Mining Intelligence and News
United States

Twin Metals Minnesota (TMM) Project

Click for more information

Categories

Overview

Mine TypeUnderground
StagePermitting
Commodities
  • Copper
  • 3E (Pt, Pd, Au)
  • Nickel
  • Platinum
  • Palladium
  • Gold
  • Silver
  • Cobalt
  • Lead
Mining Method
  • Longitudinal retreat
  • Longhole stoping
Backfill type ... Lock
Mine Life... Lock
SnapshotTwin Metals Minnesota (Twin Metals) is a wholly owned copper, nickel, and platinum group metals underground mining project.

Further development of the current project, as configured, is on hold while litigation takes place to challenge several actions taken by the US federal government to deter its development.

In 2022, Twin Metals filed a lawsuit in the US District Court for the District of Columbia challenging the administrative actions resulting in the rejection of Twin Metals’ preference right lease applications, the cancellation of its federal mining leases 1352 and 1353, the rejection of its Mine Plan of Operation (MPO), and the dismissal of the administrative appeal of the MPO rejection.

In September 2023, following a motion to dismiss filed by the government, the District Court dismissed Twin Metals’ claims.

In November 2023, Twin Metals appealed the District Court’s order to the US Court of Appeals for the District of Columbia Circuit. This action is pending.

Owners

SourceSource
CompanyInterestOwnership
Antofagasta plc. 100 % Indirect
Twin Metals Minnesota LLC. (operator) 100 % Direct
The Twin Metals Minnesota Project is wholly owned by Antofagasta plc through Twin Metals Minnesota LLC.

Contractors

Lock

- subscription is required.

Deposit type

  • Magmatic

Summary:

The Project area would be located at the contact of two major bedrock units, the Giants Range Batholith (GRB) and the Duluth Complex.

The Duluth Complex is composed of mafic to felsic tholeiitic magmas related to the Midcontinent Rift System and makes up much of the bedrock of northeast Minnesota. It is bounded byafootwall of Paleoproterozoic sedimentary rocks and Archean granite-greenstone terranes andahanging wall largely of rift-related flood basalts and hypabyssal intrusions of the Beaver Bay Complex (Miller et al., 2002).

The targeted mineralization of the Maturi deposit is hosted within the basal portion of the South Kawishiwi Intrusion (SKI), known as the BMZ. The SKI is bordered on the southwest by the Partridge River Intrusion, on the northwest by the GRB and Biwabik Iron Formation, the Anorthositic Series to the northeast, and on the southeast by the Bald Eagle Intrusion. Excluding the transmission corridor, lithologic units within the Project area include Mesoproterozoic rocks of the SKI and the Anorthositic Series of the Duluth Complex, as well as basalt xenoliths of the North Shore Volcanic Group.

Surficial geology in the Project area is dominated by glacial deposits associated with the Rainy Lobe that include areas of peat and lake sediment. In some localities along the shoreline of Birch Lake reservoir, the Rainy Lobe Till has been eroded by water, resulting inaless rugged surface expression andapossible surface lag consisting o concentrated coarse-grained clasts. The lake sediment is predominantly silt, clay, and organic material (Jennings and Reynolds, 2005). The thickness of surficial material in the Rainy Lake Watershed is generally less than (<) 50 ft (15.6 m) and is laterally discontinuous. In the vicinity of the plant site, bedrock crops out in five to 20% of the area (Ericson et al., 1976).

The deposit is composed of anorthositic troctolite to troctolites. The mineralogy consists primarily of plagioclase, olivine, pyroxenes, and oxides which make up more than 85% of the total mineralogy. The alteration minerals (e.g., serpentine, chlorite, etc.) typically comprise 1% to 6% of the mineralogy but are locally found in amounts up to 15%. Sulfide content of the ore-bearing geologic units ranges from 1% to 6%, with very local areas having sulfide contents outside of that range.

The main four sulfides present in the deposit include:
• Chalcopyrite;
• Cubanite;
• Pentlandite; and
• Pyrrhotite.

Other copper and nickel sulfides are present in the deposit but occur in minor amounts (<5% total sulfides).

Rock units and mineralization in the BMZ are planar and sub-parallel to the lower contact with an average strike of approximately 60 degrees (°) and dips of 20° to 52° to the southeast. The vertical thickness of the potentially mineable grades varies in width from 49 to over 591 ft (15 to 180 m), averaging from 197 to 328 ft (60 to 100 m). The depth of the potentially mineable grades ranges between 984 to 3,005 ft (300 to 916 m) amsl. The Maturi deposit has not been significantly deformed, but it has been subjected to minor displacements along reactivated basement faults, as well as cross faults. Mapped structures are mostly sub-vertical north–northeasterly striking faults.

Reserves

Lock

- subscription is required.

Mining Methods

Lock

- subscription is required.

Comminution

Crushers and Mills

Lock

- subscription is required.

Processing

Lock

- subscription is required.

Production

CommodityUnitsAvg. Annual
3E (Pt, Pd, Au) kt 0.5
Copper kt 158
Nickel kt 76
All production numbers are expressed as concentrate.

Operational metrics

Metrics
Daily waste mining rate 3,300 tons *
Daily processing rate 20,000 tons *
Annual ore mining rate 7.3 M tons *
Waste tonnes, LOM 33 M tons *
Ore tonnes mined, LOM 180 M tons *
* According to 2019 study.

Production Costs

Commodity production costs have not been reported.

Required Heavy Mobile Equipment

Lock

- subscription is required.

Personnel

Mine Management

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Jun 6, 2024
....................... Subscription required ....................... Subscription required Subscription required Jun 27, 2024
....................... Subscription required ....................... Subscription required Subscription required Jun 27, 2024
....................... Subscription required ....................... Subscription required Subscription required Jun 27, 2024
....................... Subscription required ....................... Subscription required Subscription required Jun 27, 2024

Total WorkforceYear
...... Subscription required 2019

Aerial view:

Lock

- subscription is required.