UNITED STATES MINERAL RESOURCES 



CRUSTAL ABUNDANCE OF ELEMENTS, AND 

 MINERAL RESERVES AND RESOURCES 



By Ralph L. Erickson 



CONTENTS 



Page 



Abstract of conclusions 21 



Abundance-resource-reserve relationships 21 



References cited 25 



FIGURE 



Graph showing domestic reserves of elements 

 compared to their abundance in the earth's 

 crust 



TABLES 



3. Abundance, mass, reserves, and resources of some 



metals in the earth's crust and in the United 

 States crust 



4. Ratio of potential resources to known reserves 



ABSTRACT OF CONCLUSIONS 



Crustal abundance data and the reserve-abundance 

 (i2=AX10°"") relationship of McKelvey are combined to 

 calculate the total amounts of several metals in the earth's 

 crust, in various segments of the crust, in United States 

 crust, in United States crust to a 1-kilometer depth, and in 

 the potential currently recoverable resources. Marginal re- 

 sources are not reported. The potential recoverable resource 

 for most elements should approach i?=2.45AX10°, where A 

 is abundance expressed in grams per metric ton or parts per 

 million and R is resource expressed in metric tons. Those 

 metals whose known reserves most closely approach the 

 calculated potential recoverable resource are the metals that 

 have been most diligently sought for the longest time (lead, 

 copper, zinc, silver, gold, molybdenum) . Those metals whose 

 known reserves are very much less than the calculated po- 

 tential recoverable resource (nickel, tin) are the metals 

 usually found in geologic environments not common in the 

 United States. Those metals whose reserve-potential re- 



source relation is intermediate between crustal abundance 

 and reserve abundance are those that have not been vital to 

 our economy in the past, whose prices are subject to great 

 fluctuation, or whose past source has been chiefly as a by- 

 product. Thus, the scheme of predicting resource potentials 

 in relation to crustal abundance seems valid — if we search 

 for an element hard enough, we find it in about the quan- 

 tities we might expect. 



If we accept the abundance-reserve relationship, it follows 

 that 12 = 2.45X10' is a minimum total resource estimate be- 

 cause the relationship is based upon currently recoverable 

 resources and does not include resources whose feasibility 

 of economic recovery is not established. Substantial varia- 

 tions of total resource estimates from this formula prob- 

 ably are caused by geologic factors and the inherent geo- 

 chemical nature of the element. However, recent discoveries 

 of several new types of mineral deposits indicate that we 

 need to critically examine our criteria for where and how to 

 look for mineral deposits. Certainly, significant mineral de- 

 posists remain undiscovered because exploration efforts are 

 commonly confined to the classic environments of ore deposi- 

 tion. 



ABUNDANCE-RESOURCE-RESERVE 

 RELATIONSHIPS 



The table of abundance, reserves, and potential 

 resources of some metals in the earth's crust and 

 United States crust presented in this chapter pro- 

 vides a broad general framework in which to ex- 

 amine the relation between abundance, reserves, and 

 resources. The abundance data used for mass and 

 resource calculations are based upon the work of 

 Lee and Yao (1970). These authors have taken into 

 account oceanic crust, variation with depth of con- 

 tinental crust, and variation between shield areas, 

 folded belts, and volcanic arcs. They also provide 

 reasonable figures for thickness and mass of the 

 various subdivisions of earth's crust. 



McKelvey (1960) reviewed the principal ap- 

 proaches to the problem of estimating ore reserves 

 and suggested a new method based on the fact that 

 the tonnage of minable reserves of the well-explored 



U.S. GEOL. SURVEY PROF. PAPER 820 



21 



