The town of Boulder began as a way-station on the road between Virginia City and Fort Benton. The first settlers arrived in July of 1862 when the prospectors left Gold Creek and began placering the Boulder River. The town incorporated in February of 1865 and, at first, was the center of active placering. The town continued to serve as a hub of transportation and trade for several mining districts, but agriculture overshadowed placering in the immediate area. The Boulder mining district was basically a placer mining district along the Boulder River (Wolle 1963).

The district is underlain by the quartz monzonite of the Boulder batholith which is overlain by Tertiary dacite and late Cretaceous andesite. The andesite and associated monzonite are cut by dikes of dacite and rhyolite. Ore deposits include small placers and lode deposits of late Cretaceous and lode deposits of Tertiary age. The older deposits contain values in silver, lead and zinc while the younger deposits contain values in gold and silver. The lode deposits are in the surrounding mountains and technically in other mining districts (Sahinen 1935; Roby et al. 1960).

Gold was first found in the Boulder area around 1870. Although the Boulder placers produced considerable gold in the early bonanza days, little production has occurred since 1904. In 1939 a scraper and dry washer treated 7,350 cubic yards of gravel for a return of 63 fine ounces of gold. The gold was probably deposited directly in the river by the stream's erosive passage over gold bearing veins (Lyden 1948; Roby et al. 1960).

Records for the initial production are not available. However, from 1902 to 1957 the district produced 23,840 tons of ore which yielded 3,124 ounces of gold; 353,712 ounces of silver; 368,337 pounds of copper; 1,946,344 pounds of lead; and 411,281 pounds of zinc. The aggregate value of the metals was $325,000 from 1902 to 1938 and $228,000 from 1938 to 1957 (Roby et al. 1960).


Sahinen (1935) places the Boulder district as one of several sub-districts within the greater Basin district. Lyden (1948) discusses the Boulder placer district as being along the whole of the Boulder River from 15 miles north of Butte to the southeast where it empties into the Jefferson River. However, most of the placer activity was concentrated between Boulder and Basin.

Roby et al. (1960) places the Boulder district directly south of the Amazon district and east of the Basin-Cataract district, essentially the area adjacent to the town of Boulder and including the few small lode mines south of town in the Little Boulder River area. The district is on the west side of the Boulder valley. Figure 1 shows the district as defined by Roby et al. (1960).


There are no lode mines of note in the Boulder district which was focused on placer operations.


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