Throughout history, gold has been a precious material, eagerly sought and cherished. It was probably the first metal to be mined because it is beautiful and imperishable (which will always exist or cannot wear out), and because beautiful objects can be made from it-even with primitive tools. The amount of gold known to ancient peoples probably totaled not much more than the amount produced each year by the world’’s largest gold mine located in the Witwatersrand district of South Africa. Stores of gold discovered by archaeologists in Greece, Scythia, and Egypt, as well as the gold from Indian treasuries in Mexico and Peru, represented years of patient collection of small quantities from streams and veins (矿脉) , often by slave labor. 　　The essential value of gold has always been known, even before gold was used in coinage. It remains the only universally recognized standard of value in international monetary exchange. Most of the world’’s refined gold is absorbed by governments and central banks to provide backing for paper currency. But the amount of gold used in arts and in industry is increasing. In addition to its use for jewelry, decorative finishes, and dentistry, its special properties have led to many applications in modern science and technology. Suce coatings of gold protect earth satellites from heat and corrosion, and certain electrical components and circuits of spacecraft are made of gold when extreme reliability is required. 　　Gold was first produced in the United States from the southern Appalachian region, beginning about 1792. These deposits, though rich, were relatively small and were quickly depleted. The discovery of gold at Sutter’’s Mill in California sparked the gold rush of 1849-50. Hundreds of mining camps sprang to life as new deposits were discovered. As a result, the production of gold increased rapidly. 　　During World War I and for some years thereafter, annual production declined to about two million ounces. When the price of gold was raised in 1934 to $35 an ounce, production increased rapidly. Shortly after the start of World WarⅡ, gold mines were closed and the government did not permit them to reopen until 1945. Since then the production of gold has not exceeded two million ounces a year. 　　The largest producing gold mine in the United States is the Homestake Mine in South Dakota, which yields about 575,000 ounces of gold each year. Other mines scattered throughout various parts of the world produce even larger amounts of this highly prized and eagerly sought yellowish material. It can be inferred from the text that