YOGO & MONTANA SAPPHIRES
Divine sapphires mined from Big Sky Country – Beautiful Montana
Montana sapphire can be found along the Missouri River District (Helena), Dry Cottonwood Creek(Deer Lodge), and Rock Creek(Philipsburg). These locations are in the western side of Montana.
Several sapphire bars can be found along the Missouri River, including the Spokane Bar, the Dana Bar and the El Dorado Bar. The El Dorado bar is one of the most famous bars due to its large deposits of both gold and sapphires. The El Dorado strike was one of the few mining operations that was allowed to operate during World War II, due to its large quantity of sapphires available for use as abrasives for the war effort. In more recent times, the El Dorado bar was a fee-digging area where diggers could pay a fee and be able to dig for their own sapphires.
Rock Creek (popularly known as Gem Mountain) near Helena, Montana is one of Montana’s more important secondary deposits. Large quantities of sapphires have been produced from this area. During the Mid-1990’s over 3.5 million carats were produced from Gem Mountain. The Rock Creek sapphires can be found in many colors including blue, green, yellow, pink, purple, and orange. These sapphires (unlike Yogo Sapphires) are heat treated.
Dry Cottonwood Creek flows northwest from the Continental Divide to join the Clark Fork River northwest of Butte. Sapphires have been mined from alluvial deposits along the South Fork of Dry Cottonwood Creek. Total production of sapphires in this area is less than that in other major sapphire deposits in Montana. Sapphires appear to be concentrated for about 2 miles along the South Fork of Dry Cottonwood Creek. They are also found in a small meadow close to the head of the South Fork. Common colors of the sapphires in this district range from pale blue to pale green to very pale blue to colorless. Some other colors that are less common include pink, pale orange, purplish pink, and amethyst. A few sapphires are dichroic, showing colors from pale green to pale blue.
Missouri River District sapphires occur in terrace gravels along a 22-mile stretch of the Missouri River northeast of Helena. They were first discovered by gold miners in 1865. Since then, at least seven individual deposits, called bars, have been mined for gold and sapphires. These bars are geologically known as strath terraces (A relatively horizontal, flat surface of gravel or other unconsolidated material that may have developed when a river was at a higher elevation.), where sapphire-bearing gravel was deposited by Missouri River. The largest of these is Eldorado Bar, which has an area of close to 2 square miles. Missouri River sapphires are typically pale green or pale bluish green. They are generally too pale to be sold as gems without heat treatment, but the percentage that responds to treatment is lower than those from Rock Creek. Rare deep blue sapphires, such as the Big Sky Sapphire recovered near French Bar in 1973, have also been found. The Missouri River features several sapphire bars including the Spokane Bar, the Dana Bar and the El Dorado Bar; these deposits are known as alluvium deposits. (Alluvium: from the Latin alluvius, from alluere, “to wash against” is loose, unconsolidated (not cemented together into a solid rock, soil or sediment that has been eroded, reshaped by water in some form, and redeposited in a non-marine setting.) In other words these deposits were created from the sapphires being eroded and washed down stream and settling in and around the banks of rivers and streams. It’s believed this is due to episodes of basin development and deformation in response to the Pacific tectonic plate folding below the western continental plate.