blocks post March 2015.