Streets of gold: mine waste potential in a circulareconomy

By Dr Geoffrey Batt, Minerals Research Institute of Western Australia

The streets of Kalgoorlie were once paved with gold. Before you rush ahead and think this is the opening to a tale of an industry in decline, let me put you at ease. With a price up seven per cent for the year and currently sitting north of US$2100 an ounce, gold is doing quite okay, thank you – and with it the fortunes of Kalgoorlie and its companion city of Boulder as a combined mining service hub in Western Australia.

No, this is a story of the waste created in winning valuable minerals from the ground, and what we do with it.

Traditional mining – an industry commonly working to low margins in a volatile marketplace – is mostly pursued as a linear process. Under this model, mine planning is focused on the value of a single resource to be extracted as quickly and efficiently as possible, before the miner moves on to the next project. Additional rock blasted and moved to access the paying grounds, and the residue left from crushing and treating ore to liberate a resource are just additional costs to figure into the economic model – waste to be moved out of the way, treated to be made safe, and then stacked up for eventual rehabilitation.

A more holistic view gaining ground today seeks to turn this business model, if not on its head, then at least back on itself to see and possibly capture some of the economic benefit being left in its wake.

While not valuable enough to extract in their own right, significant prices have already been paid to extract ‘waste’ rocks from the ground – energy and money expended to dig, blast, haul and crush the rock; the environmental cost of disturbing the landscape; and water to wash and process the ore. If even part of those residues can be converted into useful by‑products, not only can a miner create additional value streams without needing to repeat those extraction costs, but the land and energy invested in storing and rehabilitating residues in ever‑growing tailings storage facilities can also be reduced.

The further we can pursue this model – the waste products of one process becoming raw materials or useful inputs for another – the greater the economic return of mining activity, and the lower the impact of mining operations on the environment – now and into the future.

Tellurium is one of the stranger elemental beasts lurking in the periodic table – a rare silver-white metalloid (not quite a metal, but not exactly non-metallic either) whose curious properties is a capacity to form natural compounds with gold.

An unusually, possibly uniquely, high 20 per cent of Kalgoorlie’s golden endowment is found in the form of these telluride compounds – a family of exotic-sounding mineral species including calaverite, krennerite and empressite. Typically brittle and brassy in appearance, these tellurides look not dissimilar to sulphide minerals – humble pyrite and its cousins. Potentially exciting if you’re exploring for copper, zinc or other base metals, but not so appealing if you’re a 19th-century Irish prospector chasing the lure of gold in the red dust of Western Australia. So, for three years between 1893 and an increasingly astute mine workforce recognising their true nature and starting to process them in 1896, the gold tellurides coming out of the rapidly expanding workings of the Kalgoorlie district were simply discarded along with other ‘worthless’ mine waste on cart tracks and walkways, and even used as building stone for the booming town.

So yes, the streets of Kalgoorlie were once paved with gold.

Elevating this above the level of historical anecdote, this telluride tale can be read as relating three important truths that, together, underpin the modern reimagining of tailings and mine waste through the lens of the circular economy.

1. We aren’t always sure what is going into the waste stream

Geology and mineralogy are not simple sciences. Each ore body has its own unique surprises for a miner seeking to extract its bounty. It might not be on the scale of discarding tellurides on the waste pile, but even today – with the aid of all our modern industrial technology and knowledge – processing does not easily and cleanly break down minerals into their constituent elements, and many tailings facilities end up as the repository for a range of materials that might have yielded valuable products to other processing methods or chemical coaxing.

With more than 11,000 historic mine sites in Western Australia alone, deriving from a legacy of mining extending back over a hundred years of evolving technology, there may be a wealth of opportunities awaiting reconsideration.

2. The materials we value change as technology and the market change

Since the telluride component of Kalgoorlie’s endowment was first recognised in 1896, the processing goal has been to liberate the gold as quickly and efficiently as possible – sending the ‘worthless’ tellurium to the waste stream. Now that its semiconducting properties see it valued in a range of modern industrial applications (notably the production of solar cells), tellurium itself has become an increasingly attractive commodity. Kalgoorlie Consolidated Gold Mines – current operators of the Super Pit – aren’t likely to reclassify their production focus any time soon, but having already expended the environmental and resource costs of liberating the tellurium from the ground, it could make a useful additional value stream to the mine’s production.

The same journey regularly plays out in global markets. Rare earth elements, platinum group elements, and cobalt have all turned in recent years from neglect or mineralogical curiosity, to high-value commodity, and serious consideration is being given to seeking out and reprocessing tailings facilities where stores of these new industry darlings have been discarded in previous eras.

3. Mine waste needs to go somewhere – and that costs

We now operate in a more enlightened era where mine wastes are not simply scattered on the tracks and building sites of mining towns like Kalgoorlie. Tailings produced in mineral processing and related industries are today collected in dedicated storage facilities, with growing volumes of material accumulating around mine sites every year.

At the same time, sand is a key resource required by the construction industry, feeding the bulk material requirements of road projects, landfill, housing and industrial infrastructure. Western Australia’s construction industry is warning of a looming sand shortage driving up construction costs and restricting the state’s capacity to respond to the needs of a growing economy and population over the coming decades.

With innovative industries working to develop suitable product specifications and demonstration projects, and state and federal governments increasingly cultivating policy environments seeking to build confidence in recycled products while protecting the environment, these twin challenges could be addressed through the circular economy model.

Once upon a time, we accidentally paved streets with gold because we didn’t understand mine waste enough.Perhaps in a circular economy future, paving streets with mine waste could be a golden opportunity for the mining industry. 

Dr Geoffrey Batt is a Research Portfolio Manager with the Minerals Research Institute of Western Australia, a state government body working to catalyse and support impactful minerals research for the benefit of Western Australia. Batt leads the institute’s focus on alternative uses of tailings and waste, working with leading scientists and research groups to address the challenges and opportunities facing the future of the industry.

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