By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Click here for the Principle Gold Producing Districts of the United States Index
Lawrence County is in western South Dakota along the Wyoming State line. It includes much of the northern part of the Black Hills and most of the mineralized area, including the famous Homestake mine in the Lead district.
Through 1959, Lawrence County produced a total of 26,386,000 ounces of gold, mostly from the Homestake mine in the Lead district. Other gold districts that have yielded more than 10,000 ounces are the Deadwood-Two Bit, Garden, Bald Mountain, and Squaw Creek.
BALD MOUNTAIN DISTRICT
The Bald Mountain district, which includes the Portland area, is 3.5 miles southwest of the Lead district.
Claims were located in the Portland area in 1877, but early mining was handicapped by the highly refractory nature of the ore. By 1891 the milling and metallurgical difficulties were overcome by the chlorination process, and in 1892 cyanidation proved successful (Connolly and O'Harra, 1929, p. 143-147). The district entered a period of prosperous development that ended at the close of World War I owing to high costs. The increased price of gold in 1934 caused a pronounced reactivation which lasted until World War II. After the war, mining was resumed on a small scale, but increased operating costs again forced the owners to close in 1959.
About $3 million worth of bullion, mostly in gold, was produced by the Mogul Mining Co. up to 1900 (Allsman, 1940, p. 38). Other companies were also active during this early period. Total gold production of the district through 1959 was roughly 1,400,000 ounces.
Rocks of the district are chiefly southwest-tilted strata of the Cambrian Deadwood Formation, underlain by the Precambrian schist. Numerous sheets, dikes, and irregular bodies of Tertiary phonolite and rhyolite porphyry cut the older rocks (Irving and others, 1904, p. 144-145).
The gold deposits are in replacement bodies in the Deadwood Formation and are the most productive deposits of this type in the Black Hills. Ore bodies are in two zones known locally as the "upper contact" and "lower contact." Deposits in the "lower contact" are in lenticular dolomite beds interbedded with shale within a stratigraphic interval of from 6 to 30 feet above the basal quartzite unit of the Deadwood Formation. The "upper contact" is defined as a sequence of mineralized dolomite beds and shale 12 to 18 feet below the Scolithus sandstone, which is the uppermost umt of the Deadwood Formation (Irving and others, 1904, p. 122-123).
Ore deposits occur in vertical shoots, probably mineralized fractures through which the ore solutions moved and from which replacement was started. The distance to which replacement has extended away from the fractures varies with the character of the beds and intensity of the mineralizing action. The widths of the vertical shoots range from thin seams up to 10 feet, and rarely up to 40 feet. Ore bodies of considerable width may be due either to coalescence of several parallel shoots or to the existence of many intersecting fractures (Irving and others, 1904, p. 134-136). The vertical extent of the shoots depends upon the thickness of the dolomitic rocks through which they pass, although some shoots extend into both overlying and underlying sandstone or shale. The maximum length of the shoots is several hundred feet; the longer shoots probably overlap fractures arranged en echelon.
The ore is classified under two types: blue ore which is the primary ore, and red ore which is oxidized ore. The primary ore consists of pyrite and probably arsenopyrite, most of which is very fine grained to microscopic in size. In some ore the gold telluride sylvanite has been found, but most of the gold is believed to be associated with the finegrained pyrite (Connolly and O'Harra, 1929, p. 162). Small amounts of galena and sphalerite are seen in polished sections of the ore. The gangue is chiefly quartz and some fluorite, gypsum, and barite. Most of the ore mined is the red ore, which consists mainly of gold-bearing limonite and is amenable to cyaniding. Blue ore is highly refractory and is not extensively mined.
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).
GARDEN DISTRICT
The Garden (Maitland) district is 1 to 3 miles northwest of Lead, in Blacktail and Sheeptail Gulches and False Bottom Creek.
The dates of mineral discovery and earliest mining in this district have not been ascertained, but it is probable that some properties were being worked in the 1880's. In 1902 the Maitland mine, which became the principal mine in the district, was put into operation. Activity continued until 1942, when the Maitland was closed. From 1943 through 1959, no production was reported from the district. The total gold output of the district through 1959 was at least 176,000 ounces; the Maitland mine is credited with 137,000 ounces.
The district is in the northeast part of the Pre-cambrian core of the Black Hills dome. Bedrock consists of slate, schist, and quartzite beds of Pre-cambrian age, the Deadwood Formation of Cambrian age, and bodies of intrusive quartz monzonite porphyry and rhyolite of Tertiary age (Darton and Paige, 1925). The ore deposits are replacement bodies in dolomite beds in the lower part of the Deadwood Formation, immediately above the basal conglomerate. Fractures, parallel to the foliation of the Precambrian rocks, extend upward into the Deadwood and provided avenues for the mineralizing solutions. Primary ore consists of finely divided gold and silver in pyrite, but most of the ore mined was oxidized and was probably mostly gold- and silver-bearing limonite (Allsman, 1940, p. 42).
LEAD DISTRICT
The Lead district, which includes Yellow Creek, is in central Lawrence County in the central part of the mineralized area of the Black Hills. The district contains the famous Homestake mine, the leading gold producer in the United States and the only major operation in the district.
Through 1959, the Homestake Mining Co. produced a total of about 24,450,000 ounces of gold and 5,830,000 ounces of silver. Of this amount, about 1,552,665 ounces of gold and 305,600 ounces of silver were mined before 1904 by companies that were later consolidated with the Homestake (data furnished by and published with permission of the Homestake Mining Co.).
The Homestake Mining Co., which was incorporated in 1877, originally held only two fractional claims covering about 14 acres. These claims were purchased from prospectors who had located them in 1876 and had taken out about $5,000 in gold. Other companies - the Father de Smet, Highland, and Deadwood-Terra - were organized and in operation in 1878, but they were gradually assimilated by Homestake (Irving and others, 1904, p. 57). By 1931 the Homestake Co. controlled 654 mining claims covering 5,639 acres (Allen, 1931, p. 290).
The expanding operations are best reflected by production data. From 1881 through 1894, annual gold output ranged from 45,960 ounces to 66,280 ounces. In 1900, about 172,000 ounces was produced, and in 1910, about 225,000 ounces. Production exceeded 500,000 ounces in 1935 and, except for the period 1942-52, it remained above 500,000 ounces per year through 1959.
Rocks in the Lead district are mainly Precambrian in age and consist of six formations with a total thickness of about 20,000 feet. A few erosional remnants of the basal conglomerate of the Cambrian Deadwood Formation cap some of the hills and ridges. Igneous rocks are of two ages: amphi-bolite bodies derived from Precambrian gabbroic rocks, and small stocks, plugs, and dikes of Tertiary porphyries that range in composition from granite to syenite (Noble and Harder, 1948, p. 942-954).
The Precambrian rocks are dominantly iron-magnesium schistose rocks in the lower part of the sequence and argillaceous phyllites and schists in the upper part. They were isoclinally folded in Precambrian time and deformed further during the time of Tertiary intrusive activity. In the vicinity of the Homestake mine the lower three Precambrian formations - the Poorman, Homestake, and Ellison Formations - are exposed. All the major ore bodies occur in the Homestake Formation, which is a sideroplesite schist containing many bands of recrystallized chert. Where the Precambrian rocks were metamorphosed to the garnet zone of progressive metamorphism, the sideroplesite schist of the Homestake Formation was converted to cumming-tonlte schist (Noble and Harder, 1948, p. 963-965).
The ore bodies are linear or pipelike replacement deposits in the Homestake Formation. The schist is chloritized and has masses of quartz and cross-cutting and conformable veins of quartz, quartz-chlorite-arsenopyrite, pyrrhotite, quartz-ankerite, and calcite-pyrite. Arsenopyrite is also abundant in the chloritized rock near the conformable quartz veins. Four distinct stages of mineralization have been recognized. Gold is associated with arsenopyrite and also occurs in chloritized rock along the walls of quartz veins. Chlorite-pyrrhotite schist which surrounds conformable quartz masses also contains considerable gold (Noble, 1950, p. 231-236).
Noble (1950, p. 224-231) noted that the ore bodies were localized in zones of younger cross folds superimposed on the older isoclinal folds. Dilatancy, or increase of porosity in these zones, permitted a free circulation of mineralizing fluids.
The age of mineralization of the Homestake deposits has been postulated as both Precambrian and Tertiary. After reviewing the evidence and the opinions of earlier workers, Noble (1950, p. 245-247) concluded that the problem was far from solved.
In addition to those just described, two other types of gold deposits have been mined on a small scale in the district. Auriferous conglomerate in the thin remnants of the Deadwood Formation in the hills just north of the town of Lead supported small gold-mining operations, and replacement deposits in the lower dolomite bed of the Deadwood Formation in the Yellow Creek area yielded about 125,070 ounces of gold to 1920 (Connolly and O'Harra, 1929, p. 137-142; Allsman, 1940, p. 40). The Wasp No. 2 mine was the chief producer in the Yellow Creek area.
SQUAW CREEK DISTRICT
The Squaw Creek district, which includes the Ragged Top, Elk Mountain, and Carbonate areas, is in western Lawrence County west of the Bald Mountain and Garden districts. The recorded gold production of the district through 1959 was about 76,000 ounces, of which about 75,800 ounces came from the Ragged Top Mountain area.
Lead and silver ores were discovered in the Carbonate area in the early 1880's and peak production was from 1885 to 1891. Only small amounts of gold were recovered as a byproduct from this ore (Allsman, 1940, p. 53). In 1896 considerable excitement was caused by the discovery of boulders of silicified limestone containing gold in the Ragged Top Mountain area. Shortly thereafter gold lodes were found west and south of Ragged Top Mountain and in the Squaw Creek and Annie Creek areas. The deposits north of Ragged Top Mountain yielded about $316,000 in gold (15,285 ounces) from 1896 to 1899. The mines west of Ragged Top Mountain were most active from 1899 to 1906 (Allsman, 1940, p. 53). After 1914 the district declined, and only a few ounces of gold from scattered placer activities was reported from 1915 through 1959.
The Squaw Creek district is a plateau is 2.5 miles wide and 5 miles long on the northwest side of the Black Hills dome. The Mississippian Pahasapa Limestone, which forms the caprock on the plateau, is underlain by the Cambrian sedimentary rocks which are exposed along streams that have cut through the limestone. The sedimentary rocks are intruded by Tertiary porphyry bodies, and in the Ragged Top Mountain area a laccolith of phonolite is intruded at the base of the Carboniferous beds (Irving and others, 1904, p. 172). The ore bodies occur in the flat-lying Pahasapa Limestone adjoining the phonolite mass.
The ore deposits occur in silicified vertical fractures and in irregular masses of silicified limestone in the Pahasapa. The most productive ore bodies, west of Ragged Top Mountain, are flat shoots near the surface, which apparently are lateral extensions from the tops of vertical fissure veins. A thin, relatively impervious capping, which seems to cover most of the deposits, apparently caused the rising mineralizing solutions to spread below the cap, thus forming the flat ore bodies (Allsman, 1940, p. 52). The ore body consists of light-buff silicified limestone and purple fluorite containing gold, silver, and tellurium. The presence of tellurium indicates that the precious metals probably occur as tellurides in the unaltered ore. In general the veins are shallow and are said to become narrow at depth; in places ore bodies pinch out at depths of 60 feet. The veins have not been explored generally to any great depth (Irving and others, 1904, p. 173-177).
