I arrived at the University of Arizona in 1970, and Richard Graham was a student in the first undergraduate structural geology course I taught. He was already an expert on mineralization in Bisbee, and some specimens he has collected reside in the Smithsonian. Dick gave me this specimen at the end of the semester. Nice gift! In ~1972 I had a chance to go underground at Bisbee. I was lucky, for shortly thereafter the underground workings were closed, and the efforts of mining exclusively were open-pit excavation and leaching. I like this rock for a lot of reasons, including symbolizing the close connection between structural geology and ore deposits.
Age & Formation
The limestone host is Paleozoic rock. Mineralization took place in the Jurassic, ~170 Ma.