430 



UNITED STATES MINERAL RESOURCES 



nonmetallic constituents. The molybdenite is gen- 

 erally coarsely crystalline, occurring as rosettes or 

 thick books and aggregates of flakes, which are 

 erratically distributed in the host rocks. Although 

 much specimen material of excellent quality can be 

 obtained from this type of deposit, few deposits 

 have been of economic interest owing to the char- 

 acteristically small tonnage available and the erratic 

 distribution of molybdenite. Notable among the peg- 

 matite-type deposits that have yielded significant 

 quantities of erratically disseminated molybdenum 

 are those at Val d'Or and Preissac, in eastern Que- 

 bec, where molybdenite is associated with bismuth 

 in pegmatite bodies and greisen zones (Yokes, 

 1963). 



BEDDED DEPOSITS IN SEDIMENTARY ROCKS 



Although molybdenum is concentrated in coals, 

 shales, and phosphorites, no molybdenum of eco- 

 nomic grade has been found in these rocks. Only in 

 certain lignitic sandstone beds of southwestern 

 North Dakota, northwestern South Dakota, and 

 eastern Montana, and in some arkosic sandstone 

 beds in the badlands of southwestern South Dakota 

 and northeastern Utah, has the molybdenum con- 

 tent approached ore grade (0.1 to 0.2 percent Mo) 

 in deposits thick enough to be minable. 



In the United States, molybdenum is associated 

 in significant amounts with some of the bedded 

 sandstone uranium deposits in Arizona, Wyoming, 

 South Dakota, New Mexico, and Utah, and in the 

 Gulf Coast region of Texas. Similar occurrences un- 

 doubtedly exist in other parts of the world, but 

 published data are not readily available on these 

 deposits. The molybdenum is in the minerals jor- 

 disite and ilsemannite and is present in amounts 

 ranging from a few parts per million to more than 

 0.5 percent. It is irregularly distributed with respect 

 to the uranium ore bodies, commonly occurring 

 along or some distance from the outer margins of 

 the ore bodies rather than within them. Ordinarily 

 the small amount of molybdenum present in this 

 type of ore deposit is detrimental because the mo- 

 lybdenum interferes with the recovery of uranium 

 and must be segregated out of the circuits during 

 milling processes. However, where the uranium de- 

 posits are of sufficient size and the molybdenum 

 content is significant, a valuable byproduct may 

 exist. According to the U.S. Bureau of Mines, 

 molybdenum has been recovered from composites 

 of uranium ores and ash residues of some uranium- 

 bearing lignites from South Dakota and New 

 Mexico. 



RESOURCES 



IDENTIFIED AND HYPOTHETICAL RESOURCES 



About half the world's identified resources of 

 molybdenum are in the United States, and of these 

 resources, about 75 percent occur in deposits where 

 molybdenum is the principal metal sought. The other 

 half of the world's identified resources are dis- 

 tributed among more than 30 countries around the 

 world. These resources occur as large bodies of 

 fairly uniformly mineralized rock containing more 

 than 500 ppm (parts per million) (0.05 percent) of 

 molybdenum if no other valuable metal is present 

 in significant amounts, or more than 50 ppm (0.005 

 percent) of molybdenum if molybdenum is not the 

 primary metal sought. 



Most of the identified resources of molybdenum 

 are in the disseminated or porphyry-type deposits 

 of the Colorado Mineral Belt, the Sangre de Cristo 

 Range in New Mexico, and the Basin and Range 

 province of the southwestern United States; the 

 Interior Belt of British Columbia, Canada; the An- 

 dean Cordillera of Peru and Chile; and the Ural 

 and Altai Mountains of the U.S.S.R. (table 85). 

 Many of these deposits have been explored only to 

 a minimal extent, and the metal contents appear to 

 be lower than current ore grades — molybdenum in 

 porphyry molybdenum deposits in the order of 

 0.01 to 0.1 percent and copper in porphyry copper- 

 molybdenum deposits in the order of 0.1 to 0.2 

 percent — too low to be profitably mined under 

 present conditions. 



The magnitude of the identified resources of mo- 

 lybdenum can only be partly estimated directly from 

 published data and statistics, because of the large 

 fraction that is associated with copper resources. 

 Clearly a sizable part of the discussion of the re- 

 sources of molybdenum must therefore be based on 

 geologic and geochemical information. 



Large quantities of molybdenum probably are 

 still hidden in areas of known deposits, as exten- 

 sions of mining districts or mineral belts, and occur 

 in deposits similar in geologic character and grade 

 to those already known. Such hypothetical resources 

 are predicted on the basis of known distributions 

 of geologic environments favorable for molybdenum 

 deposits and on the basis of our current understand- 

 ing of the processes of deposition of molybdenum 

 deposits. The bulk of hypothetical resources thus 

 estimated amounts to about 1 billion tons of molyb- 

 denum, a large part of which appears to be equally 

 divided between the United States and the U.S.S.R. 



Table 85 is a summary of the estimated world 

 resources of molybdenum. 



