The YOGO™ Sapphire Mine

During a gold rush in 1878, about a thousand miners came to Yogo Creek, which was one of the gold-bearing streams in Montana not yet actively mined. Prospectors noticed "Blue pebbles" in their sluice boxes along with small quantities of gold. The mining camp at Yogo City only flourished for roughly three years and eventually the population dwindled to only a few individuals.
In 1894, the "blue pebbles" were recognized as sapphires. One story credits a local school teacher for recognizing the blue pebbles as sapphires. A variation is that the teacher lived in Maine, but was a friend of a local miner, who had mailed her a small box with some gold and a few "blue pebbles" in it. Another story credits a miner named S.S. Hobson for surmising that the blue stones might be sapphires and his guess was confirmed by a jeweler in Helena. Ultimately, in 1895, Jake Hoover sent a cigar box containing the sapphires he had collected while mining gold to an assay office, which in turn sent them via regular, uninsured mail to Tiffany's in New York City for appraisal by Dr. George Kunz, the leading American gemologist of the time. Impressed by their quality and color, Kunz pronounced them "the finest precious gemstones ever found in the United States". Tiffany's sent Hoover a check for $3,750 (approximately $115,200 as of 2020), along with a letter that described the blue pebbles as "sapphires of unusual high quality".
Yogo sapphires were ultimately traced from the alluvium to a large vertical dike which determined to be the source. In February 1896, a sheepherder named Jim Ettien found the sapphire mother lode: the Yogo dike. Ettien was prospecting for gold, and found sapphires after washing gravel he found in a fissure within a limestone outcrop. Ettien staked two mining claims. The vein turned out to be 5 miles (8 km) long and several other miners promptly staked claims along the dike. Ettien sold his two claims to Jake Hoover and Hoover in turn sold his interest in eight original mining claims, known as the "New Mine Sapphire Syndicate", to his two partners for $5,000 (approximately $150,000 as of 2020). This site was 5 miles (8 km) from Yogo City. In 1899, Johnson, Walker and Tolhurst, Ltd. of London purchased the New Mine Sapphire Syndicate for $100,000 (approximately $3.1 million in 2020 dollars). At that point, the operation became unofficially known as the "English Mine“.
On July 4, 1896, two other Americans, John Burke and Pat Sweeney, located six mining claims on the western portion of the Yogo dike near Yogo Creek. This was an area that Hoover had deemed to be unfit for mining. These claims were collectively known as the "Fourth of July Claims" and became known as the "American Mine". In 1904, the mine was bought by the American Gem Syndicate and it was re-sold in 1907 to the American Sapphire Company.
One of the Englishmen who came to the area was Charles Gadsden of Berkhamsted, Hertfordshire. By 1902, Gadsden was promoted to resident supervisor of the English Mine and he quickly turned its focus from gold to sapphires. Gadsden's security measures were very tight, as weight-for-weight, rough sapphires were and continue to be worth much more than gold. The English Mine flourished until the 1920s, but floods on July 26, 1923, so severely damaged the mines that they never fully recovered. Between the aftermath of flooding and hard economic times, the English Mine ceased to operate in 1929. It had recovered more than 16 million carats (3.2 tons) of rough sapphires that produced 2.5 million carats (500 kg) of finished gems valued at $25 million in 1929 dollars (approximately $470.0 million in 2020 dollars). A series of other firms mined sapphires there, but with marginal success. For much of the 1930s and 1940s Gadsden worked the mine alone and used his own money to pay its property taxes. He remained caretaker of the mines until shortly before his death on March 11, 1954.


During the initial discovery of sapphires in the Yogo district, John Burke and Pat Sweeney located the Fourth of July placer claim on, appropriately enough, July 4, 1896. The mine went through a series of owners over the next 18 years. Burke and Sweeney sold to American Sapphire Co. Yogo Lapidary Co. then ran the operations from 1904-1909, selling to Yogo American Sapphire Co. Finally, New Mine Sapphire Syndicate purchased the mine in 1914 and immediately closed it down for good.
Mining methods on the seven claims were similar to those used on the neighboring New Mine Sapphire Syndicate properties. The ore was initially reached through two adits with crosscut drifting. Crews later sank a 300-foot shaft and developed three levels. Processing of the ore was quite different, however. The American mine ran ore through a concentrator set near the portal of the mine. The ore passed first through a 4-inch grizzly to a jaw crusher. The smaller pieces were then run through a series of sizing screens, followed by Woodbury jigs; the concentrates at this point averaged 5-10 percent sapphires. After treatment in a Blake-Morscher electrostatic machine, the final concentrates were 50-90 percent sapphires. Final cleaning and sorting was done by hand. Large pieces of ore were set out to weather before running through the concentrator again. The plant could process 75 to 100 tons of ore each day.
The concentrator recovered a much higher percentage of stones than the sluicing method used by the English company. Yogo American Sapphire Co. recovered nearly 95 percent of the small stones and close to 100 percent of the large gems. All of the mine's output was sold in the United States. Starting in 1903, many of the stones were cut and polished in a special department at the cutting facility located at the mine site. Three years later, some of the stones were sent to a new sapphire cutting facility located in Great Falls. The mine had produced $30,000 worth of sapphires up to 1904. Operations picked up considerably after this, and the output for 1906 was $250,000. The total production of the Yogo American Sapphire Co. was estimated at 3 million carats.


Following the discovery of sapphires in placer deposits and the associated lode claims, the New Mine Sapphire Syndicate of London bought a majority of the claims on the eastern end of the dike in 1897. The company initially used simple hand mining methods to recover the gems, with workers hauling dirt by wagons to a sluice for washing. The company sank a 60-foot shaft in the dike that first year and mining methods resembled those used in any underground operation.
Ore from greater depth was harder than that removed from open pits, and the company altered its recovery methods. The ore was first spread out two feet thick in a disintegration yard where it was wetted periodically and left to weather. This yard was about 250 feet square and was floored with planks 2 inches thick. After weathering, crews ran the ore through sluices with iron grated riffles set a few feet apart to trap the sapphires. Unlike gold placer operations, however, rock that passed over the riffles initially was not discarded, but was instead set aside to weather again. All of the ore was weathered and run through sluices four times before being thrown on the tailing pile. The rough stones were processed in an electromagnetic separator to remove pyrites and then hand sorted. The company shipped the sapphires to London where the best quality were cut for gems while others were refined for watch jewels, instrument bearings and abrasives.