SULFUR 



613 



that gas, undoubtedly the result of long-extended 

 contact between petroleum and anhydrite. 



SULFUR ACCUMULATIONS IN COAL 



Reactions already described also occurred in 

 swamps sufficiently stagnant to preserve as peat the 

 organic matter contained in plants and trees, at the 

 original sites of our present lignite and coal beds. 

 Anaeorbic bacteria reduced any available sulfate 

 ions and emitted hydrogen sulfide, which combined 

 with organic material or was deposited as pyrite. 

 Sulfur from this source augmented the traces of 

 sulfur originally contained in the plant matter. In 

 coal low in sulfur, the element largely is in organic 

 molecules, whereas in coal high in sulfur, the ele- 

 ment largely is in pyrite or marcasite. U.S. coals 

 contain sulfur that ranges in amount from a trace 

 to 7 percent (DeCarlo and others, 1966; Walker and 

 Hartner, 1966). 



Most swamps in which coal formed in the United 

 States lay close to sea level , so the slightest changes 

 in levels produced widespread marine transgressions 

 or regressions, either bringing in an abundant sup- 

 ply of sulfate ions in sea water or bringing in fresh 

 waters from land. Williams and Keith (1963) sug- 

 gested that swamps transgressed by seas resulted 

 in coals higher in sulfur than those which lay in 

 areas of subsequent marine regression. Because sea 

 water contains very little iron, only 2-20 parts per 

 billion, marine transgression in itself cannot produce 

 coal with high pyrite content; sources of iron from 

 hinterlands behind coal-forming swamps also seem 

 to be needed. It appears to be more than coincidental 

 that most of our high-sulfur coals, those of Penn- 

 sylvanian age in the Illinois and midcontinent fields, 



were closest geographically to the iron-formations 

 and iron deposits of Wisconsin, Michigan, and Min- 

 nesota. Conversely, coals lowest in sulfur content, 

 those in our western fields, seem to have been de- 

 posited in environments in which seas were excluded 

 by offshore bars and concurrently were at some dis- 

 tance from any terrane high in iron. 



RESOURCES 



The world's total resources of sulfur are vast, but 

 only a fraction is minable or recoverable now at 

 competitive prices (Hazleton, 1970 ; Ambrose, 1965 ; 

 Lewis, 1970 ; British Sulphur Corp., 1966 ; President's 

 Materials Policy Comm., 1952; Little, 1966). The 

 previous estimates of the world's sulfur resources 

 have differed widely for many reasons, including the 

 factors discussed in the previous section on the 

 geology of the deposits, and because of the lack of 

 data on ore deposits in the remoter parts of the 

 world. 



Estimates of identified, hypothetical, and specu- 

 lative resources of sulfur in various types of de- 

 posits in the United States, Canada, and Mexico are 

 compiled in tables 126 and 127. The compilation of 

 the data for the United States is more detailed than 

 that for Canada and Mexico. Only the more eco- 

 nomically important accumulations of sulfur else- 

 where in the world are cited in the following dis- 

 cussion. 



THE UNITED STATES 

 The identified sulfur resources of the United 

 States are divided into three categories: (1) re- 

 coverable, those accumulations that can be mined 

 or recovered at prices less than $25 per long ton, 



Table 126. — Identified', hypothetical', and speculative' sulfur resources of the United States 



[In millions of long tons: +, some resources, but amount not estimated] 



Identified resources 



Subtotal 



Hypo- Specula- 



thetical tive 



resources resources 



1. Elemental sulfur deposits in evaporites 150 40 10 200 100 150 450 



2. Hydrogen sulfide in sour natural gas 10 5 15 '185 200 



3. Organic sulfur in petroleum 10 25 220 255 '1,000 .— 1,255 



4. Pyrite deposits 10 30 60 100 20 20 140 



5. Elemental sulfur in volcanic rocks 10 20 30 + + 30 



6. Sulfur contained in metallic sulfides 20 40 40 100 100 200 400 



7. Gypsum ___ 150 7,050 7,200 1,800 — 9,000 



8. Organic sulfur in tar sands 10 10 10 



9. Organic sulfur and pyrites in coal ___ ___ 21,400 21,400 ' 19,600 __. 41,000 



10. Organic sulfur and pyrites in oil shale and 



shale rich in organic matter + + + +' 81,000 



Total 200 300 28,810 29,310 22,805 370 133,485 



^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 technology and economic conditions. 



2 Hypothetical resources: Undiscovered mineral deposits, whether of recoverable or subeconomic grade, that are geologically predictable as existing 

 in known districts. 



3 Speculative resources: Undiscovered mineral deposits, whether of recoverable or subeconomic grade, that may exist in unknown districts or in un- 

 recognized or unconventional form. 



* Includes some speculative resources. 



