One widely accepted hypothesis proposes

One widely accepted hypothesis proposes that many
gold deposits, especially those found in volcanic and
sedimentary rocks, formed from circulating ground
waters driven by heat from bodies of magma (molten

Mineralizing solutions travel upward along fractures and form
primary deposits.

rock) intruded into the Earth’s crust within about 2 to
5 miles of the surface. Active geothermal systems,
which are exploited in parts of the United States for
natural hot water and steam, provide a modern analog
for these gold-depositing systems. Most of the water
in geothermal systems originates as rainfall, which
moves downward through fractures and permeable
beds in cooler parts of the crust and is drawn laterally
into areas heated by magma, where it is driven
upward through fractures. As the water is heated, it
dissolves metals from the surrounding rocks. When
the heated waters reach cooler rocks at shallower
depths, metallic minerals precipitate to form veins or
blanket-like ore bodies.