Pogo Gold Mine Symposium

By Aaron Thomas

David Rhys explains quartz vein structures at the Pogo mine.

On September 25 and 26, the University of Alaska Fairbanks hosted the Pogo Geology Symposium in a collaboration with Northern Star Resources and UAF’s Geophysical Institute to explore the geology of the Pogo gold mine. The speakers at the two day event included professors, graduate researchers, technicians, and mine workers who shared their insights and research. The symposium additionally gave students the opportunity to speak with career specialists in their field and help spark job interests in Northern Star Resources.

The Pogo gold mine opened in 2006 and is located about 30 miles northeast of Delta Junction. It is currently the eight largest producer of gold in the U.S. and one of the largest gold mining operations in Alaska. The mine lies at the intersection of geologic research and commercial interests as researchers utilize the mine to further refine gold mining processes and study the geology of the surrounding area.

Both days of the symposium drew about 70 attendees, which were a mix of Northern Star employees, UAF students and researchers. The lectures ranged from topics such as exploring the ore types of the mine, new innovations in gold recovery methods, and the potential extraction of critical minerals from the mining process. 

James Sweeney, a metallurgist for Northern Star, explained the various processes used to improve the efficiency of gold extraction and recovery. As mines age and the prime ore deposits are depleted, new recovery methods must be implemented to ensure profitability.

Sweeney explained that the easiest method of gold extraction is gravity separation, known as placer mining, which sorts particles in a rotating drum by weight in a process akin to gold panning. However, these microscopic particles of gold are only a portion of the total recoverable gold. Gold is often bound up in sulfides and other compounds that have to be chemically dissolved in a cyanide slurry to recover. 

Core samples and various minerals from the Pogo mine on display.

The efficiency of this secondary recovery process, known as leaching, is highly dependent on the grade and type of ore that is being used and how finely that ore is ground. Ores that contain high levels of clays, oxides, graphite, and talc can wreak havoc on machinery and clog tanks in the gold recovery process. Sweeney referred to these compounds as “party crashers” that present no issues in small quantities, but can upend operations at the mine in excess amounts.

The worst case of this at Pogo was the infamous “September Oxide Event” where the mill was shut down for two days after oxide rich slurry clogged equipment and flooded the facility. That event resulted in a $1.3 million loss in gold recovery and a $300,000 loss in downtime. 

Sweeney stressed the importance of learning how to process these alternative ore types. The original areas surveyed for the mine now only represent a small portion of the mill’s feed and they will be fully phased out by 2029. The new areas in the northern section of the mine that are being explored have different ore compositions and potentially much higher levels of these “party crasher” compounds.  

Sweeney explained that ore from the north portion of the mine with the current processing methods has significantly lower gold recovery than the ore from the older portions of the mine. He said that the mine must develop new processes to recover gold based on the geology of the new ore zones. Further collection of samples and research into the composition of the northern portions of the mine remains critical to smooth operation at Pogo. 

“It's important for us to continue to build that database for future roles. We have got a few samples done and we're starting a new campaign,” Sweeney said.

A presentation by Karen Spaleta explored the possibility of extracting critical minerals such as tellurium and bismuth from the ore the mine processes. The difficulty in extracting these elements is due to the fact that they make up only a miniscule fraction of the earth's crust by volume, making it not economically feasible to mine directly from deposits. Instead, they are usually extracted from tailings or as a part of another mining process such as copper or lead mining. 

Tanya Nayda and Marisa Acosta deliver closing remarks.

Most of the world’s tellurium and bismuth are mined and processed by China. Spaleta explained that this leaves insecurities in the supply chain because there is little to no domestic production of these elements in the U.S. Tellurium and bismuth are crucial for metallurgy and production of electronics such as solar panels.

The introduction of tellurium recovery would net the mine approximately $720,000 a year in an estimate from 2016 production levels and average tellurium prices from 2020 to 2024. While the mine already makes more than that in net profits in a single day from gold alone, from a perspective of national supply chain stability it would be a strategic investment. Extracting tellurium from the Pogo mine alone would boost domestic tellurium production in the U.S. by 13 percent. If issues in the global supply chain arouse, U.S. companies would have higher certainty that their access to these elements would remain stable.

“The mines that are producing tellurium as a byproduct, like Kenford and Rio Tinto, they are, you know, they're not doing it because they're making money,” Spaleta said. “They're doing it because there's social value for them to be able to say, hey, we're producing tellurium.”

The Pogo Geology Symposium concluded around 4 p.m. on the second day with closing remarks from Marisa Acosta and Tanya Nayda who were both presenters at the event, thanking attendees and organizers for making the event possible. 

While most attendees were exhausted from two days of nonstop presentations, several rounds of applause echoed throughout the auditorium. 

“I think it was very successful today, I'm just glad that everybody seemed to be really engaged,” said Nayda. 

The executive general manager for the Pogo Mine, Jim Coxon, said, “I think it's just been amazing in terms of the collaboration, the information shared, everyone coming together, and really just being part of that process.”  

As attendees left, the Pogo mine is positioned to enter a new stage in its lifecycle through expansion, diversification of gold extraction methods, and potentially introducing critical mineral extraction to the milling process.