Bornite is an early-development stage carbonate hosted copper-cobalt deposit in the Ambler Mining District within the Northwest Arctic Borough (NWAB) of Alaska, the US.
Ambler Metals, a 50/50 joint venture (JV) between Trilogy Metals and South32, is exploring the potential development of the project along with the Arctic VMS deposit also located in the Ambler Mining District.
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In January 2022, Trilogy Metals released an updated mineral resource estimate for the Bornite Project.
It outlined indicated resources of 955 million pounds of contained copper and inferred resources of 5.3 billion pounds of copper and 88 million pounds of cobalt at the property.
Location and site details
The Bornite Deposit is located in the Ambler Mining District on the southern flank of the Brooks Range in NWAB. The site is around 25km southwest of the Arctic deposit.
It forms a part of the Upper Kobuk Mineral Projects (UKMP) mineral tenure package, which includes Arctic Deposit and additional mineral deposits.
The property is situated 248km east of the town of Kotzebue, 275km west of the Dalton Highway, and 19km north of the Kobuk village and 485km northwest of Fairbanks.
There is no nearby power infrastructure, or water access to the property.
The Bornite Project’s main camp is connected to the 1,525m Dahl Creek airstrip and village of Kobuk by a two-lane, two-wheel drive gravel road.
The property is mainly accessible by air using fixed-wing aircraft and helicopters.
Geology and Mineralisation
Bornite exhibits similar characteristics to deposits such as the Mt Isa district in Australia and the Tynagh deposit in Ireland among others which show emplacement in carbonate stratigraphy; early pyrite-dolomite alteration followed by copper dominant sulphide mineralisation.
The deposit area features alternating intervals of carbonate rocks (limestone and dolostone) and calcareous phyllite. Limestone transitions laterally into dolostone near mineralisation zones.
Mineralisation occurs within the Devonian aged Bornite carbonate sequence.
Bornite’s copper mineralisation is composed of bornite, chalcopyrite, and chalcocite as stringers, veinlets, and breccia fillings distributed in stacked and roughly stratiform zones.
The cobalt mineralisation is hosted as cobaltiferous pyrite within and enveloping copper mineralised zones and cobaltite and carrollite associated with copper bearing minerals directly.
Mineral resource estimate
According to the updated resource estimate, the Bornite Project contains in-pit indicated mineral resources of 41.7 million tonnes grading 1.04% copper for 955 million pounds of contained copper at a base case 0.50% copper cut-off grade and constrained within a limiting pit shell.
In-pit inferred mineral resources are expected to be 93.9 million tonnes grading 0.98% copper for 2 billion pounds of contained copper.
The combined South Reef and Ruby Zone estimated to host additional inferred mineral resources of 50.3 million tonnes grading 2.97% copper for 3.3 billion pounds of contained copper.
As Bornite is in early exploration stage, mineral reserves are yet to be determined.
Mining and recovery
The project’s mineral resources would be extracted using open pit and underground mining methods, based on the currently available information.
Long-hole open stoping will be used for thicker and high-grade mineral resources in the South Reef Area, while conventional cut-and-fill mining would be used for extracting narrower zones of mineralisation.
For recovery, a traditional process design is expected to be implemented for the project using standard grinding and flotation methods to produce copper concentrates.
The recovery will range from 89% to 90% to deliver copper concentrate grades with 26% to 28% copper in the range of 26-28% of copper.
Around 80% of cobalt, which occurs within cobaltiferous pyrite, will report to flotation tailings.
Power Infrastructure
The Bornite Project is not connected to Alaska power and transportation infrastructure.
A study published in 2013 assesses the feasibility of trucking LNG to Fairbanks to supply local utilities including power generation plants. It estimated that LNG use could significantly lower electrical power generation costs in Fairbanks.
Contractors involved
The updated mineral resource estimate for the Bornite Project was prepared by SIM Geological (SGI) and Bruce M. Davis (BMD). They disclosed it in a technical report prepared in accordance with National Instrument 43-101 and Form 43-101F1.
In November 2022, Trilogy Metals announced the first set of drilling results from the 2022 summer field season at the UKMP. ALS Minerals in North Vancouver, British Colombia was responsible for sample preparation and analysis.
