The stretch of SH25 at the north end of the Thames township is now open after contractors completed repairs of an old mine shaft hole which caused part of the road to sink in April.
The NZ Transport Agency says the shaft is in the same location as a smaller hole which appeared in the road in January.
An old pump shaft was exposed when the road sank on April 28.
State Highway manager Kaye Clark says workers excavated the hole in January and initial investigations had indicated the shaft had been back-filled.
“It seemed some settlement in the fill was what caused the road to sink.
“This time we have excavated much further and have now exposed the full extent of an old pump shaft.”
Kaye says historic records indicate this may be the site of the first ‘Big Pump’, constructed for the Thames goldfield in 1872 and closed down in the early 1900s.
The shaft is about 6x4 metres, but it is unknown if it had been back-filled previously or how it was covered over as there is at least five metres of water in the shaft.
Local historians have been involved and discussions are also being held with the Historic Places Trust to ensure the shaft is well documented and recorded.