596 



UNITED STATES MINERAL RESOURCES 



concentrated brine with an unusually high content 

 of potassium, lithium, and heavy-metals was tapped 

 by a deep well that was drilled for geothermal pow- 

 er (White and others, 1963, p. 919-922). Evaporated 

 residue of a deep water stream sample indicates the 

 original water contains 1,000 ppm manganese, 2 ppm 

 silver, 100 ppm lead, 500 ppm zinc, and 20 ppm cop- 

 per. Dark material deposited in the discharge pipe 

 from the well contained a high concentration of cop- 

 per and silver. Such silver-bearing fluids might 

 deposit their metal content to form syngenetic sil- 

 ver deposits in such closed saline basins as the Salton 

 Sea. 



RESOURCES 



IDENTIFIED RESOURCES 



Listed in table 124 are our estimates of silver 

 reserves and identified resources of material nearly 

 commercial in grade and of hypothetical silver re- 

 sources (undiscovered but geologically probable 



Table 124. — Silver resources (in troy ounces in ores) in the 

 United States 



Identified Hypothetical 



Type of deposit resources^ resources^ 



Deposits in which silver is a byproduct 



Porphyry copper deposits 741,000,000 725,000,000 



Copper-zinc-lead replacements 

 and veins and copper-bear- 

 ing sandstones and shales ._ 398,000,000 1,585,000,000 



Massive sulfide deposits 8,000,000 81,000,000 



Lead-zinc replacement deposits 170,000,000 235,000,000 

 Mississippi Valley-type deposits 54,000,000 50,000,000 

 Alpine-type zinc deposits in Val- 

 ley and Ridge province 200,000 200,000 



Native copper deposits 50,000,000 500,000,000 



Gold veins and placers 5,000,000 35,000,000 



Other types 2,000,000 2,000,000 



Total 1,428,200,000 3,213,200,000 



Deposits in which silver is the main product 



Epithermal veins, lodes, and 



P|ipes 128,000,000 93,000,000 



Epithermal disseminated and 



breccia deposits 12,000,000 11,000,000 



Epithermal manganese and barite 



deposits 18,000,000 18,000,000 



Epithermal replacement deposits 



and mesothermal veins with 



lead and zinc 605,000,000 69,000,000 



Mesothermal cobalt-uraninite- 



silver deposits 1,000,000 



Sandstone silver deposits 2,000,000 10,000,000 



Total 765,000,000 202,000,000 



Total byproduct plus 

 main product silver 

 resources 2,193,000,000 3,415,000,000 



^Identified resources: Specific, identified mineral deposits that may or 

 may not be evaluated as to extent and grade, and whose contained 

 minerals may or may not be profitably recoverable with existing tech- 

 nology and economic conditions. 



^Hypothetical resources: Undiscovered mineral deposits, whether of 

 recoverable or subeconomic grade, that are geologically predictable as 

 existing in known districts. 



resources in known districts) in the United States. 

 They are subdivided by geologic type of deposit as 

 previously described. 



The total of identified resources is about 2.2 bil- 

 lion troy ounces, half again as large as the reserve of 

 1.4 billion ounces estimated in 1968 (table 125). The 

 difference between these two estimates is attributed 



Table 125. — Silver reserves,' in millions of troy ounces, of 

 United States and free world ' 



1 Reserves; Identified deposits from which minerals can be extracted 

 profitably with existing technology and under present economic condi- 

 tions. 



= Ckimpiled in 1968 by E. T. McKnight and T. H. Kiilsgaard, U.S. 

 Geological Survey, from all available published data, records of govern- 

 ment agencies, data provided by mining company personnel and by 

 minerals attaches, and annual reports of mining companies, based on 

 materials considered economically exploitable at or near 1965-68 metal 

 prices. 



partly to the discovery of the large disseminated 

 silver-copper deposits in the Precambrian Belt 

 Supergroup in northern Idaho and western Montana, 

 which at present constitute a conditional resource, 

 and partly to the increased potential resources in 

 porphyry copper deposits. We have not attempted to 

 estimate conditional resources in detail, but such 

 resources that might become recoverable with a 

 threefold to fourfold increase in the price of silver 

 are roughly estimated to be of about the same magni- 

 tude as the present reserves. 



Hypothetical resources are based on geologic evi- 

 dence for assumed continuations or repetitions of 

 deposits in similar geologic settings. 



The identified resources of byproduct silver are 

 nearly twice those of silver as the main product, and 

 the hypothetical resources of byproduct silver are 

 more than 15 times those of silver as the main prod- 

 uct. By far the greatest silver resources are in 

 porphyry copper deposits, massive sulfides, and cop- 

 per-zinc-lead veins and replacement deposits, but 

 very large identified resources are contained in the 

 silver-rich lead veins and replacements such as those 

 in the Coeur d'Alene district, Idaho ; in the lead-zinc- 

 silver replacement ores such as those at Leadville, 

 Colo. ; and in silver-bearing epithermal veins, lodes, 

 and pipes similar to those in the San Juan Mountains 

 of Colorado. Resources in the southeast Missouri 

 district are surprisingly large, because although the 

 percentage of silver in the ores is small, the ton- 

 nages of ore are immense. The small hypothetical 

 resources of silver in ores in which it is a main 



