World class base and precious metal deposits; a quantitative analysis
|Category||Economic geology & mineral exploration|
|Location||proceedings of economic geology journal 1976-96|
|Holding Date||04 May 2008|
Over 62 percent of the 193,000 metric tons of gold discovered to date is located in four countries and more than 68 percent occurs in four types of mineral deposits. About 55 percent of the 1,740,000 metric tons of silver found is in four countries and 45 percent is in four types of deposits. Fifty-six percent of the 1.52 billion metric tons of discovered copper is from four countries and four types of deposits contain 88 percent of the total. Over 50 percent of both the 713,000,000 metric tons of zinc and 349,000,000 metric tons of lead discovered to date come from four countries and 70 percent of both metals occur in four types of deposits. All discovered gold would fit in a cube with a height oF 22 m, silver in a 55-m cube, copper in a 550-m cube, zinc in a 460-m cube, and lead in a 310-m cube. At least 74 percent of gold, silver, zinc, and lead is in deposits having average grades above the respective median grades and 44 percent of copper is in deposits with average grades above the median grade of all deposits. Lower grade deposits contain less total metal than higher grade deposits. Tonnage of mineralized rock is an even better predictor of contained metal with over 96 percent of each metal's total residing in deposits having greater than median size and between 47 and 79 percent of metal contained in the largest 10 percent of deposits. World class deposits, defined as the upper 10 percent of deposits in terms of contained metal, account for over 86 percent of all gold, 79 percent of silver, 84 percent of copper, 71 percent of zinc, and 73 percent of lead. These giant deposits contain at least 100 metric tons (3.2 Moz) gold, 2,400 metric tons (77 Moz) silver, 2 million metric tons copper, 1.7 million metric tons zinc, or 1 million metric tons lead. Mineral deposits occur rarely in the earth's crust and large ones are especially uncommon. This analysis shows that only the unusually large deposits can significantly affect supply.