Just how big is the high-grade Bornite copper deposit in Northwest Alaska? This is one question that South32 Ltd. wants to know as it considers paying Trilogy Metals Inc. US$150 million for a 50 percent interest in the Upper Kobuk Mineral Projects, an extensive land package that encompasses Bornite, the Arctic Mine project and dozens of other high-grade metals deposits and prospects in the Ambler Mining District.
While it will likely be many years before the full scope of Bornite is understood, the drill program carried out this year provides ample evidence that it is much larger than the more than 6 billion pounds of copper outlined in the current resource there.
We have essentially doubled the size of the mineralized footprint with an overall Bornite system now measuring 1,500 meters by 2,500 meters, said Trilogy Metals President and CEO Rick Van Nieuwenhuyse.
Already largeSouth32, which agreed to fund US$30 million on the advancement of UKMP over three years to keep its option to acquire half of the project in good standing, is focusing this initial investment on gaining a better understanding of just how big Bornite could be.
Between a combination of its own drilling and re-assaying core from historical drilling completed by Kennecott, Trilogy Metals has already outlined some 2.7 billion lb of copper in an open-pit resource for Bornite averaging roughly 1 percent copper; and another 3.7 billion lb in a deeper underground resource that averages about 2.9 percent copper.
Drilling completed by Trilogy in 2013 showed that the deepest and highest grade portion of this world-class copper deposit continues beyond a 1,000-meter-wide front to the north.
RC13-0220, the most northeasterly of the 2013 Bornite holes, cut two high-grade intervals from 809.1 meters (at a 0.5 percent cut-off) 45.6 meters of 1.07 percent copper; and 80.4 meters of 1.89 percent copper.
RC13-0224, drilled about 800 meters west of hole 220, cut two high-grade intervals from a depth of 513.3 meters along this northern front 229.4 meters of 1.73 percent copper; and 6.6 meters of 7.7 percent copper.
With the copper deposit getting deeper as it dipped to the north and the pool of exploration capital getting shallower, Trilogy had not traced the Bornite deposit further north until South32s initial US$10 million investment this year.
Aggressive expansionInstead of gradually tracing this resource with modest step-out holes, South32 opted for 300- and 400-meter step-out holes that would quickly determine whether or not Bornite extended for a considerable distance beyond the resource boundaries.
And with all seven holes that were drilled to target depth tapping high-grade copper, the 2017 drill program did not find the edges of the mineralization.
RC17-0234, the first hole of 2017, cut three high-grade copper intervals roughly 250 meters north of RC13-0220 21 meters of 1.29 percent copper; 26.8 meters of 1.44 percent copper; and 36 meters of 0.72 percent copper.
The top of the Bornite mineralization in hole 234 was reached at a drill depth of 935.3 meters.
RC17-235W, drilled about 250 meters west of hole 220, cut two zones of copper from a depth of 661.8 meters 6.1 meters of 0.69 percent copper; and 26.9 meters of 0.94 percent copper.
RC17-0236, drilled 300 meters north of hole 224, cut two high-grade copper intervals from a depth of 720.8 meters 27.1 meters of 0.8 percent copper; and 89.3 meters of 1.13 percent copper.
The initial three step-out holes at Bornite demonstrate that high-grade copper mineralization continues to the north and east of previously drilled resources, said Van Nieuwenhuyse.
Results from another four holes continue to show significant intervals of high-grade copper.
RC17-238, drilled about 300 meters southwest of hole 236, cut four zones of copper from a depth of 579.7 meters 10 meters of 0.61 percent copper; 4.9 meters of 2.11 percent copper; 5 meters of 0.55 percent copper; and 12.5 meters of 1.14 percent copper.
RC17-239, which was drilled roughly 400 meters east of hole 234, cut three copper zones 16.2 meters of 1.04 percent copper; 8.2 meters of 1.67 percent copper; and 26.1 meters of 1.46 percent copper.
RC17-237, which was drilled about 400 meters northeast of hole 236 and roughly 750 meters beyond the northern edge of the current resource, cut two copper zones from a depth of 947.9 meters 18.1 meters of 0.72 percent copper and 12.4 meters of 0.75 percent copper.
RC17-240, drilled about 400 meters northeast of hole 234 and roughly 800 meters north of the resource, cut 25.1 meters of 0.96 percent copper.
Overall, the seven holes completed this year demonstrate that the Bornite deposit extends more than 700 meters northeast of the current resource and over widths of at least 1,000 meters.
While these holes are too widely spaced to recalculate the Bornite resource, it is reasonable to assume that billions of additional pounds of copper will be added to this world-class deposit if infill drilling shows this mineralization is consistent across the broad expansion area.
Planning for 2018With the success of the 2017 program, Trilogy and South32 are already making plans for 2018.
"We are in the process of planning the 2018 program with an estimated US$10 million budget. One component of the program will include a seismic program to be completed in the spring time when the ground is still frozen and the daylight has returned, said Van Nieuwenhuyse. The balance of the program will be directed at further in-fill and expansion drilling.
The seismic technology that has been so efficient at finding pockets of oil deep underground is beginning to be applied to hardrock mineral exploration.
Sulfide deposits rich in copper, zinc and nickel deposits are particularly strong reflectors of seismic energy, making them good targets for adapting the successful petroleum exploration technology to minable minerals.
While much of the 2018 drilling will likely depend upon the results from the early season seismic work, we already know the location of two holes to be drilled next year.
Hole RC17-241, which is roughly in the middle of the northern expansion holes drilled this year, and RC17-242, which is about 400 meters west of hole 238, were started but could not be finished before winter weather set in at Bornite. These holes were cemented, making them ready for finishing when drilling resumes in 2018.
"It was unfortunate that we could not complete two of the planned holes due to weather, but rest assured that we will complete these next year, said Van Nieuwenhuyse.
Arctic PFS comingIn the meantime, Trilogy continues to finalize a pre-feasibility study for the Arctic volcanogenic massive sulfide deposit about 16 miles north of Bornite.
At a 0.5 percent copper-equivalent cut-off grade, Arctic hosts 36 million metric tons of in-pit indicated resources averaging 3.07 percent (2.44 billion lb) copper, 4.23 percent (3.36 billion lb) zinc, 0.73 percent (581 million lb) lead, 0.63 g/t (728,000 ounces) gold and 47.6 g/t (55 million oz) silver.
Trilogy said this resource is sufficient to support the upcoming PFS, slated for completion in the first quarter of 2018.
Arctic is pretty special we predict it will be one of the highest grade open pit copper projects in the world, said Van Nieuwenhuyse. Arctic is also located in the geographic center of a 100-kilometer- (60 miles) long belt containing over two dozen known grade polymetallic deposits and occurrences. It is not hard to envision a central milling concept with the other deposits potentially feeding the mill beyond the mine life at Arctic.