By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Lewis and Clark County produced between 4 and 5 million ounces of gold through 1959 and is one of three counties in Montana to exceed an output of 1 million ounces. Within the county two districts - Helena and Marysville - have each produced in excess of 1 million ounces, and six others have produced in excess of 100,000 ounces. The gold yield is roughly divided equally between placer and lode deposits.
The first mineral deposits discovered and mined in the county, either in 1863 or 1864, were the gold-bearing gravels along Iowa Gulch in the northern part of the Scratchgravel Hills, about 4 miles northwest of Helena (Pardee and Schrader, 1933, p. 36). The famous Last Chance Gulch placers on the present site of Helena were discovered shortly afterwards in the summer of 1864, and rich gold lodes were discovered a few miles south of Helena in September of the same year (Knopf, 1913, p. 15).
Most placer deposits and some lode deposits were quickly exhausted, and mining languished by 1900. However, after the price of gold was raised to $35 per ounce in 1934, both placer and lode districts were reactivated and gold mining again became a major industry.
The placers of the Helena-Last Chance district have been the most productive in the county, but other highly productive placer deposits occur chiefly in the western part of the county and, from south to north, include the following (Lyden, 1948, p. 54-74) : Tenmile Creek and its tributaries in the Rimini district, Sevenmile Creek in the Scratch-gravel district, Silver Creek in the Marysville district, Virginia Creek in the Stemple district, McClellan Creek west of Stemple, and Lincoln Gulch in the Lincoln district. Rich placers were also exploited in the southeastern part of the county east of Helena in the York district on the western slope of the Belt Mountains along the Missouri River, York Gulch, and Oregon Gulch (Pardee and Schrader, 1933, p. 120-122, 176-182; Lyden, 1948, p. 68-74).
The chief lode deposits are in and near the Boulder batholith and its satellite stocks and in the roof rocks (Pardee and Schrader, 1933, pi. 1). The Boulder batholith, of Late Cretaceous or early Tertiary age, is 60 miles long from north to south and averages 18 miles in width. The Marysville district has been the largest producer of lode gold in the county, but sizable production has also come from the Helena, Rimini, Stemple, Dry Gulch, and Scratchgravel districts.
Page 1 of 6