Description:
The Big Horn Mountains are a geologically complex range that extends
over 500 square km in west-central Arizona. Three major lithologic
terranes outcrop: (1) Proterozoic amphibolite, phyllite, schists,
gneiss, and granite; (2) Mesozoic monzonite to diorite intrusives; and
(3) Cenozoic mafic to silicic volcanic rocks and clastic rocks. The
entire area is in the upper plate of a detachment fault and,
consequently, contains many low- to high-angle normal faults.
Each lithologic terrane has its associated mineral occurrences. The
Big Horn district is exclusively hosted in the pre-Tertiary terrane.
Most of its mineral occurrences are spatially related to the Late
Cretaceous intrusive rocks. One occurrence, the Pump Mine, may be a
metamorphic secretion deposit, and therefore, would be middle
Proterozoic.