MOLYBDENUM 



431 



Table 85. — Estimated magnitude, in millions of pounds, 

 of world resources of m,olybdenum 



* Identified resources are specific, identified mineral deposits that 

 may or may not be evaluated as to extent and grade, and whose_ con- 

 tained minerals may or may not be profitably recoverable with existing 

 technology and economic conditions. 



2 Hypothetical resources are undiscovered mineral deposits, whether of 

 recoverable or subeconomic grade, that are geologically predictable as 

 existing in known districts. 



' Equal to 31,660,000 tons. 



* Equal to 1.1 billion tons. 



SPECULATIVE RESOURCES 



Speculation as to worldwide distribution and mag- 

 nitude of molybdenum resources necessarily must 

 be based on geologic relationships of the deposits 

 that are best documented and most clearly under- 

 stood. Domestic deposits offer the best information 

 in this regard ; consequently models based largely on 

 occurrences in the United States and the Western 

 Hemisphere as described under "Porphyry Deposits" 

 are used to infer speculative resources. 



World molybdenum resources are likely to be di- 

 vided somewhat equally between deposits that con- 

 tain molybdenum as the primary metal and those 

 in which molybdenum is expected to be a byproduct 

 or coproduct. Porphyry-molybdenum and porphyry- 

 copper deposits are expected to contain by far the 

 bulk of molybdenum resources. 



Porphyry-molybdenum or porphyry-copper depos- 

 its are individual mineral deposits associated with 

 stocklike intrusives, breccia structures, and faults. 

 Distribution of this type of deposit worldwide, 

 therefore, should be related to the distribution of 

 certain major geologic features: 



1. The deposits are found in belts of Cretaceous- 



Tertiary tectonic activity that were disturbed 

 by subsequent igneous activity (Eimon, 1970). 

 They occur along the cordillera of North and 

 South America, the Alpide belt (Sillitoe, 

 1972), the Iranian orogenic belt, the south 

 Pacific Arc, and in the Ural and Altai Moun- 

 tains of the U.S.S.R. 



2. They are associated mostly with intrusive ac- 



tivity that ranges in age from Triassic to 

 mid-Tertiary (Sillitoe, 1972). 



3. They occur in intrusive rocks of intermediate to 



acid composition; porphyry molybdenum de- 

 posits tend to be associated with granitic in- 

 trusives and porphyry copper-molybdenum de- 

 posits with instrusives of intermediate com- 

 position. 



4. The molybdenum deposits commonly occur in 



clusters or groups of 5 to 20 miles in radius 

 (King, 1970). 



5. Porphyry deposits are commonly found in areas 



of gravity and magnetic lows; porphyry mo- 

 lybdenum deposits related to Tertiary silicic 

 intrusives tend to occur in regional gravity 

 lows. 



6. Molybdenum deposits are commonly alined in 



major structural belts and at intersections of 

 structural belts (Noble, 1970). 



7. The intrusive rocks and commonly the intruded 



rocks show evidence of local and regional f rac- 



