Microprobe analyses of sericite, chlorite, and epidote from Jerome, Arizona

Volcanic rocks in the vicinity of the massive sulfide deposits at the United Verde mine, Jerome, Ariz., have been modified in several periods of hydrothermal alteration and greenschist metamorphism. Chlorite, 2M, mica (sericite), and epidote are characteristic alteration products. Microprobe analyses for sericite, chlorite, and epidote are recalculated to structural formulas by the method employing oxygen anion equivalents. The sericite has the general composition of muscovite, but is moderately phengitic, and two samples have 6-12 percent paragonite in solid solution. Most of the chlorite is ripidolite with approximately one-third of the tetrahedral sites filled by aluminum; octahedral aluminum slightly exceeds tetrahedral. Fe:Fe+Mg+Mn ratios range from 0.34 to 0.66; low values are associated with sulfide minerals; higher values occur in a sample peripheral to the massive sulfide deposit. The epidote is a solid solution of 70 percent epidote, 30 percent clinozoisite.