Mining in New Zealand has a long history, dating back to the discovery of gold in the 1800s. While the original mine closed in 1952, new prospecting activity began in Waihi in the 1970s, sparked by rising gold prices.
Rock bolting at Correnso in the Exploration Development Drive.
Today, Newmont’s mining operations employ many local community members and the Martha open pit operation is situated in the town. In addition, our Favona and Trio underground operations are accessed by a portal on the town’s outskirts. With current operations nearing the end of the mine life, Newmont’s near-mine exploration activities are focused on the Correnso ore body, which would allow mining activities to continue in Waihi.
Newmont’s Correnso underground mine began construction with a 550 meter exploration development drive pushing out from the Trio mine in Waihi East. The Correnso Exploration Development Drive was started in December 2013. This tunnel features a number of much shorter tunnels, called ‘drill cuddies,’ from which drilling rigs will bore into the Correnso ore body to learn more about its size, shape and grade. We need this additional information before we finalize the mine design. With our Favona and Trio underground mines, we were able to do this from the surface, but the Correnso ore body lies between 250 and 300 meters beneath residential properties where it was not practicable to locate a drilling rig. As a result we will conduct this final exploration from underground.
Charlie Gawith, Newmont Waihi Gold underground manager, explains ‘decking’ charges at Trio to reduce surface vibration to David Fielden, Economic Development Officer from Hauraki District.
This is the first time a mine under residential properties has been permitted in New Zealand, and it comes with stringent consent conditions, especially those relating to blast vibration.
One of the consent conditions is that a mine plan is posted online at the beginning of each month. In addition, the Waihi Gold website also features real-time monitoring of vibration events above Correnso. Hovering a mouse cursor over any of the blue dots that represent the location of the 10 vibration monitors will bring up a dialogue box that displays the last series of vibration events. Any vibration over 0.75mm/s will register.
We’re working to ensure that the community is aware of all our activities that may cause vibrations. In addition to the real-time online monitoring, our current blast notification program keeps residents informed of upcoming blasts each day by text, email, or phone, as well as on the Waihi website.
We are also trialling a new device at Correnso that will alert residents just before a blast event. The Tsunado, a device originally developed for natural disaster alerts, can also be used as a blast alert device. When placed in a home, the Tsunado receives a signal from Newmont immediately prior to a blast and will play a short piece of music. The purpose of the device is to reduce the ‘startle effect’ should a noticeable vibration be felt after a blast event.
Based on previous experience with blast events at Trio, we expect blast events at Correnso to result in vibration levels on the surface ranging from imperceptible to obvious. While the Tsunado device will advise of an upcoming blast, residents may not feel any vibration. The trial is currently underway in a number of homes.