Pegmatites of the Back Hills, South Dakota
Pegmatites of the Black Hills, South Dakota
By Thomas A. Loomis
Dakota Matrix Minerals
For the pegmatite collector, the Black Hills may be paradise. Within its borders, thousands of pegmatites occur. In fact, pegmatite dikes crisscross Mount Rushmore. Cleophas C. O’Harra (1902) called this the “Mineral Wealth of the Black Hills”. United States Geological Survey geologists mapped individual quadrangles and reported on mined pegmatites by the thousands in the 1940’s. Over 250 mineral species are found in the Black Hills, 22 of these are new to science. Several of the Black Hills minerals can be seen in our MineralPedia: a photo database of minerals. Most of the new minerals are phosphates and are found in pegmatites. The prolific Tip Top mine accounts for a majority of these and are discussed in the accompanied article. The remainder of the new minerals along with other important pegmatite localities and Black Hills geology are discussed.
Etta Mine, Keystone, SD 2010
note Mt. Rushmore in background
The Black Hills proper includes an area of approximately 1,600 square miles. Central to the Black Hills is Harney Peak, the highest point at 7,242 feet above sea level. Harney Peak is comprised of 1.7 billion year old granite and crops out in a roughly circular area of no more than 10 miles in diameter. Flanking the granite are 2.5 billion year old metamorphic rocks in which most of the pegmatites have intruded. The pegmatites occur within an area of about 275 square miles around Harney Peak and range from a few inches to more than a mile in length and up to 500 feet wide. Rocks within the pegmatites are primarily plagioclase feldspars (oligoclase and albite), potash feldspars (perthite and microcline), and quartz. Spodumene, lepidolite, muscovite, and tourmaline are major constituents in a few pegmatites (Page, 1953 & DeWitt, 1986). In general, only about one percent of the pegmatites are compositionally zoned and are considered complex according to Norton (1962). Black Hills pegmatites are not known to contain cavities and have not produced any gem crystals of significance. Pegmatites are generally grouped within three major mining districts, which are the Keystone, Custer, and Hill City districts in the southern Hills, and the Tintic district in the northern Hills. Only the Keystone and Custer districts will be emphasized in this article. In particular, the Barker, the Big Chief, Hugo, Ingersoll, and the Tin Mountain pegmatites will be highlighted.
The McMackin mine (also known as the Crown mine) was the first pegmatite to be mined in the Black Hills for mica in 1879. This was followed by the discovery of several other pegmatites in the area through 1884 and is recognized as the first period of pegmatite mining in the Black Hills. Records indicate approximately 8,000 pounds of mica was produced during these early days of mining. The next period of pegmatite mining is marked when tin was discovered at the Etta mine in 1883. Tin mining lasted through 1893, when the Harney Peak Tin Company collapsed through scandal and practically nonexistent production. Ironically, the Black Hills would ultimately capitalize on the situation through the discovery of many viable economic minerals from pegmatites originally mined for tin. Through it all, countless pegmatites were discovered and lithium ore would define the next wave of pegmatite mining. This wave, however, would gain not collapse under false pretense, but would grow with economic vitality. The Black Hills would then become a powerhouse of mineral resource and lead the nation in the production of lithium, beryllium, mica, feldspar and many other ores.
Tin Ore - Cassiterite in Lepidolite, White Cap mine, near Keystone, South Dakota
In 1898 the Rheinbold and Company began spodumene mining at the Etta mine, which became the largest single source of spodumene in the Black Hills. Spodumene was mined for its lithium content and before long several other mines began operations with discovery of amblygonite, lepidolite, and triphylite as alternative sources of lithium. As lithium production drove economic viability at the pegmatites other minerals were discovered and mined as byproducts. These included beryl, columbite-tantalite and caesium. Westinghouse Electric and Manufacturing Company entered the Hills when electrical and other applications required the insulating qualities of mica. This event resulted in the production of mica up to 1.5 million pounds annually during the period of 1906 to 1911. Yet another boom resulted when freight rates dropped in 1923 and the vast deposits of feldspar were mined Keystone Feldspar and Chemical Company.
Etta mine, near Keystone, SD circa 1890's
William Blake postulated the first explanation of zoning in pegmatites in the Black Hills pegmatites as early as 1883. But it was Kenneth Landes who first studied the Black Hills pegmatites in detailed attempt to classify and explain their origin in 1928 and 1933. During the1940’s a group of USGS geologists invaded the Black Hills as part of its Strategic Mineral Investigations towards the war effort of quantifying viable mineral reserves. Subsequent investigations followed with detailed studies completed by USGS geologists in part for the U. S. Atomic Energy Commission. One of these studies “Geology of the Hugo Pegmatite, Keystone, South Dakota” provided a very detailed look at zoned pegmatites and disputed Landes’ theories on origin.
New York Mica mine circa 1923
USGS Photo LiIbrary. Sterrett, D.B USGS Bull. 740
Samuel Scott in 1897 wrote the first book on descriptive mineralogy of the Black Hills. Titled “Rocks, Minerals, and other Resources of the Golden Black Hills of South Dakota and Wyoming”, this short description of Black Hills minerals bestowed the first look at pegmatite minerals in the Hills. This work is today highly sought after as a Black Hills mining relic. Victor Ziegler in 1914 published his work “The Minerals of the Black Hills”. This was the first comprehensive publication on Black Hills mineralogy and also provided insight to the origin of pegmatites. Instrumental to the study of Black Hills mineralogy was Willard (“Bill”) L. Roberts. Roberts along with George Rapp in 1965 updated Ziegler’s work with hundreds of new mineral localities in “Mineralogy of the Black Hills”. Paul Moore from the University of Chicago with Bill Roberts in the 1960’s studied phosphate mineralogy of the pegmatites. Their work resulted in the discovery of three species new to mineralogy. Moore’s work culminated in a fine article titled “Pegmatite Phosphates: Descriptive Mineralogy and Crystal Chemistry” and was published in a 1973 issue of the Mineralogical Record. Through the following years several papers were written on new discoveries in the Black Hills and published in the American, Canadian, and British mineralogy periodicals.
Some of the most important locality indexes of the Black Hills include:
- Bureau of Mines staff (1953) Black Hills Mineral Atlas parts 1 & 2.
- Tullis (1952) Beryl Resources of the Black Hills.
- Roberts and Rapp (1965) Mineralogy of the Black Hills. This includes a very complete mine index as an appendix.
- Smith, A. E. and Fritzsch, E. (2000) South Dakota Mineral Index
“Type Locality Minerals of the Black Hills, South Dakota” by Triscori and Campbell (1986) provides a good summary of significant discoveries of pegmatitic minerals found in the Hills. Aside from the beryllophosphate minerals from the Tip Top mine, other rare minerals such as černỳite, olmsteadite, perloffite, sinkankasite and walentaite were first discovered from Black Hills’ pegmatites and are briefly discussed in this article. Other noteworthy occurrences in the Black Hills also include:
- The second world occurrence of scorzalite found at the Victory pegmatite near Custer (Pecora and Fahey, 1949).
- The first occurrence of montgomeryite in a pegmatite was discovered at the Etta mine (Moore, 1964).
- The first occurrence of scorodite in a pegmatite reported from the Etta mine (Zodac, 1953).
- The first occurrence of wodginite in the United States was found at the Peerless mine (Černỳ 1985).
The Black Hills can also boast the largest spodumene crystals in the world occurring up to 50 feet in length and weighing more than 90 tons!
As previously noted, many economic minerals have been mined from the Black Hills pegmatites. Early in the Black Hills history, the pegmatites led the nation in lithium and beryl production, was the only source of columbite-tantalite, and produced about one third of the nation’s mica requirements. Some highlights of mineral history are provided here:
Although beryl is an uncommon mineral worldwide, it is common in the Black Hills. Lincoln (1927) reported that beryl had been shipped intermittently from the Hills since 1914. The first economic use of beryl from the Black Hills dates back to 1930, when beryl from the Sitting Bull mine was mined and sent to Brush Beryllium Corporation in Cleveland, Ohio. A great amount of research was under way during this time. Beryllium, as early researches had known, possessed the tinsel strength of steel and were only slightly heavier then manganese. The metal is also lightweight, and does not oxidize. Beryl was and still is the primary source of beryllium and was highly sought after for its unique qualities similar to aluminum. Early applications included the use of beryllium nitrate in the manufacture incandescent gas mantles to harden the mantle skeleton. Beryllium oxide was used as a component if certain abrasive materials and also in dental cements (Connolly and O’Harra, 1929). The Bureau of Mines during the late 1920’s was actively researching beryl, as was the Bureau of Standards, National Advisory Committee of Aeronautics. Alloys of beryllium with copper, iron, nickel, gold and silver were also researched during the 1920’s. Beryllium can also absorb a great amount of heat and dissipate it rapidly. This property was called “heat sink” and applied to aviation, space flight for re-entry, and missiles. The beryl deposits in the Hills were the largest domestic source during 1943-44, when approximately 500 tons were mined from 68 mines. Beryl peaked in 1953, when 392 short tons were produced from Black Hills mines (Miller, 1959). A. I. Johnston, a well-known Black Hills mining engineer described one of the first uses of beryl (Johnson, 1989):
“The mineral beryl became of strategic interest during the second world war as a source of the metal beryllium which was used as a moderator in the mechanics of setting off an atomic explosion. By slowing down the speed of neutrons entering the uranium nucleus an unstable condition developed in the uranium atom resulting in its disintegration of the uranium atom and thus releasing the great energy stored up in the atom. Hence an intense effort on the part of the U. S. government to develop reserves of the mineral beryl or other beryllium minerals resulted in the concerted effort to develop increased tonnages from the Black Hills. The price rose to $600 per ton for 10% ore and was proportionately higher for higher-grade ore.”
Fluorapatite (6mm crystals), King Lithia pegmatite, near Keystone, South Dakota
Modern uses include alloying beryllium with copper and used in the defense and aerospace industries as lightweight structural materials in high-speed aircraft, missiles, and spacecraft. Beryllium is also used in x-ray technology, computers, and in the nuclear industry.
Tullis in 1952 on assignment from the Bureau of Mines reported that most of the deposits in the Hills contained less than one percent beryl. Although Tullis reports that beryl characteristics and quantities can vary in the Hills:
The size and form of beryl crystals depend on the zone in which they are found. Small crystals vary from 1 inch in diameter and several inches long. Shell-like crystals of beryl are found in hexagonal form, consisting of single or multiple shells enclosing a mixture of other minerals, usually quartz and feldspar…. A number of very large crystals and masses of solid beryl have been found, and these may contain several tons each.
Tullis (1952) lists 175 mines in the Hills, which contain beryl to some extant. Roberts and Rapp (1965) listed 36 notable localities. In the Black Hills excellent crystals groups have been found at the Crown Mica mine as superb white to pale green doubly terminated crystals up to five inches in diameter. At the Ross mine near Custer, beryl crystals up to five feet long have been mined. Huge crystals to ten feet or more and several tons in weight have been mined from the Tin Mountain, Ingersoll, Big Chief and many other mines. The Peerless mine was the largest producer followed by the Ingersoll during the 1920’s (Lincoln 1934). Gem grade beryl is rare in the Hills but Roberts and Rapp (1965) note a few localities. These include gem quality bottle green crystals from the Wonder Lode, gemmy green crystals from the Elkhorn mine, and gem quality sea-green aquamarine at the Helen Beryl. Most crystals are commonly terminated with basal pinacoids and very few have complex terminations
According to Connolly (1929), feldspar came on the Black Hills market in 1923 when freight rates dropped and permitted competition with eastern supplies. The principal use for feldspar was in the ceramic industry. Other uses included enameling for metal, glazes, and abrasives in soaps. The principal variety of feldspar is microcline, although albite occurs in abundance. The largest producers during the peak years were the Hugo, Big Chief, White Elephant, Nevins, and the Shamrock. During World War II annual production averaged 70,000 tons. The peak occurred in 1946, when about 75,000 tons were produced. During these years South Dakota ranked second to North Carolina in production (Miller, 1959).
Lithium from the Black Hills occurs in spodumene, amblygonite-montebrasite, lepidolite and triphylite. According to Page et al (1953), the occurrence lithium minerals are strongly dependent upon the compositional zones and fracture units of the pegmatites. Spodumene has been produced from all zones, although amblygonite occurs only in the intermediate zones and lepidolite only from cores zones. Spodumene was first produced at the Etta pegmatite in 1898 and sent to Omaha for experimentation. During the 1920’s the Etta mine was the principal producer of lithium in the United States. Virtually every reference to lithium bearing pegmatites mentions the huge spodumene crystals at the Etta. Prior to their discovery at the Etta, two-foot spodumene crystals found in New England pegmatites were considered “enormous”. The first reference to the spodumene “logs” at the Etta was by Blake in 1883 (see the Harney Peak article in SD issue I). Frank Hess in 1939, investigating rare minerals for the Bureau of Mines described these incredible crystals:
“…huge crystals of spodumene are mixed at every possible angle like toothpicks in a translucent gel (quartz). In 1904, a crystal 42 feet long and 3 feet by 6 feet in cross section was found, and the adjective “enormous” applied to the New England crystals must be transferred. The crystal weighed about 65 tons.”
It’s interesting to think that in 1819 only half the elements of the periodic table had been discovered. Lithium was one of the new elements and was discovered by the young A. J. Arfvedson, a 25-year-old Swede scientist in 1817. The Swedes were great miners in the early 1800’s and had already discovered the new elements of cobalt, nickel, manganese, tungsten, molybdenum, tantalum, barium, and selenium. Then in 1817, Arfvedson discovered lithium in petalite, which occurred in a pegmatite at an iron mine. His results were published in1819 and added to the periodic table shortly there after. Scientists soon discovered that lithium was a silvery-white metal softer than talc with a hardness of 0.6 on Mohs scale. Lithium as it was discovered was also incredibly light weighing only 33.9 pounds per cubic foot compared to 169 pounds for aluminum! Hess (1939) reports the first use of lithium was probably in medicine. Evidently people drank lithium water and dissolved the calculi in their bodies. Lithium water became so popular that a law compelled the sellers to actually include lithium in the water. (Some things never change). Several lithia springs were also very popular in the New England states. For years this was the chief use of lithia. Demand dropped when people finally came to their senses, and this actually contributed to the closing of the Etta mine for a short period.
Tiptopite (1mm spray), Tip Top mine, near Custer, South Dakota
Tiptopite is a rare alteration derivative of Beryl and Triphylite, a lithium ore.
Edison eventually discovered the lithium storage battery. This usage and other applications such as welding, pyrotechnics, photography, de-humidifiers, and specialty glass contributed to an increase in demand during the late 1800’s and early 1900’s (Hess, 1939). A. I. Johnson (1989) estimated over 50,000 tons of spodumene was mined from the Etta pegmatite. Lithium hydride was produced from Etta spodumene during World War II and used to inflate antennae carrying balloons sent up by downed pilots for rescue. During the war effort, about 15,800 short tons were produced from the Black Hills. The peak production year occurred in 1951 when 8,600 short tons were produced.
Other spodumene localities in the Hills include the Tin Mountain mine, which was also noted for large crystals. At this locality crystals up to 30 feet have been found. Crystals up to 20 feet occur at the Beecher Lode. Well-defined crystals up to eight feet occur at the Helen Beryl mine. At this locality Roberts and Rapp (1965) note that hiddenite – spodumene is suitable for “first quality faceted gem stones”. Kunzite has also been found at the Beecher and Tin Mountain pegmatites.
Amblygonite, another ore of lithium, was first produced from the Hills in 1905 (Guiteras, 1940). Although not as abundant as spodumene in the Hills, it was easier to extract the lithium from the amblygonite and thus was more desirable. The Beecher pegmatite was known to contain huge masses of amblygonite up to 200 tons. However, enormous masses up to 30 feet were found at the Ingersoll mine and up to 40 feet at the Hugo mine (Roberts and Rapp, 1965).
Lepidolite, according to Connolly (1929) was the third most important lithium mineral in the Hills. The primary use during this time was for lithium salts, although it was also used in specialty glass. Lepidolite was first mined in the Hills at the Ingersoll mine according to Page et al (1953) in 1922 but was not intensively mined until about 1936. Lepidolite from the Ingersoll was used for the seventeen-foot lens in the observatory at Mount Wilson, California (Clow, 2002). Lepidolite operations ceased at the Ingersoll in 1944. Over 8,000 tons were mined from the Ingersoll pegmatite. Other notable occurrences according to Roberts and Rapp (1965) include the Beecher, Tin Mountain, wood Tin, and the Hugo pegmatites.
Quartz crystals 12-14 inches (30-36 cm) in Albite
At one time the Black Hills supplied one third of the mica produced in the United States. Mica was the first commodity to be mined in the Black Hills at the McMackin mine in 1879. The McMackin produced about 45,000 pounds of mica. Other mines included the Climax, Lost Bonanza, and the New York mines. During this period, Westinghouse Electric operated four mines near Custer. Sheet and scrap were the two types of mica mined. Sheet mica was used primarily for insulating electrical equipment. Specifically it was used in spark plugs, lamp sockets, radio apparatus, fuse boxes, heating devices and telephones. Scrap mica was used for roofing, wallpaper, paints, for filler in rubber such as automobile tires, and lubricants (Connolly, 1929). Annual output peaked at 1.5 million pounds during the period of 1906 to 1911. Mica mining was practically nonexistent up until World War II when skilled labor was brought in from North Carolina. At this time about 175 women were employed in the mica industry supporting the war effort. Johnson (1989) reported that 135 mines were in operation during the war and produced anywhere from 20,000 to 75,000 pounds per mine. Combined total during the war was about 1.1 million pounds. According to Sterrett (1908) mica crystals in the Hills have a tendency to occur in flattened or tabular blocks lying perpendicular to the walls of the pegmatite. Crystals are commonly two to eight inches in diameter and one to five inches tick. However crystals up to three feet are not rare. Roberts and Rapp (1965) described a book of mica at the White Spar mica mine three feet wide by four feet long. Also, at the Red Deer mica mine sheets six feet long by one foot wide have been mined. The Diamond Mica mine south of the Hugo has long been a favorite of Black Hills collectors where “fine hexagonal and diamond shaped single crystals” occur. Other notable mica mines are the Old Mike, St. Louis, Firestone, and the Galesburg.
White or clear quartz has not been produced in the Black Hills to any significance. Although commercial quantities exist, the Hills were too far from the market for economic viability. However, rose quartz has been and still is mined for ornamental and decorative purposes. Lincoln (1927) noted that Dr. W. P. Jenney brought back specimens on his return from his first expedition to the Black Hills in 1875. The mineral was first exploited in 1889. The Scott Rose Quartz mine discovered in 1902 by Samuel Scott is one of the most famous and probably the longest producing pegmatite in the Black Hills. Edna Scott, wife of the late Samuel Scott, in her 1941 article in Rocks and Minerals states that her mine shipped about 1,000 pounds of rose quartz for 25 years to Germany. The author has recently visited the mine, which is still operated by the Scott family. The great grandson of Samuel Scott, Carl Scott, operates the mine intermittently and ships to several localities all over the country. Twenty to thirty foot wide veins of rose quartz can still be seen in the walls of the mine. The company report indicates a reserve of about 107,500 short tons.
There are countless other localities of rose quartz in the Black Hills. The White Elephant, Bull Moose, and the Wiley mines are the most notable. According to Larsen and Honert (1977), Idar-Oberstein in Germany cut hundreds of tons of rose quartz into beads, spheres, bowls, tabletops, lamps, and jewelry. A 3300-pound boulder from the White Elephant was cut into several large tabletops to 18 x 30 inches. An exquisite bowl was carved from the Scott’s rose quartz and is still on display at the field museum in Chicago. The Wiley mine rose quartz has been shown to produce asterism when cut and polished. According to Hurlbut (1970) rose quartz from the Black Hills was used to mark the grave of Ralph Waldo Emerson in Concord, Massachusetts.
Hand cobbing pegmatites for Columbite/Tantalite with Feldspar circa 1920's
The Spodumene Problem
Early in the history of mining pegmatites, geologists have pondered the origin and theories of formation. In 1933, Kenneth Landes, published a paper in the American Mineralogist titled “Origin and Classification of Pegmatites”. Landes hypothesized the formation of pegmatites and discussed the previous theories of his predecessors. One of the problems, which may not have been adequately explained, was the “spodumene problem”. The question was: How did the enormous spodumene crystals of the Etta pegmatite form? Geologists through the years have offered theories in an intriguing display of speculation without a committing themselves completely. A few of the excerpts are provided here to give the reader a little flavor of this interesting problem:
Blake (1883) offered the first explanation:
“In the numerous tin veins and granitic dikes bearing tinstone in the Dakota tin region all the phenomena go to show that the minerals of the dikes, the quartz, feldspar, mica, spodumene, beryl, columbite, tantalite, and other associates of the cassiterite, were contemporaneous in origin. All of these minerals appear to have crystallized out of a semi fluid or pasty magma in which the elements were free to arrange themselves from one side of the dike to the other, and separate out by slow crystallization.”
Ziegler (1914) somewhat agreed, but thought the magmatic solution was much less viscous:
“These pegmatites before solidification are very fluid and are rich in easily fusible and volatile constituents such as water, boron, tungsten, chlorine, etc., which are held in solution either as gases or liquids by great pressure. Such watery solution or fusions offer little resistance to the force of crystallization and if sufficient time be allowed this force may govern the arrangement of minute crystal particles for such distances as forty-two feet……”
Connolly (1929) debated previous theories but offered none of his own:
“An interesting problem is offered by the exceptionally large crystals of spodumene. If they were formed by direct crystallization from a magmatic solution, one wonders what conditions prevailed at the time of their formation. They are much too long and relatively slender to have supported their weight without breaking if they grew slowly out into an open cavity. We know that they must have grown very slowly, not from their huge size, but also from the fact that lithium is not an abundant constituent of the parent rock away from the pegmatite masses, and therefore must have been concentrated at a slow rate and over a long period of time”.
In response to Blake’s theory above, Connolly (1929) further states:
“But while the crystals were thus forming what held them up in the solution from which they were crystallizing? None of them shows evidence of attachment to the walls of the pegmatite body or to the walls of an open cavity. The specific gravity of the growing crystals would necessarily be higher than that of the solution from which they were crystallizing. A thin watery solution, as postulated by Zeigler, would permit these spodumene crystals to sink rapidly to the bottom of the pegmatite mass. A semi-fluid or pasty magma, as postulated by Blake would tend to support the growing crystals somewhat, but would sink slowly, and in time necessary for them to grow to the huge size they have attained it is believed they would have sunk to the bottom of the mass.”
Landes (1928 & 1933) presented the replacement theory:
“The writer believes the spodumene to be of later age than the minerals of the magmatic phase….Many spodumene crystals occur in groups with a tendency toward spherical radiation. Hess considers such an arrangement proof of replacement because the crystals must have been supported in order to so form. The specific gravity of spodumene is 3.2, and crystals of this weight would have a constant tendency to sink in magma which was undoubtedly of considerable less gravity (1928)……The large spodumene logs of the Etta pegmatite are thought to be replacement products of the first hydrothermal phase.”
Jahns (1955) was rather critical when summarizing the past efforts:
“The formation of some pegmatite minerals by replacement of others has been recognized by several generations of investigators, but there has been no broad agreement as to the nature of replacing solutions, their source and time of development, and the quantitative importance of their effects. This is attributable in part to contrasting views on the nature of replacement processes, in part to differences in the interpretation of mineral relationships and in assignments of a replacement origin to certain minerals, in part to lack of adequate quantitative data on the distribution and occurrence of pegmatite minerals, and in a large part to the absence of competent observers at those times when the replacement occurred”.
Jahnsite NaFeMg 1mm, Tip Top mine, near Custer, South Dakota
Finally, Norton et al (1962) offered the most plausible solution:
“Large crystals occur in nearly all zones of every zoned pegmatite, and if they formed by replacement, it is difficult to understand how the different mineral species forming large crystals were distributed among the zones in such a fashion as to form a consistent zonal sequence …The large crystals…may have obtained their support chiefly from others during crystallization of the pegmatite.”
The Big Chief mine
If the Tip Top mine has competition for variety of phosphates, quite possibly it’s the Big Chief mine. The Big Chief is type locality for three minerals: olmsteadite, perloffite, and metavivianite. Bill Roberts first found olmsteadite at the Hesnard pegmatite near Custer and shortly after at the Big Chief mine by Milo Olmstead. Moore et al (1976) indicated the Big Chief was chosen as the type locality since the crystal structure analysis was done on this material. Olmsteadite possesses a peculiar chemistry as a phosphate of niobium and tantalum. This mineral is very rare, highly sought after and very beautiful. Crystals are typically found in siderite matrix as thin tabular, deep red crystals. Most crystals do not exceed 0.3mm. The largest crystals do not exceed much more than 6mm, although a group of crystals at the Museum of Geology in Rapid City measures 1.1cm.
Big Chief mine, nea Keystone, SD 2009
Perloffite was first found at the Big Chief mine and described by Kampf (1977). The mineral is the iron analogue of bjarebyite and was named in honor of the well-known mineralogist, Louis Perloff. Perloffite, like olmsteadite is a very elusive mineral and found with ludlamite and vivianite as jet black, spear-shaped crystals to less than 1mm, but averaging 0.1mm.
Metavivianite was first found by Dr. David H. Garske of the South Dakota School of Mines and described in Ritz et al (1974). It was described as minute leek-green, flat, prismatic crystals intimately intergrown with dark red kryzhanovskite. Whitmoreite was actually the fourth type locality mineral found at the Big Chief. Bill Roberts first found Whitmoreite in 1971, but according to Moore (1974), Gunnar Bjareby submitted specimens of whitmoreite from the Fitzgibbon pegmatite in New Hampshire almost simultaneously. Moore snubbed both of the original localities as superior crystallized specimens collected by Bob Whitmore were later submitted in 1973. Typical crystals of whitmoreite resemble “floating naval mines” according to Moore. This is quite true, and micro crystals from the Big Chief mine are no different. However, whitmoreite also occur as isolated crystals and randomly scattered groups throughout siderite matrix. Crystals are amber to greenish-brown with chisel-shaped terminations.
The Big Chief originated as a feldspar mine with a beryl by-product. It is located about three miles southeast of Keystone and was once operated by A. I Johnson. It is a zoned pegmatite and lenticular in shape. Other minerals of interest are goyazite, hopeite, kidwellite, kryzhanovskite, leucophosphite, ludlamite, messelite, phosphophyllite, phosphosiderite, scorodite, and strunzite.
The Bob Ingersoll mine
A. I. Johnson (1989) once called the Bob Ingersoll “a mine with more varieties than Heinz has pickles”. Johnson is correct in “variety” as a number of different ores are found at the mine. The Ingersoll was the largest producer of lepidolite in the Hills and one of the largest producers of feldspar and beryl. Other economic minerals mined were mica, spodumene, columbite-tantalite, microlite, and uraninite. Five pegmatites are located on three claims of the Ingersoll mine, which was originally staked as a mica prospect in 1881 and acquired by the Harney Peak Tin Company in 1884 (Page, 1953). About 1915, a large beryl crystal was exposed at the Ingersoll, a nearly perfect hexagon 46 inches across the face. In 1933, another beryl crystal was exposed. This crystal was nine feet high and over eight feet wide and produced 24 tons of ore. A picture of this crystal appeared in the May 1934 issue of Engineering and Mining Journal. Yet another larger crystal was exposed in 1942. This beryl measured 19 feet long and five feet wide on one end and tapered to 19 inches at the other end. Dr. Frank L. Hess of the Rare Minerals Division of the Bureau of Mines during a short reconnaissance trip in September of 1908 to the Black Hills visited the mine and wanted to make a national monument of the crystal (Johnson, 1989). The crystal was eventually mined. The largest crystal of amblygonite was mined at the Ingersoll measuring 28 feet long and six feet in diameter. Blake (1884) reported a 20-inch square by 24-inch long columbite crystal calculated to weigh one ton. Large masses of uraninite have been reported with alteration “halos” of secondary uranium minerals such as becquerelite, fourmarierite, and vandendriesscheite. A. I. Johnson (1989) reported a 350-pound mass of uranium five inches in diameter and two inches thick containing thick yellow and red alteration rims of the aforementioned minerals. In 1967, a mass of löllingite 25 by 18 by 12 inches in size, weighing 604 pounds, composed of well-formed prismatic crystals to 12 inches was found (Roberts, 1969). According to Roberts, this was the largest mass of löllingite ever recorded at a pegmatite.
Bob Ingersoll mine, near Keystone, SD 2011
For years the Ingersoll was a favorite of mineral collectors. Roberts and Rapp (1965) report several species at the mine one of which is rubellite and indicolite tourmaline. The rubellite is found in lavender lepidolite and can occur in gem quality. Löllingite, jahnsite, fairfieldite, uranophane, kasolite, and autunite are also found. During a field trip in May, 1969, the Rapid City mineral club headed by Bill Roberts took a field trip to the Ingersoll mine. Roberts with a sense of humor described the field trip in the club’s newsletter, the Black Hills Prospector:
“Several carloads of avid collectors assembled at the City auditorium at 9:00 a.m., on Sunday May 25th for a field trip to the Ingersoll pegmatite mine near Keystone. Permission to collect at the mine had been obtained previously by field trip chairman Frank Tinsley (Tinsley, would later have the mineral Tinsleyite named in his honor.) …The Sunday field trip group arrived at the mine at 9:30 in the morning and immediately started climbing all over the mine dumps like giant ants. Soon after arrival at the mine, many collectors were somewhat baffled by very a high-pitched sound which alternately increased and decreased in intensity. Several of the members furtively glanced around fully expecting to find a grounded flying saucer or some other diabolic mechanism. Their expectations were shattered when they discovered that the source of their speculation was Everett Rambow giving his metal detector a workout.
Vivian Sichterman found one superb cabinet specimen consisting of several fine olive green tourmaline crystals on cleavelandite. Frank Tinsley and Milo Olmstead (Olmsteadite) spent most of their time in a somewhat futile search for good micro material: they found a few good siderite and albite micros and one iron manganese phosphate mineral that has not yet been identified. The Yargers divided their time between bird watching and mineral collecting: it was rumored around that they discovered a new species called “zircon crested albite basher”.
After lunch the day turned extremely hot and the Robesons and many others in the group sought temporary relief from the sun by frequent visits to the cool tunnel leading to the upper mine. Jean Roberts found a fine chunk of black cassiterite in white cleavelandite, plus green, pink and blue tourmaline crystals, and pink cesium beryl: Bill Roberts found a large chunk of purple lepidolite with half-inch inclusions of uraninite partially altered to bright yellow, orange and red secondary minerals.
The last stragglers reluctantly left the mine about 5:00 p.m., hot, thirsty, sun-burned, and tired, but well-pleased with their “loot” and grateful to Frank Tinsley for organizing such a pleasant and productive field trip.”
The Hugo mine
The Hugo mine, located near Keystone, is also directly west of the Etta mine. The Hugo pegmatite was discovered during a search for tin. However, the principal mineral in the early life of the mine was mica (Guiteras, 1940) and amblygonite (Norton, 1962). After 1924, about 200,000 tons of feldspar was produced (Guiteras, 1940). This mine was the first to produce potash feldspar in the Hills. The mine also produced spodumene, columbite-tantalite, and beryl. The Hugo is a complicated pegmatite, and the knowledge gained from the study of this pegmatite has clarified many problems concerning the internal structure and genesis of zoned pegmatites (Norton, 1962). There are seven zones and replacement bodies, which introduced minerals along fractures. Like the Etta, the Hugo also contained large spodumene “logs” to six feet. Many other minerals have crystallized to a huge size, such as a two-ton manganoan fluorapatite (Campbell, T. J. and Roberts, 1985) and 40-foot amblygonite crystals. Smith and Fritzsch (2000) lists 34 different minerals found at the Hugo. This list includes augelite, morinite, and wardite all rare minerals for the Black Hills. The Hugo is also co-type locality for černỳite.
Tin Mountain mine
The Tin Mountain mine is located about 8 miles west of Custer. The claim was patented in 1889 by the Tin Mountain Company and acquired by the Maywood Chemical Company in 1928. The claim was originally staked for tin, but unlike the name implies, not much tin was ever produced. Spodumene, amblygonite, beryl and pollucite were all produced at the mine. Pollucite masses up to six feet across were found and were quite different from that found elsewhere in the world. According to Connolly (1929) the pollucite is “instead of being clear and colorless, as is usually the case, it is translucent to opaque, very fine grained and white in color”. Beryl at the Tin Mountain can occur as clear, limpid, very pale pink irregular masses, which fooled earlier geologist thinking it was pollucite. Spodumene occurs at the Tin Mountain as 30-foot crystals. Occasionally kunzite of light pink grade can be found at the Tin Mountain mine. Exceptional sharp reddish brown crystals of pyramidal zircons are found at the mine to 2 inches. Other notable minerals according to Smith and Fritzsch (2000) include aurichalcite, autunite, bismuth, kasolite, and uranophane.
Other pegmatites in the Keystone area worthy of note include (Smith and Fritzsch, 2000): the Barker-Ferguson for the type locality sinkankasite plus fluellite, ludlamite, phosphuranylite, torbernite, and vivianite; the Champion pegmatite for the type locality of johnwalkite; the Dan Patch for fluorapatite and ludlamite; the Hesnard for olmsteadite, phosphosiderite, tavorite and vivianite; the King Lithia for fluorapatite; the Nickel Plate for arrojadite; the Peerless for fluorapatite, kesterite, libethenite, mushistonite, struverite, tapiolite, torbernite, and wodginite; the White Cap for azurite, bertrandite, childrenite, ernstite, fluorapatite, lazulite, ludlamite, olmsteadite, phosphosiderite, vivanite, and whitmoreite.
Helen Beryl mine, near Custer SD 2010
Dr. John Lufkin, economic geologist in foreground
In the Custer area, additional pegmatites of note include (Smith and Fritzsch, 2000): the Bull Moose for barbosalite, fairfieldite, hureaulite, kryzhanovskite, leucophosphite, ludlamite, phosphoferrite, phosphosiderite, Reddingite, strengite, tavorite, and vivianite; the Custer Mountain Lode for autunite and hureaulite; High Climb for laueite; Rock Ridge mine for rosemaryite; Ross mine for beryl, torbernite and uraninite; the Shamrock for “watermelon tourmaline; and the White Elephant mine for type locality walentaite.
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