Name of the Project
Pebble copper/gold/molybdenum/silver/rhenium 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 biggest 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 every 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), a 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 construction material for on-site roads and TSF 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 of 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 for 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 US Army Corps of Engineers (USACE) has assigned a new review officer to the appeal of the negative record of decision for the Pebble copper/gold project. The USACE denied a key water permit for the Pebble mine project in in November 2020.

The new review officer, who was named after the previous officer had been promoted, is expected to set a detailed timeline for the administrative appeal process, including scheduling a potential site visit and appeal conference, in the weeks ahead.

PLP has been advised that the administrative appeal process for Pebble will take a year or more because of the complexity of the case and the scope of the administrative record, which contains 200 000 documents.

The PLP submitted a request for appeal of the federal permitting decision in January 2021.

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

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