Gold is formed as the result of molten rock, called magma,being intruded into solid rock. As the magma cools andsolidifies, water and other volatile substances separateout from the magma under high pressure. The high pressureof hot water and steam force open fissures in thesurrounding solid rock, through which these hydrothermalsolutions travel. When the hydrothermal solutions cool,deposition of material occurs, especially quartz in theform of quartz veins.
Because gold has a relatively low melting temperature, itis sometimes carried by these hydrothermal solutions throughthe fissures in the rock and solidifies inside the quartzveins. Thus, the place to look for gold is usually inquartz veins near the intrusion of a magma body. One exampleis the so-called Mother Lode of the Sierra Nevada inCalifornia. If these quartz veins are eroded, the goldmay be found in streams and rivers; this explains whythe 49-ers of the last century were able to pan for goldin the foothills of the Sierra Nevada.
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