Mining in Waihi has a history that spans three centuries after gold was first discovered in the 1800s.
Our Waihi Operation in the North Island of New Zealand is an underground operation.
In early 2019 OceanaGold received consent to develop the Martha Underground. This project extends the life of the Waihi mine and gives our 350 staff and contractors, and the people of Waihi, an assurance that we plan to be here for the long-term.
|Type||Underground and open pit|
|2023 production guidance||50,000 – 60,000 oz gold|
|Proven and Probable Reserves||0.51 Moz|
|Measured and indicated resources||2.04 Moz|
|Inferred resources||1.5 Moz|
|Estimated mine life||~6 years|
Project Martha comprises two parts – the Martha Underground and the Martha North Wall.
More information about Project Martha is available on the Waihi Operation website.
The Martha Underground includes the area directly under the current Martha open pit and the south wall, as well as the Rex vein under residential property to the south of the pit. This project is currently being developed and we expect a mine life of at least 10 years.
The Martha Underground workings will be accessed from the existing Favona portal. Most of the workings are contained within the current footprint of the Martha open pit and will extend approximately 300 metres below the current pit floor, which is about the same depth early miners reached with shafts and tunnels before the mine closed in 1952.
All of the new stopes we develop will be backfilled and a number of historical (pre-1952) unfilled stopes that we encounter as part of our Martha underground mining will also be backfilled. We anticipate this will significantly reduce the potential for future sinkholes caused by historical unfilled workings. There will be one or more vent shafts in the Martha open pit, similar to the one which currently exists on Union Hill.
The Rex orebody to the south of the Martha open pit lies between 100 and 300 metres below the surface. This part of project is planned to last approximately three years.
Martha North Wall
The north wall of the open pit will be laid back to create a stable and safe pit wall. The haul road inside the open pit will be re-established to provide access to the pit floor. We expect this work to last approximately 10 years. However, it will not be continuous over that time. There will be periods of time when no work will be undertaken on this part of the project.
As part of the proposed Project Quattro work this pit wall lay-back would be incorporated into a full enlargement of the pit.
Tailings storage facilities
Tailings is the finely ground rock left over after precious metals (gold and silver) have been extracted. The crushed rock can be as fine as talcum powder.
A tailings storage facility (TSF) is a structure built for the purposes of storing these tailings and other by-products from the gold and silver extraction process.
Waihi’s tailings impoundments are carefully engineered rock structures made up of several separate layers and designed to the same specifications as a water-retaining structure.
The operation has two current tailings storage facilities, TSF1 and TSF2. The company will be applying for the relevant resource consents to construct a new TSF immediately east of the current facilities.
TSF3 will be situated next to the eastern side of TSF1 and the land that rises to the north. The new TSF3 will be constructed to form a similar shape and height to those already in place.
Geotechnical investigations have concluded that the bedrock is deeper than what was encountered with our current TSFs. To accommodate these different site conditions, and to provide the required geotechnical integrity, the excavation of compressible soils and backfilling with structural fill will need to take place. The topsoil excavated will be stored for use in rehabilitation.
From site selection to construction, monitoring and independent peer reviews by recognised experts, the construction of Waihi’s TSFs has been closely followed and reported on. There is strong regulatory involvement from Waikato Regional Council and Hauraki District Council to ensure consent conditions are adhered to.
Further consents will be required before we will be allowed to construct TSF3. If the required consents are granted, the structure will be extensively monitored, and the data and reports will be independently reviewed to ensure the ongoing structural integrity of the structure and safety. The independent review findings are reported to the Councils after each review.
As the impoundments are raised, each level must meet strict performance criteria relating to material type, construction, depth, and compaction. Different types of rock are placed in specific locations as per the engineering specifications before the embankment is capped with clay and topsoil. As the embankment is constructed, drainage systems and monitoring bores are incorporated into the design. Over time the tails settle and consolidate. Drilling in one of our current tailings impoundments has shown that the tails have already consolidated to become a firm mud.
When the tailings impoundments are finally closed, they will be partially capped leaving a wetland and small lake on the top. A variety of land uses is possible for the remaining area.
When mining is completed the Martha Trust will take over responsibility for the tailings impoundments. The company will fund the Trust to allow it to carry out its functions. The sum provided will generate annual interest sufficient to allow the trust to manage, monitor and maintain the site.
More information about how we approach tailings management at OceanaGold is available on our tailings management page.
Knowing we have a mine life of at least 10 more years ahead of us provides certainty for businesses and the community and ensures the continuation of employment for the approximately 350 people who currently work at the Waihi Operation.
We are continuing to explore, study and progress with other mining opportunities in and around Waihi that could extend employment and the economic contribution we make to the region, and to New Zealand as a whole.