Carolos Rivera, age 13, of Flagstaff, Ariz., for his question:
HOW IS GOLD MINED?
Gold has been valuable throughout the ages primarily because it is scarce. The methods for obtaining gold vary with the type of deposit.
Gold is found in lode or vein deposits, in placer deposits and in seawater. Lode deposits are veins in the earth's crust while placer deposits are large particles, called nuggets, and grains of gold in the beds of streams. Most of these particles have been washed and carried away from a lode by surface water, usually flood water.
All seawater contains gold in solution. There is only about one grain of gold per ton of seawater. Scientists are looking for a way to mine this gold profitably, but they haven't found it as yet.
Two steps are necessary in all types of gold mining: to obtain the gold ore and to separate the gold from the ore.
In most placer mining, both of these operations take place at the scene of the gold deposits. But in underground mining, the ore is usually mined, then transferred to mills and separated and concentrated there.
Lode deposits of gold are mined underground in much the same way as coal. Miners reach the gold by digging shafts into the ground, following the direction of the vein.
Some gold ore 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.
Placer mining is primarily a sifting process. In the early days of placer mining, men panned gold by hand, sometimes swirling water and gravel in an ordinary frying pan.
But usually the miner used a shovel to scoop gravel into a sort of cradle that held about six cubic feet of material. He rocked this cradle, washing and sifting out lighter materials until only the gold was left.
Today some gold is mined by using water directed under high pressure onto banks of gold bearing gravel. The water washes the gravel banks into troughs, which have grooves that trap the gold.
A dredge is a power driven gold mining machine. It has a chain of buckets on a barge. Each bucket holds about six cubic feet of material. The buckets are lowered into the water on a boom. They revolve in a continuous chain to bring up placer gold from the stream beds.
Power shovels are also used to mine gold. These are huge machines which scoop up large quantities of gold bearing sand and gravel from stream beds.
Leading gold mining states, provinces and territories are listed in order: Ontario, Quebec, Nevada, South Dakota, Utah, the Northwest Territory, British Columbia, Arizona, Colorado and Washington