Copper Mines Above and Below the Ground
For years, resource geologists have estimated the amount of minerals and other deposits suitable for exploitation. On the local level, these projections provide information for investment decisions by mining companies and for land use and industrial development planning by governments and communities. On the global level, estimates of resource reserves combined with data on rates of use provide perspective on long-term sustainability.
The stocks of mineral resources are extracted and mobilized from the Earth's crust and transformed into engineered commodities and goods at the desired level of quality. These goods and commodities reside in the economy as an in-use stock of resources as long as their performance does not fall below acceptable levels. A net buildup of in-use stocks usually occurs that depends on the varying lifetimes of the goods and commodities. In our technological society, the lifetimes of goods are getting shorter and, simultaneously, our rate of use of resources is increasing exponentially. This results in faster turnover of the stock of resources across its life cycle.
At the end of their useful service lives, the goods and commodities exit the economy as discards headed either to waste repositories or to remanufacture and reuse. At each life-cycle stage of the resource-production, fabrication, manufacturing, use, and end-of-lifeâ€”different types of stocks exist. This feature presents a classification of stocks and the methodology to assess them. The information on different types of stocks is useful for analyzing the economic and environmental implications of resource use and has relevance for various stakeholders (1).
The quantities, or stocks, of resources in the ground are not a sufficient guide to the future, because other stocks also need to be considered. A recent paper by Elshkaki et al. showed that flows of lead from stock in use in The Netherlands will soon exceed the amount needed for lead-containing products entering use (2). Therefore, in principle, The Netherlands's dependence on lead from mines could be replaced with metal reclaimed from discards. In another seminal study, Allen and Behmanesh showed that for many elements, the industrial waste streams being disposed of were richer in concentration than typical virgin ore bodies (3). In each case, this suggests that the concept of resource stocks must be considered much more broadly.