Fields of gold

Children play on the cyanide- and mercury-contaminated tailings, adjacent to working rice paddies on the Indonesian island of Lombok.

A colourised image of Lombok shows the upper slopes of Mount Rinjani – around the same height as Aoraki/Mount Cook – in white.

Dr Chris Anderson proposes to farm Indonesian mine tailings for gold, creating wealth for local communities and saving the environment from toxic run-off. He talks to Malcolm Wood.

Coconut palms, white sand beaches, azure seas, surf breaks and coral reefs, and behind it all the forested bulk of the volcanic Mount Rinjani. This is Lombok, the Indonesian island next along in the archipelago from Bali. In fact, some would say that Lombok is Bali as it once was. A Bali without the tourist hordes and rampant over-development. A place of unhurried grace and environmental balance. But this old Lombok is under threat. The culprit: mankind’s hunger for gold.

The evidence of the rush is everywhere, says Chris Anderson, a Manawatu–based senior lecturer in soil and earth sciences, recently returned from visiting Lombok. On the hillsides, a sea of blue tarpaulins nestles among the greenery. Beneath each one, miners labour away in narrow, hand-hewn shafts and tunnels, filling their buckets with rocks, while outside porters heft the 25-kilogram sacks of ore down to the villages to be processed.

Gold has brought good things. Parents can afford to send their children to school, and in the villages leaky thatched huts are giving way to weatherproof concrete and corrugated-iron houses. But prosperity has come at a steep environmental price.

There is no such thing as clean gold, explains Anderson. The problem lies in the same qualities that give gold its undimmed lustre. This is one of least reactive solid chemical elements, which makes extracting and concentrating it difficult. But fine gold particles will be collected by mercury to form an amalgam and gold will also dissolve in alkaline solutions of cyanide.

Mercury- and cyanide-contaminated tailings have become an environmental bane on Lombok.

But Anderson has a solution: farm the tailings for gold. It is an idea he has had in mind for a while.

Like New Zealand, Lombok forms part of the Pacific Ring of Fire. That means volcanoes, earthquakes and areas of high mineralisation. Elsewhere in Indonesia, such as in Kalimantan on the island of Borneo, gold mining has been going on for years. But on Lombok the gold rush is recent.

It began in 2008 in two villages, after the locals were alerted by the prospecting activities of a mining multinational, then rapidly spread, a people’s rush of small-scale artisanal mining operations rather than the industrial operations we are used to in Australasia. In one of Indonesia’s poorest provinces, where many people get by on less than US$2 a day, mining promised a path to unimagined prosperity. Thousands have since given their lives over to the pursuit of gold.

Alongside many of those newly built  concrete houses lie stacked sacks of ore, and, alongside them, batteries of cylindrical rod crushers, which churn away ceaselessly. Each crusher contains around a sack of ore, a cup of mercury and enough water to top it up. Four to five hours suffice to grind the rock to a slurry from which the heavier mercury-gold amalgam can be separated.

But although this process has removed the greater part of the gold from the ore, payable amounts remain, so the now-mercury-contaminated spoil is on-sold for secondary processing. This time the spoils are immersed in a solution of sodium cyanide and calcium hydroxide held in large tanks, leaching out the gold in the form of gold-cyanide. Activated carbon is then added to the mix to take up the gold from the cyanide solution, and finally the carbon is collected and burned, leaving the gold behind. As for the reprocessed spoil and barren cyanide solution – this is dumped close at hand, perhaps into the sea, onto the adjacent land, into rudimentary tailings ponds, or even into rice paddies that have been informally redesignated as tailings dams. “This is gold at all costs using whatever technology they like,” says Anderson.

On Lombok, says Anderson, there are thousands of rod grinders, hundreds of cyanide facilities and vast and unknown numbers of dumping sites.

From top: Bagged ore awaiting processing; The bagged ore, having been broken up by hand (see preceding page) and with the addition of mercury and water is processed using rod grinders.
Group of four photographs, clockwise from top left: When the rod grinders are emptied, the mercury-gold amalgam is panned from the mix; the excess mercury is squeezed from the mercury-gold amalgam; the remaining mercury is driven off using heat; the gold is assayed and sold.
At bottom: The spoil from the rod grinders is leached in large tanks using a cyanide solution, with the resulting gold-cyanide collected using activated charcoal. Once this is done, the mercury- and cyanide-contaminated tailings and wastewater are dumped, sometimes into holding ponds, sometimes simply into – or onto – whatever is to hand.

Mercury and cyanide are both highly toxic. Cyanide –  technically a chemical compound consisting of a carbon atom triple-bonded to a nitrogen atom – the  popular poison choice of murder mystery writers the world over, is surprisingly the less worrying of the two. “Cyanide is a very safe chemical provided you know what you are doing,” says Anderson. “It kills us because it takes iron out of our blood: cyanide binds more tightly to the iron than does haemoglobin, so we asphyxiate. But if you don’t have an iron transport system, that doesn’t matter: cyanide is a fertiliser, plants love it.”

Mercury, on the other hand, particularly in the form of methylmercury, is a pernicious developmental neurotoxin. Formed from metallic mercury by anaerobic bacteria, which are present in soils, sediments, wetlands, rivers and the open ocean, methylmercury accumulates in the food chain, and, if this were not bad enough, mercury is one of the few toxins that easily transits the blood-brain barrier – it has been linked to learning disability and diminished mental capacity – or can make its way from mother through the placenta to a developing foetus.

Below each dump site, a cyanide- and mercury-rich witch’s brew discharges into nearby water courses and the water table, contaminating rice paddies and turning streams and estuaries into dead zones. Coral bleaches. Sealife dies. Mercury enters the food chain with who knows what long-term effects. Anderson brings up a picture on his computer. “These are tailings dumped in an old fish farm that connects to the sea. When we went back in January there were piles of dead shellfish.”

In paddy fields taking drainage from the cyanidation tailings ponds, mercury enters the harvest. “We have seen the worst methylmercury pollution of rice recorded in the world.”

Anderson did not start out to specialise in soil science, a discipline that sits at the boundary or geology and chemistry. He wanted to become a marine biologist, but after his first year of biology, put off by the prospect of having to perform yet more dissections, he made the switch to earth science and chemistry. “Rocks don’t bleed,” he says.

Eventually he found himself doing a PhD supervised by Professor Robert Brooks, who from the 1960s on had made his name exploring the unusually high uptake of metals by some plant species. All plants take up metals, but Brooks had found that some take up huge amounts, far more than they would seem to need metabolically speaking. Hundreds of what Brooks called hyperaccumulator plants are now known. Most preferentially take up nickel, but others take up zinc, cadmium, arsenic, thallium, manganese, cobalt and copper.

Brooks and those who followed in his path could see the potential. Hyperaccumulator plants could be used in biogeochemical prospecting, as indicators for the favourable mineralisation of the underlying soils. They could be used to clean up unwanted elements from contaminated soils, a process called phytoremediation. They could even, given the right conditions, be used for phytomining: profitably harvesting minerals such as nickel from ore bodies too poor to warrant mining of the conventional kind.

But nickel is a low-value metal, coming in at under US$8 per pound. What of gold, currently at US$1660 per Troy ounce?

As Anderson helped to discover during the course of his PhD, gold can also be phytomined.  During his second year, Anderson and his supervisors authored a paper  in the journal Nature detailing how Indian mustard (Brassica juncea) had been successfully employed to take up gold from crushed and cyanide-treated ore taken from the Waihi and Tui mines.

By Anderson’s calculations, the discarded mine tailings currently poisoning the soils and sea of Lombok could instead be profitably phytomined, with each hectare producing up to a kilogram of gold and 250 grams of mercury annually over a period of years. Back in 1998, that kilogram would have been worth a little over US$9000; today it would be worth more than US$50,000.

When farming the tailings no longer realises a return, Anderson proposes that they be stabilised with plantings of timbers such as teak.

In theory, phytomining could both help to save Lombok’s natural environment and provide a profitable community enterprise. Anderson is determined to turn theory into practice – and it may well happen.

Anderson’s visit to Lombok was hosted by Professor Wani Utomo of Indonesia’s Brawijaya University on the island of Java – whose son is  undertaking a PhD in soil science at Massey – and Dr Dewi Krisnayanti, of the University of Mataram on Lombok, and supported  by the New Zealand Aid Programme (NZAID). There is also a connection to China, which has problems with mercury-contaminated soil, through Professor Xinbin Feng of the Institute of Geochemistry of the Chinese Academy of Sciences.

In September, Massey University and the three partners will open the International Research Centre for the Management of Degraded and Mining Lands at Brawijaya University in Malang. Here the practicalities of phytomining and remediation will be put to the test by researchers and postgraduate students from New Zealand, Indonesia and China, before being introduced into the field.

There are problems to be surmounted. As well as mercury, plants will need to be able to withstand the high levels of sodium remaining from the leaching process and the sometimes torrential rainfall during the tropical wet season.

“We’ll need a few agronomic tweaks to get plants to grow,” says Anderson.

He sounds quietly confident.