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How do hydrothermal veins of gold form?

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A diagram showing the periodic table entry for gold, with the symbol Au, atomic number 79, atomic weight 196.96657, electron configuration, and labels for its properties as a solid transition metal with a face-centered cubic crystal structure. — gold The precious metal gold is a chemical element with the symbol Au. Its square on the periodic table details some of its properties, including its atomic weight, atomic number, and crystal structure.

Hydrothermal veins of gold form through the movement of hot, mineral-rich water—known as a hydrothermal solution—through cracks and fissures within the Earth's crust.12

The process generally involves the following stages:

Transport: Hot water, often heated by nearby igneous rocks or other geological heat sources, acts as a transporting agent, carrying gold and other minerals from deep within the Earth.123
Deposition: As this solution flows through open fissures, the gold precipitates out of the liquid and deposits onto the rock walls. This precipitation is typically triggered by a decrease in temperature, boiling, or chemical reactions between the solution and the surrounding rock.123
Formation: Over time, these deposits fill the cavities, creating veins that are often associated with quartz and pyrite.14

When these deposits form at shallow depths near boiling hot spring systems, they are classified as epithermal veins, which are frequently noted for being exceptionally rich in gold.1