Nav: Home

Resolving the 'invisible' gold puzzle

May 01, 2019

The Carlin-type gold deposits in Nevada, USA, are the origin of five percent of the global production and 75 percent of the US production of gold. In these deposits, gold does not occur in the form of nuggets or veins, but is hidden - together with arsenic - in pyrite, also known as 'fool's gold'. A team of scientists from the Helmholtz Centre Potsdam - German Research Centre for Geosciences GFZ has now shown experimentally, for the first time, that the concentration of gold directly depends on the content of arsenic in the pyrite. The results were published in the journal Science Advances.

In the Earth's crust, the element gold occurs in concentrations of 2.5 parts per billion (ppb). In order to mine it economically, the gold concentration must be thousands of times higher and it must be found in a focused area close to the surface. In the gold deposits of the Carlin-type, the gold in the rock is not visible to the human eye. Instead, the 'invisible' gold occurs in tiny pyrite rims that grow on older 'fool's gold' grains which originate from sedimentary rocks.

In the laboratory experiments, the researchers around Christof Kusebauch, lead author of the study showed that the element arsenic plays the crucial role in extracting gold from hot solutions probably from magmatic systems, passing through the rock. The higher the concentration of arsenic, the more frequently gold chemically binds with pyrite. The shape of the older pyrite is also important: the larger the surface area of the mineral, the more gold can accumulate.

Arsenic indicates gold deposits

Similar to the natural ore system, the authors used iron-rich carbonates and sulfur-rich solutions to synthesize their 'fool´s gold' crystals. "Only then we were able to show that the partition coefficient which controls how much gold is incorporated into pyrite depends on the amount of arsenic," says Christof Kusebauch. "The major challenge was to experimentally grow gold and arsenic bearing pyrite crystals that were big enough to analyze."

The new findings may also help to track down new gold deposits. The experiments show that if hot solutions containing gold and arsenic from magmatic sources pass through sedimentary rocks with large amounts of small 'fools gold' grains present, large gold deposits can be formed.

What is gold? Gold is a chemical element of the copper group with the element symbol Au (from Latin: Aurum). In contrast to most other metals in nature, gold is mostly found in the pure form, meaning in the form of 'nuggets' composed only of one chemical substance.

In contrast, in the Carlin-type gold deposits, gold must be released from ore by chemical extraction. Here, the gold is bound to the ore mineral pyrite and has whole rock concentrations between one and tens of grams per ton of rock material (1000 to 10.000 ppb). This type of gold deposit is formed in carbonate-rich sediments. The deposits in the US formed 42 to 30 million years ago at temperatures of 150 to 250 degree Celsius and at depths of over 2000 meters, before they reached the Earth's surface through processes of plate tectonics.

How is gold formed? On the Earth's surface accessible to mankind, gold has been transported from the Earth's interior to the surface by volcanic and plate tectonic processes; a small part stems from meteorite impacts. Natural processes cannot produce new gold on Earth. The heavy chemical elements in the universe, such as lead, iron, and gold, are created by the collision of neutron stars. Gold is very rare, not only on Earth but throughout the universe.

Project funding:

Helmholtz-Recruitment-Initiative to Prof. Sarah Gleeson

Original study: Kusebauch, C., Gleeson, S.A., Oelze, M., 2019. Coupled partitioning of Au and As into pyrite controls formation of giant Au deposits. Science Advances. DOI: 10.1126/sciadv.aav5891

GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre

Related Arsenic Articles:

Arsenic in drinking water may change heart structure
Among young adults, drinking water contaminated with arsenic may lead to structural changes in the heart that raise their risk of heart disease.
Arsenic-breathing life discovered in the tropical Pacific Ocean
In low-oxygen parts of the ocean, some microbes are surviving by getting energy from arsenic.
Parboiling method reduces inorganic arsenic in rice
Contamination of rice with arsenic is a major problem in some regions of the world with high rice consumption.
UN University compares technologies that remove arsenic from groundwater
A UN University study compares for the first time the effectiveness and costs of many different technologies designed to remove arsenic from groundwater -- a health threat to at least 140 million people in 50 countries.
Arsenic for electronics
The discovery of graphene, a material made of one or very few atomic layers of carbon, started a boom.
Arsenic in combination with an existing drug could combat cancer
Investigators have discovered that arsenic in combination with an existing leukemia drug work together to target a master cancer regulator.
Moss capable of removing arsenic from drinking water discovered
A moss capable of removing arsenic from contaminated water has been discovered by researchers from Stockholm University.
Optical emission of two-dimensional arsenic sulfide prepared in plasma
Since the discovery of graphene in 2004, there has been a rapidly growing interest among scientists in the study of 2-D materials 'beyond graphene'.
Study indicates arsenic can cause cancer decades after exposure ends
A new paper published in the Journal of the National Cancer Institute shows that arsenic in drinking water may have one of the longest dormancy periods of any carcinogen.
Arsenic in domestic well water could affect 2 million people in the US
Clean drinking water can be easy to take for granted if your home taps into treated water sources.
More Arsenic News and Arsenic Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at