The mining newspaper for Alaska and Canada's North
The mining newspaper for Alaska and Canada's North
SMM Pogo to invest US$15M on exploring gold mine potential North of 60 Mining News – April 6, 2018
The mill at Pogo recovers roughly 750 ounces of gold per day from the high-grade gold veins at this Interior Alaska mine.
A gold-rich quartz vein currently being mined from the Liese zone at Pogo.
While Pogo has surpassed its original life expectancy of 10 years and 3 million ounces of gold, the air of excitement emanating from the miners, geologists and management indicates that mining is just getting started at this high-grade underground gold mine in the heart of Alaska's Interior.
Churning out 271,273 oz of gold from roughly 950,000 tons of ore in 2017, Pogo is on pace to pour its 4-millionth ounce of gold early in 2019 and based on current estimates would have enough ore in reserve to keep the underground mine in operation into 2021.
It has been a while, however, since the reserves for Pogo have been calculated and when that does happen – slated for later this year – we will likely be looking at enough high-grade ore to feed the mill for another decade.
And Pogo's exploration team is already hot on the trail of ore to extend this operation even further.
"Pogo is permitted to operate through 2021, but extensive exploration efforts are underway to identify additional ore reserves," according to the Pogo Mine website.
By extensive exploration, we are talking about a US$15 million program budgeted for defining and expanding known deposits – Liese zone, North zone, East Deep and South Pogo– as well as enticing news discoveries such as Goodpaster and Fun zone.
"Both very early staged exploration targets at Pogo but, based on the information we know, we are excited about them and are going to throw a lot of resources at them in the next couple of years," Pogo Exploration Superintendent Gabe Graf said, referring to the Goodpaster and Fun zones during a March 30 presentation at the Alaska Miners Association Spring Convention in Fairbanks.
Deeper Liese veins
The 3 million oz of gold reserves that got Pogo started were found in the Liese zone, three flat-lying, parallel quartz veins that carry high-grade gold.
"We are still mining on all three of those veins," Graf said, referring to the L1, L2 and L3 veins in the Liese zone.
Geologists theorize that Liese could host L4 and L5, veins waiting to be discovered below the mine workings, and this year's exploration program will include underground drilling aimed at seeking these deeper gold-rich veins.
While L4 and L5 are currently theories, L0, another vein above L1 is not.
L0 is now mostly eroded away, leaving behind a rich gold-in-soils anomaly that led to the discovery of the Liese zone in the 1980s.
If it was not for the gold that weathered off this surface vein, there is a good chance that geologists would not have found enough gold to intrigue future investigations of the area and Pogo could still remain hidden in the heart of Alaska's Interior.
"So, if you are out exploring in this area and you don't have a big soil anomaly like this, I wouldn't get too discouraged about it," Graf advised.
In fact, three decades after gold was first identified in the soil at Pogo and 12 years after mining began, the exploration team continues to find zones surrounding Liese that are rich in high-gold veins – most of which are not as evident on the surface.
Less evident gold zones
East Deep, a twin to Liese, is one of the less evident zones discovered by the SMM Pogo exploration team in 2010.
Geological and metallurgical evidence indicates that the Liese and East Deep zones were once a single body of gold-rich mineralization split by a wedge of gold-barren igneous rock (diorite) some 95 million years ago.
The Pogo mill sits on this wedge, making mining of East Deep as convenient as the original zone.
"We are still mining in the East Deep area," Graf said during his presentation at the AMA convention.
While East Deep and Liese appear to have been torn apart by intruding igneous rocks, the zones are linked at the North Zone, a group of higher grade vertical veins that lie at the north end of the diorite.
In 2014, SMM Pogo drove two drifts from the underground workings at East Deep to the North zone, which is now supplying ore to the Pogo mill.
The company is also getting ready to begin sourcing ore from Pogo South, two flat veins that extend off the south end of the Liese zone.
"Those are currently in development and we should start mining in there within the next year," Graf said.
The exploration team had hoped that South Pogo would be a large orebody but recent exploration has discovered that the diorite that splits the Liese and East Deep zones curls around and cuts off expansion.
"It was quite unfortunate because we were hoping to keep adding resource to that South Pogo vein," said the exploration superintendent.
Gold vein detector
Graf has identified a geophysical tool – controlled-source audio-frequency magnetotellurics or CSAMT – that is helping the exploration team see buried structures that commonly host gold veins.
Basically, CSAMT provides a picture of subsurface variations in the Earth's electrical and magnetic fields, providing geologists a clue as to the type and metals content of rocks below the surface.
After taking a look at results from older surveys and comparing the results to where there is known gold mineralization, as well as where there is not, Pogo geologists knew they had a tool finding the types of structures known to host gold veins in areas where there is not a lot of surface indications of the precious metal.
Graf requested a small CSAMT survey to be part of the 2017 program at Pogo but the mine's owners had bigger plans.
"Sumitomo came back and said, 'do the whole district," so we did a 120-line-kilometer survey last year," the exploration superintendent said.
The results from this survey are helping Graf and the rest of the Pogo exploration team choose targets for an extensive exploration drill program slated for this year.
Excited about Goodpaster
Most of the 2018 exploration drilling will target two exciting prospects to the north of current mining – Fun zone extension, which lies west of the North zone and north of the Liese zone, and Goodpaster, a high-grade gold prospect north of the Goodpaster River that has a geophysical signature that indicates it could be up to 5,000 meters long.
The Fun zone extension is a vertical structure that hosts mineralization that is different that what is typically encountered at Pogo.
While the Pogo team still has a lot to learn about Fun zone extension, one thing they do know is that it hosts some very high-grade gold.
"Our highest interval has been about 10 oz/ton," Graf said.
Despite these high grades and the Fun zone's proximity to the mill, the exploration team is even more enthusiastic about the potential just across the river.
"We are really excited about the Goodpaster right now," Graf said.
The Camp Creek fire burned off the trees and other cover across the Goodpaster prospect area in 2006, providing an ideal opportunity for Pogo geologists to take soil samples in the area.
With the soil samples returning promising gold, Pogo drill crews tested this zone last year.
The first hole drilled at Goodpaster in 2017 tapped 22.8 feet averaging 0.103 oz per ton gold
"We were pretty excited about that, being a mile or mile-and-a-half away from the Liese zone," said Graf.
The team was even more excited about the 17.5 feet of 1.739 oz/t gold cut during the second hole drilled at Goodpaster.
Graf said the core from these mineralized intercepts at Goodpaster looks identical to Liese, providing evidence that the two zones may have once been contiguous and have since been separated by a fault that runs between them along the Goodpaster River and the geophysical results indicate this Liese-like prospect could extend for 5,000 meters along strike.
With SMM Pogo throwing a lot of resources into these exciting discoveries over the next couple of years, Fun Zone extension and Goodpaster could add years to the life of Pogo and the geophysics that helped to identify them could be another tool for seeking other gold veins across the wider Pogo District.
Over his more than 16 years of covering mining and mineral exploration, Shane has become renowned for his ability to report on the sector in a way that is technically sound enough to inform industry insiders while being easy to understand by a wider audience.
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