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

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Presentation on theme: "Geology and Cu-Ni-PGE Deposits of the Duluth Complex, NE Minnesota"— Presentation transcript:

1 Geology and Cu-Ni-PGE Deposits of the Duluth Complex, NE Minnesota
Jim Miller Department of Geological Sciences Precambrian Research Center (NRRI) University of Minnesota Duluth

2 A Looming Stewardship Question for Minnesotans:
When should we develop this immense copper-nickel-precious metal mineral resource?

3 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

4 THE MIDCONTINENT RIFT _______________
An attempt at continental rifting 1.1 billion years ago

5 Tectonic and Magmatic Evolution of the Midcontinent Rift

6 Midcontinent Rift Geology in the Lake Superior Region
Duluth Complex

7 Igneous Rocks of the Midcontinent Rift

8 South Kawishiwi Intrusion
Partridge River Intrusion

9 Multiple Emplacement of Duluth Complex Intrusions

10 Sulfur Contamination creating the Cu-Ni-PGE Sulfide Deposits of the Duluth Complex
Pd + Pt + Au S S

11 Copper-Nickel-Precious Metal Deposits of the Duluth Complex
Average Grades Cu – 0.6% Ni - 0.2% Co – 0.005% Pd+Pt+Au – ppb

12 Igneous Stratigraphy of the PRI and SKI
Based on Severson (1994)

13 History of Exploration
From Severson,2008 March 15, 2013 1966 State lands open for mineral leasing Active exploration drilling Polymet, Teck, Franconia, Wallbridge (Duluth Metals) 1948 Cu-Ni sulfide discovered at Spruce Rd Cu-Ni Regional Study 1958 Bear Creek drills Babbitt State land closed to new mineral leasing 1954 INCO drills Maturi 1999 LTV shuts down 1985 PGE discovered Cu Prices Current $ - 7,060 $/ton J. Miller

14 The Current Situation Current Exploration Activity Polymet – Northmet
Teck American – Mesaba Duluth Metals – Nokomis, Maturi, Dunka Pit, Birch Lake, Spruce Rd Encampment– South Filson Cr.

15 Cu-Ni Sulfide Deposits
Dominant Mineralogy of Magmatic Cu-Ni Sulfide Deposits Pyrrohotite – FeS1-x Chalcopyrite - CuFeS2 Pentlandite - (Fe,Ni)9S8 Bornite - Cu5FeS4 Talnakhite – Cu9(Fe,Ni)8S16 Chalcocite - Cu2S Cobaltite - CoAsS

16 March 15, 2013 Why Sulfide Mining? Most of the world’s metals comes from sulfide minerals Chalcopyrite CuFeS2 Bornite Cu5FeS4 Chalcocite Cu2S Pentlandite (Fe,Ni)9S8 Sphalerite ZnS Cinnabar HgS Molybdenite MoS2 Cobaltite CoAsS Galena PbS J. Miller

17 The Environmental Challenge Preventing Acid Rock Drainage (ARD)
March 15, 2013 2FeS2(s) + 7O2(g) + 2H2O(l) → 2Fe2+(aq) + 4SO42-(aq) + 4H+(aq) J. Miller

18 Precious Metal Minerals
PMM Name Formula Total # Total PMM In Sulfide Sulfide Host Mineral cp pn cb po tn bn Kotulskite Pd(Bi,Te)1-2 15 8 Froodite PdBi2 11 10 3 6 1 Naldrettite Pd2Sb Paolovite Pd2Sn 83 68 45 7 4 Sobolevskite PdBi 2 Sperrylite PtAs2 26 22 13 5 Stibiopalladinite Pd5Sb2 Taimyrite (Pd,Pt,Cu)3Sn Telluropalladinite Pd9Te4 Undetermined PGM 93 31 24 Silver sulfide AgS 16 Empressite AgTe Hessite Ag2Te Electrum AuAg 62 12 Gold Au 17 TOTALS 347 234 135 54 19 % 67% 57% 23% 8% 7% 3% 2% PMM study of NorthMet ore, Cervin, 2011

19 PMM-Sulfide Connection /Disconnection
PdSn bt bn sperrylite pn cp cpx pn cp pn cb cp cp pn plagioclase chl Deuteric alteration seperates PMM from host sulfide – implications for beneficiation PdBi PdSbBi cp cp cp Cervin, 2011

20 Styles of Mineralization after 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

21 Transition, Open - Confined Styles
Peterson, 2001

22 100% Sulfide Plots of SKI Open vs. Confined Styles of Mineralization
Open Style N = 1,737 Open Style N = 1,737 Deposits Spruce Rd Dunka Pit Serpentine Confined Style N = 13,868 Confined Style N = 13,868 Deposits Nokomis Maturi Birch Lake Peterson, 2012

23 New Maturi Mineralization Stratigraphy
Peterson, 2012 23

24 Emplacement/Mineralization Model for the South Kawishiwi Intrusion
Peterson, 2012

25 World Class Ores of the Duluth Complex
March 15, 2013 World Class Ores of the Duluth Complex Compared to other Magmatic Sulfide Deposits, the Duluth Complex is: #1 or 2 in contained Copper #4 in contained PGE #3 in contained Nickel Only the Bushveld, Great Dyke, and Noril’sk contain more PGE From Peterson, 2010 J. Miller

26 World Class Scale of the Maturi Deposit Alone
March 15, 2013 Nokomis Maturi Maturi Maturi From Peterson, 2010 and DM press release 12/2012 J. Miller

27 The Largest UNDEVELOPED Cu-Ni-PGE Deposit on Earth
March 15, 2013 The Largest UNDEVELOPED Cu-Ni-PGE Deposit on Earth 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. From Peterson, 2010 J. Miller

28 Stewardship question - If not now, when?
March 15, 2013 CONCLUSION: The base and precious metal deposits of the Duluth Complex are a World Class Resource that will be mined …. SOMEDAY Stewardship question - If not now, when? J. Miller

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