Investors have taken a sword to gold explorer Excalibur Mining after it downgraded the indicated resource for its Juno project in the Northern Territory.

The company said a review of the project revealed the previous Juno indicated resource had been substantially overstated.

"While the magnitude of the overstatement is not yet known, Excalibur no longer has the requisite level of confidence in the previously reported Juno resource," Excalibur said.

"Based on the initial findings, the previous mining at Juno had a larger impact on Excalibur's resource than previously calculated.

"Excalibur's earlier resource estimates were based on an electronic data-base inherited from the Normandy Group."

The company said further work would be required to determine Juno's resource position which would delay the next resource statement due in March/April.

However Excalibur managing director Tim Lagdon said the company was confident on the quality of its other Tennant Creek projects.