Central Colorado's Climax Mine is the largest molybdenum mine on Earth.  It's located in the Southern Rocky Mountains, near the northern end of the Rio Grande Rift, a large, Neogene-aged rift valley on the eastern side of the Colorado Plateau.


Molybdenum (Mo - "moly") mineralization at the Climax Mine occurred as a series of igneous bodies intruded through Proterozoic basement rocks (gneisses and granites).  Seven intrusive bodies make up the composite Climax Stock (Oligocene, 24-33 m.y.).  Three of them produced significant moly mineralization in the form of molybdenite-quartz veins and disseminated molybdenite (MoS2 - molybdenum sulfide).


The rocks of the Climax Stock are alkalic felsic intrusives.  They range from porphyritic alkalic rhyolites to alkalic aplites to porphyritic alkalic granites.  In map view, the igneous bodies of the Climax Stock form a roughly circular structure.  In cross-section view, each intrusion has an inverted bowl shape.


Published studies on the origin of the Climax Molybdenum Deposit and other Climax-type moly deposits have concluded that they form principally in incipient extensional tectonic settings well inland from shallow-angle subduction zones that have recently ceased.


The 1st sample shown below is a large cut & polished slab of molybdenum ore from the Climax Mine.  Note that the thicker mineralized veins tend to have quartz (light gray) making up most of the vein and molybdenite (dark gray) lining the walls of the vein.  Compare that with the thinner veins which are principally composed of ~just light gray quartz or ~just dark gray molybdenite (such molybdenite-dominated thin veins are referred to as "moly paint").


The 2nd sample is a closeup of a molybdenite-quartz vein.


Climax Mine molybdenum ore (large cut & polished slab) - multiple molybdenite-quartz veins intruding porphyritic alkalic granite (Climax Mine, Old Glory Hole, Fremont Pass, Lake County, central Colorado, USA).

Dark gray = molybdenite (MoS2)

Light gray = quartz (SiO2)

Mottled yellowish = porphyritic alkalic granite host rock (Climax Stock, Oligocene)

CSM # 12334, Colorado School of Mines Geology Museum, Golden, Colorado, USA



Climax Mine molybdenum ore (4.6 cm across at its widest) - molybdenite-quartz vein from the Climax Mine, Lake County, central Colorado, USA).

Dark silvery gray = molybdenite (MoS2).




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