It wasnt up until the 1980s when researchers discovered that gold in pyrite can be available in different kinds– either as particles of gold, or as an alloy, in which the pyrite and gold are finely mixed.

Paradoxically, pyrite crystals can contain percentages of real gold, although it is infamously difficult to extract. Gold hiding within pyrite is often referred to as “unnoticeable gold”, since it is not observable with standard microscopes, but instead requires advanced scientific instruments.

Because of its misleading resemblance to the precious metal, the mineral pyrite was traditionally nicknamed fools gold. The term was typically utilized throughout the California gold rush in the 1840s due to the fact that unskilled prospectors would declare discoveries of gold, but in truth it would be pyrite, composed of worthless iron disulfide (FeS ₂).

In our new research study, released in Geology, my colleagues and I found a 3rd, previously unrecognised manner in which gold can hide inside pyrite. When the pyrite crystal is forming under severe temperature or pressure, it can develop tiny imperfections in its crystal structure that can be “embellished” with gold atoms.

What are these crystal flaws?

The chemistry of these atomic-scale imperfections is notoriously tough to study because they are so small, so any pollutants are present in absolutely small quantities. Spotting them needs a specialised instrument called an atom probe.

Our research study exposes that dislocations within pyrite crystals can be “decorated” with gold atoms. This is especially typical where the crystals have actually been twisted during their history; here, gold can be present at concentrations several times greater than in the remainder of the crystal.

Gold (Au) atoms concealing within a pyrite crystal, alongside other flaws consisting of nickel, copper and bismuth. Scale bar shows 20 nanometres.
Author supplied

When crystals twist or stretch, the bonds in between neighbouring atoms are broken and remade, forming billions of tiny flaws called “dislocations”, each roughly 100,000 times smaller than the width of a human hair, or 100 times smaller sized than a virus particle.

The atoms within a crystal are arranged in a characteristic pattern called an atomic lattice. But when a mineral crystal such as pyrite is growing inside a rock, this lattice pattern can establish imperfections. Like many minerals, pyrite is difficult and difficult at Earths surface, but can end up being more twisty and elastic when forming deep in the Earth, which is also where gold deposits form.

An atom probe can evaluate materials at exceptionally high resolution, however its main benefit over other approaches is that it enables us to construct a 3D map revealing the exact locations of pollutants within a crystal– something that was never ever possible before.

A potential goldmine

Possibly pyrite still measures up to its historical track record of “fools gold” till much better, more ecologically sustainable ore processing techniques are developed.

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Why should anybody appreciate something so small? Well, it provides fascinating insights into how mineral deposits form, and is also a possible advantage for the gold mining industry.

Dislocation sites within crystals might possibly provide an enhanced partial leaching or a target for bacteria to attack and break down the crystal, releasing the gold in a process understood as “bio-leaching”, thus possibly reducing energy consumption necessary for extraction. This idea is still untested, but certainly benefits investigation.

Our discovery may likewise assist gold miners more efficiently extract gold from pyrite, potentially minimizing greenhouse emissions. To draw out the gold, the mineral is typically oxidised in large reactors, which uses significant quantities of energy.

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Eureka! X-ray vision can find hidden gold

Previously, it was thought that gold in anomalously rich pyrite crystals remained in reality made of gold particles formed throughout a multi-step process, suggesting the pyrite and gold crystallised at different times and then ended up being clumped together. Our discovery that gold can embellish these crystal imperfections suggests that even pyrite crystals with relatively high gold content can form in a single process.

Possibly deceives gold isnt so absurd after all if it helps pave the way for more sustainable gold-mining methods.