28 April 2015

Epidotized tuff, Tucson Mountains, Arizona

Posted by Callan Bentley

I was in Tucson this past weekend for a book project meeting, and my editor and coauthor and I took a hike on Sunday morning in the Tucson Mountains to Wasson Peak. Not far from the summit, we saw an epidotized tuff, where the fiamme and pumice blobs had undergone reactions to produce pods of epidote, giving the rock a look like a sick dalmatian:


This is a cool rock (in my mind) because it tells a story with two chapters –

1) explosive eruption of a volcano, and

2) later wet metamorphism/alteration.

There was an adit (mine opening) in heavily epidotized rocks a few meters away – probably a fault or other vein of mineralization that had been tapped and explored a bit, but was clearly never a ‘big time’ operation. We did see a little bit of malachite, too – so presumably it would have been copper the miners were after.