James D. Miller
Department of Geological Sciences
and Precambrian Research Center
University of Minnesota Duluth
Talk Outline
•What is the Duluth Complex?
•How did it form?
•How did it become mineralized?
•Why is it being considered for mining?
Stillwater Complex, Montana
Great
Dyke,
Zimbabwe
Second
Largest
Gabbro
Complex in
the World
Sudbury
Complex,
Ontario
Duluth
Complex
Bushveld Complex,
South Africa
Origin of Igneous Rocks
GEOLOGY OF
NORTHEASTERN
MINNESOTA
Age (billions of years)
Cu-Ni
Deposits
1.1
1.9
2.6
The Animikie
Basin and
Penokean
Mountains
1.9-1.7 Ga
MESABI-TYPE IRON FORMATION
Geologic Marker of a Major
Evolutionary Event
STROMATOLITES
(Fossilized Algal Mats)
A Key to the Origin of
Mesabi-type Iron Formation
Mary Ellen Mine
Shark Bay, Australia
LTV Mine
S
Penokean
Orogeny
1.85 Ga
Thomson Dam
Eveleth
St. Cloud
Mesabi
Range
Jay
Cooke
St. Cloud
Penokean Mountains (1.85 -1.75 Ga)
Continental Rifting
Making Ocean Crust
200 Ma
The Most Recent
Example of
Continental
Rifting
The Break-up of
Pangea
Laurasia
Gondwanaland
125 Ma
75 Ma
Mantle Plumes
and
Hot Spots
Current
Hotspots
_______________
THE
MIDCONTINENT
RIFT
_______________
An attempt at
continental rifting
1.1 billion years
ago
A. Rift Magmatism
The Evolution of
the
Midcontinent
1,109-1,086 Ma
Rift
Basalt
Flows
Gabbro
Crust
Mantle
Mantle
Plume
B. Sediment Infilling
Sandstone
1,090-900 Ma
C. Compression
1,000-900 Ma
Igneous Rocks of the Midcontinent Rift
Present-day
Erosion Surface
Creation of the Cu-Ni-PGE Sulfide Deposits of the Duluth Complex
Cu
S
Ni
Co
S
Pd + Pt
Au
Cu-Ni Sulfide
Mineralization
Chalcopyrite - CuFeS2
Bornite - Cu5FeS4
Pentlandite - (Fe,Ni)9S8
Chalcocite - Cu2S
Cobaltite - CoAsS
.
.
.
World Class
Ore Deposit
(Eckstrand and Hulbert, 2007)
History of Cu-Ni-PGE Exploration
History of Cu-Ni-PGE Exploration in the Duluth Complex
1948 – Cu-sulfide mineralization discovered by F.W. Childers
1951 – Childers and Whiteside drill first exploration drill hole at Spruce Road
1954 – INCO begins drilling program at Maturi deposit
1958 – Bear Creek (Kennecott) begins drilling program at Babbitt deposit
1966 – Minnesota opens state lands for minerals lease sale
1967 – INCO sinks shaft at Maturi deposit
1969 – Total of 198,000’ of drill core acquired
1974-78 –State conducts Cu-Ni Regional Study
1974-82 – State suspends lease sale
1976 – AMAX sinks shaft at Babbitt deposit
1981 – AMAX abandons Babbitt deposit
1985 – High PGE values discovered at Birch Lake deposit
1988 – Lehmann and Assoc. begin drilling of the Birch Lake deposit
1997-2000 – Polymet, Teck Cominco, Wallbridge (Duluth Metals) begin active
exploration drilling
2007 – Total of 322,000’ of drill core acquired
5,000
4,000
3,000
$/ton
Cu-Ni Regional Study
LTV shuts down
PGE discovered
8,000
7,000
Cu Prices 1948-2006
6,000
2,000
1,000
0
2006
2004
2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
1982
1980
1978
1976
1974
1972
1970
1968
1966
1964
1962
1960
1958
1956
1954
1952
1950
1948
Current Exploration Activity
Polymet – Northmet
Teck Cominco – Mesaba
Franconia – Birch Lake, Maturi, Spruce Rd
Duluth Metals – Nokomis, Dunka Pit
Encampment– South Filson Cr.
Global Boom in the
Exploration for
Metals & Minerals
Why the
Boom?
China
Ni
Au
Cu
Historically High Metal Prices
Pd
Pb
Pt
Zn
03------- 04------- 05------ 06------- 07-------
1992
2000
2008
Base Metal Projections: Supply to Outstrip Demand
Requires New Discoveries
Metals Economics Group, 2005
31%
Data from 2006 USGS Mineral Commodity Summary
THEN
NOW
Gypsum
Sudbury, Ont.