Shaw said the unexpected discovery generated a great deal of excitement.
The area around the log was carefully dug out while iwi was consulted and the Northland Regional Council and Ministry for Primary Industries was advised.
A karakia was conducted by kaumatua Eddie Court when Ngāwhā Marae Trustees Komiti members and advisors visited the site on February 9.
Shaw said there was no doubt in his mind the ancient log should come under the guardianship of Ngāwhā Marae.
Komiti chairman Richard Woodman described the remnant from an ancient kauri forest as a precious cultural artefact.
It would live on for generations as a taonga tuku iho (a treasure to be handed down) for Ngāti Rangi ki Ngāwhā, he said.
Ngāwhā Marae Trustees would treat the taonga with utmost respect and were holding it for purposes that would enhance the hapū's cultural identity.
Earthworks for the geothermal power station expansion started in 2017 and will continue until July this year, when construction will begin. It is due to be completed in late 2020.