Standard chemical tests and spectroscopic analyses of altered Tertiary lavas that occur above blind ore bodies in the East Tintic district, Utah, have failed to show any evidence of the mineralization in the underlying dolomites. A new technique involving dithizone was used in the field to test ammonium acetate extracts of crushed samples of the lava for soluble heavy metals, with significant results. Concentrations of heavy metals, believed to be chiefly zinc, with some lead and rarely copper (?), were found in pyritized rhyolite above and up-rake from known blind ore bodies, and were lacking in similarly altered rhyolite underlain by barren rocks. An incompletely prospected area of pyritic alteration shows a definite pattern of positive tests and seems worthy of further exploration. The theory and practice of the dithizone method as used in the field is described briefly.