Ken Cameron, age 14, of Las Vegas, Nev., for his question:
WHERE DO WE FIND GOLD?
Gold is a precious, yellow metallic element. It is found in nature in quartz veins and in gold bearing soil as a free metal or in a combined state. It is widely distributed although it is rare, being 58th in order of abundance of the elements in the crust of the earth.
Scientists say that gold is deposited from gases and liquids rising from beneath the earth's surface. These gases and liquids travel toward the surface through faults or cracks in the crust. Gold is found in lode, or vein, deposits, in placer deposits and in seawater.
Lode deposits, which are also called veins, are found in the earth's crust.
Placer deposits are large particles, called nuggets, and grains of gold in the beds of streams. These particles have been washed and carried away from a lode, or vein, by surface water, usually floodwater. Some nuggets are very large.
Placer deposits are of two types: eluvial and alluvial. Eluvial deposts are found close to the vein of gold. Alluvial deposits are farther away, usually in stream beds.
All seawater contains gold in solution. Seawater yields about one grain of gold per ton of water. Scientists are seeking ways to mine this gold profitably.
Gold is seldom found in a pure state. It is usually combined with silver in a natural alloy called an electrum. But it is usually associated with quartz, calcite, lead, tellurium, zinc or copper and is usually mined as by product of these metals. Only about 40 percent of the gold production of this country is obtained from what may rightly be called gold mines.
In most placer mining, the ore is taken from underground mines and then transported to mills and separated and concentrated there. Some gold is mined from the surface of the ground. Miners drill long holes into the rock and insert explosives. The explosion breaks up the ore and the pieces are hauled away to the mills.
South Africa, Russia, Canada and the United States are the chief gold producing countries.
Extensive underground deposits of gold bearing rocks are often discovered by a small outcrop on the surface. Shafts are sunk, as in coal mining, and the ore is brought to the surface. It is then crushed in special machines.
Gold is extracted from gravel or from crushed rock by dissolving it either in mercury (the amalgam process) or in cyanide solutions (the cyanide process).
Some ores, especially those in which the gold is chemically combined with tellurium, must be roasted before extraction. The gold is recovered from the solution and melted into ingots.
Gold bearing rock with as little as one part of gold to 300,000 parts of worthless material may be worked at a profit.
The rarest form of gold is a nugget. The largest known nugget, the Welcome Stranger, weighing about 156 pounds, was turned up accidentally, just below the surface of the ground, by a wagon wheel in Victoria, Australia, in 1869.