ALL ABOUT THE YOGO SAPPHIRES

Yogo sapphires are a variety of corundum found only in the Yogo Gulch area, in Judith Basin county, Montana.  This gemstone rich area was inhabited by the Blackfeet Indians long before anyone thought about mining Montana sapphires.  Mining Yogo sapphires has been much more troublesome than other deposits because of the fact that Yogo sapphires occur within a vertical Dike.  Through the years, mining efforts have been off and on and rarely profitable.  The Yogo mine was recently closed again, this time due to the untimely death Mike Roberts. Luckily the Vortex mine has since re-opened and the Yogo sapphires will again be available to all those that love them.  Even after years of mining and with countless Yogo sapphires sold in Europe, it’s estimated that at least 28 million carats of Yogos still remain in the ground.     In 1969, the sapphire was co-designated along with the agate as Montana’s state gemstones.  Today, several sapphires are part of the Smithsonian Institutions gemstone collection including a Yogo over 10cts in size.

Photo by Chip Clark.

Discovery of the Yogo Sapphire

Sapphires were first discovered in Montana in 1865, in the gravel along the Missouri River. Finds in other locations in the western half of the state occurred up to 1892, and 1894.  Yogo sapphires were not recognized or valued at first. Gold was discovered at Yogo Creek in 1866, and though “blue pebbles” were noticed alongside gold in the stream gravel by 1878.  It was not until 1894 that the “blue pebbles” were recognized as sapphires.  Yogo sapphire mining began in 1895 after a local rancher named Jake Hoover sent a cigar box of gemstones he had collected to an assay office. The assay office then sent them to Tiffany’s in New York, where an appraiser pronounced them “the finest precious gemstones ever found in the United States”.  Tiffany’s fell in love with the Montana gemstone and is still a large retailer of the beautiful Yogo sapphires today.  Hoover then purchased the location of the original mother lode from a sheepherder, later selling it off to other investors. This became the highly profitable “English Mine”, which flourished from 1899 until early 1920.  A second operation, the “American Mine”, was owned by a series of investors in the western section of the Yogo dike. This yogo sapphire mine was less profitable and was bought out by the syndicate that owned the English Mine. In 1984, the Vortex mine opened and found montana yogo sapphires to be gemmy and plentiful.  Unlike the gem mountain sapphire mine, these gems didn’t need heat treating for color and clarity reasons.  Yogo sapphire mine Lewistown Montana was on a few miners bucket lists.

In the early 1980’s Intergem Limited controlled most of the Yogo sapphire mining at the time. They started  marketing Yogo sapphire as the world’s only guaranteed “untreated” sapphire. Thus exposing a practice of the time wherein 95 percent of all the world’s sapphires were heat-treated to enhance their natural color. Although Intergem went out of business, the gemstone it mined appeared on the market throughout the 1990’s. Citibank had obtained a large stock of Yogo sapphire as a result of Intergem’s collapse. They hoarded their stock of sapphire for nearly a decade before selling the collection to a Montana sapphire jewelry store in 1994. Mining activity today is largely confined to hobby miners in the area; the Vortex yogo sapphire mine is the only major commercial mine currently in operation.

Montana Yogo sapphire deposit

Yogo sapphires are mined in Montana at Yogo Gulch, 12 miles southwest of Utica, 45 miles west-southwest of  Lewistown and east of Great Falls.  The yogo sapphire mine site resides inside Judith Basin County and was carved out from parts of western Ferguson and eastern Cascade counties.  This minor change in county lines appears to have had no effect on yogo sapphire mining in the Lewistown area.

Yogo Gulch and the foothills of and including Yogo Peak, Yogo Creek, and the Yogo dike, are all in the Little Belt Mountains. The Gulch is located along the lower reaches of Yogo Creek and west of the Judith river. The west end of the Yogo dike shows up just southwest of Yogo Creek.  After about 3 miles north and half mile east until you stop short of the Judith river. Yogo Creek starts just south of Yogo Peak, which is about 15 miles west of the Judith River. From there the creek flows southeast into the Middle Fork of the Judith River.  The Judith River then flows northeast from the Little Belts toward Utica. Just east of the Judith River is Jake Hoover’s ranch; the person who discovered Yogo sapphires.

Difference between Yogo sapphire and Montana sapphire

The term “Yogo sapphire” is the preferred wording for gems found in the Yogo Gulch.  Yogo Sapphires are the only sapphires in Montana still being mined from the primary deposit.  Yogo sapphire are typically cornflower blue, a result of small amounts of iron and titanium. They have high uniform clarity and maintain their brilliance under artificial light.

Dick Berg, industrial minerals geologist with the Montana Bureau of Mines and Geology in Butte, studies these gems for decade.  He found one thing clear, he doesn’t know why the 48-million-year-old Yogo sapphires are deep blue where as the other Montana sapphires, like those from the Rock Creek District near Philipsburg and the El Dorado deposit outside of Helena,  are much lighter shades.  These sapphires require heat treatment to enhance their colors. He speculates that the Yogo’s  cooling history may have something to do with it. Longer cooling times might’ve allowed the titanium and iron to spread more uniformly through the crystals, affecting the color. Yogos result from the luck of geology—just the right elements and just the right cooling history making a gemstone that is just about perfect.

All other “Montana sapphires” are found in alluvial deposits.  The term “Montana sapphire” generally refers to sapphires from any other Montana sapphire deposit besides the Yogo Gulch area.  More gem-quality sapphires are produced in Montana than anywhere else in North America.  Montana sapphire jewelry is going to be a sensation for many years to come.  Millennials have recognized the falsely inflated diamond market for what it is and are looking for responsibly mined alternatives.  Any of the Montana sapphires fit that bill.

The Rock Creek Montana sapphire location, near Philipsburg, is the most productive site in Montana.  Here these loose montana sapphire gemstones inspired the name of the nearby Sapphire Mountains.  Sapphire mining in Philipsburg, Montana persists at the Gem Mountain sapphire mine. The rest of the gem mountain mt area is predominantly being mined by the Potentate mining company.  Making this loose montana sapphire available to the jewelry community was a dream come true. These hero’s continue today, liberating these beautiful gemstones from the hills of Montana, supplying Montana jewelers for generations to come.

Yogo Physical Qualities

Montana yogo sapphire tend to be beautiful, small, and very expensive.  Sapphires are a 9 on the Mohs hardness scale, so they’re a gem that can withstand daily wear and be handed down for generations. The rough yogo sapphire crystal tends to be small and flat, so cut Yogo sapphires heavier than 2 carats are rare.  The largest recorded Yogo rough, found in 1910, it weighed 19 carats and was cut into an 8-carat gemstone.  The largest cut Yogo is 10.2-carat.  Large rough Yogo sapphires are rare and prices really jump once the gemstone is over a carat.  Montana sapphire prices are more reasonable and come in a rainbow of colors as well.  Yogo sapphire prices are crazy at this time with the closing of the roberts yogo sapphire mine in Lewistown.  Montana yogo sapphire can be a good investment – as long as they remain unique, the value will hold.  There’s a yogo sapphire jewelry company around Bozeman, Mt. that has resurrected the Vortex mine.  Many montana jewelers are anxiously awaiting loose yogo sapphires for sale.  These montana blue sapphires have been coveted for years, making this montana state gemstone a must have in any collection.  The Gem Gallery promises the shortage will be over before any real damage to the market has occurred.  Keeping customers happy and interested in gems in montana is important to all yogo sapphire jewelry dealers.  Answer this question…what color is montana?

Montana sapphires are a variety of corundum that have color in their crystalline form.  Corundum is one of the hardest minerals, rating 9 on the Mohs scale. Almost as hard as a diamond these gemstones are not only tough but show up in all colors of the rainbow. These gemstones are called sapphires, except for red ones, which are called rubies.  The term “Yogo sapphire” refers only to sapphires from the Yogo Gulch.  The cornflower blue color of the Yogo sapphire is mother natures results from trace minerals. Yogo sapphires are unique in that they are free of cavities mostly ,and have high uniform clarity, and do not need heat treating because their cornflower blue coloring is uniform and deep. Montana sapphires generally come in a variety of colors, but yogo sapphires are almost always blue. A very small amount are purple or sometimes violet in color. You will not find any green Montana sapphire at this deposit.  Gem mining in this area can be tricky so do your homework before you dig your gem dirt.

Value of a Yogo Sapphire

Color is the most important part in estimating the value of Montana sapphire.  Saturation of color through the gemstone will have the next greatest effect on the value. Hue counts, the closer to a pure blue the better, but saturation is more important.  Many of the gems on the market today are actually grayish.  And finally tone is also an important consideration as gemstones are examined. Dark sapphires are abundant and never reach very high values.  The same can be said for all dark gems, too dark and they will only be moderately valuable.  Too much light and they won’t stand out in any montana jewelry the yogo’s are set in.  Inclusions can be a common problem with all colored gemstones including the Montana sapphire.  Location is a huge part of the valuation of montana yogo sapphire, as these sapphires were formed differently than the rest of Montana sapphires.  Putting the yogo sapphire in a catagory of its own enables this gem to command a much higher price than typical montana sapphire.   The expense of sapphire mining in montana has increased which only adds to the over all cost of yogo’s.   Specialized sapphire mining equipment and explosives just piles on more.  Montana gem and Montana Gems both have yogo sapphire jewelry for sale with value based pricing.  As long as the world wants to buy montana sapphire its future is guaranteed.  As the public decides on the popularity of yogo sapphires demand will ultimately rule on the price.

Famous Yogo Sapphires

Jewelry containing Yogo sapphire was given to First Ladies Bess Truman and Florence Harding. First lady Florence Harding was given an “all Montana” ring made from a Yogo sapphire and Montana gold. In 1952, President Harry Truman had received cut yogo’s along with his wife Bess, and their daughter Margret from a yogo mine owner.  Many Yogo’s were also sold in Europe, as some Yogo mining was conducted by British interests.  Montana yogo sapphires may have been in the personal collections of some members of the British royal family in the 1910’s.  Yogo sapphire appeared in the personal gem collections of the Duchess of York, Princess Mary and Queen Victoria of England.  Historian’s also believe thay montana yogo sapphires, possibly misrepresented as oriental sapphire, were used for the British Royal Crown Jewel Collection.  Promotional claims that Yogo’s are in any of the crown jewels of England cannot be conclusively proven or disproven. Claims that the gemstone in the engagement ring of Lady Diana and Kate Middleton is a Yogo sapphire are suspicious; the gem is thought to be of Sri Lankan origin. The story that the gem is a Yogo can be traced to a  Los Angles Times article that described the ring as a 9-carat montana  sapphire, and quoted Intergem president Dennis Brown’s claim that the gemstone may have come from a British-owned Yogo mine.  

 Sapphire mining at yogo gulch

The yogo dike was a unique mining area compared to other sapphire sources in the world.  Unlike foreign sapphire deposits, all production records were known.  Intergem had mined only around 700,000 carats in the first 5 years.  Hardly a drop in the bucket compared to what was estimated in the reserves, literally only scratching the surface!  The reserves based on only a depth of 500 feet totaled around 40 million carats of montana yogo sapphire.  The actual depth of the dike however was estimated at over 7000 feet deep.  Without any exaggeration, the quantity of gem-quality blue montana sapphires contained in montanas yogo dike exceeded the sum total of those remaining in all of the worlds other known sapphire deposits.                                                                                                                                                                                                     This yogo sapphire mine was already planning for the day in the not so distant future when surface mining at the yogo dike would no longer practical or economical.  The switch to underground mining called for a unique mining method designed specifically for the way the dike was shaped and the nature of the dike rock.  Two shafts would be dug into the dike and regular mining methods would be used to prepare  the first stage of mine creation.  Overhead supports set into the adjoining limestone walls would suspend a moveable platform.  From the platform, miner’s would point high pressure water jets across the face of the dike rock.  The 600 pound per square inch water jets would break down the soft dike rock into a slurry which would fall to the bottom of the large underground room.  As the slurry fell to the lowest levels, grizzlies would retain the large fragments.  The slurry, containing the loose montana sapphire, would then pass through a series of gravitational and sizing jigs where the stones would be recovered.  The many advantages to this proposed system of underground sapphire mining involved minimal surface disruption which was friendly to the environment.  The elimination of mechanical mining and hauling steps that might damage or destroy the montana yogo sapphires were a long time coming.  A perfect security system for the sapphire recovery process was established in the easily controllred area of the underground workings of the mine.  A final advantage would be the elimination of surface disposal problems.  The tailings would be used to backfill mined out area’s of the underground portion of the yogo sapphire mine.

Our Tour of the Yogo Mine

We were lucky enough to get an invite to tour the Yogo sapphire mine.  We left early in the morning to start our adventure.  Our 3 boys were 10, 12 and 14 and this would be a real adventure for them and an unforgettable experience for us all.  It was a long drive to the Judith Basin area.  We stopped at a small cafe and had a nice breakfast before we headed out into the mountains to find the entrance to the Vortex Mine.  When we arrived, Mike greeted us and our fun was about to start.

We were all given hard hats and a brief explanation of what to expect. We donned our hard hats and headed into the darkness of the famous   Yogo sapphire mine.  Mike took us down the winding tunnels into the dark to show us where he was working the Yogo sapphire seam.  The material doesn’t occur in a very wide area but it was hopefully the location of the next big Yogo sapphire.  Along the way, we enjoyed beautiful calcite caves lined with sparkling crystals and found delicate mineral specimens that had formed deep inside the earth.  Mikes genuine love for the Yogo sapphire was unmistakable and his enthusiasm was contagious.

Now that we had a better idea of where the Yogos were coming from, the next stop was the Jig.  Mike offered our 12 year old to drive the mine cart out of the tunnels.  We left our boys in Mikes hands (figuring he couldn’t get off track too far due to the tunnel walls) and we headed up the tunnels back into the light. We got to see the trommel where all the dike material rolled around, hopefully releasing the yogos.  Then we headed up to see where the final, and most

exciting work took place.   Lou, Mike’s good friend and helper, and Mikes kids showed us around the jig where we all got to help pluck the fine blue yogo sapphires out of the steel shot.
The Natural beauty of these gems never ceases to 

amaze me.  The final part of our day consisted of Mike letting our boys hurl blasting sticks into the settling pond.  Although not actually necessary for  sapphire mining, it was definitely a highlight for the boys. We’d seen an actual, underground mine.  We got to see where the Yogo sapphires were coming from.  We got to see how the Yogo sapphires were released from their host material and how the miners then recover those sapphires out of the jigs. It’s a long process and Yogo’s are the most difficult sapphires to mine in all of Montana so we felt fortunate to have seen the process.

After a long day touring the Yogo sapphire mine, we were all pretty tired and extremely hungry.  Mining activities can take a lot out of you!  We sadly left the Vortex mine, figuring we wouldn’t get another experience like this anytime soon.  We were absolutely correct when not 6 months later, Mike had his fatal accident in the mine, changing Yogo sapphire mining as we knew it.

“The Finest Sapphire in the world…Bar None” ~ From the late Mike Roberts.