Nevada Fourmile: Journey to a High-Grade Au Discovery
In late 2015, Barrick was nearing completion of an important exploration drilling program in Nevada—and it wasn’t going well. The program, located in an area known as Fourmile, involved drilling 11 holes. Expectations for the program were high because the site was only about a kilometer away from one of the largest gold discoveries in recent memory, Goldrush.
Fourmile, it was hoped, would enhance the growth potential of Barrick’s Nevada properties, building on major projects already underway at Goldrush, Cortez, and Turquoise Ridge.
Yet, despite the proximity to Goldrush, the first 10 drill holes at Fourmile came up snake eyes. “We didn’t hit much gold,” says Nancy Richter, U.S. Exploration Manager at Barrick.
Lucky number 427
Then the core from the final drill hole, hole 427, arrived at the core shed. Keith Testerman, District Geologist for Barrick’s Cortez District and project lead on Fourmile, was there when the core was logged.
“A geologist on my team brought the core from the drill rig and laid it out,” Testerman recalls. “Within a few minutes, he called me over and said, ‘You might want to come and look at this.’”
Like most geologists, Testerman uses technical terminology when talking about rocks. In describing the findings from hole 427, he notes that the silicification, brecciation, and high sulfide levels in the core sample were all very encouraging. In layman’s terms, this means there were clues in the sample, or what geologists refer to as alteration, that were strongly indicative of high-grade ore.
“Grade is king in the mining business. The mineralization in hole 427 looked like high-grade ore encountered at other mines,” Testerman says.
Ore grade refers to the amount of gold contained in rock. The higher the grade the better, because less rock has to be removed from the ground to recover each ounce of gold, reducing operating costs.
While the sample from hole 427 looked promising, only lab tests could verify the presence of gold. Those results came several weeks later, confirming what Testerman and his team suspected: there was indeed high-grade ore in 427. Very high grade. One intercept included 5.8 meters grading 49.7 grams per tonne of gold—almost unheard of today in a mature industry where high-grade deposits are increasingly rare.
To put those numbers in perspective, the average ore grade of the measured and indicated resources at the Goldrush deposit stands at 9.27 grams per ton, according to the most recently published data. And the highest average reserve grade at any Barrick mine is 15.81 grams per ton at Turquoise Ridge, which is among the highest in the industry.
With the positive result from hole 427 in hand, the Fourmile drilling program continued. A series of new holes was sunk 300 meters to the north and south of hole 427, an activity known as wide-space drilling.
“In simple terms, we’ve got a fish on a hook, hole 427,” says Kevin Creel, Vice President, North American Discoveries. “Now we’re casting the net to try to see if there’s a school of fish in the area and how big it might be.”
In 2016, eight holes were drilled to depths of more than 900 meters, deeper than Barrick typically drills in Nevada. Two of those holes returned samples with high-grade gold mineralization. Last year, eight more holes were drilled with six returning high-grade gold mineralization.
As drilling progressed, the project team continued detailed mapping of the surface, interpreted the geology, and created 3-D models of subsurface rock formations. “You start with a blank slate and you slowly paint a picture that helps determine the potential scope of the deposit and where to drill next,” Richter says.
In June, drill results hit another geyser so to speak. The hole in question, hole 18-01, which is located about 120 meters from hole 427, intersected even higher-grade mineralization than hole 427. Testerman, Richter, and Creel are all highly-experienced geologists who rarely betray their emotions. Yet, even as they preach caution, noting that it’s still early days for Fourmile, their enthusiasm sometimes bubbles to the surface, like when they talk about hole 18-01.
“It was just like, ‘yes!’” Richter says. “This is what we’re looking for.”
In July, during its second-quarter conference call, Barrick confirmed that Fourmile is now considered a high-grade discovery with a footprint more than 600 meters long by 200 meters wide and growing. More positive results were announced in the Company’s recently completed third quarter
Based on this success, Barrick increased the budget for the Fourmile project by more than $10 million, allowing for a significant increase in drilling activity. The Company expects to drill 47 holes by year end, and it also expects to provide an ‘initial modest inferred resource’ for the deposit at that time. An inferred resource is a preliminary estimate of the total number of ounces in areas drilled to date. As drilling continues, in-depth studies will be conducted to confidently determine the size of the deposit.
A bright future in Nevada
At this stage, it is too early to answer questions such as whether Fourmile and Goldrush could eventually be mined together, says George Fennemore, Manager of Growth for Barrick Nevada. However, what is clear is that Fourmile is a potential world-class deposit that enhances Barrick’s already compelling growth story in a attractive mining jurisdiction where Barrick has extensive infrastructure, experience, and deep partnerships. That story will, Fennemore acknowledges, take time to play out and rely on sound execution as Barrick works to secure permits, obtain water rights, build infrastructure, preserve habitats, and ensure the sustainable benefits are shared by all.
“We have a really fascinating story in terms of what the future of Barrick Nevada looks like,” Fennemore says. “We’re not gold limited. We’re only limited by our ability to make good plans and get the work done.”