Tailings from Newcrest Mining’s proposed copper-gold mine in Papua New Guinea will be deposited into the ocean, under updated plans for a higher-capacity project with an improved rate of return.
Newcrest is developing the Wafi-Golpu project in a joint venture with Harmony Gold.
An updated feasibility study released on March 19 envisages an average of 13.4 million tonnes of ore processed annually, to produce averages of 161,000 tonnes of copper and 266,000 ounces of gold each year.
In a process dubbed ‘deep sea tailings placement’, tailings will be dumped into the ocean, rather than into a terrestrial tailings dam.
Newcrest says the landscape around the future Wafi-Golpu mine site is prone to geological activity, has high rates of rainfall, and is high in biodiversity.
By contrast, the Western Huon Gulf – where tailings will be deposited – is relatively low in biodiversity due to a high rate of naturally-occurring sediment already deposited into the environment by several rivers.
“Oceanographic and environmental studies in the Western Huon Gulf to date have confirmed that area to be a highly suitable environment for DTSP,” the miner said.
“The tailings are expected to mix and co-deposit with a significant, naturally occurring loading of riverine sediments.”
The updated feasibility study for the project shortens the proposed mine life from 35 to 27 years, while producing nearly the same amount of copper, and more gold, resulting in a 24% increase in annual copper production, and a 32% increase in annual gold production.
The mine would cost US$2.83 billion, up US$169 million on the 2016 estimate, but ongoing costs would total US$2.56 billion over the life of the mine, down over US$1.2 billion.
The proposed processing plant would be built to process up to 17 million tonnes of crushed ore each year.
The facility would comprise a semi-autogenous grinding mill, two ball mills and a recycle crushing configuration, along with flotation, thickening, concentrate pumping and tailings pumping systems.
Roughly 95% of copper and 68% of gold would be recovered from the ore, as life-of-mine averages.
Newcrest has become more familiar with the risks of terrestrial tailings dams in recent weeks.
On March 9, a 270-metre-long section of embankment at Newcrest’s Cadia mine’s northern tailings facility slumped into the southern tailings facility, below it. The mine remains closed as the company manages the issue.