Why? This is all I need to know:

"... (James Briscoe) concluded that much earlier regional geologic work had reached erroneous conclusions and that Tombstone was a large and ancient (72 million years before the present – or Laramide in age) volcanic structure – a caldera.

 He brought this to the attention of the US Geological Survey caldera experts, who after study concluded that Briscoe was correct. 

Subsequently, more than seventeen calderas of various ages have been identified in Arizona by the US Geological survey, the Arizona Geological Survey and others. Such calderas of Laramide age are all associated with porphyry alteration and copper  and  associated  mineralization;  many  of  these  have  become  very  large  copper  mines.  

Studies  by  Mr.  Briscoe  over  the  years,  and  more  recently  using advanced technology, have indicated that alteration associated mineralization at Tombstone is much more extensive than originally thought. This alteration lies largely under cover and is indicated by geochemistry, geophysics and projection of known geology into covered areas."(From the link you provided).

If Briscoe caught what many before him failed to realize and was proven right by other experts, I have faith that he will be right about the resources in the ground at that location and will bring forth fruit from his labor. And what I really like about the statement was "...much more extensive than originally thought..."