Destination: Helena, Montana - The Yoga Dike
Planning a trip to dig for yoga sapphires. We will be going to the mine, so will let everyone know if we get lucky. Packed up a couple of classifying trays, pails, pan and shovel. The mine provides prospecting equipment, however, I am not sure what they offer and and I am used to my own tools. I won't need my metal detector for this trip but will take it along. Might find a spot that looks like it needs exploring.
Digging For Sapphires
"When the Yogo Dike, in Montana's Little Belt mountains, was formed millions of years ago, rocks located deep in the earth's mantle, melted to form molten magmas. Some of those magmas contained materials foreign to the continental crust.
One of these magmas rose into the Madison Limestone deposit, where it slowly cooled to form a dike an average of eight feet in width, but over five miles long. As the magma in the dike crystallized, atoms of oxygen combined with atoms of aluminum to form corundum, the mineral form of aluminum oxide. the corundum formed tiny, perfectly shaped transparent crystals rather than the usual blue gray prisms.
Virtually every crystal contained traces of iron and titanium that gave each crystal a beautiful cornflower blue color. Which makes Yogo Sapphire the most precious gemstone mined in the United States.
is one of the state's gemstones. Indoctrinated in 1969 along with Montana Moss agate. Sapphire's fame began a century earlier in the 1860's. Unpopular at the time because the small multicolored pebbles clogged gold sluices. In a time when, Gold, was the treasure of the day.
Eventualy the US Geological Survey termed the location "America's most important gem location." The British controlled the mines for nearly 30 years, explaining why the beautiful "Cornflower Blue" Yogo's are found in the Royal Crown Jewel Collection in London.
Over the years the Yogo mines have produced an estimated 40 million dollars in the precious blue gems. The original Yogo mines are currently being worked by commercial companies. The largest cut Yogo is 10.2 carats and is in the Smithsonian Institution in Washington, DC
The production of gem-quality sapphires in the United States is not new or recent. In 1865, the first U.S. sapphires were found in the gravels of the Missouri River in Lewis and Clark County, Montana. This was followed by subsequent discoveries on Dry Cottonwood Creek in Deer Lodge County in 1889, on Rock Creek in Granite County in 1892, and in Yogo Gulch in Judith Basin County in 1895. Additionally, small amounts of sapphire are recovered from Quartz Gulch in Granite County, Pole Creek in Madison County, the Missouri River in Chouteau County, and Brown's Gulch in Silver Bow County. Furthermore, corundum crystals, from which star sapphires have been cut, are found in Beaverhead and Madison Counties. Also, in 1895, the first sapphires were produced from the Cowee Valley in Macon County, North Carolina. But until very recently, with the exception of Yogo Gulch material, the commercial gemstone industry has had limited interest in U.S. sapphires.
Montana.--Mining of Yogo Gulch sapphires began within a year of their discovery in 1895 and continued for 39 years. In 1923, the mine was damaged so badly by rain that it could not economically recover. Other attempts have been made to commercially mine the deposit, but to date, all of these attempts have ended in economic failure.
Yogo's are unique among the world's sapphires. They lack the color zoning so prevalent in other sapphires, their uniform "corn-flower blue" color is natural (not the result of heat-treating), and their clarity is uniformly high. These features rank them among the world's finest sapphires. Unfortunately, the rough is both small and flat, wafer-like in shape. The majority of the crystals or pieces of crystals recovered are too small to be cut, most are less than 1 carat and finds of over 2 carats are rare. Reportedly, the largest crystal was a 19 carat stone found in 1910 that was cut into an 8-carat stone. The size of the cut stones greatly restrict the market for Yogo's, they are beautiful, small, very expensive sapphires.
Currently, Yogo sapphires are produced from three sources: Rancor lnc., produces material from the original Yogo Gulch deposit; Vortex Mining produces from a recently discovered extension of the Yogo dike; and material is produced by individuals from privately owned lots in Sapphire Village. The first two producers market only cut stones and finished goods and the third is comprised essentially of hobbyists.
Historically, the amount of sapphires produced from the Missouri River and Rock Creek areas greatly exceeded that from Yogo Gulch. However, the value of the material produced from Yogo, reported to be in excess of $30 million, is significantly greater than that of the combined values of the other areas. This relationship is rapidly changing.
The combination of large volume commercial operations on the Missouri River, and to some extent Rock Creek, plus the advent of successful heat-treating techniques for the material has greatly enhanced the acceptance of these sapphires by the gemstone industry. This enhanced acceptance has resulted in a significant increase in the market for and value of U.S. sapphires. Unconfirmed reports have circulated that a parcel of select 3- to 10-carat material, suitable for heat-treating, was sold for as much as $40,000 per kilogram. A more realistic price for 3- to 10-carat, sorted mine-run material is in the range of $5,000 per kilogram, with many kilograms of mine-run rough selling for $1,000 per kilogram.
The sapphires from the Missouri River gravels in Lewis and Clark County are a mixture of rough and pitted crystals showing well defined faces and completely rounded and smooth-surface highly stream worn pebbles. The majority of the material is pale blue or blue-green, with deep blue stones quite rare. Stones also are found in pastel blue, green, pink, pale red, purple, yellow, and orange. Most of the stones recovered are less than 6.4 millimeters in diameter, but material 6.4 to 12.7 millimeters in diameter are not uncommon. Material greater than 12.7 millimeters in diameter is rare.
Currently there are seven operations on the Missouri River that commercially produce sapphires and/or operate a dig-for-fee area. Not all of these may be active in any one year. It is the author's understanding that one operation, currently inactive, (a self-propelled floating 16-inch suction dredge) is for sale. The mines operate from about the last week of May through the first week of September.
The Rock Creek sapphires are very similar to the sapphires from the Missouri River but differ in the general shape of the crystals. The stones are basically crude hexagonal plates about the same dimension in width and height, with a much higher percentage of the material being well rounded water worn pebbles. There appears to be more of the larger sized (greater than 12.7 millimeters) material. Additionally, it is reported that the Rock Creek material has a greater percentage of stones that can be heat-treated for color enhancement.
During the past several years, there has been only a single producer on Rock Creek. The producer operated both a commercial recovery plant and a fee recovery area. The fee recovery area sold buckets of gravel for washing and also offered, for a predetermined fixed fee, the output of one day's operation of the commercial wash plant. There is work underway which would result in a second, much larger producer, opening an operation on another deposit in the area. If things go as planned, the new operation on Rock Creek would be the largest sapphire producer in Montana.
There are a number of locations between Dillon in Beaverhead County and Ennis in Madison County that produce lavender, grayish-lavender, bluish-gray, and gray hexagonal sapphire crystals that, when cut, produce stones that contain four- or six-ray stars. At least one producer from the Dillon area is currently advertising the availability of this type of material. The remainder of the sapphire deposits in Montana appear to be operated by individual hobbyists.
More should be said about the effects of heat-treating techniques on Montana sapphires, and the variety of fancy colored sapphires available. Not all Montana sapphires are suitable for heat- treating because of variations in chemical composition. Also, the sapphires from the Missouri River respond to heat-treating differently than those from Rock Creek The response to heat-treating can vary also depending upon the method (individual) used to treat the sapphires.
The yield on treatment of Missouri River sapphires is lower than for Rock Creek. It is reported that 20% to 30% of Missouri River sapphires heat-treat from deep, well saturated blue to pale, pale blue. The corresponding treatment rate for Rock Creek material is in the range of 60%. Heat-treating also yields or improves the color of fancy colored sapphires. Bright yellows and oranges are the result of heat-treating, whereas heat-treating improves the color of some pinks by removing colors that can interfere with the desirable pink shades. Montana sapphires can be diffusion treated, but because of their high iron content they are not particularly well suited for this form of enhancement.
North Carolina.--North Carolina is well known for its hobbyist production of sapphire. Sapphire have been produced from the Cowee Valley in Macon County since 1895 when the American Prospecting and Mining Co. systematically mined and washed the gravels of Cowee Creek. Today a number of dig-for-fee operations are located in the Cowee Valley. Each year many people pay to dig or purchase buckets of gravel to wash in hopes of finding a sapphire, garnets, and other gem materials. Many of the dig-for-fee operations have enriched the gravels with gem materials from other locations.
Every year articles appear in magazines and newspapers about large and valuable sapphires found at one or more of the mines in Cowee Valley. No doubt large corundum crystals and pieces of corundum are found each year. By the same token, valuable sapphires may be found, but the number of large valuable gemstones are far less than reported, and the values are generally not as great as reported. During the period when the area was commercially mined, gem material was found that would cut fine quality 3- to 4-carat stones, but the amount of quality gem material available has greatly declined. It is doubtful that North Carolina will ever again boast of commercial sapphire production, or that the commercial gemstone industry will seriously consider the State's sapphire deposits."