Lawrence County South Dakota Gold Production |
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DEADWOOD-TWO BIT DISTRICT
The Deadwood-Two Bit district is near the town of Deadwood in east-central Lawrence County. The district includes mining camps on Deadwood, Two Bit, Strawberry, and Elk Creeks. Both placers and lodes have been productive; however, most of the gold has come from placers in Deadwood Gulch. The total minimum gold output through 1959 was about 284,000 ounces.
The Deadwood Gulch placers, discovered in 1875, yielded an estimated $4 million (193,500 ounces) in gold by 1880. Stimulated by the rich placer finds, prospectors combed the area and quickly found a variety of other gold-bearing deposits, including placerlike deposits in the basal conglomerate of the Cambrian Deadwood Formation.
The first quartz mill brought into the Black Hills reached Deadwood in September 1876 and was erected near Gayville in Deadwood Gulch (Connolly and O'Harra, 1929, p. 138). It treated conglomerate ore from the Hidden Treasure mine in Spring Gulch and before the close of the year had produced $20,000 in gold. Additional mills were built, and by the early part of 1878, milling of conglomerate ore was at its height with 20 mills and 500 stamps in operation. After 1878 the richer deposits gradually became exhausted, and by 1881 work upon them had practically ceased. The amount of gold recovered is not known (Allsman, 1940, p. 22-23; Irving and others, 1904, p. 98-111).
In 1878 gold ore was discovered in the Precam-brian rocks in the Cloverleaf mine in the southeastern part of the district near Roubaix on Elk Creek about 8 miles southeast of Deadwood. It was worked for only about 10 years, but during this period $400,000 in gold was extracted. Periodic operations continued in later years, but the mine was closed in 1937. Total production of the mine was about 43,885 ounces of gold and about 300 ounces of silver (Allsman, 1940, p. 14, 15).
The earliest record of production from replacement deposits in the Deadwood Formation is in 1892, when the Mascot mine, about 3y% miles east of Deadwood, began shipping ore (Allsman, 1940, p. 50). The discovery of veins in the Tertiary eruptive rocks in Strawberry Gulch, about 3 to 4 miles southeast of Deadwood, dates back at least to 1893 when the Oro Fino property of the Gilt Edge Mines, Inc., was worked (Allsman, 1940, p. 56).
The history of the Deadwood-Two Bit district is characterized by sporadic activity, and there has been no major producer with sustained output. The district was virtually dormant from 1937 through 1959.
The deposit of the Cloverleaf mine is in Precam-brian rock composed of mica schist, slate, chlorite schist, quartzite, and amphibolite. The ore consists of galena, sphalerite, pyrite, and native gold in a saddle-shaped mass of quartz on a southeast plunging anticlinal fold in the mica schist (Connolly and O'Harra, 1929, p. 113).
The so-called placer deposits in the Deadwood Formation consist of a gold-bearing conglomerate overlying the Precambrian rocks. Pebbles and small boulders of quartz, quartzite, and schist are cemented by pyrite or iron oxide where the conglomerate is gold bearing. The barren conglomerate is characterized by a quartzitic or calcareous matrix. Though Irving and Emmons (in Irving and others, 1904, p. 99, 111) did note that some of the gold may have been introduced with the pyrite and some may have been chemically reprecipitated in the conglomerate by ferric sulfate solutions, they postulated that much of it was of detrital origin and was derived from erosion of the gold lodes in the Precambrian rocks nearby. Noble (1950, p. 246), on the other hand, considered it doubtful that any of the gold was of placer origin.
Gold has also been mined from replacement deposits in dolomite beds of the Deadwood Formation. Two zones, known as the "lower contact" and "upper contact," contain the ore bodies. The "lower contact," which ranges from a few feet to 30 feet in thickness, consists of several dolomite beds inter-layered with shale beneath an impervious shale and immediately overlying the basal conglomerate unit. The "upper contact" is near the top of the formation and consists of two to six beds of dolomite separated by shale. The ore bodies are lenticular masses parallel to bedding and consist of aggregates of quartz, chalcedony, barite, and fluorite and contain disseminated fine-grained pyrite, arsenopyrite, and local stibnite. Tellurium is present in analyses, and the gold and silver probably occur in fine-grained telluride minerals (Irving and others, 1904, p. 124-143).
A few gold deposits in the Deadwood-Two Bit district, near Strawberry Gulch, occur in Tertiary eruptive rocks and in adjacent brecciated Precambrian and Cambrian rocks. Most of the ore is in the form of auriferous limonite fissure fillings in a large mass of decomposed quartz monzonite porphyry. The limonite gives way at depth to pyrite and a little galena and copper sulfides (Allsman, 1940, p.57).
