24 



UNITED STATES MINERAL RESOURCES 



are not included. (See "Introduction" to this volu- 

 ume.) 



Some of the metals are listed in table 4 in order 



Table 4. — Ratio of potential resources to known reserves 



United States 

 _ 1 

 _ 1 



- 1.6 



- 3.2 



- 4.1 



- 6.3 



- 11 



- 15 



- 20 



- 31 



- 37 

 -830 



Pb 



Mo 



Cu 



Ag 



Au 



Zn 



Sb 



Hg 



U - 



Th 



W . 



Ni . 



Sn Very high 



of increasing ratio of potential resources to known 

 reserves, as shown in table 3. The ratios indicate, 

 for example, that we can anticipate discovery of 

 about 4 times as much minable gold ore as our pres- 

 ent known reserves. Because lead was chosen as the 

 base for calculating potential resources, its ratio is 

 necessarily one. 



It is interesting that for the United States those 

 metals whose known reserves most closely approach 

 the potential recoverable resources are the metals 

 most diligently sought for the longest time (lead, 

 molybdenum, copper, silver, gold, zinc). Although 

 uranium is a relatively recently sought metal, the 

 intensity of the search for it has moved its ratio 

 close to the ratio of the traditionally sought metals. 

 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 quantities we might expect. The largest 

 ratios, for nickel and tin, are caused by lack of 

 known favorable host rocks in the United States. 

 However, the large ratios suggest that we should 

 take another look for these metals in the United 

 States, but perhaps in different geologic environ- 

 ments from those in which we have traditionally 

 looked. Commonly, the higher the ratio, the greater 

 is the tendency for the element to form oxide or 

 silicate minerals rather than the commonly sought 

 sulfide ores. 



Those metals with intermediate ratios are those 

 that have not been vital to our economy in the past, 

 or whose prices are subject to great fluctuation, or 

 whose past source has been chiefly as a byproduct. 

 But certainly these elements must also be present 

 in the crust in crudely predictable amounts. 



As we might expect, the ratios for world re- 

 sources generally are much higher than United 

 States ratios because many land areas of the world 



have not been intensely explored. Those few metals 

 that do have lower potential ratios than the United 

 States (antimony, tin, and nickel) are contained in 

 old, well-known districts — the antimony of main- 

 land China, the tin of Bolivia, Cornwall, and Ma- 

 laysia, and the nickel of shield areas such as Canada 

 and Australia. 



Data on a few of the elements listed in table 3 

 deserve further comment. The tellurium ratio of 

 potential resource to known reserve (0.11) indicates 

 that we have 10 times more known reserves than 

 predictable by R=2A5 AxlO^ Perhaps the crustal 

 abundance figure is too low, but there is another, 

 more important factor: most tellurium production 

 comes as a byproduct of copper refining, and the 

 known reserve figure for tellurium is equated with 

 copper production and reserve (0.4 lb of tellurium 

 per ton of copper produced). Therefore, copper ore 

 that averages 0.86 percent Cu contains only 0.00017 

 percent tellurium. Thus we are in the unique situa- 

 tion of equating our known tellurium reserves to 

 raw materials that contain only 1.7 ppm tellurium! 

 Obviously rock containing 1.7 ppm tellurium, exclu- 

 sive of other metals, could not be considered ore 

 grade, and the relationship 72=2.45 Ax 10^ does not 

 apply. 



The same explanation holds for the low selenium 

 (6) and bismuth (0.5) ratios. Selenium reserves 

 also are equated with copper production (1 lb selen- 

 ium per ton copper produced or about 4.3 ppm 

 selenium in 0.86 percent copper ore). Bismuth re- 

 serves are equated to lead reserves (about 7 lbs bis- 

 muth per ton of western United States lead or 100 

 ppm bismuth in 3-percent lead ore). 



Ratios that are extremely high can usually be ex- 

 plained by what we already know about the geo- 

 chemistry and United States distribution of that 

 element. Aluminum, for example, shows a very high 

 ratio of potential resource to known reserve. Alu- 

 minum occurs chiefly in silicates, whereas currently 

 minable aluminum ore (bauxite) is a weathering 

 product and the vertical extent to which weathering 

 can occur is limited. Thus much of the crust is re- 

 moved from a possible resource category for alumi- 

 num until we can economically recover aluminum 

 from feldspar or clay. 



The high manganese ratio (2,450) results from a 

 reserve figure based upon a 35-percent manganese 

 concentrate produced by normal concentration 

 methods. The word "normal" is the clue to the high 

 ratio. The U.S. Bureau of Mines estimates that 

 manganese deposits in the United States contain 

 68 million tons of manganese, but they are low grade 

 and must be considered resources. However, if the 



