By Jane R. Ward (and Nancy L. Attaway)
Jane Ward shared her knowledge of Yogo sapphires and explained the geology and the history of these unique Montana beauties. She began by citing several references: Yogo: The Great American Sapphire by Stephen M. Voynick, Corundum by Richard W. Hughes, and Heat Treatment of Ruby and Sapphire by Ted Themelis. Jane and her father, facetor Ken Ward cataloged Yogo sapphire inventory for Citibank, organizing and sorting the Yogos into specific parcels.
Four primary deposits yield Montana sapphires: Missouri River, Rock Creek, Dry Cottonwood Creek, and Yogo Gulch. The Yogo Gulch sapphire deposit is “in situ”, an extremely rare geologic occurrence for sapphires. Most Montana sapphires are sifted from alluvial (glacial) deposits of sands and gravels along riverbanks that originate from an unknown source a long time ago.
Yogo sapphires are quite different from the other sapphires found in Montana. For example, Yogo sapphires are not heat-treated, yet their color ranges in hue from cornflower to royal blue. An occasional violet blue or red color has been found. By comparison, other Montana sapphires show a rich diversity of color. The sapphires from the various Montana locales require heat-treatment to enhance their colors, a technology not made available until the 1970’s. Yogos are generally free of inclusions, while other Montana sapphires contain mineral inclusions. Glass and fluid cavities are also common in other Montana sapphires, showing as interference patterns. The other Montana sapphires exhibit crystal growth zoning, while Yogos show little or none. Yogos exhibit a characteristic trigon pattern that sometimes forms two interlocking triangles resembling the Jewish Mogan-David hexagonal star.
Yogo Gulch is located in Judith Basin County, Montana, east of the other sapphire mining sites. The Yogo sapphires are found in the Madison Limestone. This limestone was formed three hundred million years ago, when an inland sea covered Montana. The resulting sediment of silt and shell animals combined to produce a layer of limestone. This limestone layer is a part of the Big Snowy Group that includes shales, sands, and silts.
A fault that trended northeast/southwest sliced through the limestone. Groundwater percolation through the faulted limestone hollowed out caves (karst topography) near and at the center of the fault. The collapse of the caves formed breccia (broken rubble).
The sapphires were conceived at depth and were brought to the surface along the fault. Three hundred thousand years ago, dike material intruded along the fault system around the breccia fragments. Geologists date the dike as post-Pennsylvanian and call it a Lamprophyre. The dike is nearly vertical, measuring three to twenty feet thick. It lies seven thousand feet deep and runs five miles long, with a descent of eight hundred feet from Judith Meadow to the walls of Yogo Canyon. The dike brought fine-grained crystals of pyroxene, biotite, anorthite, olivine, nepheline, along with diopside, orthoclase, magnetite, ilmonite, pyrite, hematite, zircon, feldspar, apatite, lencite, and spinel.
More limestone solution occurring around the fault generated additional caverns. Sediments collapsed the caverns, and the dike fell in with the silts and sandstones.
The chemical formula reads as:
Al2SiO5 + SiO2 + NaAlSiO4 => Al2O3 + NaAlSi3O8
Kyanite plus quartz plus nepheline converts to corundum plus albite. The presence of nepheline is significant, because nepheline provided aluminum to make aluminum oxide. The cause of the strong saturation of blue is from an intervalence charge transfer, where iron and titanium combine and share an electron, replacing aluminum. The concentration of the iron and titanium ions determine the saturation level of sapphire. The blue hue of the Yogo sapphire trends toward purple, rather than green. The few rubies from Yogo Gulch obtain their red color from chromium 3+.
The slow crystallization of Yogo sapphires, over approximately fifty million years, produced clean sapphire crystals having a relatively even distribution of color saturation. It also allowed time for the foreign materials to be pushed out of the crystal matrix.
Sapphire mining in southwest Montana evolved from the gold rush during the 1860’s. Drawn by the promise of vast riches, people traveled great distances to search for gold in Montana. Those prospectors with gold mining experience in California constructed wooden sluice boxes to separate the gold from the river gravel. Heavier than gravel, the sapphires sank to the bottom of the gravel concentrate and clogged the sluice boxes. Most of the goldminers threw away these “nuisance” pebbles.
Gold prospector, Ed Collins first discovered Montana sapphires in 1865. He correctly identified as sapphires the unusual small colored translucent pebbles found in the sluice mixes. He judged their value to be significant and sent parcels to Tiffany and Co. and to M. Fox and Co., both of New York. The sapphires that Ed Collins collected were from the Missouri River and did not have the strong blue color of Yogo sapphires. Quality was lacking, and this gave sapphires from Montana a bad name.
Working another area, goldminer, animal trapper, and mountain man, Jake
Hoover collected the blue pebbles
from Yogo Gulch and in 1894 sent them to George F. Kunz of Tiffany and Co. in New York. Hoover soon received a check for $3750 from Tiffany for “sapphires of unusual quality”. He formed the New Mine Sapphire Syndicate in 1894. A London jewelry firm purchased all the shares and changed the name to the English Mine. The English Mine was in production under the direction of Charles Gadsden and sold in 1922 for $150,000.
Jim Eiten, a sheepherder, noticed a row of gopher holes corresponding to the fault line. He filed a claim on Yogo Gulch and sold it to Hoover for $2,450.
Since most of the recovered Montana sapphires from other locations were of pale colors, they attracted little interest in the gem markets at that time. Marketing the Montana sapphire hues proved difficult in an era when the classic royal blue color from Kashmir and Ceylon stood as the benchmark of comparison in all of Europe. The lack of an American cutting and marketing organization also contributed to the problem of promoting Montana sapphires. However, the natural blue hue of the Yogo sapphires interested the London marketeers, who sold the Yogos as sapphires from the exotic and romantic location of Ceylon. Yogo sapphires compared well with the sapphires from Ceylon, but Yogos did not have the intense color saturation as the sapphires from Kashmir.
Charles Gadsden, who was quite familiar with mining techniques, began
work at the English Mine in 1902. He re-worked the old mining tailings,
installed timber shorings, and organized bucket brigades. He allowed the
rock time to weather for a year or so, which was all very time consuming,
but in the end, was most efficient.
Burke and Sweeney filed claims west of the English Mine and formed the American Gem Syndicate in 1901, which was sold to the American Sapphire Company in 1904 for $100,000. The English Mine purchased the American Mine in 1908 for $80,000 and sold it in 1913.
A cloudburst from a severe storm flooded the English Mine in 1923, destroying holding dams and washing away weathering piles. The mine closed in 1927. During World War Two, four million carats of Montana sapphires were used in the war effort for abrasives, bearings, and jewels in watches. Siskon, Inc. purchased the Yogo Mine in 1965 for $75,000, and he promoted the area to California investors in 1968 as a “sapphire village” tourist mecca.
Chikara Kunisaki, one of the sapphire village partners, purchased the
Yogo Mine and formed the Sapphire International Corp. in the early 1970’s.
He invested $5 million in constructing a 3,000-foot-long tunnel going eastward
into the dike at the old American Mine site. Sapphire International Corp.
closed in 1976. Intergem contracted to purchase the Yogo Mine in 1981 from
Sapphire International Corp., now Roncor, Inc. However, Intergem failed
to make their payment deadlines, and ownership reverted back to Roncor,
Sapphire-Yogo Mines, Inc., headed by Victor di Suervo, leased the Yogo Mine property in 1978. With his idea of an grand advertising and marketing campaign for Yogos, di Suervo sought and won official trade recognition for Yogos. He wanted the Yogo sapphire to also become the official American gemstone. Many complications led to his subsequent failure.
Other individuals and companies leased the Yogo Mine, including American Yogo Sapphire, Ltd., who attempted an ambitious fund-raising campaign. Later, Amax core-drilled and opened up a new area fifty feet down. Jeff Kunisaki, G.G. currently heads Roncor, Inc.
Perhaps, one of the most famous Yogo sapphires was the one chosen to
be set in a ring for a princess. Lady Diana Spencer received from England’s
Prince Charles a magnificent nine-carat oval Yogo sapphire that was set
in a gold ring and surrounded by diamonds to mark their engagement. The
rest, as they say, is history.
Stories of riches and ruin surround Yogo sapphires. Many perceived the true value of Yogos and recognized their great potential. Many companies attempted to extract them commercially and failed. One difficulty is that such hard rock requires weathering to loosen the Yogos from their source. Blasting only fractures the sapphire crystals. Today, a small market for Yogos exists.