SILVER 



597 



product reflect the fact that most such deposits are 

 restricted to shallow depth, and thus have small 

 vertical extents. 



Silver consumption in the United States and in 

 the world will probably continue to greatly exceed 

 the newly mined supply, because silver is, and will 

 continue to be, a byproduct or coproduct of copper, 

 lead, zinc, and gold ores, and therefore its supply 

 depends largely upon the production of these metals. 

 In the future, silver will probably be produced more 

 from the many types of copper deposits and from 

 zinc-rich, lead-lean massive sulfides than from the 

 silver-lead-zinc replacement and gold deposits that 

 supplied most of the silver in the 20th century. The 

 marked decline in western silver-lead and zinc pro- 

 duction will continue because the high-cost western 

 mines and smelters cannot compete with eastern ore 

 until new, more efficient mining and recovery meth- 

 ods are commercially developed (which will take at' 

 least 5-10 years) , and until the price of silver is high 

 enough to assure that the western silver industry 

 will once more be competitive. A rise in the silver 

 price would aid the opening of low-grade dissemi- 

 nated silver deposits such as those at Calico, Calif. 

 Opening of more porphyry copper deposits and of 

 large, recently developed silver-bearing copper de- 

 posits in sandstone and ^hale, such as the dissemi- 

 nated copper-silver deposits of Idaho, Montana, 

 Michigan, Oklahoma, and New Mexico, will partly 

 fill the gap. 



Imported silver comes largely from Canada, 

 Mexico, Peru, Ireland, and Australia. Most of the 

 Canadian deposits are copper- or zinc-rich massive 

 sulfides, silver deposits, gold deposits, or porphyries. 

 The Mexican deposits are largely silver-rich epi- 

 thermal and replacement deposits and copper por- 

 phyries. Those in Peru are copper porphyries and 

 silver-lead deposits. The deposits in Australia and 

 Ireland are largely massive sulfides. Increased pro- 

 duction from these foreign deposits to obtain more 

 silver in the immediate future will seriously affect 

 our balance of payments and the present balance 

 between supply and demand of base metals. 



HYPOTHETICAL RESOURCES 



The potential resources of silver will be increased 

 substantially when economic conditions will justify 

 exploration for large, low-grade deposits. 



Stratabound copper deposits may be a very large 

 worldwide potential resource of silver that is not yet 

 widely exploited except in Poland, East Germany, 

 and Michigan. The existence of possible economic 

 concentrations of copper and silver in the sandstones 

 and shales of the Precambrian Belt Supergroup in 



Montana and Idaho, for example, has been recog- 

 nized only recently. An enormous potential resource 

 with more than 0.2 percent copper and 0.4 of an 

 ounce of silver per ton is suggested by current in- 

 vestigations of the Belt Supergroup, and a hypo- 

 thetical resource of 1 billion ounces of silver is 

 possible. In addition, anomalous amounts of copper 

 are known in sedimentary or low-grade metasedi- 

 mentary rocks of Belt age in Africa, Australia, Rus- 

 sia, and Canada (Harrison, 1972, p. 1232). The 

 southwest Oklahoma copper shales are known to 

 extend at depth throughout most of the Anadarko 

 Basin, eastward across much of Oklahoma, and 

 northward into Kansas, and to grade into silver-rich 

 deposits in southeastern Oklahoma. The sandstone 

 silver deposits of Silver Reef, Utah, are probably a 

 variant of the Colorado Plateau uranium and copper- 

 uranium deposits, many of which contain some sil- 

 ver. New sources are probable among the hundreds 

 of uranium prospects not rich enough to be mined, 

 where silver is a trace element and copper is com- 

 mon. The Silver Reef ore minerals are so nearly 

 invisible that new deposits will not be found without 

 careful sampling and analysis. Small sandstone sil- 

 ver deposits are known elsewhere in southwest Utah, 

 indicating that Silver Reef is not unique. 



Massive sulfides, which are the source of so much 

 of the world's base- and precious-metal ores, are 

 abundant in the Appalachian Mountains. Under 

 favorable economic conditions, many new commer- 

 cial ore bodies can probably be found by prospecting 

 and following prospects along known belts of meta- 

 volcanic rocks. A similar possibility for new deposits 

 exists in the Precambrian of the Basin and Range 

 province, outward from the well-known deposits in 

 Arizona into central New Mexico, and northward 

 into Colorado and southern Wyoming. These three 

 States have large areas of exposed Precambrian 

 rocks that contain many small massive sulfide de- 

 posits which have been largely overlooked because of 

 the nearby Laramide and Tertiary deposits. The 

 Sierra Nevada foothills in California and the north- 

 ern California Shasta deposits are similar promising 

 areas to search. A point worth remembering is that 

 in 1950 the great massive sulfide deposits of Bath- 

 hurst (New Brunswick), Gaspe (Quebec), Timmins 

 (Ontario), and Newfoundland were unknown, but 

 their presence was marked by small, nearly forgot- 

 ten prospects of sulfide, which had been discounted 

 and ignored by exploration geologists for many 

 years. 



SPECULATIVE RESOURCES 



The United States, including Alaska and Puerto 



