Name of the Project
Pebble copper/gold/molybdenum project.

Location
South-west Alaska, US.

Project Owner/s
Pebble Limited Partnership (PLP), wholly owned by Northern Dynasty Minerals.

Project Description
The Pebble project is the world’s largest undeveloped copper and gold resource. The project’s tonnes, grade, metallurgy and geometry have the potential to support a modern, long-life mine.

The project’s current resource estimate includes 6.44-billion tonnes in the measured and indicated categories containing 57-billion pounds of copper, 70-million ounces of gold, 3.4-billion pounds of molybdenum and 344-million ounces of silver. The inferred category of 4.46-billion tonnes contains 24.5-billion pounds of copper, 37-million ounces of gold, 2.2-billion pounds of molybdenum and 170-million ounces of silver. The deposit also contains palladium and rhenium.

The PLP is proposing to develop the Pebble copper/gold/molybdenum porphyry deposit as an openpit mine, with associated on- and off-site infrastructure, including:
• a 230 MW power plant located at the mine site,
• a 134 km transport corridor from the mine site to a port site on the west side of Cook Inlet,
• a permanent, year-round port facility near the mouth of Amakdedori Creek on Cook Inlet and
• a 303 km natural gas pipeline from the Kenai Peninsula to the Pebble project site.

The proposed mine will operate for about 20 years. This includes 14 years of mining using conventional drill-blast-shovel operations, followed by six years of milling material from a low-grade-ore stockpile. The mining rate will average 90-million tons a year, with 58-million tons of mineralised material being processed through the mill each year for an extremely low life-of-mine waste-to-ore ratio of 0.1:1.

Mine site facilities will include an openpit mine, tailings storage facilities (TSFs), an low-grade-ore stockpile, overburden stockpiles, quarry sites, water management ponds, milling and processing facilities, as well as supporting infrastructure such as the power plant, water treatment plants, camp facilities and storage facilities.

The openpit will be developed in stages and will eventually be 1 981 m long, 1 676 m wide and between 405 m and 533 m deep. A total of 1.2-billion tons of material will be mined, including 1.1-billion tons to be processed through the mill and 100-million tons of waste rock.

Nonpotentially acid-generating (non-PAG) waste rock will be used as a construction material for on-site roads and TSFs embankments. 

A small amount of waste rock considered non-PAG will be stored in a lined low-grade-ore stockpile until mine closure, at which time it will be back-hauled to the openpit for permanent subaqueous storage.

Mineralised material will be processed using conventional froth flotation. On average, the process plant will produce about 600 000 t/y of copper/gold concentrate containing an estimated 287-million pounds of copper, 321 000 oz of gold, 1.6-million ounces of silver and 15 000 t/y of molybdenum concentrate containing about 13-million pounds molybdenum.

A TSF, located in the North Fork Koktuli drainage, will store 1.1-billion tons of tailings generated over 20 years of mine operations. About 88% will be non-PAG bulk tailings; the remaining 12% will be pyritic PAG tailings, which will be stored subaqueously in a separate, fully lined cell within the TSF. Four TSF embankments, ranging from 18.3 m (east embankment) to 183 m (main embankment) in height, will be developed, with centre-line or downstream construction methods used for all external embankments. A conservative 2.6:1 (horizontal:vertical) slope is targeted to ensure safety and stability under all operating conditions, including maximum possible flood and seismic events.

Potential Job Creation
The Pebble project will directly employ about 2 000 workers during its four-year construction phase and an estimated 850 workers during its 20-year operations phase.

Net Present Value/Internal Rate of Return
Not stated.

Capital Expenditure
Capital expenditure on Pebble is estimated at between $6-billion and $8-billion.

Planned Start /End Date
Not stated.

Latest Developments
The Environmental Protection Agency (EPA) has moved to ensure it has a role negotiating the terms of any permit for the Pebble project, a move that may bolster the permit’s chances of approval.

The EPA’s action comes as the US Army Corps of Engineers evaluates how the mine will affect the region’s water, land and thriving salmon fishery. In comments filed with the Army Corps, the EPA has invoked a provision in a federal clean-water law that will enable top officials from both agencies to work out disagreements over a potential mine permit.

The EPA has decided to resume the consideration of proposed water pollution restrictions that have threatened the project since the Obama administration outlined the restrictions in 2014.

The EPA’s continued involvement could be welcomed by supporters of the mine and Northern Dynasty Minerals.

However, the EPA has emphasised that its action should not be viewed as a decision on the project or what to do about the five-year-old proposed restrictions. Regional EPA officials are coordinating with the Army Corps “to ensure that the EPA can continue to work with the Corps to address concerns raised during the permitting process,” the agency has said.

Under another administration, the EPA’s intervention might signal the agency’s desire to prod the Army Corps into rejecting a permit, Natural Resources Defense Council senior advocate Taryn Kiekow Heimer has said. Now that President Donald Trump’s EPA is reconsidering the 2014 restrictions, the opposite outcome is possible, she has said.

The EPA has told the Army Corps that it believes the proposed mine poses a “substantial and unacceptable” impact on an “aquatic resource of national importance” – a legal threshold for the agency’s continued involvement.

The EPA has also criticised the Army Corps’ draft environmental-impact statement on the project, saying it “appears to lack certain critical information” and “likely underestimates impacts and risk”. The EPA has said it has “concerns regarding the extent and magnitude of the substantial proposed impacts to streams, wetlands and other aquatic resources that may result” from the project.

Project critics have said the Army Corps’ analysis takes a narrow view of its potential impacts, failing to consider the collective damage from potential leaks and spills at the site.

“The Pebble Mine project is the largest, most complex and riskiest resource project proposed in Alaska . . .In spite of this, it is being evaluated with the most flawed and rushed environmental impact statement that I have ever been aware of,” former deputy commissioner of the state’s Department of Fish and Game McKie Campbell has said.

EPA general counsel Matthew Leopold has said that the consultation procedure is needed “to align the EPA with the Army Corps process to ensure that all potential significant impacts to the environment are thoroughly vetted and raised before any final decision on the permit can be reached”.

Developers, who have spent millions lobbying on behalf of the project, say the mine will tap a massive gold and copper resource. However, the project is located in an area that drains into Bristol Bay, home to the world’s most productive wild salmon fishery, raising concerns about its potential environmental cost.

Key Contracts and Suppliers
Wardrop Engineering (preliminary assessment report).

On Budget and on Time?
The Pebble deposit has inspired intense controversy, as a broad and bipartisan coalition – including environmentalists, Alaska natives and commercial fishermen – has fought its planned development, resulting in the EPA stopping the project in 2014. The election of US President Donald Trump, however, has fuelled hopes that a more mining-friendly EPA will enable the project to progress.

Contact Details for Project Information
PLP, tel +1 907 339 2600, fax +1 877 450 2600 or email receptionist@pebblepartnership.com.