Abstract

The Marysvale volcanic field includes four important mining districts that have produced gold, uranium, silver, zinc, lead, copper, antimony, alunite, and mercury over the past 120 years: Mt. Baldy–Ohio, Gold Mountain (Kimberly), Marysvale (Central), and Antimony (Coyote). These districts represent the most productive mining districts within the volcanic field.

The first mineral discovery in the volcanic field was placer gold along Pine Creek in 1868. After word leaked out of the discovery, the rush began in earnest and many more discoveries soon followed: polymetallic veins in the late 1860s, polymetallic replacement deposits in the late 1870s, and antimony replacement and gold-silver quartz vein deposits in the early 1880s. Later discoveries include alunite veins and replacement deposits around 1916 and uranium veins in 1949.

Mineralization began 23 million years ago with the formation of gold-silver-quartz-carbonate veins in the Gold Mountain (Kimberly) district and replacement alunite deposits in the Marysvale (Central) district. These deposits were created by the alteration of volcanic rock from the effects of multiple magma intrusions. The second round of mineralization occurred during two periods, 19 to 18 million years ago and about 14 million years ago, with the creation of uranium veins in the Marysvale (Central) district and alunite veins, lead-silver-zinc veins, and lead-zinc-silver-gold-copper bedded replacement deposits in the Mt. Baldy–Ohio district. Hydrothermal fluids associated with magma bodies produced these forms of mineralization. The antimony replacement deposits of the Antimony (Coyote) district formed probably during one of these episodes of mineralization, but more work must be done to determine the age.