Gem News International Gems & Gemology, Spring 2025, Vol. 61, No. 1

Update on Montana’s Rock Creek Sapphire

Tao Hsu

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Figure 1. Left: The open pit mining operation in the “meadow” area of the Rock Creek deposit. Right: The recently built 10-jig processing plant at the new mining area. Courtesy of Potentate Mining.
 
Figure 1. Left: The open pit mining operation in the “meadow” area of the Rock Creek deposit. Right: The recently built 10-jig processing plant at the new mining area. Courtesy of Potentate Mining.

Sapphire, rough and faceted, from the Rock Creek deposit in Montana has become one of the pillar gems of American origin in the global colored gemstone market. Over the past 10 years, Potentate Mining, the company operating the mine and marketing Rock Creek sapphire, has successfully developed a solid clientele base in North America. The rough sapphire business has been robust, including successful sales at this year’s AGTA show.

The company has had a mission to bring Montana sapphire to a wider retail market in the United States. To accomplish this goal, steady sizable production of rough sapphire and a more diverse clientele around the globe are some of the prerequisites.

Figure 2. An assortment of rough sapphires (5–10 mm in diameter) extracted from the new mining area displaying characteristics typical of stones from the Rock Creek deposit, including many with a yellow “yolk” at the center. Courtesy of Potentate Mining.
 
Figure 2. An assortment of rough sapphires (5–10 mm in diameter) extracted from the new mining area displaying characteristics typical of stones from the Rock Creek deposit, including many with a yellow “yolk” at the center. Courtesy of Potentate Mining.

Potentate Mining has secured both the Eureka Gulch and the Rock Creek mining properties over the past 10 years in the Gem Mountain District near the historic town of Philipsburg in Montana. This includes the old alluvial workings and the surrounding hilltops, the largest privately held sapphire mining claim since the late 1800s. The newest development at the mine occurs in the “meadow” area that has not been worked on for decades (figure 1, left). To increase the processing capacity, a new washing plant was recently added to the site (figure 1, right). The new plant features 10 jigs and a water recycling system. Six out of the 10 jigs work on sapphires of a normal size range. Two other jigs process oversized sapphires, and the last two manage the tiny sapphires and the limited amount of fine gold. The new mining area produces sapphire rough ranging from 2.5 to 12 mm, and the production looks similar to that of older mining areas on the hilltops (figure 2). With this new area in operation, the production of rough sapphire has increased.

Figure 3. The inaugural Montana sapphire tender was held in Bangkok at the end of 2024. Left: The auction space featured ample natural light and private cubicles for clients to view the lots. Right: Some of the larger Montana sapphire rough offered at the inaugural tender in Bangkok. Courtesy of Potentate Mining.
 
Figure 3. The inaugural Montana sapphire tender was held in Bangkok at the end of 2024. Left: The auction space featured ample natural light and private cubicles for clients to view the lots. Right: Some of the larger Montana sapphire rough offered at the inaugural tender in Bangkok. Courtesy of Potentate Mining.

In an effort to expand the Montana sapphire market globally, Potentate Mining in collaboration with the Bonas Group, a reputable diamond and gemstone tender company, hosted an inaugural Montana sapphire tender in December of 2024 in Bangkok, Thailand (figure 3). As the global hub of colored gemstone trading, Bangkok attracts buyers from all around the world and is a crucial location for Montana sapphire trading. The tender offered nearly 80 kg of Montana sapphire rough. Most buyers had sapphire cutting and jewelry manufacturing expertise and were mainly from India, Thailand, and other Asian countries. According to Potentate Mining, the heated rough was their best seller, with its risk of heat treatment eliminated. This inaugural tender provided a good learning opportunity for both the buyers and the hosts. Most buyers were not very familiar with Montana sapphire; it will take them time to learn about the potential of these stones and their reaction to heat treatment. The seller will also need time to learn the preferences of these new buyers in order to provide proper goods.

The success of the inaugural tender moved Potentate Mining one step closer to bringing Montana sapphire to more consumers and being a key supplier of sapphire in the global marketplace. More tenders have been planned for the next few years. The increased sapphire production from this deposit will be able to supply both the North American market and the newly developed global clientele base.

Tao Hsu is technical editor for Gems & Gemology at GIA in Carlsbad, California.