Old mineworkings found in new Midland Metro track project
Old mineworkings which may date back to the 18th Century have been found by workmen preparing foundations for new tram track in Wolverhampton.
The discovery under the line near The Royal stop was the "latest in a string of complications", Midland Metro said.
The Royal was originally planned to open this month but was not now scheduled to open until early December, transport authority Centro said.
Midland Metro said the ground would have to be "filled in properly".
The old mineworkings, about 4m (13ft) deep, were found just past The Royal on the A41 Bilston Road near the junction with Steelhouse Lane.
Centro, the region's public transport co-ordinator, which is carrying out a £4.5m track replacement programme, said they were "thought to be a remnant of the coal, limestone or iron ore mine works that criss-cross Wolverhampton and the wider Black Country".
The workings were discovered as workmen dug into the ground to prepare foundations for new Midland Metro track going from The Royal to a rebuilt terminus at St George's in the city centre.
No announcement was being made on when St George's would reopen "until the mineworkings have been fully evaluated", Centro said.
Midland Metro programme director Paul Griffiths said: "It is a problem that we cannot ignore - the ground will have to be excavated then filled in properly to provide a strong and durable base for the track.
"We regret the delay but the discovery of this shaft is the latest in a string of complications."
Work began in September but the strength of the foundations under the old track was "worse than anticipated" and "the discovery of unmarked public utility pipes and a culvert also hit the timetable", Centro said.