Resource Depletion Calculated by the Ratio of the Reserve Plus Cumulative Consumption to the Crustal Abundance for Gold Takashi Nishiyama 1 and Tsuyoshi Adachi 2 'Faculty of Engineering, Kyoto Univer- sity, Salo/o=ku,Kyoto 6067, Japan, and "Faculty of Engineering, The Universi- ty of Tokyo, Bunkyo-ku, Tokyo 113, Japan The magnitude of the world's mineral consumption has increased sharply, and there is no sign that growth is likely to stop in the near future. Currently, new discoveries and technology add to the reserves of various mineral commodities at a rate that has exceeded depletion. As a result, life expectancies have remained nearly constant. However, it is questionable whether this condition is sustainable in the future. Therefore, most of our attention to the future has been focused on potentially recoverable resources. The potentially recoverable re- sources for 35 minerals in the Earth's crust were estimated based on the relationship between crustal abundance and the reserve of cur- rentiy recoverable gold. The ratio of the reserve plus cumulative con- sumption to the abundance of gold is appropriate for calculating re- serves of other mineral resources because gold has the highest profit margin for exploration of reserves. From an economic perspective, the price of gold is 350 times the mean value of 33 other resources for calculating production versus price. Hew mining technologies and new processing methods have been developed during the last 20 years as a response to high prices. As a result, five times the reserves avail- able in 1970 have now been discovered, and two times the reserves available in 1970 were consumed during the past two decades. It is questionable whether other mineral commodities can reach the ratio of reserve plus cumulative consumption to abundance that gold does. Using this concept, the limit of the Earth's resources under present technology was calculated fur 35 mineral resources, based on the ratio of the reserve plus cumulative consumption to abundance for gold. Even though recoverable tonnage of lead, silver, tin, boron, copper, and mercury from ore deposits in the Earth's crust is relatively low, the abundance of these metals is apparently sufficient for future sup- plies. However, considering the special situation of gold created by its very high price compared to world production, there is anxiety concerning steep increases in the price or depletion of these metals, which have a shorter lifetime from a geochemical point of view. Key words: Resource depletion Potentially recoverable resources Crustal abundance Forecast in supply and demand 9 1995OxfordUniversityPress 0961-1444/95/$4.00 I 253