How are coarse gold veins formed? (BCG.V)

Nearly all coarse and fine placer gold originates from the erosion of primary hard rock gold deposits. Some placers are re-concentrated from older placers, but in the past, some time these came from primary deposits. A small amount of coarse gold has probably resulted from secondary enrichment processes, but the majority grew as a primary deposit from circulating hot water solutions under pressure – these are often called hard rock deposits

If water is hot enough, pressure high enough, and the chemistry is right (acids, and other elements like sulfur are present), then gold, quartz and other things can dissolve and go into solutions. The solutions move by natural convection (hot rises). As the solutions rise, the water cools as they move farther from the heat source in the ground and closer to the surface. The sulfides become less soluble and they come out of solution to follow natural fault zones to form veins (long and narrow plane). Veins are also commonly formed at the meeting of two different rock types. Sometimes a zone of broken or fractured rocks can develop a series of small parallel veins.

The small veins were difficult for old time miners to find and mine profitably. Therefore, with the new modern technology, geologists' jobs were made a lot simpler - larger areas can be covered and residual placers can be found quicker.


Some coarse gold veins districts that were found:

Goldfield, Nevada 1903 - the most productive gold vein district in Nevada - 5M oz of gold

Randsburg, South California - over 1M oz of gold

Kofa placers of Yuma county

North Star and King of Arizona

Source: http://www.nuggetshooter.com/articles/CRGeologyofcoarsegoldformation.html

You are reminded that you are responsible for your own due diligence. We share in neither your profit nor your losses.