Drill results add to Ambler-area copper prospect’s high-grade reputation

  • Core samples taken from a bore hole near the center of the proposed Arctic mine pit reveal significant veins of chalcopyrite, a common copper ore. (Photo courtesy Trilogy Metals)

Alaska weather hampered drilling at the remote Arctic hard rock mine prospect for much of the summer, but Ambler Metals was still able to identify mineralization that bolsters the company’s claims of a high-grade deposit, according to recently published drilling results.

The first two infill drilling holes located near the center of the proposed open-pit mine combined to hit three mineralized zones with copper equivalent grades of at least 4.77%. Those results were highlighted by a 19.9-meter interval of mineralization containing more than 6.7% copper, nearly 7.6% zinc and approximately 97 grams of silver per ton of ore, for an overall copper equivalent grade of more than 11.7%, according to the drilling report.

Trilogy Metals, the firm that first advanced the multi-metal Arctic prospect and is now an owner in Ambler Metals, the joint-venture operator, released the results Nov. 22 and Nov. 29.

Richard Gosse, vice president of exploration at Trilogy, said the zones hit near the heart of the pit are some of the best in the long history of the prospect.

“These assays from the 2021 drill program are an exciting start to the infill drill program at Arctic. Grades of almost 12% copper equivalent over 20 meters, considered close to true width, is one of the best intervals at Arctic since the first hole was drilled in 1967,” Gosse said.

Initially targeted for its copper, the Arctic deposit is the most advanced exploration project in the broad Ambler mining district along the southern edge of the Brooks Range in the Interior. Currently envisioned as a 12-year, open-pit mine with a startup cost estimated at just more than $900 million, according to a feasibility study published last year, the deposit is currently believed to contain about 2.1 billion pounds of probable copper reserves at an average grade of more than 2.2%.

Copper reserve averages exceeding 1% are generally considered high-grade deposits for large-scale mines. It’s that concentration of mineralization that has made the prospect attractive, Trilogy leaders have said.

The company also owns the nearby Bornite prospect currently estimated to hold roughly 6 billion pounds of copper.

Drilling on the northern edge of the delineated pit hit zones of nearly 25 meters averaging 3.5% copper equivalent and a 5.6-meter zone with a nearly 10.2% copper equivalent grade. The two bore holes hit multiple zones of silver exceeding 25 grams per ton, which contributed to the boosted grades of blended mineralization.

Gosse said the high-grade extensions were discovered in holes drilled primarily to collect geotechnical information.

Ambler Metals originally planned to drill and collect roughly 14,500 meters of core samples last summer but persistent low clouds kept the helicopters needed to support drilling grounded for extended periods, company leaders said in September. The Arctic program ultimately consisted of about 4,100 meters of drilling, according to Trilogy.

A decision to ultimately build the mine will depend primarily on how quickly the Alaska Industrial Development and Export Authority can progress development of the Ambler access road. Trilogy leaders have long said the 211-mile industrial-use road is a prerequisite to constructing any mine in the remote mineral belt.

Local governments for villages near the road’s planned intersection with the Dalton Highway have formally opposed the road over concerns it will impact migrating caribou and could eventually be opened to the public — thus increasing hunting and recreational pressure — in areas relied upon for subsistence harvests.

Critics have also questioned the economics of the toll road concept given the Arctic prospect is the only one in the region anywhere close to development-ready.

Elwood Brehmer can be reached at [email protected].

Updated: 
12/01/2021 - 10:20am