Cripple Creek has produced almost half of all the state’s gold and silver. The ores are located in or at the edge of a large mass of middle Tertiary volcanic rocks which form an elliptical basin or _caldera_ several miles across. The caldera, surrounded by Precambrian gneiss and granite of the Pikes Peak massif, was probably formed by collapse of a volcanic center that had erupted through the older rock. The collapse shattered the rocks around the basin margin, and subsequent volcanic activity introduced mineral-rich solutions into the many faults and fissures produced by the collapse. Tellurides of gold, silver, and copper, as well as pyrite, sphalerite, galena, tetrahedrite, and other minerals, are characteristic. Climax [Illustration: At Climax, the ore occurs scattered through the intrusive Climax Granite Porphyry and the intruded Idaho Springs Formation. Visitors can tour the surface workings during the summer months.] Tertiary dikes Shell of Climax stock Core of Climax stock Ore zone Precambrian granite Fault Dykes Molybdenum now ranks as the number one metal mined in Colorado. Over $105,000,000 of “moly” was mined here during 1969, almost all of it from the Climax Mine, the world’s largest single source of this metal. The Climax deposit is located high on the west slope of Ten Mile Range in central Colorado, about 100 miles southwest of Denver. It is in the central part of the Colorado mineral belt, near the Mosquito Fault, a prominent structural feature which extends about sixty miles along the north-south trend of the mountains. Rocks on both sides of this fault are intruded by Tertiary granite dikes, sills, and stocks. The Climax Mine is in a stock just east of the fault, near the axis of a broad anticline in Precambrian metamorphic rocks. Ore minerals at Climax are molybdenite, huebnerite, and cassiterite; pyrite is recovered also for the manufacture of sulfuric acid. The ore is very low in metal content, containing only one-third of a percent of molybdenum, 0.005% tungsten trioxide, and 0.0001% tin. The great size of the ore body and efficient recovery by modern methods make Climax a profitable mine, however. Production has risen each year since the mine began operation. Urad Mine near Berthoud Pass is a newly developed near-surface molybdenum mine similar to Climax. Nearby at the Henderson Mine the ore body is more than half a mile below the surface of the ground. RADIUM, URANIUM, AND VANADIUM