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Gold nuggets have long been a fascinating subject in geology, primarily found embedded within quartz veins. Traditionally, it was believed that these nuggets formed as a result of changes in temperature, pressure, and fluid chemistry within dilute, hot, water- or carbon dioxide-rich fluids. However, this explanation has always been at odds with the sheer size of some gold nuggets and the chemical inertness of quartz. A recent study published in Nature Geoscience by Christopher R. Voisey and colleagues offers a compelling new mechanism that could resolve this paradox: earthquake-induced piezoelectricity in quartz.
- Gold Nugget Formation: Earthquake-induced piezoelectricity in quartz can drive the electrochemical deposition of gold from solution, leading to the formation of large gold nuggets.
- Quartz’s Role: Quartz, the most abundant piezoelectric mineral, generates electrical charges under stress, particularly during seismic activity, which facilitates gold deposition.
- Gold as a Conductor: Gold’s conductive properties allow existing gold grains to act as focal points for further deposition, accelerating the growth of nuggets.
- New Geological Insight: This study offers a novel explanation for the frequent association of gold nuggets with quartz veins, resolving a long-standing geological mystery.
- Broader Implications: The findings could have implications for understanding the formation of other mineral deposits linked to piezoelectric minerals, expanding the scope of geochemical research.
Quartz is the most abundant piezoelectric mineral on Earth, capable of generating electrical charges under mechanical stress. During the cyclical nature of earthquake activity, quartz crystals in veins are subjected to repeated episodes of stress. This stress can generate a voltage through piezoelectric discharge, which in turn can electrochemically deposit gold from aqueous solutions present within the quartz veins.
The research team conducted deformation experiments on quartz and piezoelectric modeling to test this hypothesis. Their findings revealed that the stress experienced by quartz during earthquakes can indeed produce sufficient voltage to drive the deposition of gold from solution, even at the low concentrations typically found in natural fluids. Over time, these small accumulations of gold can coalesce into larger nuggets, explaining their frequent association with quartz.
One of the key insights from this study is the role of gold’s conductive properties in this process. While quartz itself is an insulator, making the initial nucleation of gold a slow process, gold’s conductive nature allows existing gold grains to become focal points for further deposition. This phenomenon helps to explain not only the formation of large gold nuggets but also the highly interconnected gold networks often observed within quartz vein fractures.
This research not only sheds light on a long-standing geological mystery but also provides a broader understanding of the complex interplay between geological processes and mineral formation. The implications of this study could extend beyond gold, offering insights into the formation of other mineral deposits associated with piezoelectric minerals.
Resources
Voisey, C. R., Hunter, N. J. R., Tomkins, A. G., Brugger, J., Liu, W., Liu, Y., & Luzin, V. (2024). Gold nugget formation from earthquake-induced piezoelectricity in quartz. Nature Geoscience.
Previous Understanding of Gold Nugget Formation
Before the recent findings, the prevailing theory about gold nugget formation was that gold precipitated from dilute, hot, water- or carbon dioxide-rich fluids deep within the Earth’s crust. These fluids, often found in quartz veins, would deposit gold as they experienced changes in temperature, pressure, and fluid chemistry. The idea was that as these conditions fluctuated, the dissolved gold in the fluids would precipitate out, gradually forming nuggets over time. However, this theory did not fully explain the formation of large gold nuggets, especially considering the typically low concentration of gold in these fluids and the chemical inertness of quartz.
Were Gold Veins Formed by Asteroids?
Gold veins themselves are not typically formed by asteroids. Instead, they are generally associated with orogenic processes—tectonic activities such as mountain-building events where significant pressure and heat are involved. These processes can create the conditions necessary for quartz veins to form and for gold to precipitate within them.
However, there is some evidence that meteorite impacts have contributed to gold deposits in certain cases. For example, some researchers have suggested that asteroid impacts could create hydrothermal systems that might lead to the formation of gold deposits. But these are specific scenarios and not the general mechanism by which most gold veins, particularly those associated with large nuggets, are formed. The majority of gold veins are related to the tectonic activities mentioned earlier, rather than extraterrestrial impacts.
Quartz on the Periodic Table
Quartz is a mineral composed primarily of silicon and oxygen, with the chemical formula SiO₂. On the periodic table:
- Silicon (Si) is the 14th element, found in Group 14 (IVA) and Period 3.
- Oxygen (O) is the 8th element, located in Group 16 (VIA) and Period 2.
Quartz is a crystalline form of silicon dioxide, which is one of the most abundant minerals in the Earth’s crust. Silicon and oxygen form a strong, stable bond in the quartz structure, resulting in its high hardness and chemical inertness.
Gold on the Periodic Table
Gold is a chemical element with the symbol Au and atomic number 79. It is located in:
- Group 11 (IB), also known as the “coinage metals” group, which includes copper (Cu), silver (Ag), and gold (Au).
- Period 6, among the transition metals.
Gold is known for its high density, malleability, ductility, and its resistance to tarnish and corrosion, making it a highly valuable and durable metal.
Relationship Between Quartz and Gold
While silicon and gold are both elements found on the periodic table, they belong to different groups and have distinct chemical properties. There is no direct chemical relationship between quartz (SiO₂) and gold (Au).
However, geologically, quartz and gold are often found together. Quartz veins can act as a host for gold deposits because the conditions that form quartz veins—high temperature and pressure—can also cause gold to precipitate out of solution. Quartz’s piezoelectric properties, as discussed in the recent study, can influence the deposition of gold within these veins during geological processes like earthquakes. So, while there’s no chemical bonding between quartz and gold, their association in nature is significant due to their shared geological environments.
Gold’s Origin in Supernovas
Scientists widely believe that gold, along with many other heavy elements, originated from supernovae and neutron star collisions. These cosmic events are powerful enough to produce the extreme conditions necessary for creating elements heavier than iron, which cannot be formed through the nuclear fusion processes that power stars.
In a supernova, a massive star explodes at the end of its life cycle, producing intense heat and pressure that can fuse protons and neutrons together, forming heavy elements like gold. Neutron star collisions, which involve the merging of two extremely dense remnants of supernova explosions, are also believed to be significant sources of heavy elements, including gold.
The Earth’s Formation and Supernova Contributions
While the Earth itself wasn’t directly formed by a supernova, the material that makes up the Earth—including gold—was. The Earth formed about 4.5 billion years ago from the solar nebula, a giant cloud of gas and dust left over from the death of earlier stars, including supernovae.
These supernova explosions enriched the gas and dust clouds in our region of the galaxy with heavy elements. Over time, gravity caused these clouds to collapse and coalesce into the Sun and the planets, including Earth. So, while Earth didn’t form in a supernova, the building blocks of the Earth, including the gold within it, were created in supernovae and similar cosmic events.
Summary
- Gold: Originated from supernova explosions and neutron star collisions, where extreme conditions allow the formation of heavy elements.
- Earth: Formed from a solar nebula composed of material enriched by earlier supernovae, but the Earth itself was not formed by a supernova. The heavy elements in Earth, however, owe their existence to such stellar events.
Other Ways Gold Can Be Created
Gold is a naturally occurring element and cannot be synthesized by ordinary chemical reactions. However, there are a few processes, both natural and artificial, that can result in the creation of gold:
1. Neutron Star Collisions
Neutron star collisions are among the most significant natural processes for creating gold. When two neutron stars merge, the extreme conditions produce rapid neutron capture processes (r-process), which create heavy elements like gold. This is one of the primary ways gold is formed in the universe.
2. Supernova Explosions
As mentioned earlier, gold can also be formed in the intense conditions of a supernova explosion. The rapid fusion of atomic nuclei in these explosions produces heavy elements, including gold, which are then scattered into space and eventually incorporated into forming planets.
3. Artificial Nuclear Reactions
It is theoretically possible to create gold in a laboratory setting through nuclear reactions. This involves bombarding atoms of a different element, such as mercury or platinum, with neutrons or other particles in a nuclear reactor or particle accelerator. This process changes the number of protons in the atom’s nucleus, potentially turning it into gold.
However, this method is extremely costly, inefficient, and produces only tiny amounts of gold. The energy and resources required to create even a small quantity of gold in this way far exceed the value of the gold produced, making it impractical for commercial use.
4. Transmutation (Alchemy)
Historically, alchemists attempted to transform base metals into gold, a practice known as transmutation. While these efforts were based on mystical and pseudoscientific ideas rather than actual science, they laid the groundwork for modern chemistry. Today, true transmutation of elements is only possible through nuclear reactions, as mentioned above, but not through chemical means as the alchemists believed.
Summary
- Natural Creation: Primarily occurs through neutron star collisions and supernovae, where gold is produced via nuclear fusion and rapid neutron capture processes.
- Artificial Creation: Possible through nuclear reactions in reactors or accelerators, but this is highly inefficient and not commercially viable.
- Alchemy: Historical attempts at gold creation through chemical means, which are now understood to be scientifically impossible.
In summary, while gold can technically be created artificially through nuclear reactions, the primary natural methods involve cosmic events like supernovae and neutron star collisions.
The heavier elements in our solar system, including gold, were primarily created by both supernovae and neutron star collisions. These cosmic events are responsible for the synthesis of elements heavier than iron, which cannot be produced by the normal fusion processes occurring in stars.
Supernovae
Supernovae are the explosive deaths of massive stars. When a star exhausts its nuclear fuel, it can no longer support itself against gravitational collapse, leading to a supernova explosion. During this explosion, the star’s core can undergo rapid neutron capture processes (r-process), where neutrons are rapidly absorbed by atomic nuclei, creating many of the heavy elements found on the periodic table, such as uranium, thorium, and a portion of the gold.
Neutron Star Collisions
Neutron star collisions, or kilonovae, occur when two neutron stars—extremely dense remnants of supernova explosions—merge. These collisions are particularly efficient at producing heavy elements, including a significant portion of the gold, platinum, and other precious metals. The extreme conditions during the merger facilitate the r-process, creating and dispersing these elements throughout space.
Contributions to Our Solar System
The material from both supernovae and neutron star collisions was scattered throughout the interstellar medium, enriching the gas and dust clouds that eventually coalesced to form our solar system. As a result, the Earth and other bodies in the solar system contain heavy elements produced by these two types of cosmic events.