Geology and Cu-Ni-PGE Geology and Cu-Ni-PGE Deposits of the Duluth Deposits of the Duluth Complex, NE MinnesotaComplex, NE Minnesota

Jim MillerDepartment of Geological Sciences

Precambrian Research Center (NRRI)University of Minnesota Duluth

A Looming A Looming StewardshiStewardship Question p Question

for for MinnesotaMinnesota

ns:ns:

When should we

develop this immense copper-nickel-

precious metal

mineral resource?

Talk Outline

Geological origin of the Duluth Complex

Cause and character of the Cu-Ni-PGE sulfide mineralization

World-class ore deposit by any measure

_______________

THE THE MIDCONTINENMIDCONTINENT RIFTT RIFT_______________An attempt at continental rifting 1.1 billion years ago

A. Rift Magmatism

Gabbro

MantlePlume

BasaltFlows

CrustMantle

B. Sediment Infilling Sandstone

C. Compression

1,109-1,086 Ma

1,090-900 Ma

1,000-900 Ma

Tectonic and Tectonic and Magmatic Evolution of Magmatic Evolution of the Midcontinent Riftthe Midcontinent Rift

Midcontinent Rift Midcontinent Rift Geology in the Geology in the Lake Superior Lake Superior

RegionRegion

DuluthComplex

Igneous Rocks of the Igneous Rocks of the Midcontinent RiftMidcontinent Rift

Partridge Partridge River River IntrusionIntrusion

South South KawishiwKawishiwi i IntrusionIntrusion

Multiple Multiple Emplacement Emplacement of Duluth of Duluth Complex Complex IntrusionsIntrusions

Sulfur Contamination creating the Cu-Sulfur Contamination creating the Cu-Ni-PGE Sulfide Deposits of the Duluth Ni-PGE Sulfide Deposits of the Duluth

ComplexComplexSSCu Ni Co Pd + Pt + Au

SS

Copper-Nickel-Precious Copper-Nickel-Precious Metal Deposits of the Metal Deposits of the Duluth ComplexDuluth Complex

Average GradesCu – 0.6%Ni - 0.2%Co – 0.005%Pd+Pt+Au – 500-1000 ppb

Based on Severson (1994)

Igneous Stratigraphy of the PRI and Igneous Stratigraphy of the PRI and SKISKI

$/t

on

Cu Prices 1948-2006

Cu-Ni Regional Study

1985 PGE discovered

1999 LTV shuts down

1948 Cu-Ni sulfide discovered at Spruce Rd

1954 INCO drills Maturi

1958 Bear Creek drills

Babbitt

1966 State lands open for mineral

leasingActive exploration

drilling Polymet, Teck, Franconia, Wallbridge

(Duluth Metals)

State land closed to new mineral leasing

Current $ - 7,060

History of ExplorationHistory of ExplorationFrom Severson,2008

Current Exploration ActivityPolymet – NorthmetTeck American – MesabaDuluth Metals – Nokomis, Maturi, Dunka Pit, Birch Lake, Spruce Rd Encampment– South Filson Cr.

The Current SituationThe Current Situation

Chalcopyrite - CuFeS2

Bornite - Cu5FeS4

Cobaltite - CoAsS

Chalcocite - Cu2S

Pentlandite - (Fe,Ni)9S8

Dominant Mineralogyof Magmatic Cu-Ni Sulfide DepositsPyrrohotite – FeS1-x

Talnakhite – Cu9(Fe,Ni)8S16

Why Sulfide Mining?Most of the world’s metals comes from sulfide minerals

ChalcopyriteCuFeS2

BorniteCu5FeS4

CobaltiteCoAsS

SphaleriteZnS

GalenaPbS

ChalcociteCu2S

MolybdeniteMoS2

Pentlandite(Fe,Ni)9S8

CinnabarHgS

The Environmental ChallengePreventing Acid Rock Drainage (ARD)

2FeS2(s) + 7O2(g) + 2H2O(l) →

2Fe2+(aq) + 4SO42-(aq) + 4H+(aq)

Precious Metal MineralsPrecious Metal MineralsPMM Name Formula Total #

Total PMM In Sulfide

Sulfide Host Mineral

cp pn cb po tn bn

Kotulskite Pd(Bi,Te)1-2 15 8 8 0 0 0 0 0

Froodite PdBi2 11 10 3 6 1 0 0 0

Naldrettite Pd2Sb 3 3 3 0 0 0 0 0

Paolovite Pd2Sn 83 68 45 10 7 4 1 1

Sobolevskite PdBi 2 2 1 0 0 0 1 0

Sperrylite PtAs2 26 22 13 5 3 1 0 0

Stibiopalladinite Pd5Sb2 11 5 4 1 0 0 0 0

Taimyrite (Pd,Pt,Cu)3Sn 2 2 2 0 0 0 0 0

Telluropalladinite Pd9Te4 1 1 1 0 0 0 0 0

Undetermined PGM   93 68 31 24 3 4 3 3

Silver sulfide AgS 16 11 7 3 1 0 0 0

Empressite AgTe 2 2 1 0 0 1 0 0

Hessite Ag2Te 3 3 1 1 1 0 0 0

Electrum AuAg 62 22 12 3 3 3 1 0

Gold Au 17 7 3 1 0 3 0 0

TOTALS   347 234 135 54 19 16 6 4

%     67% 57% 23% 8% 7% 3% 2%

PMM study of NorthMet ore, Cervin, 2011

PMM-Sulfide Connection PMM-Sulfide Connection /Disconnection/Disconnection

PdSn

cp

bn sperrylite

cp

pn

pn

cb

cp

cppn

cpx

bt

chl

cp

PdBi PdSbBi

cp

pn plagioclase

cp

Cervin, 2011

Deuteric alteration seperates PMM from host sulfide – implications for beneficiation

Styles of Mineralizatio

nafter Peterson (2001)

• Open (early)– vertically extensive (>

450 meters)– low - mod Cu-Ni grades

and very low Au+PGE– Cu-Ni grades typically

increase towards the basal contact

• Confined (late)– vertically restricted (<

150 meters) – mod - high Cu-Ni grades

and mod to high Au+PGE

– Cu-Ni grades typically are the highest near the top of the mineralized zone

P

Transition, Open - Confined Styles

Peterson, 2001

100% Sulfide Plots of SKI Open vs. 100% Sulfide Plots of SKI Open vs. Confined Styles of MineralizationConfined Styles of Mineralization

Deposits

Spruce RdDunka PitSerpentine

Deposits

NokomisMaturiBirch Lake

Open StyleN = 1,737

Open StyleN = 1,737

Confined StyleN = 13,868

Confined StyleN = 13,868

Peterson, 2012

New Maturi Mineralization New Maturi Mineralization StratigraphyStratigraphy

23Peterson, 2012

Emplacement/Mineralization Emplacement/Mineralization Model for the South Kawishiwi Model for the South Kawishiwi

IntrusionIntrusion

Peterson, 2012

World Class Ores of the Duluth ComplexWorld Class Ores of the Duluth Complex

#1 or 2 in contained Copper#4 in contained PGE#3 in contained Nickel

Compared to other Magmatic Sulfide Deposits, the Duluth Complex is:

Only the Bushveld, Great

Dyke, and Noril’sk contain more PGE

From Peterson, 2010

World Class Scale of the World Class Scale of the Maturi Deposit AloneMaturi Deposit Alone

Nokomis

From Peterson, 2010 and DM press release

12/2012

Maturi

Maturi

Maturi

The Largest UNDEVELOPED Cu-Ni-PGE The Largest UNDEVELOPED Cu-Ni-PGE Deposit on EarthDeposit on Earth

From Peterson, 2010

Duluth deposits are perceived as low grade. But compared to the source of most of the world’s copper - Porphyry Copper

Deposits...

…the Duluth Complex ores are HIGHER GRADE with MORE CONTAINED METAL than nearly all porphyry systems.

The largest copper ore deposits in the USA are on this diagram, and the Duluth Complex ores are much larger then all of them.

Stewardship question - If not now, when?Stewardship question - If not now, when?

CONCLUSION: CONCLUSION: The base and precious metal deposits of the Duluth Complex are a World Class Resource that will be mined …. SOMEDAY