In the _United States_ are a very large number of small molybdenum deposits, scattered over the western states from Washington to Arizona and from Colorado to California. There are two common minerals--molybdenite, or molybdenum sulphide, and wulfenite, or lead molybdate. Generally speaking, molybdenite is found in the northern states, and wulfenite in the southern states, but this rule is not without exception. In Arizona and New Mexico, the principal mineral is wulfenite, but there are some fairly large deposits of molybdenite, probably the best being at the Leviathan mines, in Copper Canyon, Mohave County, Arizona. This is the only molybdenite deposit that is being worked in New Mexico or Arizona. It is in the Cedar Valley mining district about three miles southeast of Copperville and about 25 miles east of Yucca. This ore carries a good deal of copper, as well as small traces of gold and silver. Some analyses have shown 2 or 3 per cent. MoS₂ and 1¹⁄₂ to 2 per cent. copper with 0.02 ounce of gold and 1 to 4 ounces of silver per ton. The percentage of molybdenite is undoubtedly above the average, which does not exceed 1 per cent. The country rock is medium-grained gray granite, consisting of quartz, feldspar, biotite, muscovite and small amounts of other accessory minerals, such as zircon and apatite. The company has erected a mill and has succeeded in making a satisfactory separation of the copper from the molybdenite. The largest possibilities in Arizona and New Mexico are in mining wulfenite. This mineral is widely scattered over these two states, especially Arizona, and is, to a great extent, associated with vanadinite. One of the greatest difficulties in concentrating wulfenite has been the separation from vanadinite. The Bureau of Mines has worked on this problem for some time with partial success.