Economic Geology of the Greater Helena Area: Helena to Montana Tunnels Mine, Lump Gulch, Grizzly Gulch, Fort Harrison and Marysville

Route

Start point

Helena, MT

End point

Mount Belmont, MT

Roads

I-15, county roads north and south of Helena

Total distance

78.6 miles

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Geology

Summary

The Helena area has a long history of base- and precious-metal production from the Corbin-Wickes District on the south to the Marysville gold district northwest of the Capitol City. Gold has also been mined from the placers along Last Change Gulch now within the city limits. This field trip examinations the volcanic-hosted ore body at the recently opened Montana Tunnels mine south of Helena. From this mine, participants will travel north to Helena through an area of numerous inactive base- and precious-metals mines at the northern margin of the Boulder batholith and then onto the Marysville district northwest of Helena where the gold deposits are related to the Marysville stock.

Key Lithologic Features

• Proterozoic metasedimentary rocks
• Paleozoic sedimentary rocks
• Tertiary rhyolite
• pyroclastic flows
• breccia plug
• perlitic obsidian chill zone
• Meagher Formation limestone
• Clancy granodiorite contact
• metalliferous quartz
• alluvial deposits of Prickly Pear Creek

Structures

• Bald Butte fault
• Lewis and Clark line (fault zone)

Landforms

Other Features

• Kaiser Cement's plant
• Quarries near Prickly Pear Creek
• Meadow mine
• Lump Gulch mine
• Alhambra Hot Springs
• Carbonate Chief mine
• Bell mine
• Pegasus Gold's Montana Tunnels mine
• Wickes mining district
• Washington mine
• Bluebird mine
• Minah mine
• Liverpool/Washington mines
• Pretty Girl placer mine

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Reference

Herrin, J., Walker, G., Baltzer, C.W., and Ratcliff, M., 1987, Road Log No. 1, Economic geology of the greater Helena area: Helena to Montana Tunnels Mine, Lump Gulch, Grizzly Gulch, Fort Harrison and Marysville, in Berg, R.B., and Breuniger, R., eds., Guidebook of the Helena Area, West-Central Montana: Guidebook for the 12th Annual Field Conference , Montana Bureau of Mines and Geology Special Publication 95, p. 1-12.

Availability

Order from the Tobacco Root Geological Society c/o the Montana Bureau of Mines and Geology. Go to the TRGS publications page for ordering information.