Alaska’s natural resources have proved to be a benefit to the United States, thus proving the value of this purchase. Its economy has benefited from its natural resources as well from supplying jobs and business opportunities. Alaska’s mining industry produces petroleum, natural gas, gold, zinc, silver, sand and gravel. Alaska first discovered oil and natural gas in 1968 at Prudhoe Bay. Shortly after Gold was found in 1896 at Yukon, Alaska. Later in the late 1960’s zinc was found in Red dog Creek. Then silver was found in 1987 at Green Creek's Mine. Alaska’s oil mine has produced over 18 billion barrels of oil since the discovery of natural resources there. In Alaska, the oil industry accounts for one-fourth of employment and one-half of the economy. Since the discovery of oil in Alaska the oil produced has dropped about 75 percent since its peak in 1988. The oil and natural gas industry in Alaska pays over $3.1 billion dollars worth of taxes every year.