ABOUT
OCEANA GOLD
OceanaGold Macraes Operation opened in 1989 and is the largest gold mine in New Zealand. OceanaGold is a major contributor within the Macraes community. It employs a large workforce and is a great supporter of community events and initiatives.
Check to see if there are any current employment opportunities at the mine: Careers
Whilst more details about OceanaGold Macraes Operation can be found by visiting their Website or Facebook Page, a brief insight into operations at OceanaGold Macraes is described below with amazing photos to help tell the story.
The Mining Process at OceanaGold Macraes Operation:
The mining process at the Macraes is circular and follows a cycle of exploration, mining, processing, rehabilitation and closure. With a 30-year history of development spanning fluctuating gold prices, there are multiple examples of where an area has been explored, mined, processed and rehabilitated, only to be explored mined, processed and rehabilitated again 10 to 20 years later.
(Left) A Montabert drill rig works to drill pre-determined drill holes. The holes can be up to 15 metres long and will produce rock chip samples. (Right) Core samples from a Diamond Drill rig show at what points the drill hole has intersected gold bearing ore and what type of rock surrounds it.
(Left) Material collected from drill rigs is sent to the SGS lab to be assayed and measure the concentration of gold in the sample. The information obtained from the samples is used to determine what is ore and what is overburden. Ore is mined and sent to the Processing Plant while overburden is backfilled into previously mined pits or built up into piles near the mining operations. Information from the ore samples helps the Processing Plant adjust their process to match the grade of ore coming in and best extract the gold from the rock. (Right) A core sample showing visible gold. Macraes ore has relatively low concentrations of gold as result of the geochemical conditions during the ore formation, some millions of years ago. Most of the gold was deposited within the sulphide minerals where it can’t be seen. Very rarely were the conditions just right for enough native gold to precipitate and form specs of gold visible in the core.
(Left) There are several open pit areas operating at the OceanaGold Macraes Operation. Once an area has been blasted, excavators and haul trucks operate from a bench (a strip of land cut into the side of the mine pit). They may not look like it, but each excavator can weigh over 360 tonnes and stand at 12 metres in height with a vertical reach of up to 18 metres in total. Haul trucks have a gross vehicle mass (GVM) of 324 tonnes and stand at 6 metres in height (about the same height as a two-storey building). (Right) Haul trucks move material around the site, with gold-bearing ore being transported to the Processing Plant and waste rock being transported to stacks for backfilling areas after they have been mined. These trucks can carry up to 180 tonnes in one run.
(Left) A haul truck exits the portal entrance of Frasers Underground, one of two underground mines operating at the OceanaGold Macraes Operation. The entrance is 6 metres high by 5.5 metres wide making the tunnels only wide enough for one-way movement so underground teams rely on radio communication to move around underground. The Frasers Underground tunnel system is 72 kilometres long in total, with the end of the tunnel sitting at 595 metres below the portal entrance and 295 metres below sea level. This is almost two times the height of the Auckland Sky Tower (328 metres). (Right) A jumbo is used to drill and bolt tunnel faces and walls. This secures the area as the tunnel continues to be mined. Many other machines like boggers, haul trucks and loaders are part of the Underground fleet.
(Left) Once the material has been mined from both open pit and underground areas, it is transported to the Processing Plant. Here the material goes through the processing cycle (crushing, grinding, flotation, oxidisation, leaching and adsorption) to extract the gold particles from the ore (rock with gold in it). (Middle) Part of this process involves the autoclave. This is a high-pressure, high-temperature vessel, used to oxidise the sulphide particles in the ore, making it very acidic but releasing the gold. It is the only one of its kind in the southern hemisphere and it is essential for the unique type of ore at Macraes. (Right) The final stage of this process is smelting where the gold is purified by being heated up to 1,064 degrees Celsius. At this temperature, the gold becomes liquid and separates from impurities around it. Once this has happened, the liquid gold is poured into a mold to create the gold doré bar.
(Left) After the bar has cooled, it is cleaned, weighed and numbered before being sent to the Perth Mint in Australia. (Right) Macraes gold doré bars weigh on average 15 kilograms (460 ounces) and have a 95% purity. Each doré bar is worth around NZ$ 1 million. Since opening in 1989, the OceanaGold Macraes Operation has produced over 5 million ounces of gold.
(Left and middle) The OceanaGold Macraes Operation has a range of programmes for managing the effects of mining on the local flora and fauna. One of the latest programmes was a Lizard Salvage programme, in which lizards were removed from mining areas and placed in protected areas. It was one of the largest salvaging programmes of its kind in New Zealand. (Right) The Trout Hatchery is a partnership between OceanaGold Macraes Operation and Otago Fish and Game to breed and raise rainbow trout. The fish are used to populate urban water reservoirs around Dunedin, irrigation dams in the Maniototo and DOC-approved put-and-take fisheries in Central Otago. These waters have no natural spawning or recruitment areas but are important angling destinations, so they rely on the hatchery for fish.