The Montana City mining district is, for the most part, the Jefferson County extension of the Helena mining district. Its history is closely intertwined with the Helena District and is largely overshadowed. The Big Indian mine which was the most significant producer is commonly included in the descriptions of the Helena mining district. The foothills southwest of the city of Helena consist of a large number of small mines and prospects. One of the more significant was the Bonanza Chief which had a 20-stamp mill for working the ores. However, by 1890 the mines of Montana City had been mined out (Pardee and Schrader 1933; Byrne 1899; Swallow 1891).
The topography is hilly and the elevation is between 4,100 in Prickly Pear Creek to 6,000 ft in the upper drainages of Holmes and Clark Gulches. The bedrock is composed of Precambrian to recent sedimentary rock and the quartz monzonite of the Boulder batholith. Erosional remnants of rhyolite and dacite flows may be found on top of the sediments. Several rhyolite volcanic plugs are also present near the Montana City railroad siding. Silver-lead and gold-silver deposits occur in two groups. The older group of deposits was formed after the intrusion of the Boulder batholith and before the eruption of the rhyolitic and dacitic lavas and are probably of late Cretaceous or early Eocene age. The younger group was formed after the extrusion of the volcanic rocks and are probably post-Miocene. The ores in this region are free milling down to permanent water (Roby 1960; Swallow 1891).
After the Big Indian closed down in 1904, the district was worked only sporadically and never with great activity. Only 505 tons of ore were produced, primarily in 1905, 1934, 1936, 1948 and 1952. The net value for the ore was only $6,909.
BOUNDARIES OF THE DISTRICT
Roby (1960) defines the Montana City district as embracing (Figure 1):
that part of Jefferson County drained by Clark and Holmes Gulch. The heart of the district lies approximately three miles southeast of East Helena. The northern and western boundaries of the district are the county line; the southern boundary, the divide between Clark Gulch and Jackson Creek; and the eastern boundary, the divide between Prickley Pear and McClellan Creeks. The district lies in the northern half of T9N, R3W and is bisected by the Butte-Helena highway, Prickly Pear Creek, and the Northern Pacific Railway.
HISTORIES OF SELECTED MINES
The few mines in the Montana City district were minimal producers and there was little activity other than the Big Indian.
The Big Indian mine is located four miles south of Helena in Jefferson County. The two claims, the Alabama and the Gold Hill were located in 1875. The mine was developed from two open cuts; 200 x 300 ft and 75 x 100 ft. The deepest reached 75 ft. Ore was drawn from the cuts through a glory hole and trammed through an adit to the mill. Initially this was a 10 stamp mill, which was reported to have produced $110,000 from $5 per ton gold ore. This mill was replaced by an electric 60-stamp mill in 1902. In 1904 the Big Indian mine was the biggest producer in Jefferson County. Between 1902 and 1904 the mine produced 14,808 tons of ore which yielded 4,456 ounces of gold. In total the mine made $60,000 from ore valued at $5 per ton. The mine apparently shut down shortly after (Knopf 1913; Pardee and Schrader 1933; Roby 1960).
Little is known about the Overland Mine. In 1898 the operation employed 10 men. In that year the shaft had been lowered to 400 ft level and a steam hoist installed (Byrne 1899).
Byrne, John and Frank Hunter
Tenth Annual Report of the the Inspector of Mines of the State of Montana for the Year ending November 30th, 1898
. Independent Publishing Company, Helena.
1913 "Ore Deposits of the Helena Mining Region, Montana",
US Geological Survey, Bulletin 527
, Vol. 1, p. 92.
Roby, R. N., W. C. Ackerman, F. B. Fulkerson and F. A. Crowley
Mines and Mineral Deposits (Except Fuels), Jefferson County
, Montana Bureau of Mines and Geology Bulletin 16, Montana School of Mines, Butte, Montana.
Swallow, G. C., J. B. Trevarthen and Jacob Oliver
Reports of Inspectors of Mines, State of Montana, year ending November 30th, 1890
. Journal Publishing Company, Helena.