Michele Dooley, age 9, of Peoria, I11., for her question:
HOW IS GOLD MADE AND FOUND?
We aren't sure when gold was first discovered, but we know that gold cups and jewelry were made as early as 3500 B.C. at Ur in Mesopotamia, which is now Iraq. Gold items from about this same time were also found in the Egyptian tombs. Craftsmanship in these objects suggests that the craft of working in gold had actually been developed hundreds of years earlier.
Gold is a metallic element that was one of the first known of all metals. The ancient Egyptians discovered thousands of years ago that it could be hammered out thinner than paper and used to decorate works of art. Although scientists have succeeded in making gold in an atom smasher, all of the gold produced commercially comes from the earth.
Scientists say that gold is deposited from gases and liquids rising from beneath the surface of the earth. These liquids and gases move toward the surface through cracks or faults in the crust.
Gold can be found in lode deposits, placer deposits, as a minor element in porphyry copper and in seawater.
Lode deposits are actually veins of gold found in the earth's crust. Placer deposits are large lumps of gold, called nuggets. In most cases they have been washed and carried away from a lode by surface water. A bit of gold is found in bulky copper deposits called porphyry copper deposits. Seawater contains about 1 grain of gold per ton but scientists haven't as yet found it profitable to obtain the precious metal this way.
Much of the world's gold is mined in much the same way as coal. Miners dig shafts into the ground and then follow the direction of gold bearing veins. The ore is transported to mills where it is separated and concentrated.
At an ore mill the rock is ground into powder, freeing most of the gold particles. Mercury is added and this coats the gold. Both then go to a furnace where the gold is separated from the mercury. The entire procedure is a long and very difficult one.
In a refinery, furnaces melt and purify the gold particles which are poured into molds to form bricks weighing 35 troy pounds each. It takes about 3 million pounds of ore to produce one gold brick.
Cyanidation is a process where ground gold ore is put in a tank containing a weak solution of cyanide. The gold in the solution is then separated, or precipitated, by contact with metallic zinc. The resulting material is then smelted or melted and cast into gold bricks.
Leading gold mining states and provinces, in order of importance, are Ontario, Quebec, Nevada, South Dakota, Northwest Territory, British Columbia, Arizona and Colorado.
South Africa is the world's leading gold mining country, followed by Russia, Canada and the United States in fourth place.