From August 25 to September 11, world-renowned gem mining company Gemfields held an emerald rough auction for the Kagem mine in Zambia in Bangkok, Thailand, attracting widespread industry attention. Ruby, President of GUILD Gem Laboratories, and Andrew Lucas, Dean of GUILD Gemology Education, were invited to the auction site to gain an in-depth understanding of the auction dynamics.
Auction Overview
The total weight of rough material in this auction was approximately 140 kilograms, with the majority of the crystals exhibiting exceptional quality in core indicators such as clarity, size, and color.
The auction venue featured large windows and inspection stations with excellent natural lighting, allowing bidding companies to examine each auction lot at numbered stations.
The absolute focus of this auction was the giant emerald rough from the Kagem mine — the 11,685-carat "Imboo". On-site, Ruby, President of GUILD Gem Laboratories, and Andrew Lucas, Dean of GUILD Gemology Education, conducted a detailed examination of the "Imboo" emerald rough.
This rough crystal was discovered on August 3, 2025, by geologist Dharanidhar Seth and senior miner Justin Banda at the Chama pit in the Kagem mine. Justin Banda has previously played a key role in multiple major emerald discoveries. This particular find is not only remarkable in weight but also displays a complete hexagonal prismatic crystal habit — a characteristic particularly rare in large-sized emeralds.
Due to its immense size, Gemfields named it "Imboo," which means "Buffalo" in the local language. Jackson Mtonga, a senior expert at the Kagem sorting facility, stated: "In my 30 years of working at the Kagem mine, I have rarely encountered such exceptional high-quality large crystals. This is truly a masterpiece of nature."
"Imboo" exhibits a rare, high-quality color saturation typical of emeralds. According to Adrian Banks, Managing Director of Product and Sales at Gemfields, even though strong illumination is required to view the details, "Imboo" still reveals a rich emerald-green hue with a hint of warm golden glow, demonstrating good transparency.
Regarding the value and potential of "Imboo," Adrian Banks, Managing Director of Product and Sales at Gemfields, indicated that the "Imboo" rough could potentially yield several extremely high-quality, large-sized finished emeralds. He stated, "Such a rare batch of gem rough could very well be crafted into a complete high jewelry suite." He also noted that the Swiss jewelry brand Chopard once created an entire high jewelry suite using the 6,225-carat "Insofu" emerald discovered in 2010.
Notably, this "Imboo" auction includes a cutting-edge technological safeguard: future buyers will have access to traceability technology provided by Provenance Proof, a long-term partner of Gemfields. This technology ensures complete provenance for the gem; even after cutting, polishing, and other processing stages, subsequent owners can verify the gem's origin, confirming that their possession is indeed this historical discovery from the Kagem mine.
The Kagem Mine
As the single largest emerald-producing mine globally, the potential of the Kagem mine has long been verified. In addition to "Imboo" and the aforementioned "Insofu," the Chama pit has produced numerous heavyweight emeralds: the 5,655-carat "Inkalamu" discovered in 2018, and the 7,525-carat "Chipembele" (meaning "Rhino" in the local language) discovered in 2021. In 2022, it even produced a cluster of emerald rough crystals weighing nearly 190,000 carats in total, named the "Kafubu Cluster," repeatedly reshaping the industry's perception of large-sized emeralds.
In November 2022, the GUILD team was also invited to participate in the rough emerald auction held by Gemfields in Bangkok, observing this cluster of emerald rough crystals, totaling nearly 190,000 carats, up close.
In August 2019, Ruby, President of GUILD Gem Laboratories, and Andrew Lucas, Dean of GUILD Gemology Education, visited Zambia to observe the entire modern large-scale mining operation process at the Kagem mine. They also studied Gemfields' emerald classification and grading system, as well as their methodology for auctioning emerald rough through their auction system.
The mine is located in the Copperbelt Province of Zambia, in north-central Zambia, near the Kafubu River, approximately 45 kilometers from Kitwe, the center of Zambia's Copperbelt mining region. In 2007, Gemfields initiated two mining operations in this area. By 2008, Gemfields entered into a partnership with the Zambian government, holding a 75% stake and managing operations (with the government holding 25%). At that time, the mine had almost no output and was continuously incurring losses. It was only after Gemfields invested significant capital and technical expertise that it transformed into the world's largest emerald-producing region.
The total operational area of the Kagem mine is 42 square kilometers. Among these, the Chama emerald open-pit extends approximately 2 kilometers in length and reaches a depth of about 140 meters, making it likely one of the largest colored gemstone open-pits in the Kagem mine.
The formation of emeralds relies on stringent geological conditions. The Chama pit's ability to continuously produce giant emeralds is intrinsically linked to its unique geological structure, as well as benefiting from Gemfields' mining methods.
Gemfields explains that the pit is located at a typical triple junction, an intersection of three distinct geological structures and rock layers, consisting of talc-magnetite schist (TMS layer), concordant quartz-tourmaline veins (QT veins), and discordant quartz-feldspar veins (QF veins). This unique geological environment provides ideal conditions for the formation of emeralds (particularly large-sized crystals), establishing the Kagem mine as a core mining district in the global emerald industry.
Additionally, Gemfields is one of the few companies investing significant capital in colored gemstone mining operations. The Kagem mine employs modern large-scale mining methods, which not only ensure high extraction efficiency but also allow for the long-term, stable supply of emeralds. This secures their own returns while providing support for the entire emerald supply chain.
To assess reserves, Gemfields has conducted extensive geological surveys. According to third-party independent analysis, mining operations at the Chama pit and another pit, Fibolele, in the Kagem mine can continue until 2044. Furthermore, Gemfields holds over 200 square kilometers of potential reserve areas, which may further extend the future mining lifecycle.
Conclusion
This emerald rough auction has not only garnered significant industry attention due to "Imboo" but has also once again highlighted the value of the Kagem mine as a core global emerald-producing region. The continuous production of heavyweight, high-quality rough from this mine consistently injects significant vitality into the global high-end emerald market. Following the auction, Gemfields will announce core transaction data, such as the total sales volume of the entire auction. GUILD Gem Laboratories will continue to track the final results of this auction and will subsequently convey more on-the-ground insights from various perspectives to global gem professionals and collectors, helping the market better grasp the cutting-edge trends and value trajectory in the emerald sector.
