Where Does Gold Come From?

Gold is a fascinating precious metal that has captivated human interest for thousands of years. Gold (Au) is a chemical element known for its lustrous yellow color, resistance to corrosion, and malleability. It's highly valued for use in jewelry, electronics, and as a store of wealth. Here is an overview of how gold is formed and where gold comes from.

Gold Formation

Unlike many other elements, gold cannot be created on Earth. Its creation is rooted in cataclysmic cosmic events, far beyond Earth's geological processes. Here are the primary stages of gold formation:

Gold Formation in the Universe

Supernova Explosions: When a massive star (at least eight times the mass of our Sun) reaches the end of its life, it undergoes a supernova explosion. The core collapses under gravity, triggering a massive explosion that can briefly outshine an entire galaxy.

During this explosion, the rapid neutron capture process (r-process) occurs, where neutrons are absorbed by atomic nuclei at an incredibly fast rate. This process forms heavy elements, including gold.

Stellar Nucleosynthesis: Regular stellar nucleosynthesis, which involves the fusion of lighter elements into heavier ones, does not form gold. Instead, gold is formed during the r-process in supernovae. The extreme conditions of a supernova explosion enable rapid neutron capture, leading to the creation of gold and other heavy elements.

Distribution of Gold in the Universe

The gold produced in supernova explosions scatters across the universe. Over billions of years, this cosmic dust, including gold particles, coalesces into larger bodies like asteroids and planets. This dispersion process ensures that gold becomes part of the materials that eventually form planetary bodies, including Earth.

Gold Formed by Supernovae.

Geological Processes: Earth's Gold Deposits

When gold-bearing cosmic dust becomes part of Earth's crust, it undergoes several geological processes that lead to gold deposits. These processes include hydrothermal, magmatic, and metamorphic activities.

Hydrothermal Processes: Within the Earth's crust, hot, mineral-rich fluids from the Earth's interior move through cracks and fissures in rocks. As these fluids cool, they deposit minerals, including gold, in veins. These hydrothermal veins are often found in quartz or sulfide minerals, creating rich sources of gold.

Magmatic Processes: Gold can also be concentrated through magmatic processes. Here, molten rock (magma) cools and crystallizes, causing minerals to separate. As the magma solidifies, gold may be deposited in the surrounding rocks, forming significant mineral deposits.

Metamorphic Processes: During the metamorphism of rocks, gold can be remobilized and concentrated. High pressures and temperatures cause gold to migrate to new locations within the Earth's crust, often associating with sulfide minerals. This process ensures that gold can be found in various types of metamorphic rocks.

Where Does Gold Occur?

While gold originally came from space, it is now widely distributed on Earth, occurring in various geological environments. Here we explore the different types of gold deposits, how they form, and where they are typically found.

Gold-bearing quartz veins in Argillite

Gold's Geological Presence

Gold typically occurs in its native form, meaning it is found as pure metal rather than in compounds. This precious metal is often associated with quartz veins, but can also be found in placer deposits (loose sediments), hydrothermal veins, and even in seawater. Its distribution is influenced by geological processes and historical events, leading to the formation of various types of deposits:

Primary Deposits

Primary gold deposits are those where the gold is found in its original location within the rock, often referred to as "lode" deposits. These deposits are typically found in quartz veins or associated with sulfide minerals in metamorphic rocks. There are two main types of primary deposits:

Lode Deposits: These are veins of gold found in rock formations, typically quartz veins. The gold in these deposits is often in its native form and can be extracted through mining operations.
Disseminated Deposits: These consist of fine particles of gold dispersed throughout a large volume of rock, often found in association with other minerals such as copper and silver.

Secondary Deposits

Secondary deposits, also known as "placer" deposits, form when gold is weathered out of its primary rock and transported by water. This gold accumulates in riverbeds, streambeds, and along beaches. There are several types of secondary deposits:

Placer Deposits: Formed by the weathering and erosion of primary deposits, placer deposits consist of gold particles found in riverbeds, streambeds, and other sedimentary environments. The gold is typically in the form of dust, flakes, or nuggets and is extracted through panning, sluicing, or dredging.

Alluvial Deposits: Gold eroded from primary deposits is carried by water and deposited in alluvial deposits, which can be found in river valleys, floodplains, and ancient riverbeds.

Unique Geological Settings

Gold's distribution is also influenced by specific geological settings and processes:

Orogenic Belts: These are regions where tectonic plates collide, causing mountain-building and metamorphic processes that concentrate gold. Famous orogenic gold belts include the Witwatersrand Basin in South Africa and the Canadian Shield.
Byproduct of Other Metal Mining: Gold is often found alongside other metals like copper and silver, making it a valuable byproduct of mining operations for these metals.
Oceans: Trace amounts of gold are dissolved in seawater, though in very low concentrations.
Ancient Rock Formations: Some of the world's richest gold deposits are found in areas with ancient geological structures, such as the Witwatersrand Basin in South Africa.

Global Distribution

Gold deposits are found on every continent, with significant gold-producing countries including China, Australia, Russia, the United States, Canada, and South Africa. These regions host a combination of primary and secondary deposits, contributing to their gold production capabilities.

Map of Gold Deposits

How Much Gold Is in the World?

Estimating the total amount of gold that has been mined and the amount still available in the Earth's crust involves both historical data and geological surveys:

Mined Gold:

As of recent estimates, approximately 201,296 metric tons of gold have been mined throughout history. This gold, if melted down, would form a cube roughly 21.7 meters on each side. The majority of this gold is held in the form of jewelry, investment products, and central bank reserves.

Reserves and Resources:

The United States Geological Survey (USGS) estimates that there are about 53,000 metric tons of gold reserves that are economically viable to mine.

Gold in the Earth's Crust and Oceans

Oceans:

Gold is also found in seawater, albeit in trace amounts. The concentration of gold in seawater is about 0.0000000001 parts per million. While the total amount of gold in the oceans is estimated to be around 20 million metric tons, extraction is not currently economically viable.

Earth's Crust:

Gold is present in the Earth's crust in very low concentrations, averaging about 0.004 parts per million. This translates to a vast amount of gold (145,000 tonnes of gold) in the crust, but it is dispersed and often inaccessible with current technology.

Undiscovered Resources:

Beyond known reserves, there are potentially large amounts of undiscovered gold resources. Advanced geological modeling and exploration techniques continue to identify new potential gold-bearing regions.

Recycling:

A significant portion of gold supply comes from recycling old jewelry, electronics, and other products. This secondary source is crucial for meeting the ongoing demand for gold without solely relying on new mining.

Gold's unique formation process, involving both cosmic events and terrestrial geology, underscores its rarity and value. Its global distribution is concentrated in specific regions rich in deposits, and while substantial quantities have been extracted, significant reserves still lie beneath the Earth's surface.