MOLYBDENUM 



429 



delineated completely and the possibility therefore 

 exists that additional reserves may be discovered 

 that will at least in part replace reserves currently 

 being mined. Detailed descriptions of the geology 

 of the Climax area and of the deposit were given 

 by Vanderwilt and King (1955) and Wallace, Baker, 

 Johnson, and MacKenzie (1960). 



URAD-HENDERSON, COLORADO 



The Urad-Henderson porphyry molybdenum de- 

 posit near Empire, about 50 miles west of Denver, 

 is a prime example of the discovery and develop- 

 ment of a huge deposit as a result of careful and 

 exhaustive geologic study and the use of modern 

 exploration techniques. The Urad ore body, known 

 for many years, was first developed on high-grade 

 quartz-pyrite-molybdenite fissures and fracture 

 zones, from which about half a million pounds of 

 molybdenum was produced during the early part 

 of the century and in the 1940's. The Urad molyb- 

 denite ore body is localized in a zone of fractured 

 and altered granite around the southern margin of 

 a composite granite porphyry stock (Carpenter, 

 1960, p. 321) of middle Tertiary age. Molybdenite 

 also occurs in veinlets and as disseminations in the 

 altered and fractured granite between the fracture 

 zones and fissures, forming a massive porphyry type 

 body of many millions of tons of molybdenite ore 

 containing from 0.3 to 0.5 percent molybdenite. 



About 2,000 feet below the Urad ore body, and 

 separated from it by altered rocks that contain only 

 traces of molybdenite, is the Henderson molybdenite 

 ore body. According to the Climax Molybdenum 

 Co., reserves in the Henderson ore body amount to 

 over 300 million tons at a grade of 0.49 percent 

 molybdenite. Very few geological data have been 

 published on the Henderson deposit, but it is a 

 typical porphyry or stockwork deposit. The mine is 

 expected to be brought into production late in the 

 1970's, with a planned milling capacity of 50,000 

 tons per day. 



QUESTA, NEW MEXICO 



Molybdenite at Questa occurs in massive quartz 

 veins, in a stockwork of discontinuous veinlets, and 

 as fine disseminated flakes in a hydrothermally 

 altered and fractured zone several thousand feet 

 wide. The quartz-molybdenite veins exploited dur- 

 ing the earlier development period, as well as the 

 stockwork molybdenite, lie along the contact of a 

 composite intrusive body of granite and the over- 

 lying andesitic volcanic rocks. Molybdenite is the 

 only mineral of economic importance in the deposit 



although rhodochrosite, fluorite, and a little chal- 

 copyrite are present. The grade of the ore body is 

 low, averaging only about 0.1 percent molybdenum. 

 According to company reports, more than a quarter 

 of a billion tons of ore has been developed at the 

 property. Despite its low grade, the Questa deposit 

 promises to be one of the major domestic sources 

 of molybdenum for many years. 



CONTACT-METAMORPHIC DEPOSITS 



In the molybdenum-bearing contact-metamorphic 

 deposits (tactites and skarns), molybdenite is com- 

 monly associated with scheelite, bismuthinite, or 

 copper sulfides in zones of silicated limestone near 

 granitic intrusive rocks. Molybdenite also occurs 

 alone in contact-metamorphic deposits. The Pine 

 Creek mine in California is an example of the con- 

 tact type of deposit from which molybdenum and 

 tungsten have been recovered as coproducts since 

 1939 (Bateman, 1956). 



Significant amounts of molybdenum also occur in 

 contact-metamorphic deposits in the northeastern 

 Caucasus of the U.S.S.R., in China, and in Morocco 

 (Kruschov, 1959). The molybdenite deposits of the 

 Knaben mine in Norway are in quartz-rich amphi- 

 bolitic gneisses of probable sedimentary origin and 

 may be included in this category. The ore ranges 

 from 0.1 to 0.2 percent molybdenite, and although 

 production from the deposit has been persistent for 

 many years, it has been relatively small. 



QUARTZ VEINS 



Quartz veins containing molybdenite are widely 

 distributed throughout the world. Early production 

 about 1900 was made from the relatively high grade 

 deposits of this type. A prime example of vein type 

 bodies is found at the Questa molybdenite deposit 

 at Red River, N. Mex., where small tonnages of 

 molybdenite were produced between the 1920's and 

 the mid-1950's from high-grade quartz-pyrite mol- 

 lybdenite gash veins along the contact between a 

 sodic granite and overlying andesitic volcanic rocks. 

 The molybdenite content of the veins ranged from 

 1 to 30 percent molybdenite. Not until the late 

 1950's was it discovered that the veins were asso- 

 ciated with mineralized rocks having the character- 

 istics and potential for a large low-grade porphyry- 

 type molybdenite ore body associated with a com- 

 posite granite stock. 



PEGMATITES 



Commonly, pegmatite bodies and aplite dikes con- 

 tain molybdenite among many other metallic and 



