Humanity’s fascination with gold stretches back thousands of years. Gold mining is described in ancient Greek and Roman sources, and gold rushes – especially in the 19th century – played a powerful role in shaping the modern world.

The dense, yellow metal is often found in the veins of the rocky mineral quartz. This is because the two condense together from hot fluids underground as a result of changes in temperature, pressure and chemistry.

Geologists understand this process quite well, but large gold nuggets have been a bit of a mystery. Gold is only dissolved in natural fluids at around one part per million, so how does it concentrate into lumps that weigh tens or even hundreds of kilograms?

As we report today in Nature Geoscience, the answer likely has to do with the unusual electrical properties of quartz – and what happens when an earthquake puts it under pressure.

Quartz under pressure

Quartz is what is called a piezoelectric material. There aren’t many minerals like this on Earth, and quartz is by far the most abundant.

Piezoelectric materials generate an instantaneous electric charge when put under stress – when there is a physical force compressing or stretching them. The bigger the force, the bigger the charge.

Not only did we see gold deposited onto the quartz surface, we also saw it clumping together into nanoparticles. What’s more, once the process began, gold was more likely to be deposited onto existing grains of gold than on quartz.

This actually makes a lot of sense, as quartz is an electrical insulator and gold conducts electricity. The existing gold grains adopt the electric potential from the nearby quartz and become the focus of reactions that deposit gold.

Industrial gold-plating works in much the same way, only here we are gold-plating other gold.

Back to nuggets

Now we know how quartz and gold behave this way in the lab, we can think about geology again.

Some of the most impressive gold nuggets ever found have been in quartz veins where gold-bearing fluids flow through faults in earthquake-prone rock.

During seismic activity, the stress on quartz can generate piezoelectric voltages capable of drawing gold from these fluids. Once deposited, gold becomes the focus of further piezoelectric plating as fluid infiltration continues – so the gold deposits grow bigger over time.

Over millions and millions of years, this process will be repeated again and again. Is this the reason we see such large gold nuggets in this kind of quartz vein? We think it must be at least part of the picture.

Christopher Voisey, Research Fellow in the School of Earth, Atmosphere, & Environment, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

In this photo released by the Indonesian National Search and Rescue Agency (BASARNAS), rescuers prepare to head out to the site of a landslide that killed a number of people, in Suwawa on Sulawesi Island, Indonesia on July 8, 2024. Photo: BASARNAS via AP

Rescue workers searched for dozens of missing people on July 9, digging through tons of mud and the rubble left by a landslide that hit an unauthorised traditional gold mining area on Indonesia’s Sulawesi island and killed at least 11 people.

More than 100 villagers were digging for grains of gold on July 7 in the remote and hilly village of Bone Bolango when tons of mud plunged down the surrounding hills and buried their makeshift camps, said Heriyanto, head of the provincial Search and Rescue Office.

Rescue operations

Rescuers recovered six more bodies buried under tons of mud in a devastated hamlet where the gold mine is located.

“Improved weather allowed us to recover more bodies,” said Heriyanto, who goes by a single name, like many Indonesians.

According to data released on July 9 by his office, some 52 villagers managed to escape from landslide, about 23 people were pulled out alive by rescuers, including 18 injured, and 17 bodies were recovered, including three women and a 4-year-old boy. Some 45 others are missing, it said.

National Disaster Management Agency spokesperson Abdul Muhari said torrential rains that have pounded the mountainous district since July 6 triggered the landslide and broke an embankment, causing floods up to the roofs of houses in five villages in Bone Bolango, which is part of a mountainous district in Gorontalo Province. Nearly 300 houses were affected and more than 1,000 people fled for safety

Challenging Rescue Operations Amid Adverse Conditions

Authorities deployed more than 200 rescuers, including police and military personnel, with heavy equipment to search for the dead and missing in a rescue operation that has been hampered by heavy rains, unstable soil, and the rugged, forested terrain, said Afifuddin Ilahude, a local rescue official.

“With many missing and some remote areas still unreachable, the death toll was likely to rise,” Mr. Ilahude said, adding that sniffer dogs were also being mobilized in the search.

Videos released by the National Search and Rescue Agency show rescue personnel using farm tools and sometimes their bare hands, pulling a mud-caked body from the thick mud before placing it in a black bag to take away for burial.

Monsoon rains cause frequent landslides and flash floods in Indonesia, an archipelago nation of more than 17,000 islands where millions of people live in mountainous areas or near floodplains.

Informal mining operations in Indonesia

Informal mining operations are common in Indonesia, providing a tenuous livelihood to thousands who labour in conditions with a high risk of serious injury or death. Landslides, flooding and collapses of tunnels are just some of the hazards facing miners. Much of gold ore processing involves highly toxic mercury and cyanide and workers frequently use little or no protection.

The country’s last major mining-related accident occurred in April 2022, when a landslide crashed onto an illegal traditional gold mine in North Sumatra’s Mandailing Natal district, killing 12 women who were looking for gold.

In February 2019, a makeshift wooden structure in an illegal gold mine in North Sulawesi province collapsed due to shifting soil and the large number of mining holes. More than 40 people were buried and died.

Afghan miners dig inside a tunnel of a gold mine in the mountains of Yaftal Sufla district in Badakhshan province.
| Photo Credit: AFP

Tearing off a piece of mouldy flatbread, Homayon gulped tea in a brief reprieve from the din of the machines he and a dozen other men were using to dig for gold on a mountainside in northeastern Afghanistan.

The 30-year-old found little work as a mechanic in nearby Faizabad city, so he banded with other unemployed men to try their luck carving out a living in the rocky mountains that dominate Badakhshan province.

“Five, six of us were jobless, we came here to see if we can find anything,” Homayon said, as the handful of men finished their break and returned to work at the small-scale mine they had set up.

Their efforts digging four tunnels have borne little fruit, even as they pour money into fuel, tools and labour.

Other mines in the area had proved productive, Homayon said, so they kept digging — the promise of a windfall outweighing the risks of debt.

‘Significant losses’

The losses can be significant, warned fellow miner Qadir Khan. “There are people who went into debt and were not able to find anything from these kinds of tunnels,” he said.

“They lost two to three hundred thousand Afghanis (roughly $2,800-$4,200), and there was nothing to do but try to find different work, make money, and come back to pay their debts.”

Despite being 74 years old, Mr. Khan says he has no choice but to keep working, as he hunches over a pile of rocks to break them into smaller pieces.

The Afghan Taliban’s takeover of the country in 2021 may have seen an end to two decades of war with the U.S. and its allies, but, according to a World Bank report, half the population is still living in poverty.

Labourer Sharif, 60, said he used to keep livestock but has been mining for the last year. Two of his sons had left for Iran to find work. “We are still farming, but it is not the way it used to be,” he said, complaining of a lack of water — another shortage drought-hit Afghanistan has faced in recent years.

The rocks Sharif helps mine are broken up and hoisted down the steep mountainside, then pulverised into a flour-like substance. On the banks of the Kokcha River, which snakes between snow-capped peaks, men use makeshift buckets to scoop water over piles of the powder. It is then sifted as it runs down a sluice covered by material pulled from car interiors.

The proceeds of the first wash are used to fund the equipment and labour and to keep the mine going. The gains from the second and third washes are shared between those bankrolling the operation.

Even if the miners can collect significant amounts of gold, a fifth of proceeds will go to the Taliban authorities.

High stakes

Delving deep into the Afghan mountains, the miners risk not just debt, but death as well. Mine collapses are common in Afghanistan, which is rich with precious minerals like the lapis lazuli Badakhshan is famous for.

The miners on the Kokcha said they had lost friends recently, and local media reported earlier this month that a gold miner died when part of a mine collapsed in neighbouring Takhar province.

In 2019, at least 30 people were killed when a gold mine collapsed in Badakhshan.

Despite the risks, the men continue digging.

“So far we have not found much of anything,” said Homayon. “But we have hope, we trust in God.”

A bird is caught in a mist nest set up in a forest to trap small animals while researching signs of mercury contamination, at the Los Amigos Biological Station, in Los Amigos, in the Madre de Dios region, Peru. File
| Photo Credit: Reuters

Tropical birds, from kingfishers to wrens to warblers, are showing signs of mercury contamination as artisanal and small-scale gold mining operations reach deeper into jungles, finds a new research.

Birds living within 7 km (4 miles) of such gold mining activity were found to have mercury concentrations over four times higher than those living at other sites across the tropics of Central and South America, according to the study published on Tuesday in the journal Ecotoxicology.

“It’s a wake-up call for bird conservation internationally across the tropics,” said lead author Chris Sayers, a conservation biologist at the University of California Los Angeles.

Tropical bird biodiversity has been declining in recent decades, but scientists are not fully sure why. “Based on the levels here, it’s reasonable to suggest that mercury may be playing a role,” Mr. Sayers said.

Over a 17-year period ending in 2023, dozens of scientists collected thousands of feather, blood and tissue samples from 322 bird species across nine countries in Central and South America and the West Indies, creating the world’s largest database to date on mercury concentrations in birds.

The research adds to a growing understanding of how mercury, which is used by gold miners to separate the precious metal from sediment, is impacting wildlife in the tropics.

Artisanal gold mining is often either carried out illegally in protected areas, or done informally outside reserves but without explicit government permission.

Earlier this year, Reuters reported for the first time that scientists were finding mammals, from titi monkeys to ocelots, showing signs of mercury contamination near a Peruvian gold mining hotspot.

Absorbing or ingesting mercury-contaminated water or food has been found to cause neurological illness, immune diseases and reproductive failure in humans and some birds.

Birds are the “canary in the gold mine,” Mr. Sayers said, as they are sensitive to mercury pollution and easily accessible, allowing scientists to take the temperature of overall ecosystem health.

The collected samples revealed some of the highest-ever recorded mercury concentrations in songbirds. Birds that ate meat or lived in aquatic habitats were also found to have the highest overall mercury levels.

Hotspots for mercury contamination included Madre de Dios, Peru, and Ayapel, Colombia — centres of artisanal gold mining.

Birds in central Belize also had high mercury concentrations, with scientists speculating it could be due to gaseous mercury emissions from local landfill incineration, or coal combustion in the surrounding region.