Do the platinum group metals exist in rocks in Arizona?
The answer to this question is a qualified, “Yes.” Tiny or trace amounts of the platinum group elements are distributed throughout the earth’s crust. The average is reported to be about 0.00016 troy ounces per ton for platinum and about twice that for palladium. The others are about five times as rare as platinum. The platinum group elements are found mostly in geologic association with mafic and ultramafic rocks, such as peridotite, norite, and dunite. They may also be found in placer deposits derived from such rocks, if the rocks carried the minerals. Ultramafic rocks are very uncommon in Arizona. Thus, it is probable that the average platinum group element content of rocks in Arizona would be less than the crustal average for the world. However, the geologic history of Arizona encompasses a few billion years and the possibility of the past occurrence of such rocks containing platinum elements, does exist. If such rocks have been destroyed through weathering or alteration, it is conc
