ABSTRACT

The lure of gold is probably responsible for the initial settling of this corner of Montana, but as shallow high-grade deposits and placers were worked out, interest in mining waned and agriculture assumed the interests of the citizens. The polymetallic deposits at Butte are the dominant metallogenic features in the region and will probably continue to be in the foreseeable future, however the variety of metallic deposits in the southwestern part of the state present interesting subjects in terms of genetic study and mineral potential.

Pre-Mesozoic rocks have served as hosts for deposits of different commodities; iron occurs in the Precambrian crystalline rocks as does gold though not in geographic proximity. Throughout the region silver-lead-zinc deposits in Cambrian carbonates appear as a distinctive form and also appear to be confined to this host. Mississippian rocks in the area around Bannack host gold deposits that probably generated the placers on nearby Grasshopper Creek and, recent work in the Pioneer Mountains has identified porphyry-type mineralization in several Tertiary granitic plutons.

Although many geologists would relate these deposits only to tectonic and magmatic phenomema, others consider them as integral parts of particular geologic environments defined on the basis of tectonism, sedimentation, age, and mode of occurrence. As the body of knowledge concerning mineral deposits evolves, so will the potential of different deposits, including some of those in southwestern Montana.