Page 36 - Curriculum Visions Dynamic Book

Gold in the Earth
Gold mostly forms in veins in rocks.
The source of gold is probably hot liquids that boiled off the great molten bodies that feed volcanoes. These hot fluids forced their way up through the cracks in the overlying rocks, where they cooled and solidified.
Gold is among a number of metals (including silver, copper and tin) that form in this way. Scientists call the
veins hydrothermal (hot water) deposits.
Gold is so unreactive chemically that it does not easily form oxides or other compounds and remains as “native” (pure) metal in the rocks.
Mining
Vein, or lode, mining is the most important of all gold recovery methods (see page 30). Although each ounce of gold recovered requires about 100,000 ounces of ore to be processed, so much gold is deposited in rock veins that this method accounts for
more than half of the world’s
total gold production today. The gold in the veins may be microscopic particles, nuggets, sheets, or gold compounds. Regardless of how it
is found, the ore requires extensive extraction and refining.
 A vein carrying gold in a mine tunnel.
 A modern open-cast gold mine near Bendigo, Australia.
36
36