Mineral Commodity Summaries 2011 - Environmental and Energy ...

APPENDIX C—Reserves and Resources193Reserves data are dynamic. They may be reduced asore is mined and/or the extraction feasibility diminishes,or more commonly, they may continue to increase asadditional deposits (known or recently discovered) aredeveloped, or currently exploited deposits are morethoroughly explored and/or new technology or economicvariables improve their economic feasibility. Reservesmay be considered a working inventory of miningcompanies’ supply of an economically extractablemineral commodity. As such, magnitude of thatinventory is necessarily limited by many considerations,including cost of drilling, taxes, price of the mineralcommodity being mined, and the demand for it.Reserves will be developed to the point of businessneeds and geologic limitations of economic ore gradeand tonnage. For example, in 1970, identified andundiscovered world copper resources were estimated tocontain 1.6 billion metric tons of copper, with reserves ofabout 280 million metric tons of copper. Since then,about 400 million metric tons of copper have beenproduced worldwide, but world copper reserves in 2010were estimated to be 630 million metric tons of copper,more than double those in 1970, despite the depletionby mining of more than the original reserves estimate.Future supplies of minerals will come from reserves andother identified resources, currently undiscoveredresources in deposits that will be discovered in thefuture, and material that will be recycled from current inuse-stocksof mineral or from minerals in waste disposalsites. Undiscovered deposits of minerals constitute animportant consideration in assessing future supplies.USGS reports provide estimates of undiscoveredmineral resources using a three-part assessmentmethodology (Singer and Menzie, 2010). Mineralresourceassessments have been carried out for smallparcels of land being evaluated for land reclassification,for the Nation, and for the world.Reference CitedSinger, D.A., and Menzie, W.D., 2010, Quantitative mineral resourceassessments—An integrated approach: Oxford, United Kingdom,Oxford University Press, 219 p.Part A—Resource/Reserve Classification for Minerals 1INTRODUCTIONThrough the years, geologists, mining engineers, andothers operating in the minerals field have used variousterms to describe and classify mineral resources, whichas defined herein include energy materials. Some ofthese terms have gained wide use and acceptance,although they are not always used with precisely thesame meaning.The USGS collects information about the quantityand quality of all mineral resources. In 1976, the USGSand the U.S. Bureau of Mines developed a commonclassification and nomenclature, which was published asUSGS Bulletin 1450–A—“Principles of the MineralResource Classification System of the U.S. Bureau ofMines and U.S. Geological Survey.” Experience with thisresource classification system showed that somechanges were necessary in order to make it moreworkable in practice and more useful in long-termplanning. Therefore, representatives of the USGS andthe U.S. Bureau of Mines collaborated to revise Bulletin1450–A. Their work was published in 1980 as USGSCircular 831—“Principles of a Resource/ReserveClassification for Minerals.”Long-term public and commercial planning must bebased on the probability of discovering new deposits, ondeveloping economic extraction processes for currentlyunworkable deposits, and on knowing which resourcesare immediately available. Thus, resources must becontinuously reassessed in the light of new geologicknowledge, of progress in science and technology, andof shifts in economic and political conditions. To bestserve these planning needs, known resources should beclassified from two standpoints: (1) purely geologic orphysical/chemical characteristics—such as grade,quality, tonnage, thickness, and depth—of the materialin place; and (2) profitability analyses based on costs ofextracting and marketing the material in a giveneconomy at a given time. The former constitutesimportant objective scientific information of the resourceand a relatively unchanging foundation upon which thelatter more valuable economic delineation can be based.The revised classification system, designed generallyfor all mineral materials, is shown graphically in figures 1and 2; its components and their usage are described inthe text. The classification of mineral and energyresources is necessarily arbitrary, because definitionalcriteria do not always coincide with natural boundaries.The system can be used to report the status of mineraland energy-fuel resources for the Nation or for specificareas. 1RESOURCE/RESERVE DEFINITIONSA dictionary definition of resource, “something inreserve or ready if needed,” has been adapted formineral and energy resources to comprise all materials,including those only surmised to exist, that have presentor anticipated future value.Resource.—A concentration of naturally occurring solid,liquid, or gaseous material in or on the Earth’s crustin such form and amount that economic extraction ofa commodity from the concentration is currently orpotentially feasible.Original Resource.—The amount of a resource beforeproduction.Identified Resources.—Resources whose location,grade, quality, and quantity are known or estimatedfrom specific geologic evidence. Identified resourcesinclude economic, marginally economic, and subeconomiccomponents. To reflect varying degrees ofgeologic certainty, these economic divisions can besubdivided into measured, indicated, and inferred.1 Based on U.S. Geological Survey Circular 831, 1980.