A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits 

Related to Proterozoic Massif Anorthosite Plutonic Suites

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5091
COVER. McIntyre mine located in the Adirondack State Park, New York (photo taken by Laurel 

G. Woodruff, U.S. Geological Survey).
A Deposit Model for Magmatic IronTitanium-Oxide Deposits Related to 

Proterozoic Massif Anorthosite Plutonic 

Suites

By Laurel G. Woodruff, Suzanne W. Nicholson, and David L. Fey

Scientific Investigations Report 2013–5091

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Woodruff, L.G., Nicholson, S.W., and Fey, D.L., 2013, A deposit model for magmatic iron-titanium-oxide deposits 

related to Proterozoic massif anorthosite plutonic suites: U.S. Geological Survey Scientific Investigations Report 

2013–5091, 47 p., http://pubs.usgs.gov/sir/2013/5091/.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................3

Deposit Type and Related Commodities ....................................................................................................4

Name.......................................................................................................................................................4

Synonyms...............................................................................................................................................4

Brief Description...................................................................................................................................4

Associated and Transitional Deposit Types .....................................................................................7

Stratiform Mafic-Ultramafic Iron-Titanium-Vanadium Deposits..........................................7

Nickel-Copper-Magmatic Sulfide Deposits.............................................................................8

Contact Metasomatic Rutile with Alkalic Anorthosite ..........................................................8

Heavy-Mineral Deposits.............................................................................................................8

Primary Commodities ...........................................................................................................................8

Byproduct Commodities ......................................................................................................................8

Example Deposits..................................................................................................................................9

Important Deposits ...............................................................................................................................9

Historical Evolution of Descriptive and Genetic Knowledge and Concepts........................................9

Regional Environment .................................................................................................................................10

Geotectonic Environment and Magmatic Temporal Relations....................................................10

Temporal (Secular) Relations of Oxides to Host Rocks ................................................................11

Relations to Structures ......................................................................................................................12

Relations to Igneous Rocks...............................................................................................................12

Relations to Metamorphic Rocks.....................................................................................................12

Relations to Sedimentary Rocks ......................................................................................................12

Physical Description of Deposit ................................................................................................................12

Dimensions in Plan View ...................................................................................................................12

Size of Hydrothermal System Relative to Extent of Economically Mineralized Rock..............14

Vertical Extent .....................................................................................................................................14

Form and Shape ..................................................................................................................................14

Host Rocks ...........................................................................................................................................14

Structural Setting(s) and Control .....................................................................................................15

Geophysical Characteristics......................................................................................................................15

Magnetic Signatures..........................................................................................................................15

Gravity Signatures ..............................................................................................................................16

Electrical Signatures..........................................................................................................................16

Hypogene Ore Characteristics ..................................................................................................................16

Mineralogy and Mineral Assemblages...........................................................................................16

Paragenesis.........................................................................................................................................17

Zoning Patterns...................................................................................................................................19

Textures and Grain Size.....................................................................................................................20

Gangue Mineral Characteristics...............................................................................................................20

Mineralogy and Mineral Assemblages...........................................................................................20

Paragenesis.........................................................................................................................................21
iv

Zoning Patterns...................................................................................................................................21

Textures and Grain Sizes ...................................................................................................................21

Hydrothermal Alteration .............................................................................................................................22

Supergene Ore and Gangue Characteristics..........................................................................................22

Weathering and Supergene Processes...................................................................................................22

Geochemical Characteristics ....................................................................................................................22

Trace Elements and Element Associations ....................................................................................22

Zoning Patterns...................................................................................................................................22

Isotope Geochemistry of Ores..........................................................................................................23

Stable Isotope Geochemistry ..................................................................................................23

Radiogenic Isotope Geochemistry..........................................................................................23

Petrology of Associated Igneous Rocks..................................................................................................23

Rock Names.........................................................................................................................................24

Forms of Igneous Rocks and Rock Associations ..........................................................................24

Mineralogy...........................................................................................................................................24

Textures, Structures, and Grain Size...............................................................................................24

Petrochemistry....................................................................................................................................25

Major-Element Geochemistry..................................................................................................25

Trace-Element Geochemistry ..................................................................................................25

Isotope Geochemistry of Igneous Rocks........................................................................................27

Stable Isotope Geochemistry ..................................................................................................27

Radiogenic Isotope Geochemistry..........................................................................................29

Petrology of Associated Sedimentary Rocks..........................................................................................31

Petrology of Associated Metamorphic Rocks ........................................................................................31

Theory of Deposit Formation......................................................................................................................31

Ore Deposit System Affiliation...................................................................................................................31

Sources of Ti-Fe-P-Ore Components........................................................................................................31

Mechanisms that Concentrate Ore ..........................................................................................................31

Summary of the Origin of Magmatic Fe-Ti-Oxide Deposits ..................................................................32

Geological Assessment Guides.................................................................................................................34

Attributes Required for Inclusion in Permissive Tract at Various Scales ..........................................34

Geochemical Considerations.....................................................................................................................34

Geophysical Attributes................................................................................................................................34

Geoenvironmental Features and Anthropogenic Mining Effects ........................................................34

Soil and Sediment Signatures Prior to Mining...............................................................................34

Secondary Minerals...........................................................................................................................34

Drainage Signatures...........................................................................................................................34

Climate Effects on Geoenvironmental Signatures ........................................................................35

Past and Future Mining Methods and Ore Treatment ..................................................................35

Metal Mobility from Solid Mine Waste ...........................................................................................35

Pit Lakes ...............................................................................................................................................36

Volume of Mine Waste and Tailings ................................................................................................36

Smelter Signatures.............................................................................................................................36

Human Health Issues .........................................................................................................................36

Acknowledgments.......................................................................................................................................36
v

References Cited..........................................................................................................................................37

Appendix........................................................................................................................................................46

Figures

1. World map showing distribution of Proterozoic massif anorthosite....................................2

2. Simplified geologic map of part of the Grenville Province showing the distribution 

of Proterozoic massif anorthosite suites ..................................................................................3

3. Simplified geologic map of the Rogaland Anorthosite Province showing the 

distribution of the main geologic units, including the Egersund-Ogna, HålandHelleren, Åna-Sira, Garsaknat, and Hidra massif anorthosites and the BjerkreimSokndal layered intrusion............................................................................................................4

4. Simplified geologic map of the Duluth Complex, Minnesota...............................................10

5. Classification of rock association and iron-titanium-oxide (Fe-Ti-oxide) mineralogy 

for massif anorthosite based on silica activity and oxygen fugacity for idealized 

lithologies.....................................................................................................................................11

6. Surface outline of the three main orebodies at the Lac Tio deposit, Quebec, 

Canada, and a north-south cross section of the Main orebody showing the 

reconstructed exploited ore removed from the open pit and remaining ore ...................13

7. Simplified geologic map of the host Åna-Sira anorthosite, Norway, and location

and three cross sections of the Tellnes ilmenite-norite orebody.......................................13

8. Photograph showing deformed layers and remobilized veins of massive 

titaniferous magnetite and ilmenite and oxide-rich leucogabbro norite in 

labradorite-type anorthosite of the Rivière-au-Tonnerre Massif of the HavreSaint-Pierre anorthosite suite, Quebec, Canada...................................................................14

9. Aeromagnetic profile of the Allard Lake anorthosite across the Lac Tio deposit, 

Quebec, Canada, displaying a contour line of equal magnetic-field intensity.................15

10. The subsystem FeO-Fe2O3-TiO2 showing major solid solution joins for the cubic 

(ulvøspinel-magnetite), rhombohedral (ilmenite-hematite), and orthorhombic 

(pseudobrookite) series.............................................................................................................17

11. A. Reflective-light photograph of hemo-ilmenite from the Lac Tio deposit, 

Quebec, Canada. B. Reflective-light photograph of titanomagnetite (Ti-Mte) and 

ilmenite (llm) from the Hervieux East massive titaniferous lens in the La Blache 

anorthosite complex, Quebec, Canada...................................................................................18

12. Cross sections of the Tellnes orebody, Norway ....................................................................19

13. Photograph of massive hemo-ilmenite ore from the floor of the Main pit at the 

Lac Tio deposit, Quebec ............................................................................................................20

14. Al2O3–FeO–MgO triangular diagrams showing simplified compositional character 

of rocks related to Proterozoic massif anorthosite...............................................................26

15. All Adirondack massif anorthosite and related rocks plotted on a 

CaO-Na2O+K2O-Fe2O3 triangular diagram.................................................................................27

16. Chondrite-normalized rare earth elements (REE) patterns for representative 

samples of the anorthosite suite from the Marcy massif anorthosite, Adirondacks, 

New York ......................................................................................................................................28

17. Whole-rock δD (WR δD) versus δ18O for the Åna-Sira anorthosite, the Tellnes 

orebody, and norite dike hosting the Tellnes orebody; the Bjerkreim-Sokndal 

layered intrusion (BKSK) and apophysis and the metamorphic envelope of 

gneiss in the Rogaland Anorthosite Province........................................................................29
vi

18. Compilation of δ8O whole-rock and plagioclase values for Proterozoic 

anorthosites.................................................................................................................................30

19. Hypothetical model for the magmatic evolution of Fe-Ti-oxide deposits..........................33

A1. Varying rocks types related to Fe-Ti-oxide deposits hosted within Proterozoic 

anorthositic plutonic suites and related layered rocks are classified based on 

their proportional mineralogy ...................................................................................................33

Table

1. Selected Proterozoic massif anorthosite suites and contained magmatic irontitanium-oxide deposits or districts with multiple deposits...................................................5
vii

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2) 0.0002471 acre 

square kilometer (km2) 0.3861 square mile (mi2)

Volume

cubic meter (m3) 6.290 barrel (petroleum, 1 barrel = 42 gal)

liter (L) 33.82 ounce, fluid (fl. oz)

liter (L) 2.113 pint (pt)

liter (L) 1.057 quart (qt)

liter (L) 0.2642 gallon (gal)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

microgram (mg) 0.00000003527 ounce, avoirdupois (oz)

milligram (mg) 0.00003527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

tonnes (t) 2204.6226 pound avoirdupois (lb)

tonnes (t) 1.1023 ton (US, short) 

million tonnes (Mt) 1.1023 million tons (US, short)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8×°C) + 32

An isogam is a line joining points on the Earth’s surface having the same value of the 

acceleration of gravity.

A gal is a unit of acceleration equal to a centimeter per second per second; a milligal is one 

thousandth of a gal.
Abstract

This descriptive model for magmatic iron-titanium-oxide 

(Fe-Ti-oxide) deposits hosted by Proterozoic age massif-type 

anorthosite and related rock types presents their geological, 

mineralogical, geochemical, and geoenvironmental attributes. 

Although these Proterozoic rocks are found worldwide, the 

majority of known deposits are found within exposed rocks of 

the Grenville Province, stretching from southwestern United 

States through eastern Canada; its extension into Norway is 

termed the Rogaland Anorthosite Province. This type of FeTi-oxide deposit dominated by ilmenite rarely contains more 

than 300 million tons of ore, with between 10- to 45-percent 

titanium dioxide (TiO2), 32- to 45-percent iron oxide (FeO), 

and less than 0.2-percent vanadium (V).

The origin of these typically discordant ore deposits 

remains as enigmatic as the magmatic evolution of their host 

rocks. The deposits clearly have a magmatic origin, hosted 

by an age-constrained unique suite of rocks that likely are the 

consequence of a particular combination of tectonic circumstances, rather than any a priori temporal control. Principal ore 

minerals are ilmenite and hemo-ilmenite (ilmenite with extensive hematite exsolution lamellae); occurrences of titanomagnetite, magnetite, and apatite that are related to this deposit 

type are currently of less economic importance. Ore-mineral 

paragenesis is somewhat obscured by complicated solid solution and oxidation behavior within the Fe-Ti-oxide system. 

Anorthosite suites hosting these deposits require an extensive 

history of voluminous plagioclase crystallization to develop 

plagioclase-melt diapirs with entrained Fe-Ti-rich melt rising 

from the base of the lithosphere to mid- and upper-crustal 

levels. Timing and style of oxide mineralization are related to 

magmatic and dynamic evolution of these diapiric systems and 

to development and movement of oxide cumulates and related 

melts. 

Active mines have developed large open pits with extensive waste-rock piles, but because of the nature of the ore and 

waste rock, the major environmental impacts documented at 

the mine sites are reported to be waste disposal issues and 

somewhat degraded water quality. 

Introduction

Overviews of magmatic iron-titanium-oxide (Fe-Ti-oxide) 

deposits include Lister (1966), Rose (1969), Force (1991), 

Gross (1996), Korneliussen and others (2000), and Corriveau 

and others (2007). Economic magmatic ilmenite and titaniferous-magnetite (Fe-Ti-oxide) deposits have spatial and temporal 

connections with massif anorthosite suites found in Proterozoic 

rocks on all continents (Anderson, 1969; Ashwal, 1993) 

(fig. 1). Many deposits occur in rocks of the Proterozoic 

Grenville Province, which are exposed from the Adirondack 

Mountains (Adirondacks) in New York, through eastern 

Canada (fig. 2), and into the Rogaland Anorthosite Province, 

Norway (fig. 3). The Grenville Province is considered the largest titanium province in the world (Corriveau and others, 2007) 

(table 1). 

Understanding the formation of magmatic Fe-Ti-oxide 

deposits relies on understanding the nature of anorthosite and 

related rocks hosting these deposits, the evolution of parent 

magma from which oxide and silicate minerals crystallized, 

and the tectonic setting of these rocks and ores (Weihed and 

others, 2005). Massif anorthosites are igneous bodies ranging in size from small individual plutons to large (15,000 to 

20,000 km2)intrusive complexes, typically composed of more 

than 90-percent plagioclase of fairly restricted composition, 

and mainly Proterozoic in age (Ashwal, 1993; Ashwal, 2010). 

Related rock types have a complex nomenclature that includes 

leucotroctolite, leuconorite, troctolite, norite, gabbronorite, 

ferrogabbro, ferrodiorite, jotunite, mangerite, and charnockite 

(see appendix 1 for rock classification scheme used in this 

report). These related unusual rock types are commonly part of 

what is referred to as anorthosite-mangerite-charnockite-granite 

(AMCG) suites (Emslie, 1991). The structures of massifs range 

from composites of multiple diapiric intrusions (for example, 

Havre-Saint-Pierre anorthosite suite, Quebec; van Breemen and 

Higgins, 1993) to dozens of discrete layered troctolite, gabbro and anorthosite intrusions (for example, Duluth Complex, 

Minnesota; Miller and Ripley, 1996) to large, layered mafic 

intrusions (for example, Bjerkreim-Sokndal intrusion, Norway; 

Wilson and others, 1996; fig. 3), all of which can host significant concentrations of magmatic Fe-Ti oxides. 

A Deposit Model for Magmatic Iron-Titanium-Oxide 

Deposits Related to Proterozoic Massif Anorthosite 

Plutonic Suites

By Laurel G. Woodruff, Suzanne W. Nicholson, and David L. Fey
Figure 1. World map showing distribution of Proterozoic massif anorthosite (locations from Ashwal, 1993). Anorthosite suites that host soxide deposits are denoted by open red circles. The numbers given for these anorthosite suites corresponds to the numbers in table 1. GRENVILLE PROVINCE ROGALAND ANORTHOSITE PROVINCE 1 2 3 45 6−13 14 15
Introduction 3

The principal ore minerals are ilmenite (FeTiO3), hemoilmenite (ilmenite with abundant hematite (Fe2

O3) exsolution 

lamellae), and titanomagnetite (a solid solution of magnetite 

(Fe3O4) and ulvöspinel (Fe2TiO4) (Gross, 1996). The presence or absence of discrete crystals of ilmenite is the key 

factor determining the economic value of these deposits 

(Force, 1991). Magmatic ilmenite deposits typically contain 

less than 300 million tons (Mt) of ore with 10- to 45-percent 

TiO2, 32- to 45-percent Fe, and less than 0.2-percent vanadium (V) (Gross, 1996). There are only two currently active 

magmatic Ti mines, Lac Tio in Quebec, Canada, and Tellnes in 

Norway. Other Fe-Ti-oxide deposits with past mining operations include deposits in numerous anorthosite suites of the 

Grenville Province in Quebec (see Hébert and others, 2005; 

Corriveau and others, 2007), the Storgangen and Blåfjell 

deposits, among others, in the Rogaland Province in Norway 

(Schiellerup and others, 2003), and four deposits (Sanford 

Hill/South Extension, Cheney Pond, Mt. Adams, and Upper 

Works) in the Sanford Lake district in the Adirondacks of 

New York (Gross, 1968). Additional potential Fe-Ti-oxide 

resources in the United States include oxide-bearing ultramafic 

intrusions (OUIs) in the Duluth Complex, Minnesota (Severson, 1995; Hauck and others, 1997), ilmenite (with rutile) in 

the Roseland Anorthosite, Virginia (Herz and Force, 1987), 

Fe-Ti-oxide mineralization (dominantly titanomagnetite with 

ilmenite) in the Laramie Range, Wyoming (Diemer, 1941), 

and Fe-Ti-oxide mineralization (dominantly titanomagnetite 

with ilmenite) in the San Gabriel Range, California (Force 

1991) (fig. 1 and table 1). 

Purpose and Scope

This report is part of an effort by the U.S. Geological 

Survey’s Mineral Resource Program to update existing mineral deposit models and develop new, more complete deposit 

models to be used for an upcoming U.S. Geological (USGS) 

national mineral resource assessment. The deposit model presented here replaces previously published USGS descriptive 

model 7b for anorthosite Ti (Force, 1992). 

EXPLANATION

Phanerozoic rocks

Grenville front

Massif anorthosite

Parautochthon

Allochthonous monocyclic belt

Allochthonous polycyclic belt

Water

Grenville Inlier

9 6

7

8

10

11

4

12

Nain

Complex

CANADA

UNITED STATES

0 200 KILOMETERS

0 100 MILES

CANADA

UNITED STATES

N

Figure 2. Simplified geologic map of part of the Grenville Province showing the distribution of Proterozoic massif 

anorthosite suites (modified from Davidson, 2008). Numbers correspond to numbers shown in figure 1 and table 1. 

Inset shows the extent of the Grenville Province (black) in North America.
4 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

Deposit Type and Related Commodities

Name

Iron-titanium-oxide (Fe-Ti-oxide) deposits hosted by Proterozoic massif anorthosite plutonic suites and related mafic 

layered intrusions

Synonyms

These Fe-Ti-oxide deposits are referred to informally 

as anorthosite Ti deposits, hard-rock Fe-Ti-oxide deposits, 

or magmatic Fe-Ti-oxide deposits. However, the qualifier of “hosted by Proterozoic massif anorthosite plutonic 

suites and related layered mafic intrusions” is used here to 

distinguish these discordant massive oxide lenses, weakly 

discordant oxide layers, and more stratiform oxide layers of 

predominantly ilmenite and titaniferous magnetite in massive 

anorthosite and related rocks as well as layered mafic intrusions within anorthositic provinces from consistently stratiform mafic-ultramafic Fe-Ti-V-oxide deposits dominated by 

magnetite in the upper parts of large, layered intrusions, such 

as the Bushveld Complex in South Africa. This latter class of 

magmatic Fe-Ti-oxide deposits belongs in a separate, distinct 

deposit model (USGS descriptive model 3; Bushveld Fe-Ti-V; 

Page, 1992). 

Brief Description

It is estimated that the two active magmatic Fe-Ti-oxide 

mines, Tellnes and Lac Tio, together produce about 32 percent 

of the world’s titanium dioxide (TiO2) (Gross, 1996; Schiellerup and others, 2003). The remaining 68 percent comes from 

ilmenite and rutile in shoreline placer deposits (Force, 1991). 

About 95 percent of the world’s Ti is refined into TiO2, a 

pigment used to impart a durable white color to paints, paper, 

toothpaste, sunscreen, and plastics; the remaining 5 percent is 

used for production of corrosion-resistant Ti metal (Towner 

and others, 1988). 

Magmatic Fe-Ti-oxide deposits occur as discordant 

lenses—dike-like or pipe-like bodies—and as layers or disseminations within Proterozoic plutonic suites dominated by 

anorthosite, norite, and gabbro; related rock types may include 

mangerite (hypersthene-bearing monzonite), jotunite (hypersthene-bearing monzodiorite), nelsonite (oxide-apatite rock 

with few or no silicates), oxide-apatite gabbronorite (oxideand apatite-rich rock with plagioclase and two pyroxenes), 

and minor ultramafic rocks, such as pyroxenite, peridotite, 

and dunite (Gross, 1996; Owens and Dymek, 1992; Hauck 

and others, 1997; Schiellerup and others, 2003; Hébert and 

others, 2005; Corriveau and others, 2007) (see appendix 1 

for details on rock name classifications). Discordant relations 

between ore-bearing bodies and host rocks and incorporation of anorthositic xenoliths within some ore-bearing bodies 

EXPLANATION

Mangerite

Anorthosite/foliated anorthosite

Jotunite

Norite/layered norite

Charnockite

Basalt dikes

Migmatitic gneiss

NORWAY

T

S

B

ÅNA-SIRA

HÅLANDHELLEREN

EGERSUNDOGNA

BJERKREIMSOKNDAL

F

FL

HIDRA

GARSAKNAT

N

0

0 5 MILES

5 10 KILOMETERS

Figure 3. Simplified geologic 

map of the Rogaland Anorthosite 

Province showing the distribution 

of the main geologic units, 

including the Egersund-Ogna, 

Håland-Helleren, Åna-Sira, 

Garsaknat, and Hidra massif 

anorthosites and the BjerkreimSokndal layered intrusion. Irontitanium-oxide deposits: T=Tellnes, 

B=Blåfjell, S=Storgangen, 

F=Flordalen, and Fl=Frøtlog 

(modified from Duchesne and 

Schiellerup, 2001).
Deposit Type and Related Commodities 5

Table 1. Selected Proterozoic massif anorthosite suites and contained magmatic iron-titanium-oxide deposits or districts with 

multiple deposits. 

[Numbers in parentheses given to the 15 listed anorthosite suites correspond to numbers applied to anorthosite suite locations in figure 1. The name of the anorthosite suite, deposit mineralogy, resource, and host rock information are compiled from Towner and others (1988), Force (1991), Ashwal (1993), Duchesne and 

Schiellerup (2001), Severson and others (2002), Hébert and others (2005), U.S. Geological Survey (2005), Gross (1996), Corriveau and others (2007), 

von Seckendorff and others (2000), and Arianne Resources (2012). Resources are in millions of tons (Mt) and TiO2 and Fe grades are in weight percent]

Anorthosite suite Oxide deposit or 

district name Ore mineralogy Resources Mt

Grade

TiO2

Grade

Fe Host and related rocks

Laramie Range complex (1)

 Wyoming, U.S.A.

Iron Mountain titanomagnetiteilmenite-magnetite 134.0 9.69 20.2 troctolite/leucogabbro/

anorthosite

Shanton titanomagnetiteilmenite-magnetite --- --- --- anorthosite

Taylor ilmenite-magnetiteapatite --- --- --- anorthosite

San Gabriel Range (2)

 California, U.S.A.

unnamed oxide

bodies

titanomagnetiteilmenite 4.8 12 --- pyroxenite/ferrodiorite/

anorthosite

Duluth Complex (3)

 Minnesota, U.S.A.

Section 17 ilmenitetitanomagnetite --- --- --- pyroxenite/peridotite/troctolite

Longear ilmenitetitanomagnetite --- --- --- pyroxenite /troctolite

Longnose ilmenitetitanomagnetite 50 21 --- pyroxenite/peridotite/dunite/

troctolite

Wyman Creek ilmenitetitanomagnetite --- --- --- pyroxenite/peridotite/

troctolite

Skibo ilmenite (+ sulfidesgraphite) --- --- --- dunite/peridotite/troctolite

Section 22 ilmenitetitanomagnetite --- --- --- picrite/peridotite/troctolite

Water Hen ilmenite (+ sulfidesgraphite) 62 14 --- picrite/peridotite/troctolite

Section 34 titanomagnetiteilmenite --- --- --- peridotite/pyroxenite/

anorthosite/troctolite

Boulder Creek titanomagnetiteilmenite --- --- --- peridotite/picrate/dunite/

troctolite

Boulder Lake 

North

ilmenite-magnetiteapatite --- --- --- peridotite/pyroxenite/

anorthosite/troctolite

 Boulder Lake 

South

ilmenite-apatite --- --- --- peridotite/pyroxenite/

troctolite

Marcy (4)

Adirondacks, New York, 

U.S.A

Sanford Lake district 

(four deposits)

titanomagnetiteilmenite (+ apatite) 8.6 35 --- gabbro/anorthosite

Roseland (5)

Virginia, U.S.A.

Piney River district ilmenite-apatite --- --- --- ferrodiorite/nelsonite/

anorthosite

Rivière-Pentecôte (6)

Quebec, Canada

Rivière Pentecôte titanomagnetiteilmenite (+ sulfides) --- --- --- anorthosite

Lac Saint-Jean (7)

Quebec, Canada

Saint-Charles titanomagnetiteilmenite-apatite 5.4 10.1 29.5 anorthosite

La Hache-Est titanomagnetiteilmenite-apatite 20.3 5.12 24.75 anorthosite

Buttercup titanomagnetiteilmenite-apatite 3.5 19 49 leuconorite/leucogabbro/

nelsonite

Lac à Paul ilmenite-apatite 348 8.4 anorthosite/leuconorite/

nelsonite

Morin (8)

Quebec, Canada

Desgrobois titanomagnetiteilmenite 5 11 40.8 anorthosite

 
6 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

Table 1. Selected Proterozoic massif anorthosite suites and contained magmatic iron-titanium-oxide deposits or districts with 

multiple deposits.—Continued 

[Numbers in parentheses given to the 15 listed anorthosite suites correspond to numbers applied to anorthosite suite locations in figure 1.The name of the anorthosite suite, deposit mineralogy, resource, and host rock information are compiled from Towner and others (1988), Force (1991), Ashwal (1993), Duchesne 

and Schiellerup (2001), Severson and others (2002), Hébert and others (2005), U.S. Geological Survey (2005), Gross (1996), Corriveau and others (2007), 

von Seckendorff and others (2000), and Arianne Resources (2012). Resources are in millions of tons (Mt) and TiO2 and Fe grades are in weight percent]

Anorthosite suite Oxide deposit or 

district name Ore mineralogy Resources Mt

Grade

TiO2

Grade

Fe Host and related rocks

Morin (8)

Quebec, Canada

Ivry hemo-ilmenite 0.16 33.23 42.5 anorthosite

Saint-Hippolyte titanomagnetiteilmenite 10 20 27 anorthosite

Havre-Saint-Pierre (9)

Quebec, Canada 

Grader hemo-ilmenite-apatite 7.62 32 36.9 anorthosite

Lac Tio (Allard Lake; 

Lac Allard)

hemo-ilmenite 125 34.2 38.8 anorthosite

Everett (Puyjalon) ilmenite-magnetiteapatite 294 9.75 16.2 anorthosite

Big Island hemo-ilmenite (+ rutile 

+ sapphirine)

 --- --- --- anorthosite

Mills hemo-ilmenite --- --- --- anorthosite

La Fournier (10)

Quebec, Canada

Magpie Mountain 

(four deposits)

ilmenite-magnetiteapatite 1,500 10.9 56 oxide gabbro/leuconorite

Saint-Urbain (11)

Quebec, Canada

Furnace

Seminaire

hemo-ilmenite

hemo-ilmenite (+ rutile)

 2

 ---

 37

 ---

 26

 ---

 anorthosite

 anorthosite

Coulombe East & 

West

hemo-ilmenite (+ rutile 

+ sapphirine)

 6.71 39 36 anorthosite

General Electric hemo-ilmenite (+ rutile) 6.5 29.2 37.3 anorthosite

Bignel hemo-ilmenite-apatite 

(+ rutile)

 2.5 36.4 35.7 anorthosite

Glen hemo-ilmenite --- --- --- anorthosite

Dupont hemo-ilmenite 2.27 33.6 31.1 anorthosite

Bouchard hemo-ilmenite-apatite --- --- --- anorthosite

Labrieville (12)

Quebec, Canada

Lac Brûlè hemo-ilmenite 5.8 35 43 anorthosite

La Blache (13)

Quebec, Canada

Hervieux East ilmenite-magnetiteulvöspinel --- --- --- anorthosite

Hervieux West ilmenite-magnetiteulvöspinel 71.7 20.1 48 anorthosite

Schmoo ilmenite-magnetiteulvöspinel --- --- --- anorthosite

Lac Dissimieu ilmenite-apatite 235 45 --- anorthosite

Åna-Sira (14)

Norway 

Tellnes hemo-ilmenite 380 18.4 1 norite/anorthosite

Blåfjell hemo-ilmenite 

(+ magnetite-apatite)

 --- --- --- pegmatitic norite/anorthosite

Storgangen hemo-ilmenite 

(+ magnetite)

 70 19.6 --- leuconortite/norite/

anorthosite

Flordalen hemo-ilmenite --- --- --- anorthosite

Frøytlog hemo-ilmenite (+ trace 

magnetite)

 --- --- --- anorthosite

Kunene (15)

Namibia

unnamed oxide bodies titanomagneite-ilmenite --- --- --- anorthosite

 
Deposit Type and Related Commodities 7

suggest intrusion of oxide-bearing units into older anorthosite 

host rocks. In contrast, conformable oxide concentrations in 

gabbro and layered rocks related to anorthosite indicate an 

origin by crystal settling and accumulation. Both discordant 

and conformable styles can be found together in composite 

anorthosite suites. 

Principal ore minerals are ilmenite, hemo-ilmenite, 

and titanomagnetite; titaniferous magnetite is a general term 

applied to granule aggregations of ilmenite (typically formed 

by oxidation of ulvöspinel), magnetite, hematite, and titanomagnetite (Krause and others, 1985; Gross, 1996). Magmatic 

Fe-Ti-oxide deposits related to anorthosites are classified 

based upon orebody mineralogy (see for example, Duchesne, 

1999; Hébert and others, 2005; Corriveau and others, 2007) 

and host rock composition (see for example, Force, 1991; 

Gross, 1996). The two currently economic deposits are Lac 

Tio in Quebec, Canada, and Tellnes in Norway. Lac Tio consists of massive hemo-ilmenite in anorthosite with andesinetype plagioclase; Tellnes is dominantly hemo-ilmenite hosted 

by a norite dike-shaped body cutting andesine-type anorthosite. Deposits with a mineral assemblage of titanomagnetite+

ilmenite±apatite, more commonly hosted by anorthosite with 

labradorite-type plagioclase or in related gabbro and norite, 

are less economic for Ti, although deposits with abundant 

apatite may contain an economic phosphorus (P) or rare earth 

element (REE) resource (Hébert and others, 2005). Massive 

titanomagnetite+ilmenite-oxide deposits, thought to be derived 

from late-stage residual melts from anorthosite, occur in 

troctolite and olivine gabbro in the Laramie Range anorthosite 

complex (Mitchell and others, 1996). A recently recognized 

potentially important resource for Ti is ilmenite-dominated 

deposits in ultramafic plugs cutting troctolite in the Duluth 

Complex of northern Minnesota (Hauck and others, 1997). 

A single complex anorthosite suite composed of multiple 

anorthosite lobes with varying ages and plagioclase compositions can host differing styles of Fe-Ti-oxide mineralization. 

For example, seven separate anorthosite lobes have been 

recognized in the Havre-Saint-Pierre anorthosite suite, Quebec 

(Gobeil and others, 2003). The 1139 to 1129 Ma (Wodicka 

and others, 2003) labradorite-type Rivière Sheldrake anorthosite lobe has non-economic concentrations of massive 

titaniferous magnetite. In contrast, the 1061 Ma (Morisset and 

others, 2009) andesine-type Allard Lake anorthosite lobe (also 

referred to as the Lac Allard anorthosite in the literature) hosts 

numerous hemo-ilmenite deposits (for example, Lac Tio) and 

ilmenite-magnetite-apatite deposits (for example, Everett) 

(Perreault, 2003). This contrast in both plagioclase composition and related Fe-Ti oxides over a time span of about 60 million years likely reflects the tectonic and magmatic evolution 

of the Grenville Province (Morisset and others, 2009). 

It is generally accepted that Fe-Ti-oxide deposits are 

magmatic in origin, but questions remain about the magmatic 

processes creating Ti-enriched oxide accumulations in economic quantities. Current genetic models rely on combinations 

of fractional crystallization, mineral accumulation and density 

separation processes, dynamic magma chamber replenishment and mixing mechanisms, multiple pulses of magma 

flowing through restricted conduit systems, and formation and 

mobilization of late-stage residual liquids (see for example, 

Duchesne and Schiellerup, 2001; Dymek and Owens, 2001; 

Charlier and others, 2006; Charlier and others, 2010; Morisset 

and others, 2010). 

Deposits dominated by hemo-ilmenite may represent 

accumulations resulting from fractional crystallization of 

TiO2-rich magma with ilmenite as an early liquidus mineral. 

Segregation and emplacement of these early ilmenite-laden 

liquids are likely related to dynamic crystallization and 

emplacement of massive anorthosite (Duchesne and Schiellerup, 2001; Charlier and others, 2006). An assemblage of 

titanomagnetite+ilmenite±apatite can form primary massive 

layers in labradorite-type anorthosite or weakly discordant 

magnetite- and oxide-rich leuconorite dikes emplaced roughly 

parallel to regional tectonic fabric in anorthosite (Dymek and 

Owens, 2001). These deposits may represent concentration of 

Fe, Ti, and P in residual magmas. In contrast, a nelsonite layer 

of primarily ilmenite and apatite (with minor plagioclase) in 

the Grader layered intrusion, Quebec, probably has a cumulate 

origin (Charlier and others, 2010). Thus, the timing and nature 

of oxide saturation in a crystallizing magma will determine the 

type and style of oxide mineralization. 

Associated and Transitional Deposit Types

Stratiform Mafic-Ultramafic Iron-TitaniumVanadium Deposits

Variants of magmatic Fe-Ti-oxide deposits are large 

stratiform Fe-Ti-V deposits that are hosted worldwide in the 

upper parts of large repetitively layered mafic-ultramafic intrusions. We define these as a distinct deposit type not included in 

this present deposit-model description. Examples include the 

Bushveld Complex, South Africa (McCarthy and Cawthorn, 

1983) and the Sept-Îles layered intrusion, Quebec (Namur and 

others, 2010). These deposits typically comprise concordant, 

laterally continuous magnetite-rich layers ranging in thickness 

from centimeters to meters. The Sept-Îles layered intrusion 

also contains significant horizons of nelsonite (Namur and others, 2010). Major differences between magmatic Fe-Ti oxides 

related to (a) Proterozoic massif anorthosite plutonic suites, 

which may include layered intrusions and (b) stratiform Fe-TiV-oxide deposits include one or more of the following: (1) a 

more typical form of host plutonic rocks (for example (a) massive domical intrusions and related layered intrusions versus 

(b) large, repetitively layered intrusions); (2) major mineralogy of the deposits (for example, (a) ilmenite-dominated 

versus (b) magnetite-dominated); (3) plagioclase composition 

of related anorthosite (for example, (a) labradorite-andesine 

versus (b) bytownite-anorthite); (4) magmatic crystallization sequence (for example, (a) ilmenite as an early liquidus 
8 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

mineral versus (b) magnetite as a late-stage residual mineral); 

and (5) age distribution (for example, (a) Proterozoic age 

versus (b) no apparent geologic age restrictions). 

Nickel-Copper-Magmatic Sulfide Deposits

Nickel-copper (Ni-Cu) sulfides occur in small quantities 

in a number of magmatic Fe-Ti-oxide deposits and related 

gabbro-anorthosite rocks. Significant disseminated Ni-Cu 

mineralization occurs with OUIs in the Duluth Complex 

(Ripley, 1986), in several noritic intrusions in the Rogaland 

Province (Schiellerup and others, 2003), and in pyroxenite 

and melanorite of the Nord-Ouest anorthosite massif, HavreSaint-Pierre anorthosite suite (Perreault, 2003). Discovery of 

Ni-Cu deposits at Voisey’s Bay in a Proterozoic anorthosite 

suite within the Nain Complex of Labrador, and recognition 

that sulfides in that deposit were concentrated by dynamic 

fluid processes in magma conduits (see for example, EvansLamswood and others, 2000), suggests genetic parallels to 

proposed concentration of ilmenite in dynamic magma settings 

by similar processes (see for example, Charlier and others, 

2010; Morisset and others, 2010). Based on observations from 

the Voisey’s Bay deposits, Kerr and Ryan (2000) suggest that 

anorthosite-hosted massive Ni- and Cu-bearing sulfide mineralization can be viewed as part of a spectrum of magma processes in which metal-bearing liquids are introduced by mafic 

magmas but separated from host magmas to variable degrees. 

Factors that may drive magmatism toward sulfide mineralization rather than oxide mineralization may be related to parent 

magma compositions, depth of fractionation and subsequent 

separation of plagioclase and mafic minerals and residual melt, 

and possible magma contamination by sulfide-bearing country 

rock (Kerr and Ryan, 2000). 

Contact Metasomatic Rutile with Alkalic 

Anorthosite

Iron-Ti-oxide mineralization can be present in skarn 

rock and alteration zones near the contact of ilmenite-bearing 

anorthosite and country rocks. The Roseland district, Virginia, 

contains magmatic ilmenite in dike-like bodies cutting anorthosite and contact metasomatic rutile developed in country 

rocks cut by swarms of anorthosite dikes (Herz and Force, 

1987). The presence of rutile with ilmenite in highly metamorphosed rocks, including alkali anorthosite, near the town 

of Pluma Hidalgo, Mexico, is similar to the Roseland rutile 

occurrence suggesting a possible similar contact metasomatic 

origin (Paulson, 1964; Force, 1991).

Heavy-Mineral Deposits

Much of the high-grade ilmenite and rutile used today 

is extracted from heavy-mineral deposits in unconsolidated 

shoreline placers and dunes and older equivalents. Deposits 

develop when relatively resistant Ti-bearing and other heavy 

minerals are eroded from oxide-bearing parent rocks, subsequently transported, sorted, and finally deposited in fluvial, 

alluvial, or eolian settings. Many productive heavy-mineral 

provinces, such as the east coast of the United States, the west 

coast of South Africa, and both the east and west coasts of 

Australia, are located on trailing continental margins usually backed by elevated, often highly weathered, high-grade 

metamorphic or mafic igneous hinterlands (Force, 1991). Terranes that have prominent anorthosite and gabbro intrusions 

hosting Fe-Ti-oxide deposits can be an important source for 

heavy-mineral placer systems (Gross, 1996). An example is a 

large heavy-mineral deposit in deltaic sands of the Natashquan 

River on the north shore of the Saint Lawrence River in Quebec (Gauthier, 2003).

Primary Commodities

Titanium is the primary economic commodity from 

hemo-ilmenite deposits, with Fe commonly occurring as a 

co-product, particularly from deposits that also contain titanomagnetite and magnetite. Ilmenite deposits typically have 

10- to 75-percent TiO2, 41- to 58-percent FeO, and less than 

0.2-percent vanadium (V) (Gross, 1996). Titaniferous magnetite at the Sanford Hill/South Extension deposit in New York, 

also referred to as the McIntyre mine, was an early Fe resource 

before the presence of Ti was recognized (Gross, 1968). In the 

mid-1880s, a number of small mines in the Rogaland Province 

shut down when the high Ti content of ore limited the value of 

extracted Fe (Schiellerup and others, 2003). Currently titaniferous magnetite is thought be objectionably high in Ti for iron 

ore, yet too low in Ti for titanium ore; however, if metallurgical problems with extraction and separation could be resolved, 

then deposits containing very large reserves of titaniferous 

magnetite could become economically viable for both elements (Rose, 1969).

Some deposits also have significant phosphate (P2O5) 

potential from apatite-bearing oxide-rich rock related to anorthositic rocks. The Lac à Paul deposit, in the Lac Saint-Jean 

anorthosite complex, Quebec, contains numerous layers with 

abundant apatite-ilmenite (nelsonite), olivine, and magnetite in 

anorthosite, norite, and leuconorite. The deposit has indicated 

resources of 348 Mt with 6.5-percent P2O5 and 8.4-percent 

TiO2 (Arianne Resources, 2012). Phosphate resources reported 

for other Fe-Ti-oxide deposits in the Lac Saint-Jean anorthosite complex are 5.4 Mt with 9.25-percent P2

O5 for the SaintCharles deposit and 20.3 Mt with 5.2-percent P2

O5 for the La 

Hache-Est deposit; the Everett (Lac Puyjalon) deposit in the 

Havre-Saint-Pierre anorthosite suite has 294 Mt with 4.0-percent P2

O5 (Corriveau and others, 2007). 

Byproduct Commodities

Byproducts from the Tellnes deposit include Ni and Cu 

from trace amounts of sulfides and V from magnetite (Schiellerup and others, 2003). Vanadium (as V2

O5) and chromium 
Historical Evolution of Descriptive and Genetic Knowledge and Concepts 9

(Cr) are reported as potential byproduct commodities for 

a number of deposits in the Grenville Province of Quebec, 

including 5.4 Mt with 0.1-percent V2O5 at the Saint-Charles 

deposit, 3.5 Mt with 0.67-percent V2O5 at the Buttercup 

deposit, and 810 Mt with 0.2-percent V2O5 and 1.55-percent 

Cr for the Magpie Mountain deposits (Corriveau and others, 

2007). 

Example Deposits

In general, Fe-Ti-oxide deposits occur as discordant 

tabular intrusions, lenses, sills, or dikes emplaced into anorthosite massifs. In layered segments of anorthosite massifs 

or in related layered mafic intrusions, oxide mineralization 

can be weakly concordant or stratiform. Hemo-ilmenite is 

the ore mineral at the two currently active mines, Lac Tio in 

Quebec, Canada, and Tellnes in Norway. The Lac Tio deposit, 

hosted within the Allard Lake anorthosite in the Havre-SaintPierre plutonic suite in the Grenville Province, is estimated 

to contain more than 52 Mt of proven and probable reserves 

of titanium dioxide (Rio Tinto, 2011). The ore averages 

34.2-percent TiO2 as ilmenite and 27.5-percent FeO, 25.2-percent Fe2

O3, and 3.1-percent magnesium oxide (MgO) (Gross, 

1996). Tellnes, a hemo-ilmenite-bearing norite body cutting 

the Åna-Sira anorthosite in the Rogaland Province, has ore 

reserves estimated to be 380 Mt averaging about 18-percent 

TiO2 as ilmenite and 2-percent FeO as magnetite (Gross, 1996; 

Schiellerup and other, 2003). Titanium deposits in the entire 

Duluth Complex may represent the largest known resource of 

Ti in North America (Ulland, 2000). Hauck and others (1997) 

estimate that the Duluth Complex may contain as much as 245 

Mt of >10-percent TiO2 in numerous deposits (fig. 4). The four 

mineralized deposits in the Sanford Lake district in western 

New York (Sanford Hill/South Extension, Cheney Pond, 

Mt. Adams, and Upper Works) are dominated by titaniferous magnetite in gabbro and anorthosite and contain between 

9.5- to 30-percent TiO2 (Gross, 1968; table 1). The Big Island 

massive hemo-ilmenite dike, cross-cutting the Allard Lake 

anorthosite body in the Havre-Saint-Pierre anorthosite suite, 

can contain as much as 15-modal-percent magmatic rutile; 

assays give values of 40.3-percent TiO2, 26-percent FeO, and 

21.1-percent Fe2O3 (Perreault, 2003; Morisset and others, 

2010). The Magpie Mountain deposits, consisting of massive 

titanomagnetite hosted in gabbro, is one of the largest titanomagnetite resources in the Grenville Province with resource 

estimates greater than 1,500 Mt with 56-percent FeO and 

10.9-percent TiO2 (Gross, 1996).

Important Deposits

• Lac Tio, Quebec, Canada (Hammond,1952; Charlier 

and others, 2010) (in production)

• Tellnes, Norway (Krause and others, 1985; Duchesne 

and Schiellerup, 2001) (in production)

• Sanford Hill/South Extension, New York, United States 

(Gross, 1968) (now closed)

• Longnose and Water Hen, Minnesota, United States 

(Severson, 1995; Hauck and others, 1997) (speculative)

• Lac à Paul, Quebec, Canada (Arianne Resources, 2012) 

(speculative)

Historical Evolution of Descriptive and 

Genetic Knowledge and Concepts

The origin of magmatic Fe-Ti-oxide deposits is obscured 

by their relative paucity and their problematic relation to their 

enigmatic anorthositic host rocks. It has long been recognized 

that these deposits had a magmatic origin, and originally it 

was hypothesized that they formed either from accumulation of oxide minerals in magma or by immiscibility between 

Fe-Ti±P liquids and silicate liquids (for example, Lister, 1966; 

Philpotts, 1967; Kolker, 1982; Force, 1991). However, experimental results have not successfully replicated any combination of possible Fe-Ti±P melts at reasonable magmatic temperatures, and it seems inescapable that liquid immiscibility 

as an explanation for the development of these deposits is not 

geologically viable (Lindsley, 2003; Tollari and others, 2006). 

More recent work, including detailed trace-element analyses, 

stable and radiogenic isotopic work, and precise geochronology, supports formation by physical and chemical magmatic 

processes (see for example, Duchesne, 1999; Dymek and 

Owens, 2001; Charlier and others 2006; Charlier and others, 

2010; Morisset and others, 2010).

Petrologic questions regarding the origin of anorthosite 

massifs and related rocks, such as jotunite, charnockite, and 

oxide-rich rock, continue to be thoroughly debated (see for 

example, Ashwal, 1993; Vander Auwera and others, 2000; 

Seifert and others, 2010). The combination of accumulation 

processes, magma mixing, fractional crystallization, solidstate remobilization, and cotectic crystallization necessary to 

form the immense ilmenite-dominated deposits of Lac Tio 

and Tellnes remain to be resolved (Charlier and others, 2006). 

Dynamic emplacement mechanisms involving multiple pulses 

of crystal-laden magma flowing through restricted conduit systems, as suggested for major Ni-Cu deposits such as Voisey’s 

Bay (see for example, Evans-Lamswood and others, 2000), 

have recently been invoked to explain the high hemo-ilmenite 

concentrations in the Tellnes and Lac Tio deposits (Wilmart 

and others, 1989; Charlier and others, 2010). 

Interaction with crustal rocks also plays an important role 

in anorthosite development. Assimilation prior, during, and 

following differentiation and diapiric uprise of plagioclasebearing magmatic mush will influence oxygen fugacity and 

silica activity of anorthosite parent magmas and thus play a 

critical role controlling oxide mineralogy (Morse, 2006; Frost 
10 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

and others, 2010). Assimilation of silica-rich rocks by ascending and differentiating mafic magma can increase oxygen 

fugacity (fig. 5), consuming magnetite and making ilmenite 

more abundant as well as increasing the hematite component 

of ilmenite (Frost and others, 2010). The control exerted by 

redox conditions and silica activity corroborates observations 

by Anderson and Morin (1969) of the dominance of titaniferous magnetite in labradorite-type anorthosite plutons versus 

the dominance of hemo-ilmenite in andesine-type anorthosite 

plutons. 

Regional Environment

Geotectonic Environment and Magmatic 

Temporal Relations

Economic magmatic Fe-Ti-oxide deposits have spatial and temporal associations with massif-type anorthosite 

suites, which are found in Proterozoic rocks on all continents 

(Anderson, 1969; Ashwal, 1993). The time span during which 

massif-type anorthosite formed is largely restricted from 

about 930 Ma (Rogaland, Norway; Schärer and others, 1996) 

to about 2120 Ma (Labrador, Canada; Hamilton and others, 

1998), but most anorthosite suites were emplaced between 

about 1800 and 1060 Ma (Ashwal, 2010). A long-lived, 

geologically active geotectonic setting operating over length 

scales of several thousand kilometers seems to be a critical 

favorable factor for development of massif-type anorthosite 

suites permissive for economic magmatic Fe-Ti-oxide deposits 

(Rivers, 1997; Morse, 2006; Ashwal, 2010). 

There is now an apparent consensus on a general tectonic 

evolution of the Grenville Province that favors an accretionary model rather than a plume model (see for example, 

Rivers, 1997; Morse, 2006; Ashwal, 2010; McLelland and 

others, 2010; Hynes and Rivers, 2010). Main crustal buildup of the Grenville Province occurred through Andean-type 

continental arc and intercontinental back-arc magmatism 

with additional accretion of magmatic arcs followed by 

post-collisional replacement of mantle lithosphere by asthenosphere, perhaps by delamination or convective thinning. 

Midcontinent

rift

Area of

larger map

LAKE SUPERIOR

Hypabyssal intrusives

(Beaver Bay Complex)

North Shore Volcanics Group

Felsic series

Layered series

(cumulate gabbro and troctolite)

Anorthositic series

Biwabik Iron-Formation

Rove and Virginia Formations

(Paleoproterozoic sedimentary rocks)

Archean granites/metavolcanics

Duluth

Complex

Oxide-bearing ultramafic deposit

Ni-Cu±PGE sulfide deposit

EXPLANATION

0 N

0

10

10 MILES

20 30 KILOMETERS

Figure 4. Simplified geologic map of the Duluth Complex, Minnesota (modified from Hauck and others, 1997). The 

basal part of the complex contains world-class nickel-copper±platinum group elements (Ni-Cu±PGE) deposits (shown 

in pink) and numerous Fe-Ti-oxide-bearing ultramafic deposits (shown in dark blue).
Regional Environment 11

Rivers (1997) suggests that anorthosite complexes in the 

Grenville Province were emplaced in two contrasting extensional environments: (1) areas of backarc extension inboard 

from an active continental-margin magmatic arc and (2) within 

a collisional orogen during periods of tectonic collapse and 

rising isotherms. During such periods of extension, hot mantle 

lithosphere would have had access to the base of a previously 

thickened continental crust (Rivers, 1997). The ultimate source 

of anorthosite and related rock types is thought to be related 

to decompression melting of asthenospheric mantle (referred 

to as lithospheric delamination; Emslie, 1978; Corrigan and 

Hanmer, 1997; McLelland and others, 2010) or delaminationrelated melting of lower crustal material underthrust into the 

mantle at depths greater than 40 km (referred to as the crustaltongue model; Duchesne and others, 1999; Longhi and others, 

1999) producing mafic magmas that would pond at the base of 

the crust.

Morse (2006) suggests that restricted time constraints 

for anorthosite development were imposed by a continental 

lithosphere that was just thick enough to suppress volcanism 

and to permit failed rifting that trapped magma capable of 

generating anorthosite at depth. Vander Auwera and others 

(2011) propose a model for anorthosite generation requiring 

a balance between sufficiently high mantle temperatures and 

availability of subducted continental crust for partial melting. 

They hypothesized that an ideal combination of these two factors occurred only during the Proterozoic, thus restricting the 

anorthosite time window.

For Fe-Ti-oxide deposits in Proterozoic massif-type 

anorthosite in the Grenville Province, further age and mineralogical generalizations are given in Hébert and others (2005): 

(1) labradorite-type massif anorthosite is associated with gabbro and occurs only in plutons older than 1130 Ma, and Fe-Ti 

oxides in these rocks are dominantly titaniferous magnetite; 

(2) ages for andesine-type massif anorthosite are younger than 

1160-Ma, although this generalization is complicated by the 

1354-Ma Rivière-Pentecôte anorthosite, Quebec, that has both 

labradorite- and andesine-type anorthosite; and (3) no massive hemo-ilmenite deposits are known in anorthositic plutons 

older than 1160 Ma. 

The Havre-Saint-Pierre anorthosite suite is a microcosm 

for these observations by Hébert and others (2005). In the 

Havre-Saint-Pierre anorthosite suite, older (about 1139 to 1129 

Ma) labradorite-type anorthosite contains abundant titaniferous magnetite and younger (about 1056 to 1045 Ma) andesinetype anorthosite contains abundant hemo-ilmenite (Wodicka 

and others, 2003; Perreault, 2003; Morisset and others, 2009).

Temporal (Secular) Relations of Oxides to Host 

Rocks

Typically, massive Fe-Ti-oxide ore has sharp, crosscutting contacts with its anorthositic host forming lenses tens 

to hundreds of meters wide and several hundred meters long. 

Massive ore also may have apophyses cutting host rock, be 

associated with intrusive breccias, and contain anorthositic 

xenoliths, all of which suggest that oxide deposits postdate 

host anorthosite intrusion. A zircon uranium-lead (U-Pb) 

age for the Åna-Sira anorthosite host to the Tellnes deposit 

is 931±2 Ma, whereas a zircon age for the deposit itself is 

920±3 Ma, suggesting a 10 million-year gap between anorthosite intrusion and injection of the hemo-ilmenite-bearing 

norite dike (Schärer and others, 1996). However, based on 

more recent detailed petrologic and geochemical research on 

ilmenite-zircon relations at Tellnes, Charlier and others (2007) 

suggest the younger age may have been influenced by latestage interstitial crystallization and exsolution of zircon from 

ilmenite rather than be indicative of the age of ore formation. 

They conclude that the hemo-ilmenite-bearing norite is only 

Figure 5. Classification of rock association and iron-titaniumoxide (Fe-Ti-oxide) mineralogy for massif anorthosite based 

on silica activity and oxygen fugacity for idealized lithologies 

(modified from Morse, 2006). The anticipated oxide mineralogy 

is given along the top: Ti-Mte = titanomagnetite; Ilm = ilmenite; 

Hemo-ilm = hemo-ilmenite. Oxygen fugacity (fO2) buffers are 

indicated semi-quantitatively along the bottom axis: WM = 

wüstite-magnetite; FMQ = fayalite-magnetite-quartz; NNO = 

nickel-nickel oxide; HM = magnetite-hematite. The dashed arrow 

indicates a trend of increasing titanium-ore grade for potential 

Fe-Ti-oxide deposits.

f 02

Silica activity

Andesine norite

Norite

Gabbronorite

Gabbro

Troctolite

Melatroctolite

 Ti-Mte Mte + Ilm Ilm Hemo-ilm

-0.5

1.0

WM FMQ NNO HM

Increasing Ti 

ore grade
12 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

marginally younger than enclosing host anorthosite. This relation would thus link massive oxide deposition more closely to 

the magmatic processes responsible for the anorthosite host. 

The Big Island massive Fe-Ti-oxide dike that cross-cuts the 

Allard Lake anorthosite has overlapping ages for oxide and 

host rock. The Big Island dike is dated at 1052.9±6.5 Ma, and 

its anorthosite host has an age of 1057.4± 5.7 Ma (Morisset 

and others, 2009). This overlap in ages also suggests a close 

link between processes of ore formation and the dynamics of 

anorthosite intrusion.

In layered intrusions, including the Bjerkreim-Sokndal 

intrusion in the Rogaland Anorthosite Province (Wilson and 

others, 1996), the Sybille monzonite in the Laramie Range 

anorthosite complex (Scoates and others, 1996), and the 

Grader layered intrusion (Charlier and others, 2008), Fe-Ti 

oxides crystallized contemporaneously with host rock. In 

the Duluth Complex, the OUIs that intrude troctolite are 

interpreted to represent late-stage residual magmatic liquids 

(Hauck and others, 1997). Contact relations of the OUI body 

at Water Hen suggest emplacement of the main OUI body 

before its troctolite host had fully crystallized (Severson, 

1995).

Relations to Structures

Emplacement of a number of anorthosite complexes may 

be related to large crustal zones of weakness and lithosphericscale discontinuities (Emslie and others, 1994; Scoates and 

Chamberlain, 1997; Duchesne and others, 1999). In the Grenville Province, some ilmenite-rich deposits formed in anorthosite intrusions located along deep-seated fault zones at the 

margins of major tectonic provinces and belts (Gross, 1996). 

Relations to Igneous Rocks

Magmatic Fe-Ti-oxide deposits are related to igneous 

rocks simply by definition of the ore type. The fundamental 

constraint on where these deposits occur is a specific association with Proterozoic massif anorthosite and related rock 

types. The geotectonic spatial and temporal setting favorable 

for formation of these rock types apparently resulted in formation of distinct magmas enriched in Ti and Fe, and subsequent 

magmatic processes controlled crystallization and concentration of ilmenite- or titanomagnetite-dominated orebodies.

Relations to Metamorphic Rocks

Massif anorthosites display a wide range of metamorphic 

grades, from strongly metamorphosed (for example, Marcy 

Anorthosite, Adirondacks, New York) to essentially unmetamorphosed (for example, Åna-Sira anorthosite, Norway). In 

the Adirondacks, anorthosite and related rocks were emplaced 

in mid- to upper-crustal levels between 1175–1155 Ma producing low-pressure contact metamorphism in country rocks 

(Valley and Essene, 1980; Valley, 1985). In turn, contact metamorphism was overprinted by high-pressure, high-temperature 

granulite-grade regional metamorphism during the Grenville 

orogeny, which had its metamorphic peak at about 1050–1040 

Ma (McLelland and others, 1996). Country rocks for the 

Morin and Lac Saint-Jean anorthosite suites, Quebec, were 

strongly metamorphosed prior to anorthosite emplacement; 

surrounding country rock and the Havre-Saint-Pierre suite 

were strongly metamorphosed after anorthosite emplacement 

(Corriveau and others, 2007). Thus, as supported by highly 

variable field relations to metamorphic rocks, metamorphism 

has no role in development of magmatic Fe-Ti-oxide deposits.

Relations to Sedimentary Rocks

Sedimentary rocks are not genetically related to Fe-Tioxide deposits hosted by rocks of Proterozoic massif anorthosite plutonic suites. Many Proterozoic sedimentary or 

metasedimentary rock lithologies can act as country rocks to 

ore-related plutonic suites.

Physical Description of Deposit

Dimensions in Plan View

Magmatic Fe-Ti-oxide bodies are highly variable in size 

and shape reflecting diverse magmatic and physical processes 

that lead to their development. The Lac Tio deposit is made up 

of three orebodies, the Main deposit, the Northwest deposit, 

and the Cliff deposit (fig. 6) (Perreault, 2003). The Main 

deposit is an equant tabular sheet, 1,097 m by 1,036 m with 

an estimated thickness of 110 m inclined about 10° to the east. 

The Northwest deposit, separated from the Main deposit by a 

late normal fault, forms a band of massive ilmenite alternating with anorthosite that varies from 7 to 60 m in thickness, 

inclined gently to the east. The Cliff orebody is roughly elliptical in plan, about 380 m by 230 m and 60 m thick (Hammond, 

1952). 

In the Rogaland Province, discordant Fe-Ti-oxide deposits occur as dikes, pods, veins, or stockworks in anorthosite 

(Krause and others, 1985) (fig. 3). The Tellnes orebody is 

within a sickle-shaped, hemo-ilmenite-bearing norite, dikeshaped intrusion more than 2.5 km long and 400 m thick, 

extending on both ends into a 5- to 10-m-thick jotunite dike 

(Wilmart and others, 1989) (fig. 7). The Blåfjell deposit is 

made up of several irregularly shaped bodies that are as much 

as 15 m thick and 55 m long (Krause and others, 1985). The 

Storgangen orebody is a dike with numerous offshoots extending about 4 km in a wide arch cutting the Åna-Sira anorthosite 

with thickness varying between several meters to about 50 m 

in the center (Krause and others, 1985).

Small OUIs within the Duluth Complex are irregular 

pipe-like bodies. Diamond drilling at the Longnose deposit 

indicates a roughly elliptical orebody, 700 m by 600 m and 
Physical Description of Deposit 13

Main

Cliff

Northwest

A

A'

A' A

Exploited ore

Unexploited ore

N

0

0 375 FEET

200 METERS

0

0 375 FEET

200 METERS EXPLANATION

Figure 6. Surface outline of the three main orebodies at the Lac Tio deposit, Quebec, Canada, and a 

north-south cross section of the Main orebody showing the reconstructed exploited ore removed from the 

open pit and remaining ore (modified from Charlier and others, 2010).

Figure 7. Simplified geologic map of the host Åna-Sira anorthosite, Norway, and location and three cross sections of the Tellnes 

ilmenite-norite orebody (modified from Krause and others, 1985).

C`

C

B`

B

A

A`

200

100

0

A A` B B` C C`

500 m

400

300

200

100

0

EXPLANATION

Leuconorite

Ilmenite-Norite

Anorthsite

Basalt

Mangerite dike

Lake

Fault

N

m

CROSS SECTIONS
14 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

about 150 m thick (Hauck and others, 1997). The Water Hen 

intrusion is about 490 m by 150 m by 210 m thick with ilmenite concentrations from 5 to 50 percent in various ultramafic 

lithologies (Strommer and others, 1990) 

Size of Hydrothermal System Relative to Extent 

of Economically Mineralized Rock

Magmatic Fe-Ti-oxide deposits do not develop large 

hydrothermal systems; they are magmatic accumulations of 

ore minerals. 

Vertical Extent

The vertical extent of Fe-Ti-ore deposits is as variable 

as their dimensions in plan view ranging in thickness from 

centimeters to hundreds of meters. 

Form and Shape

Iron-Ti-oxide deposits are commonly discordant or 

weakly concordant within their host rocks and less commonly 

occur as conformable layers. Most deposits can be generally 

classified by form and shape into six groups: (1) flat-lying 

tabular bodies of large areal extent (for example, Lac Tio 

deposit), (2) steeply to shallowly dipping dike-like bodies 

(for example, Tellnes deposit in a norite dike), (3) irregular 

lenticular masses and pods (for example, Furnace deposit), (4) 

elliptical plug-like pipes and bodies (for example, Longnose 

and Water Hen deposits), (5) oxide concentrations in crosscutting pegmatitic dikes (for example, Blåfjell deposit), and 

(6) layered, stratiform, and concordant bodies (for example, 

the Grader deposit (a massive ilmenite deposit in the Grader 

layered intrusion that was mined in the late 1940s). Numerous Fe-Ti-oxide deposits in the Allard Lake anorthosite of 

the Havre-Saint-Pierre anorthosite suite display at least three 

of the form-shape groups listed above (Hammond, 1952). 

Deposits also can be deformed and remobilized by tectonic 

and metamorphic events (fig. 8). Deposits in the Sanford Lake 

district have multiple examples of varying forms and shapes 

(Gross, 1968). Deposits in the Duluth Complex are all pluglike in form with the exception of the Boulder Creek deposit 

that is stratabound (Hauck and others, 1997). 

Host Rocks

Massif anorthosite and related rocks are the most important hosts for economic magmatic Fe-Ti-oxide deposits. In 

general, deposits dominated by hemo-ilmenite are hosted 

by andesine-type anorthosite and deposits dominated by 

titanomagnetite with ilmenite are hosted by labradorite-type 

anorthosite. Deposits with significant apatite can be hosted by 

a variety of rock types from oxide gabbronorite to nelsonite.

Figure 8. Deformed layers and remobilized veins of massive titaniferous magnetite and ilmenite and oxiderich leucogabbro norite in labradorite-type anorthosite of the Rivière-au-Tonnerre Massif of the Havre-SaintPierre anorthosite suite, Quebec, Canada. Photograph provided by Serge Perreault, used with permission.
Geophysical Characteristics 15

Structural Setting(s) and Control

The shape and orientation of some Fe-Ti-oxide deposits 

suggest mobilization of oxide minerals through magmatic 

conduits or zones of weakness within anorthosite host rocks. 

The Tellnes body is an ilmenite-bearing norite dike extending 

on both ends into a 15-km-long jotunite dike (Wilmart and 

others, 1989). Parallelism of magnetic foliation trajectories 

with the contacts of the Tellnes orebody and homogeneity of 

magnetic lineation pattern over the entire body strongly point 

to a fabric acquired during magma flow along a feeder zone 

from southwest to northwest (Diot and others, 2003). Diot 

and others (2003) suggest that magma injection at Tellnes was 

favored by a transcurrent, dextral opening of a west-northwest 

to east-southeast striking zone of weakness across the host 

Åna-Sira anorthosite when the host rock was somewhat brittle. 

However, this interpretation is disputed by Charlier and others 

(2006) who suggest that the Tellnes norite dike actually represents remnants of a sill deformed by ductile subsidence of the 

host Åna-Sira anorthosite. 

Most OUIs in the Duluth Complex are spatially arranged 

along linear trends and are generally related to faults or are 

positioned in the immediate vicinity of fault zones. This suggests that structural control was important to their genesis 

(Hauck and others, 1997). 

Geophysical Characteristics

Fe-Ti-oxide deposits have been exploited for a long time. 

Mining in the Rogaland Province began in 1785 (Duchesne 

and Schiellerup, 2001). Whereas many of these deposits were 

initially discovered through geological field mapping and 

related exploration activities, geophysical methods are now 

widely applied to regional exploration in permissive terranes. 

The Tellnes deposit was discovered in 1954 by an aeromagnetic survey (Krause and others, 1985) as were extensions of 

known orebodies in the Grader layered intrusion (Charlier and 

others, 2008).

Magnetic Signatures

Aeromagnetic surveys have long been used in ilmenite 

exploration, although distinctive patterns for anomalies vary 

greatly. An underlying concept in aeromagnetic exploration 

rests on an assumption of a direct correlation between strong 

magnetic conductors and mineralization. However, most valuable Fe-Ti-oxide deposits contain ilmenite intergrown with 

hematite or ilmenite of a stoichiometric composition. Magnetite may be absent (for example, Blåfjell), occur only as a 

minor phase (for example, Tellnes), or be somewhat abundant 

in less economically attractive deposits (for example, Sanford 

Lake district). A scarcity of magnetite in the largest hemoilmenite deposits means that the magnetic signature of these 

deposits can be quite subdued (McEnroe, 1996; McEnroe 

and others, 2001; Brown and others, 2011). For Lac Tio and 

similar orebodies containing ilmenite with very fine exsolution lamellae of hematite, remanent magnetization commonly 

acquired in an ancient magnetic field with an orientation different from the present Earth’s field can contribute to or even 

dominate the current magnetic response of the host-rock body 

(McEnroe and others, 2001). Many hemo-ilmenite orebodies 

have a large negative aeromagnetic anomaly dominated by 

reversed natural remanent magnetization (NRM) and exhibit 

very high coercivity and low susceptibility (Bourret, 1949; 

Hargraves, 1959; McEnroe and others, 2001; McEnroe and 

others, 2007) (fig. 9). This high coercivity is attributed to a 

Figure 9. Aeromagnetic profile of the 

Allard Lake anorthosite across the Lac 

Tio deposit (in red), Quebec, Canada, 

displaying a contour line of equal 

magnetic-field intensity. The datum 

or zero anomaly isogam was selected 

arbitrarily by inspection (modified from 

Bourret, 1949). 

–2,000

–1,000

0

1,000

1,500

500

–500

–1,500

365

120

Hemo-ilmenite ore

Anorthosite

Isogams

Distance kilometers

0 1 2 3 4 5

EXPLANATION

METERS
16 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

very fine scale micro-texture of exsolution lamellae in hemoilmenite and ilmenite (that is, lamellar magnetism) resulting from a prolonged cooling history (McEnroe and others, 

2002). The ratio of NRM to induced magnetism (susceptibility 

multiplied by the ambient field) is the Koenigsberger ratio (Q). 

When Q values are greater than 10, NRM will overwhelmingly dominate a rock’s magnetic response (McEnroe and 

others, 2001). 

Brown and others (2011) examined magnetic anomalies 

over seven different anorthositic bodies. Different bodies had a 

large range of magnetic susceptibility values and NRM intensities, which depended on the mineral phase, composition, 

concentration, and grain size of oxides in anorthosite. Samples 

with high susceptibility all contained magnetite; samples with 

low susceptibility contained only hemo-ilmenite. Samples 

dominated by magnetite had moderate NRM values; samples 

with the strongest NRM had mixed hemo-ilmenite+magnetite 

or just hemo-ilmenite. Thus, ilmenite-dominated deposits 

may exhibit either a subdued or a strong negative magnetic 

anomaly; commonly a subdued response displays characteristic irregular patterns of negative and positive anomalies that 

can show broad, smooth profiles (Gross, 1996).

In the Duluth Complex, Q is commonly greater than 1 

indicating that NRM for these rocks dominates the magnetic 

anomaly signature (Chandler, 1990). The OUIs bodies themselves are commonly expressed as small, circular magnetic 

highs, which may be related to magnetite developed by alteration of olivine in host ultramafic rocks (Severson, 1995). 

Gravity Signatures

Gravity surveys in Canada show areas of gravity lows 

(negative gravity anomalies) over or near anorthosite bodies (Rose, 1969). Zones of Fe-Ti oxides typically provide 

a density contrast to anorthositic or gabbroic host rock and 

thus have a positive gravity anomaly. Both the Longnose and 

Longear OUI bodies have surprisingly strong gravity anomalies (amplitudes of 2 to 3 milligals), reflecting the high density 

of the bodies (Chandler, 2002). Geophysical exploration targets for OUIs in the Duluth Complex are thus marked by small 

dot-like gravity and magnetic anomalies that stand out from 

surrounding rocks.

Electrical Signatures

The OUIs in the Duluth Complex also can produce 

detectable electromagnetic and induced polarization anomalies, provided the deposits are fairly close to the surface. 

Airborne electromagnetic surveying detected anomalies over 

both the Longnose and Longear deposits with Fe-Ti oxide and 

perhaps graphite the likely conductors (Chandler, 2002). 

Hypogene Ore Characteristics

Mineralogy and Mineral Assemblages 

Most Fe-Ti oxides in igneous rocks are members of two 

solid solution series—the hematite-ilmenite rhombohedral 

series (Fe2O3–FeTiO3) and the magnetite-ulvöspinel spinel 

series (Fe3O4–Fe2TiO4) (fig. 10). Above about 800 °C, the 

ilmenite-hematite series forms an extensive solid solution; the 

magnetite-ulvöspinel series has complete solid solution above 

about 600 °C (Haggerty, 1976). In slowly cooling plutonic 

rocks, hematite will exsolve from ilmenite forming hemoilmenite (Lindsley, 1981; fig. 11A). Titanium in titanomagnetite exsolves to form either lamellae of ilmenite in magnetite 

or granular, interlocking discrete grains of ilmenite and magnetite (Buddington and Lindsley, 1964; fig. 11B). Observed 

mineralogy in Fe-Ti-oxide deposits has typically undergone 

exsolution, oxidation, diffusion, and other subsolidus effects 

such as Ostwald ripening. In many deposits, metamorphism 

has further altered oxide mineralogy. Detailed modal studies 

and careful textural examinations are required to distinguish 

between primary precipitated oxides and oxides grown from 

late-stage interstitial liquids. 

Magmatic rutile is found at several deposits in the 

Saint-Urbain anorthosite in the Grenville Province (Charlier 

and others, 2008; Morisset and others, 2010). Rutile in the 

Roseland anorthosite may be metasomatic (Herz and Force, 

1987). Rutile, along with magnetite and anatase, at Lac Tio 

results from late-stage alteration of hemo-ilmenite (Charlier 

and others, 2010). Geikielite (MgTiO3) can occur as lamellae 

in hemo-ilmenite, although with slow cooling, Mg in oxide 

can exchange with Fe in surrounding silicates.

The presence or absence of discrete crystals of ilmenite 

is a key factor that determines the economic value of an oxide 

deposit (Force, 1991). Titanium in solid solution in magnetite 

or as exsolution lamellae in magnetite is considered uneconomic (Force, 1991). Coarser grain sizes are more desirable 

than finer grain sizes. Economic ore minerals in oxide deposits are ilmenite and hemo-ilmenite (ilmenite with less than 

50-percent exsolved hematite). Less economic titanomagnetite is typically a mixture of Ti-poor magnetite, ilmenite, 

and ulvöspinel. Proportions of these ore minerals vary from 

deposit to deposit, but mineral assemblages can be classified 

into four groups (see for example, Duchesne and Schiellerup, 

2001; Hébert and others, 2005; Corriveau and others, 2007; 

Hauck and others, 1997): (1) hemo-ilmenite (± magnetite 

± rutile) that cross-cuts or is concordant in anorthosite and 

related rocks (for example, Tellnes, Lac Tio, Big Island), (2) 

titaniferous magnetite+ilmenite disseminated or as layers 

in anorthosite and related intrusions (for example, Sanford 

Lake district, Magpie Mountain, Buttercup), (3) titaniferous 

magnetite with ilmenite and apatite cross-cutting anorthosite 

or concordant in oxide-apatite gabbro (for example, Everett, 

La Hache-Est, Lac à Paul), and (4) ilmenite+magnetite in 

ultramafic rocks cross-cutting (rarely stratabound) layered 
Hypogene Ore Characteristics 17

troctolite (for example, Longnose, Water Hen). Combinations 

of these mineral assemblages can be found in various deposits 

within the same anorthosite suites (see for example, Perreault, 

2003; Hébert and others, 2005; Corriveau and others, 2007).

Paragenesis

Paragenetic sequences of Fe-Ti-oxide deposits are typically complex due to widely varying proportions of ilmenite, hemo-ilmenite, titanomagnetite, and magnetite among 

deposits. Postcumulus high-temperature re-equilibration, 

complex exsolution textures, secondary mineral reactions, and 

possible metamorphic overprinting further complicate mineral 

relations. Thus, the sequence of mineralization of ore minerals may be unique for individual deposits (Gross, 1996). The 

primary oxide paragenetic sequence depends on original TiO2

content, silica activity, and the oxygen fugacity path of parent 

magma (see fig. 5). These parameters will determine whether 

ilmenite is an early liquidus mineral, potentially leading to 

concentrations of massive ilmenite or hemo-ilmenite with 

little or no magnetite, or whether silicate crystallization alone 

will drive fractionated liquids toward Fe-Ti-P enrichment, 

potentially resulting in late-stage concentrations of ilmenite, 

titanomagnetite, and apatite crystallizing from residual liquids.

For massive hemo-ilmenite deposits, ilmenite along with 

plagioclase is an early liquidus mineral, controlled primarily by the TiO2

 content of the parent magma and the oxygen 

fugacity of the silicate magma from which oxides crystallize (Haggerty, 1976; Wilson and others, 1996; Duchesne, 

1999; Charlier and others, 2008). In a magmatic system 

closed to oxygen, the Fe2+/Fe3+ ratio of the system is fixed, 

and crystallization of Fe3+-bearing minerals (such as ilmenite) increases this ratio in the melt, thereby lowering the melt 

oxygen fugacity and driving the system toward crystallization of magnetite. In an open system, ilmenite crystallization 

will have little effect on oxygen fugacity because a melt can 

readjust and keep oxygen fugacity relatively constant. IronTi-oxide deposits in the Rogaland Province fit an evolutionary 

trend exemplified by Fe-Ti oxides in the Bjerkreim-Sokndal 

layered intrusion. The Bjerkreim-Sokndal trend has early 

precipitation of hemo-ilmenite with minor Ti-poor magnetite 

followed by a gradual decrease in the hematite component 

in ilmenite, matched with increasing Ti content of magnetite 

and an appearance of apatite (Wilson and others, 1996). In the 

Adirondacks, there is a perceptible compositional trend among 

the Fe-Ti oxides. In anorthosite and other early cumulates, 

ilmenite tends to be richer in hematite, and coexisting spinels 

are richer in magnetite compared to later cumulates and mafic 

rocks (Ashwal, 1982). 

Figure 10. The subsystem FeO-Fe2O3-TiO2 showing major solid solution joins for the 

cubic (ulvøspinel-magnetite), rhombohedral (ilmenite-hematite), and orthorhombic 

(pseudobrookite) series. Temperatures along the cubic and rhombohedral joins are consulate 

temperatures (critical points for the solvi).

Ti4+O2

Fe3+

2 O3

(hematite,

maghemite)

Fe3+

2 TiO5

 (pseudobrookite)

 Fe2+

2 Ti2

O5

(ferropseudobrookite)

 Fe2+ TiO3

(ilmenite)

Fe2+

2 TiO4

Fe2+ O

(wustite) Fe2+Fe3+

2 O4

~800 o

C

Ilmenite-hematite series

(hemo-ilmenite)

Pseudobrookite series

~600 o

C

Ulvøspinel-magnetite series

(titanomagnetite)

(rutile,

anatase,

brookite)

(magnetite)

(ulvøspinel)
18 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

A

B

Figure 11. A. Reflective-light photograph of hemo-ilmenite from the Lac Tio deposit, Quebec, Canada. 

Light-colored lamellae are hematite exsolving from the brown-pink ilmenite. Scale bar is 0.5 mm. 

B. Reflective-light photograph of titanomagnetite (Ti-Mte) and ilmenite (Ilm) from the Hervieux East 

massive titaniferous lens in the La Blache anorthosite complex, Quebec, Canada. Scale bar is 0.5 mm. 

Photographs provided by Serge Perreault, used with permission.
Hypogene Ore Characteristics 19

At the Longnose OUI deposit, ilmenite and titanomagnetite are cumulus minerals, titanomagnetite is also intercumulus, magnetite occurs as an alteration product of olivine and 

rutile, and hematite rims ilmenite (Cardero Resource Corporation, 2012).

Zoning Patterns

Physical and chemical conditions in the magmatic 

environment where Fe-Ti-oxide minerals are crystallizing 

control the physical distribution and chemical composition 

of oxides. Charlier and others (2006) document variations in 

modal proportions of both silicates and oxides in a large-scale 

zonation of the Tellnes orebody reflecting in-place crystallization history and development of varying proportions of 

residual liquid. The deepest parts of the Tellnes orebody 

contain mainly plagioclase and ilmenite, with little magnetite 

or sulfide, suggesting that plagioclase and ilmenite were early 

liquidus minerals. In the upper part of the orebody, olivine 

and orthopyroxene appear as cumulus phases, with magnetite, 

clinopyroxene, biotite, apatite, and hornblende present as 

intercumulus phases. Based on modal contents of ore-forming 

minerals, the Tellnes orebody has been divided into four 

zones (fig. 12): (1) an upper marginal zone with high modal 

contents of plagioclase and Fe-Mg silicates (orthopyroxene 

and clinopyroxene) and low contents of ilmenite; (2) an upper 

central zone with low plagioclase contents but high Fe-Mg 

silicate and ilmenite contents; (3) a lower central zone with 

low Fe-Mg silicate contents, plagioclase contents intermediate between the upper central zone and upper marginal zone, 

and the highest ilmenite contents; and (4) a lower marginal 

zone with decreasing ilmenite contents and increasing silicate 

contents (Kullerud, 2003). 

On a larger scale, hemo-ilmenite deposits are typically 

contained within anorthosite hosts, whereas rocks carrying ilmenite+magnetite+apatite (oxide-apatite gabbronorite) 

typically occur as discordant to concordant sill-like bodies 

within anorthosite, as layers along or near the outer limits 

of anorthosite massifs, or as layers within related jotunite 

(Dymek and Owens, 2001). Nelsonite can occur as dike-like 

Figure 12. A. Location of three selected cross sections on the geological map of the Tellnes orebody, 

Norway (in red; cut by basalt dikes, in green; see fig. 7 for details); B. cross section 1600; C. cross section 

1200; and D. cross section 800; cross sections are showing spatial distribution of the four different 

orebody zones, based on silicate and oxide mineralogy and concentration (modified from Charlier and 

others, 2006). UCZ = Upper central zone, with low plagioclase contents and high Fe-Mg-silicate and 

ilmenite contents; UMZ = Upper marginal zone with high plagioclase and Fe-Mg-silicate contents and 

low ilmenite contents; LCZ = Lower central zone with low Fe-Mg-silicate contents, plagioclase contents 

intermediate between the UCZ and UMZ, and the highest ilmenite contents; and LMZ = Lower marginal 

zone with decreasing ilmenite and increasing silicate contents.

500

0 400

0 1,000 METERS

800 FEET

UCZ

LCZ

LMZ

UCZ

LCZ

LMZ

UMZ

UCZ UMZ

LCZ

Section 1200 LMZ Section 800

Section 1600

1600

1200

800

100 METERS

100 METERS

100 METERS

100 METERS

SSW NNE

SSW NNE

SSW NNE

A B

100 METERS C D

100 METERS

N
20 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

bodies in anorthosite and as layers or segregations within 

massive deposits of ilmenite or magnetite (Dymek and Owens, 

2001). The Grader layered intrusion in the Havre-Saint-Pierre 

anorthosite suite has massive ilmenite at its base, then layers of ilmenite alternating with anorthosite layers grading 

upward into ilmenite-apatite ore with variable proportions of 

plagioclase, and oxide-apatite gabbronorite at the top (Charlier 

and others, 2008). This sequence for the Grader intrusion is 

interpreted as evidence of successive appearances of liquidus 

minerals in a continually fractionating magma.

Textures and Grain Size

Textures and compositions of oxides indicate post-crystallization modification by re-equilibration and consolidation 

of loose grains into polycrystalline materials at subsolidus 

temperatures (annealing). Ore at Tellnes is medium-grained. 

Oxides are about 0.5 to 2 mm in diameter, with cumulate, 

equigranular, and massive textures. Discrete hemo-ilmenite 

grains are typically greater than 1 mm, commonly forming 

coarse-grained polygonal aggregates with interstitial green 

spinel and locally subsidiary amounts of magnetite (Schiellerup and others, 2003). Where hemo-ilmenite and magnetite 

are in contact, a symplectite of magnetite, ilmenite, and spinel 

can form by re-equilibration during cooling in which Fe3+

in ilmenite is exchanged for Fe2+ in magnetite (Schiellerup 

and others, 2003). Zones of clear ilmenite free of hematite 

lamellae also can develop where hemo-ilmenite is adjacent 

to magnetite because of subsolidus Fe migration; this texture 

does not appear at contacts with silicates or between two 

ilmenite grains (Duchesne, 1972). Two types of magnetite are 

recognized at Tellnes. These are small magnetite grains associated with sulfides and larger magnetite grains, about 0.5 mm 

in diameter, with exsolution lamellae of pleonaste that occur 

with olivine and prismatic orthopyroxene (Charlier and others, 

2007).

At the Lac Tio mine, hemo-ilmenite is dense, black, and 

mostly present as coarse-grained, thick, tabular crystals, about 

5 to 20 mm in length (Hammond, 1952; Charlier and others, 

2010) (fig. 13 ). In the Sanford Lake district, Gross (1968) 

described titaniferous magnetite deposits as having anorthositic ore and a lean gabbro ore. Anorthositic ore consists of 

massive lenses of titaniferous magnetite (Fe:Ti ratio greater 

than 2:1) that are phaneritic ranging from equigranular to 

porphyritic to reticulated with coarse-grained subhedral to 

euhedral magnetite in a mesh of fine-grained anhedral ilmenite 

with no flow structures. Gabbro ore is oxide-enriched conformable bands in gabbro (Fe:Ti ratio less than 2:1) that are 

typically more fine-grained with porphyritic or reticulated 

textures. Both types of ore are present in the Sanford Hill/

South Extension deposit with anorthositic ore forming a footwall orebody and gabbro ore forming a hanging-wall orebody 

(McLelland and others, 1993). Titanomagnetite, the dominant 

oxide in the Section 34 OUI in the Duluth Complex, occurs 

as round grains, coalesced rounded grains with or without 

embayed edges, subhedral grains, and skeletal blades (Severson, 1995). In the Skibo OUI, ilmenite is more abundant than 

magnetite; both oxides can be interstitial to major cumulate 

silicate phases and occur as rounded lobate grains (Severson 

and Hauck, 1990).

Gangue Mineral Characteristics 

Mineralogy and Mineral Assemblages

The principal gangue minerals with magmatic Fe-Tioxide deposits are the silicates of the host rocks. Gangue 

minerals in the Tellnes norite are plagioclase (An45-42), bronzite, augite, Ti-biotite, olivine, hornblende, magnetite, sulfides 

(bravorite, chalcopyrite, covelite, marcasite, millerite, pentlandite, pyrite, pyrrhotite, and violarite), and apatite (Krause 

and others, 1985; Wilmart and others, 1989). Bronzite and 

primary augite typically contain fine Schiller-type exsolution 

of ilmenite and hemo-ilmenite and rarely magnetite (Diot and 

others, 2003). At Lac Tio, hemo-ilmenite is hosted by anorthosite; accessory minerals include aluminous spinel, orthopyroxene, and Ti-phlogopite with minor amounts of sulfide (pyrite, 

pyrrhotite, chalcopyrite, and millerite) (Charlier and others, 

2010). In the Duluth Complex, OUIs are hosted in ultramafic 

rocks—typically dunite, pyroxenite, and peridotite—intruding troctolite. Gangue mineralogy is dominated by olivine, 

plagioclase, augite, hornblende, biotite, and minor amounts 

of Ni-Cu sulfides (chalcopyrite, pyrrhotite, cubanite, and 

pentlandite) (Strommer and others, 1990; Severson, 1995). 

Graphite is also found in a number of OUIs (Severson, 1995). 

Gangue minerals in the Sanford Lake district are both igneous 

Figure 13. Massive hemo-ilmenite ore from the floor of the Main 

pit at the Lac Tio deposit, Quebec. Coin used for scale is about 26 

mm in diameter. Photograph provided by Serge Perreault, used 

with permission. 
Gangue Mineral Characteristics 21

and metamorphic and include feldspar, garnet, orthopyroxene, 

clinopyroxene, hornblende, and sulfides (chalcopyrite, sphalerite, molybdenite, pyrrhotite, and pyrite) with minor apatite, 

prehnite, barite, orthoclase, leucoxene, scapolite, epidote, and 

quartz (McLelland and others, 1993).

Trace zircon and baddeleyite are common in many oxide 

deposits, typically occurring as rims surrounding ilmenite 

(Charlier and others, 2008; Morisset and others, 2010). Sapphirine (Mg-Fe-Al silicate) is unique to Fe-Ti-oxide deposits in the Saint-Urbain anorthosite suite and the Big Island 

deposit in the Havre-Saint-Pierre anorthosite suite and is 

interpreted as a subsolidus reaction of spinel and orthopyroxene in the presence of magmatic rutile (Morisset and others, 

2010). Apatite can be a prominent mineral in some magmatic Fe-Ti-oxide deposits. Apatite+oxide (mainly ilmenite) 

rocks with few silicates occur most commonly with massif 

anorthosite as a nelsonite (Kolker, 1982). The assemblage 

apatite+ilmenite+magnetite is typical of many anorthosite 

suites, with the rock referred to as an oxide-apatite gabbronorite (OAGN) (Owens and Dymek, 1992). An abundance 

of apatite with Fe-Ti oxides, such as at the Lac à Paul deposit, 

can result in a phosphate resource. Some ilmenite deposits in 

the Allard Lake anorthosite locally contain as much as 8- to 

10-percent fluorapatite (Gross, 1996). The concentration of 

rare earth elements (REE) in apatite could make some apatiterich Fe-Ti-oxide deposits a speculative REE resource.

Paragenesis

The paragenetic sequence for gangue minerals in host 

rocks generally follows predicted silicate crystallization 

sequences for mafic intrusive rocks. Gangue mineral paragenesis at Tellnes is intimately linked to oxide mineral paragenesis. 

Plagioclase is an early liquidus mineral with ilmenite followed 

by crystallization of orthopyroxene, clinopyroxene, hornblende, biotite, and magnetite (Krause and others, 1985). Olivine is present only in the upper part of the body and is typically interstitial to other minerals or occurs as small inclusions 

in orthopyroxene (Charlier and others, 2006). Plagioclase, 

orthopyroxene, and olivine are considered cumulus minerals; magnetite, clinopyroxene, biotite, apatite, and hornblende 

are considered intercumulus minerals (Charlier and others, 

2006). In the Adirondacks, large, euhedral plagioclase was the 

first phase to crystallize followed by augite and pigeonite and 

Fe-Ti oxide; apatite is cumulus only in very late stage lowCa pyroxene-deficient or olivine-bearing cumulates (Ashwal, 

1982). Primary mineralogies and textures of anorthosite in the 

Adirondacks have been affected to varying degrees by subsolidus recrystallization, which has resulted in the production of 

metamorphic garnet and hornblende (Ashwal, 1982). 

The cumulate sequence for the Bjerkreim-Sokndal intrusion is plagioclase cumulates in the lower section, plagioclasehypersthene-ilmenite cumulates in the middle section, and 

plagioclase-hypersthene/pigeonite-augite-ilmenite-magnetiteapatite cumulates in the upper section (Wilson and others, 

1996). This sequence is interpreted as crystallization of a continuously fractionating, periodically replenished magma chamber (Wilson and others, 1996) and represents a progressive 

appearance of liquidus minerals. The sequence of cumulate 

minerals in the Grader layered intrusion in the Havre-SaintPierre suite is somewhat similar with ilmenite and plagioclase 

as the early liquidus minerals (Charlier and others, 2008). 

However, in the Grader intrusion, apatite joins the cumulate 

assemblage of plagioclase+ilmenite prior to crystallization of 

Fe-Mg silicates and magnetite, and, in some layers, plagioclase is very low or absent, producing nelsonite (Charlier and 

others, 2008). 

Hydrous minerals, including biotite and hornblende, 

occur in many deposits and are typically late and volumetrically insignificant.

Zoning Patterns

The zoning pattern for gangue minerals is tied to ore 

mineral zonation as described above for a number of deposits, including the Tellnes deposit (Charlier and others, 2006) 

and the Grader deposit (Charlier and others, 2008), as well as 

the Bjerkreim-Sokndal layered intrusion (Wilson and others, 1996). Some OUIs in the Duluth Complex have a crude 

zonation from an olivine-rich core of dunite, peridotite, and 

melatroctolite, to an outer clinopyroxenite margin (Severson 

and others, 2002).

Textures and Grain Sizes

Gangue minerals in the Tellnes norite have a subophitic 

texture with euhedral plagioclase and bronzite and subordinate olivine; plagioclase laths are commonly slightly bent and 

locally granulated (Wilmart and others, 1989). Symplectic 

intergrowths of bronzite with magnetite or with oxide and sulfide found in the upper part of the orebody are considered to 

be products of the breakdown of primary olivine (Krause and 

others, 1985). Prismatic plagioclase and bronzite have features 

such as bending, undulatory extinction, deformation twins in 

plagioclase, kinking in bronzite, and local dynamic recrystallization into aggregates of small grains. Diot and others (2003) 

suggest that these textures were acquired during magma injection through the Tellnes dike and are indications of solid-state 

deformation in the presence of interstitial liquid. Charlier and 

others (2006) suggest that these textures were acquired by 

dynamic subsidence of underlying anorthosite during crystallization of the Tellnes oxide-bearing norite.

In the Poe Mountain anorthosite, one of three large 

composite anorthosite intrusions in the Laramie Range anorthosite complex, Wyoming, deformation and recrystallization 

of plagioclase were apparently continuous from subliquidus 

to subsolidus temperature conditions during emplacement of 

the intrusion (Lafrance and others, 1996). In addition, anorthosite with the highest degree of recrystallization has the 

lowest modal percentages of Fe-Mg silicates and Fe-Ti oxides 
22 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

suggesting plagioclase separation from more mafic constituents during deformation and recrystallization (Lafrance and 

others, 1996). Tabular plagioclase in anorthosite in the Sanford 

Lake district can be 10 cm or more in length with subparallel 

alignment of the longest plagioclase dimensions forming a 

planar fabric generated by flow (Ashwal, 1982).

Hydrothermal Alteration

Hydrothermal alteration does not play a role in development or enrichment of Fe-Ti-oxide deposits related to Proterozoic massif anorthosite suites.

Supergene Ore and Gangue 

Characteristics

Supergene enrichment is not important for Fe-Ti-oxide 

deposits related to Proterozoic massif anorthosite suites.

Weathering and Supergene Processes

Weathering and supergene processes have no role in the 

formation of magmatic Fe-Ti-oxide deposits related to Proterozoic massif anorthosite suites. However, weathering can play 

an important role in secondary enrichment and concentration of 

magmatic Fe-Ti-oxides. For example, ilmenite and rutile were 

mined from saprolite developed over the Roseland anorthosite 

and adjacent rocks (Herz and others, 1970), and weathering of 

ilmenite to form secondary leucoxene or rutile is important for 

the value of heavy mineral deposits (Force, 1991).

Geochemical Characteristics

Trace Elements and Element Associations

Trace-element contents of ilmenite are critical because 

they can impact the economic value of an Fe-Ti-oxide deposit 

by complicating the pigment production process (Chernet, 

1999). For example, Cr and V can affect pigment color (Chernet, 1999). Trace-element abundances and element associations in ore minerals reflect magmatic evolution and subsolidus re-equilibration, complicated by varying Fe-redox states. 

In Fe-Ti oxides, elements that preferentially substitute for trivalent Fe3+ are Cr3+, V3+, and Al3+. Elements that preferentially 

substitute for divalent Fe2+ are Mg2+, Mn2+, and Zn2+. Finally, 

Zr4+ can substitute for Ti4+ in ilmenite. Vanadium, Cr, and Al 

thus show a preference for a magnetite phase, whereas Mg, 

Mn, and Zn have a preference for an ilmenite phase, although 

these generalizations are complicated by the presence/absence 

of exsolution lamellae (McEnroe and others, 2000). Typically 

the fine size of exsolution lamellae in oxide minerals makes it 

impossible to resolve trace-element distributions in the different phases. 

Trace-element concentrations in oxide phases depend on 

the original element concentration in the parent magma, the 

sequence of mineralization for both silicates and oxides, the 

oxygen fugacity of magma during crystallization, and subsolidus re-equilibration among oxide minerals (Duchesne, 1999; 

Vander Auwera and others, 2003; Charlier and others, 2007). 

For example, Mg is concentrated in the ilmenite phase, so 

the presence of hematite lamellae in ilmenite will reduce the 

overall Mg content of ilmenite. Magnesium will also decrease 

in ilmenite during cooling by re-equilibration with surrounding silicates with Mg moving out of oxide and into silicate. 

Thus, ilmenite in massive ore will retain relatively high concentrations of Mg compared to isolated ilmenite surrounded 

by silicate minerals (McEnroe and others, 2000). Vanadium 

and Cr are concentrated in hematite-rich exsolution lamellae 

in ilmenite, but appearance of magnetite as a liquidus mineral 

will quickly deplete magma in these elements. 

Thin zircon rims surrounding ilmenite at a number of 

deposits in the Grenville Province (Morisset and Scoates, 

2008) and at Tellnes (Charlier and others, 2007) formed by 

migration of Zr4+ out of the ilmenite structure. Magnetite at 

Tellnes can contain coarse lamellae of zinciferous-aluminous 

spinel (Wilmart and others, 1989). Aluminous spinel also commonly occurs as granules external to ilmenite from exsolution 

and migration of Al3+ out of oxide at a number of deposits 

(McEnroe and others, 2000; Charlier and others, 2010). 

Concentrations of P and REE in parent magmas are mainly 

controlled by apatite crystallization. 

Zoning Patterns

Zoning patterns of trace elements in Fe-Ti-oxide deposits 

are the product of magmatic evolution and subsolidus re-equilibration. The percentage of cumulus minerals to intercumulus 

trapped liquid exerts an important control on zoning patterns 

in layered deposits. From the lower to the upper part of the 

Tellnes orebody, the Mg content of cumulus ilmenite increases 

when plagioclase and ilmenite are cumulus minerals and then 

begins to decrease with the advent of orthopyroxene and olivine crystallization (Charlier and others, 2007). Ilmenite with a 

high hematitic component near the margins of the deposit has 

lower Mg contents. Chromium and V decrease continuously 

from the lower to the upper part of the orebody, consistent 

with their compatible behavior in the ilmenite structure (Charlier and others, 2007). An overall magmatic trend for oxides 

in the Bjerkreim-Sokndal intrusion from hemo-ilmenite with 

minor magnetite to hematite-poor ilmenite with titanomagnetite is accompanied by decreasing Mg and Cr and increasing V 

until magnetite is a primary mineral, after which V decreases 

(McEnroe and others, 2000).
Petrology of Associated Igneous Rocks 23

Isotope Geochemistry of Ores

Stable Isotope Geochemistry

Ilmenite and titanomagnetite separates from oxide-rich 

ultramafic intrusions in the Duluth Complex have d18O values 

of 4.5 to 5.6 per mil (‰) (Ripley and others, 1998). Wholerock and mineral separates including plagioclase, pyroxene, 

olivine, and, to a lesser extent, oxides from OUIs have higher 

d18O values than similar minerals in other troctolites in the 

Duluth Complex. Based on observed whole-rock dD values 

(–70 to –87 ‰) as well as plagioclase (d18O up to 13.2 ‰) 

and pyroxene (d18O up to 10.1 ‰) separates, Ripley and others (1998) suggested that the OUI rocks may reflect isotopic 

exchange with a d18O-rich fluid at about 500 °C. Such a fluid 

could arise from dehydration reactions of shale and greywacke 

in adjacent country rock (Virginia Formation) driven by the 

thermal pulse of Duluth Complex intrusion events (Ripley 

and others, 1998). Whole-rock d18O values of ilmenite norite 

from the Tellnes orebody range from 5.1 to 5.4 ‰ (Wilmart 

and others, 1994). Leuconorite and ilmenite norite whole-rock 

samples from the orebody yield dD values of –66.9 and –76.6 

‰, respectively. Wilmart and others (1994) concluded that 

these values were consistent with a mantle origin and did not 

suggest evidence of significant hydrothermal exchange, in 

contrast to the OUIs in the Duluth Complex.

In the Kunene anorthosite complex in Namibia, Gleissner 

and others (2010) analyzed mineral separates from major rock 

units including ilmenite and magnetite from an older white 

andesine-type anorthosite and a younger dark labradorite-type 

anorthosite. Ilmenite and magnetite from white anorthosite 

have d18O values of 1.3 and 1.2 ‰, respectively, whereas 

ilmenite and magnetite from dark anorthosite have d18O values 

of 2.3 to 4.0 and 0.8 ‰, respectively. 

Radiogenic Isotope Geochemistry

Strontium (Sr) analyses of plagioclase separates from the 

Tellnes orebody gangue assemblage show remarkably homogenous initial 87Sr/86Sr isotopic ratios ranging from 0.704368 

to 0.704533 (Charlier and others, 2006). Such consistent 

ratios suggest that mixing of magmas was not likely, nor was 

there significant contamination from crustal rocks. Based in 

part on these data, the authors conclude that Tellnes hemoilmenite was likely derived through fractional crystallization 

of jotunitic magma.

At the Grader deposit, initial Sr isotopic compositions 

for plagioclase in host anorthosite (average = 0.703995) are 

slightly different from plagioclase in norite of the Grader 

deposit itself (average = 0.704319) (Charlier and others, 

2008). Charlier and others (2008) concluded that this minor 

difference arose from slightly different magma sources for 

the two rock types, although overall both rocks developed by 

continuous fractional crystallization with small geochemical

variations controlled by successive appearance of various 

liquidus phases.

Rhenium (Re) content in Fe-Ti-oxide deposits is a function of the proportion of Fe-Ti oxide in ore as Re is preferentially incorporated into titanomagnetite. Analyses of rheniumosmium (Re-Os) isotopic compositions of Fe-Ti-oxide ores 

from the Kunene anorthosite complex indicate that initial 

187Os/186Os ratios range from 10.7 to –4.9, with the negative 

values suggesting disturbance of the Re-Os isotope system by 

post-magma processes and therefore yielding unreliable initial 

compositions (Gleissner and others, 2012). 

Petrology of Associated Igneous Rocks

Petrologic questions surrounding the origin of anorthosite 

massifs and related rocks continue to be thoroughly debated 

(see for example, Ashwal, 1993; Vander Auwera and others, 

2000; Seifert and others, 2010). A generic two-stage model for 

massif anorthosite is generally accepted. First, there is stagnation of magma at the crust-mantle interface with crystallization 

of plagioclase and mafic silicates. Density separation of plagioclase from mafic minerals occurs by diapiric upwelling of 

a plagioclase-melt mush and sinking of mafic silicate minerals 

back into the mantle. This is followed by a stage of emplacement of a plagioclase-melt mush into the upper to middle crust 

where a complex magma chamber forms. Further fractional 

crystallization is dominated by plagioclase, Fe-Ti oxides, and 

Fe-Mg silicates (Ashwal, 2010). 

Duchesne and Schiellerup (2001) attribute the complex 

evolution of massive anorthosite compared to layered mafic 

intrusions to explain differing deposit styles between ilmeniterich deposits discordant to host anorthosite (for example, Lac 

Tio and Tellnes) and ilmenite-rich cumulates in layered intrusions (for example, Bjerkreim-Sokndal and Grader layered 

intrusions). Layered intrusions represent crystallization within 

relatively static magma chambers at near constant pressures. 

In contrast, development of massive anorthosite results from 

synchronous crystallization and deformation over a range of 

pressures, which would potentially mobilize magmatic liquids, 

crystal-magma liquids, or crystal mushes (Duchesne and 

Schiellerup, 2001). Within this dynamic environment, oxideladen liquids (1) could be injected into extensional openings 

in cooling and contracting host rocks along zones of weakness 

(see for example, Vander Auwera and others, 2006), (2) could 

become concentrated in physical traps in magma-conduit 

systems (see for example, Charlier and others, 2010), or (3) 

could form irregular pod- to dike-like oxide concentrations 

that cross-cut host anorthosite representing keels to larger 

intrusions in which Fe-Ti-oxide minerals accumulated near 

the base of an intrusion separated from plagioclase within an 

ascending and crystallizing magma (see for example, Morisset 

and others, 2010). In all scenarios, density contrasts among 

oxide, silicate, and liquid are critical.
24 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

Rock Names 

Anorthosite complexes are complicated and exhibit a 

wide range of rock types, not all of which are present in every 

complex (Emslie and others, 1994). Typical rock types include 

anorthosite, leucotroctolite, leuconorite, troctolite, norite, 

gabbronorite, ferrogabbro, ferrodiorite, jotunite, mangerite, 

and charnockite. Collectively, plutonic suites containing these 

rocks are commonly referred to as anorthosite-mangeritecharnockite-granite (AMCG) suites. Local terminology and 

imprecise usage of rock names over time have complicated 

descriptions of anorthosite complexes in the literature, particularly with respect to the terms “charnockite” (Frost and Frost, 

2008), “nelsonite” (Dymek and Owens, 2001), “jotunite” 

(Vander Auwera and others, 1998), and “ferrodiorite” (Force, 

1991). To bring a sense of order to the confusion, a classification scheme that includes the common rock associations for 

massif-type anorthosite and related rocks using consistent 

terminology has been constructed and is given in figure A1 in 

appendix 1.

Forms of Igneous Rocks and Rock Associations 

A number of Proterozoic terranes host large composite 

anorthosite massifs commonly made up of multiple diapiric 

intrusions or well-layered leucocratic troctolite, leuconorite, 

and leucogabbro overlain by thick anorthosite units (Longhi 

and others, 1999). Mafic rocks associated with anorthosite 

massifs include large layered intrusions and smaller ferrodiorite intrusions and dikes; commonly, granitic intrusions of 

various compositions (for example, mangerite and charnockite) are also present. Careful mapping in areas of well-exposed 

and undeformed anorthosite massifs typically reveals several 

dozen multiple intrusions of variable composition, as in the 

Rogaland Province (Michot and Michot, 1969), the HavreSaint-Pierre suite (Gobeil and others, 2003), and the Nain 

Complex (Labrador) (Emslie and others; 1994; Ashwal, 1993, 

and references therein). For example, the Havre-Saint-Pierre 

anorthosite complex covers an area of 20,000 km2 with as 

many as seven individual anorthosite lobes of varying ages 

within this complex separated by monzonitic, mangeritic, or 

granitic envelopes (Gobeil and others, 2003; Charlier and others, 2010). 

In eastern Canada, geophysical studies were used to 

distinguish large, flat tabular anorthosite bodies 2 to 4 km 

thick, either with or without accompanying feeder pipes (for 

example, Marcy, Morin, and Harp Lake anorthosites), from 

anorthosite bodies with smaller related gabbro or troctolite 

intrusions (for example, Nain Complex and Lac Saint-Jean 

anorthosite suite). Layered intrusions related to anorthosite 

complexes may exhibit well-defined cumulate layering in 

broadly basinal structures (Ashwal, 1993). 

In the Grenville Province, anorthosite bodies have 

undergone substantial regional deformation (see for example, 

McLelland and others, 2010). Original intrusion shapes may 

now be elongated by ductile deformation and drawn out in 

shear zones (Ashwal, 1993; McLelland and others, 2010). 

Some metamorphosed anorthosite bodies exhibit domical 

structures locally related to the deformation (Ashwal, 1993). 

Likewise, earlier intrusions may be structurally altered and 

deformed by emplacement of later intrusions.

Mineralogy

Anorthosite is typically composed of greater than 95 

percent plagioclase with rare orthopyroxene megacrysts (Charlier and others, 2006). Anorthositic rocks are often classified 

by the overall anorthite content of contained plagioclase (that 

is, percent An, equivalent to the percent of the CaAl2Si2O8

end member; appendix 1). Anorthosites can be divided into 

andesine-type anorthosites with plagioclase compositions 

of An23–48 accompanied by orthopyroxene and ilmenite and 

labradorite-type anorthosite with plagioclase compositions of 

An45–63 accompanied by olivine or orthopyroxene and lowFe2

O3 ilmenite (Anderson and Morin, 1969). In the Åna-Sira 

andesine-type anorthosite, host to the Tellnes deposit, plagioclase is the predominant cumulus phase with ilmenite, 

orthopyroxene, and lesser olivine occurring as both cumulus 

and interstitial phases. Minor phases include intercumulus 

magnetite, clinopyroxene, biotite, apatite, and hornblende, 

and accessory phases include sulfides, spinel, baddeleyite, and 

zircon (Charlier and others, 2006). The Allard Lake andesinetype anorthosite, host to the Lac Tio deposit, comprises plagioclase (An37–49) and less than 5-percent orthopyroxene, ilmenite, 

and, locally, clinopyroxene (Charlier and others, 2010).

The OUI host rocks in the Duluth Complex are rich in 

olivine and clinopyroxene, and their oxide content ranges from 

15 to 20 percent to locally massive zones (Severson, 1995). 

The OUIs in the southern part of the complex typically intrude 

rocks that include anorthosite, troctolite, gabbro, pyroxenite, 

and basalt (Severson, 1995). 

More acidic rocks related to anorthosite, such as jotunite, 

mangerite, quartz mangerite, and charnockite, are noncumulus 

and composed of plagioclase (typically antiperthitic), orthopyroxene, clinopyroxene, ilmenite, magnetite, and apatite. Potassium feldspar (typically perthitic), zircon, and quartz occur in 

the most differentiated units (Owens and others, 1993; Vander 

Auwera and others, 2011). Amphibole may occur locally in 

quartz mangerite and charnockite; biotite may also occur as a 

trace phase (Owens and others, 1993). 

Textures, Structures, and Grain Size

Anorthosite complexes have a broad spectrum of 

cumulate textures ranging from orthocumulate (cumulates 

composed chiefly of one or more cumulus minerals plus the 

crystallization products of intercumulus liquid) to heteradcumulate (cumulates in which cumulus crystals and unzoned 

poikolitic crystals have the same compositions) with ophitic to 

subophitic textures. Anorthosite textures may be massive (with 
Petrology of Associated Igneous Rocks 25

no preferred crystal orientation or stratification) or have igneous layering, including modal layers (defined by variations in 

percentage of mafic phases), as well as size-graded layering

 (defined by variations in plagioclase grain size) (Ashwal, 

1993). Rhythmic layering is common, although layers may not 

be laterally persistent. Syndepositional cumulus features, such 

as cross-bedding, scour features, and slump structures, are 

well-developed in many intrusive complexes, including parts 

of the Nain Complex, the Laramie Range anorthosite complex, 

and the Kunene anorthosite complex (Ashwal, 1993 and references therein). Anorthosites may include xenoliths and roof 

pendants of country rocks, ranging in diameter from centimeters to kilometers, respectively.

Plagioclase crystals are typically coarse, 1 to10 cm in 

length, tabular crystals; megacrysts as much as 1 m long are 

known (Ashwal, 1993). Pyroxene is present typically as a 

subophitic or ophitic phase; it may appear as a late fractionate 

cumulus phase typically ranging in diameter from 10 to 50 cm 

and commonly related to Fe-Ti-oxide rocks (Ashwal, 1993). 

Low-Al orthopyroxene megacrysts can also be as long as 1 

m. Orthopyroxene is the typical pyroxene present in anorthosite massifs; inverted pigeonite and augite are less common. 

Olivine is a common cumulus phase in troctolite and leucotroctolite. Iron-Ti oxides are common accessory phases and 

can be either primary, early liquidus minerals, or late-stage 

concentrations. 

Some massif anorthosite bodies have been variably 

affected by regional metamorphism ranging from greenschist 

to granulite facies commonly resulting in a metamorphic overprint of original igneous textures. Such metamorphic overprinting includes mineral replacement (for example, plagioclase replacement by sericite, epidote, or scapolite; pyroxene 

alteration to amphibole or chlorite), deformation (plagioclase 

lineations), and development of coronas surrounding crystals 

(for example, growth of orthopyroxene, clinopyroxene, amphibole, and garnet at the boundaries between plagioclase and 

olivine) (Ashwal, 1993). 

Petrochemistry

Major-Element Geochemistry

During the last century, numerous studies have described 

the geochemistry and petrogenesis of Proterozoic massif anorthosite (see for example, Ashwal, 1993 and references therein; 

Buddington, 1972; Emslie, 1978, 1991; Morse, 2006; Seifert 

and others, 2010; McLelland and others, 2010). Anorthosite, 

reflecting its plagioclase-rich mineralogy, is characterized by 

enrichments of SiO2, Al2O3, CaO, and Na2O. With increasing 

differentiation in a suite of rocks ranging from anorthosite to 

leuconorite to norite to ferrogabbro, Fe, Mn, Mg, Ti, and P 

tend to increase, whereas Si, Al, and Ca decrease, in contrast 

to more typical fractionation trends (see for example, Emslie, 

1991; Ashwal, 1993). 

Seifert and others (2010) reviewed several hundred 

major-element analyses of massif anorthosite and associated 

rocks from the Adirondacks. The authors summarized the 

major-element content of anorthosite and related rocks 

(fig. 14). Anorthosite (greater than 90-percent plagioclase) 

compositions have high SiO2 (about 53 to 56 weight percent), 

high Al2O3 (about 24 to 27 weight percent), and high CaO 

(about 9 to 11 weight percent). Leucogabbro compositions 

(70- to 90-percent plagioclase) have similar SiO2 (50 to 56 

weight percent) but lower Al2O3 and CaO than anorthosite 

because of lower plagioclase content. Gabbro and norite are 

characterized by widely variable compositions ranging from 

gabbro to oxide-rich gabbronorite (OGN) or oxide-apatite gabbronorite (OAGN). For Adirondack gabbro, SiO2

 ranges from 

about 46 to 52 weight percent, TiO2 is typically high (greater 

than 2 weight percent) for gabbro to very high (4 to 12 weight 

percent) for OGN and OAGN. Two groups of gabbro can be 

broken out by MgO content: low MgO (2.45 to 3.06 weight 

percent) and high MgO (4.3 to 7.34 weight percent). Low 

MgO gabbro and some high MgO gabbro fall in the tholeiitic 

field, whereas remaining high MgO gabbro falls in the calcalkaline field (fig. 14A).

Oxide-gabbronorite and OAGN have widely varying compositions due to variable mineralogies. These rocks 

typically have SiO2 less than 45 weight percent; high Fe2O3, 

about 16 to 41 weight percent; TiO2, about 3.5 to 12.7 weight 

percent; and P2O5, from about 1.3 to 3.7 weight percent. 

Noncumulus rocks have increasing average SiO2 and K2O 

with differentiation. For example, jotunite is characterized by 

46- to 53-weight percent SiO2, 2- to 8-weight percent MgO, 

and 1- to 3-weight percent K2O; monzodiorite is characterized by 54-weight percent SiO2

 and 3.3-weight percent K2O; 

mangerite is characterized by 59-weight percent SiO2 and 

4.8-weight percent K2O; and charnockite is characterized by 

66- to 71-weight percent SiO2 and 5.4-weight percent K2O. 

Anorthosite suites have strong Fe-enrichment compared 

with mangerite suites. Anorthosite-leucogabbro-gabbroOGN+OAGN create one geochemical trend; monzodioritemangerite-charnockite create a second geochemical trend; and 

jotunite overlaps with gabbro where the trends meet (fig. 15). 

Trace-Element Geochemistry

Anorthosites, dominated by plagioclase, are enriched 

in trace elements substituting for Ca2+ in plagioclase (for 

example, strontium (Sr) and europium (Eu)) and are depleted 

in other trace elements (Ashwal, 1993). Compared to layered 

intrusions, massif anorthosites have generally high Sr concentrations in the range of 600 to 1,000 parts per million (ppm); 

some massif andesine anorthosites have Sr concentrations as 

high as 1,400 ppm (Saint-Urbain) to 2,600 ppm (Labrieville, 

Quebec) (Ashwal, 1993, and references cited therein). Another 

distinction between layered intrusions and massif anorthosite 

is an inverse correlation between Sr concentration and the 

anorthite content of plagioclase that is common in layered 
26 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

Figure 14. Al2O3–FeO–MgO triangular diagrams showing simplified compositional character of rocks related to Proterozoic massif 

anorthosite (modified from Seifert and others, 2010). A. Anorthosite containing little potash feldspar plots on both sides of the tholeiitic/

calc-alkaline boundary (heavy red line) as defined by Irvine and Baragar (1971). Assuming all gabbro follows a tholeiitic trend, then 

for the Adirondacks, shifting the field boundary (heavy blue line) to include all gabbro on the tholeiitic side may better account for the 

iron-rich nature of gabbro. Plagioclase-rich anorthosite and leucogabbro trend toward the Al203 corner, whereas the iron-rich oxidegabbronorite (OGN) and oxide-apatite-gabbronorite (OAGN) trend toward the FeO corner of the diagram. B. Mangerite, monzodiorite, 

and charnockite trend toward the Al2O3 corner with increasing potash feldspar contents. Most jotunites plot with the low-MgO gabbros.

Anorthosite

OGN and OAGN

High-MgO gabbro

Leucogabbro

Low-MgO gabbro

20

40

60

80

0

100

FeO

Al MgO 2

O3 100 80 60 40 20 0

20

100

40

60

80

0

40

60

80

0

100

FeO

Al MgO 2

O3 100 80 60 40 20 0

20

100

40

60

80

0

20

OGN and OAGN

Low-MgO gabbro

High-MgO gabbro

Jotunite

Monzodiorite

Mangerite

Charnockite

EXPLANATION

EXPLANATION A

B
Petrology of Associated Igneous Rocks 27

intrusions but may or may not be present in massif anorthosite. 

This suggests a complicated fractionation process for massif 

anorthosite with mixtures of plagioclase crystals formed under 

a variety of conditions (Ashwal, 1993).

Plagioclase has an affinity for Eu2+ creating plagioclase 

crystals with strong positive Eu anomalies and residual liquids 

with significant Eu depletions following plagioclase fractionation. Anorthosite is commonly light REE-enriched with REE 

concentrations in massif anorthosite generally an order of 

magnitude higher than concentrations in Archean anorthosite 

(Ashwal, 1993). When late-stage rocks, such as ferrodiorite, 

have high overall REE concentrations, negative Eu anomalies, 

and flat or depleted light REE concentrations, as noted for 

the Marcy Anorthosite (Ashwal and Seifert, 1980) and in the 

Laramie Range anorthosite complex (Goldberg, 1984), the 

rocks developed from fractionated liquids after anorthosite 

generation and extraction of significant plagioclase (fig. 16). 

However, in the Rogaland Province, ferrodiorite and related 

rocks have smooth REE patterns with no Eu anomaly suggesting that these rocks were not derived by the same fractionation 

process that produced anorthosite (Duchesne and others, 1974).

Isotope Geochemistry of Igneous Rocks

Stable Isotope Geochemistry

Stable isotopes have been used to assess the importance 

of crustal contamination in establishing the origin for Fe-Tioxide deposits related to Proterozoic massif anorthosite, study 

possible fluid-rock exchange, and evaluate depth of emplacement of host massif anorthosite intrusions. 

In the Rogaland Province, Wilmart and others (1994) 

analyzed carbon (C), hydrogen (D), and oxygen (O) isotopic 

compositions in whole-rock and plagioclase samples from the 

Åna-Sira anorthosite, the Tellnes orebody, and surrounding 

granulite-facies gneisses. Whole-rock and plagioclase δ18O 

values from anorthosite have strong homogeneity with an 

average δ18O value of 6.1± 0.3 ‰, suggesting a mantle origin 

for anorthosite with little to no crustal contamination. Wholerock δ 18O values of norite from the Tellnes dike have a similar 

narrow range (δ18O = 4.9 to 6.0 ‰). Surrounding gneisses 

have a much broader variation (δ18O = 2 to 9 ‰) considered 

to reflect the original compositions of the gneisses. Low-water 

Figure 15. All Adirondack massif anorthosite and related rocks plotted on a CaONa2

O+K2O-Fe2O3 triangular diagram (modified from Seifert and others, 2010). Two distinct 

trends are apparent. One trend is produced by anorthosite-leucogabbro-gabbroOGN+OAGN, whereas a separate trend is produced by monzodiorite-mangeritecharnockite. Jotunite overlaps with gabbro. OGN, oxide-gabbronorite; OAGN, oxideapatite-gabbronorite.

Anorthosite

OGN and OAGN

High-MgO gabbro

Leucogabbro

Low-MgO gabbro

20

40

60

80

0

100

FeO

Al MgO 2

O3 100 80 60 40 20 0

20

100

40

60

80

0

40

60

80

0

100

FeO

Al MgO 2

O3 100 80 60 40 20 0

20

100

40

60

80

0

20

OGN and OAGN

Low-MgO gabbro

High-MgO gabbro

Jotunite

Monzodiorite

Mangerite

Charnockite

EXPLANATION

EXPLANATION A

B
28 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

content of all analyzed igneous and metamorphic rocks suggests little modification of granulite-facies rocks after intrusion emplacement. Whole-rock dD (about –82 to –63 ‰) and 

d18O (about 6.1 ‰) values suggest a dominantly magmatic 

signature in intrusions and orebody (fig. 17). As a cumulate 

rock, anorthosite is low in carbon content. Interstitial carbonate is present within a few hundred meters of the margin of the 

anorthosite; however, carbonate appears to have precipitated 

from magmatic fluids with an estimated d13C value of –5.3 ‰ 

and related to late intrusions, rather than being derived from 

the surrounding metamorphic gneisses (Wilmart and others, 

1994).

Valley and O’Neil (1982) analyzed wollastonite from 

skarns surrounding Adirondack anorthosite bodies. Plagioclase 

phenocrysts in anorthosite have d18O values ranging from 7.8 

to 9.3 ‰. Amphibolite into which anorthosite was emplaced 

has d18O values from 6.3 to 9.3 ‰. In contrast, wollastonite in 

skarn within 130 m of anorthosite is strongly depleted, with 

d18O values from 2.9 to –1.3 ‰. This zone of strong d18O 

depletion suggests interaction with hot meteoric water, which 

can only occur at shallow levels of less than 10 km. This 

observation led Valley and O’Neil (1982) to conclude that 

Adirondack anorthosites may have intruded at a wide range of 

depths, not necessarily just under granulite-facies conditions at 

depths of 20–30 km.

Taylor (1969) determined a range of d18O values from 5.8 

to 7.6 ‰ for “normal” unmetamorphosed massif-type Adirondack anorthosite. This range is similar to d18O values for 

Figure 16. Chondrite-normalized rare earth element (REE) patterns for representative 

samples of the anorthosite suite from the Marcy massif anorthosite, Adirondacks, New 

York (modified from Ashwal and Seifert, 1980).

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

0.5

1

10

100

Sample conchntration/Chondrite concentration

Leucogabbro

Ultramafic cumulate layers

Mafic-rich dikes

Anorthosite

Plagioclase megacrysts

EXPLANATION
Petrology of Associated Igneous Rocks 29

mantle-derived basalt and gabbro (d18O = 5.4 to 7.4 ‰; Kyser 

and others, 1982). Morrison and Valley (1988) examined the 

unusual Marcy Anorthosite and reported significantly different 

values: most whole-rock anorthosite analyses had an average 

δ18O value of about 9.5 ‰. Although a few rocks had depleted 

values (d18O = 3.0 to 5.8 ‰), from of a total of 93 analyses, 

only two values plotted in the range of expected magmatic 

values. After ruling out d18O enrichment caused by regional 

metamorphism, Morrison and Valley (1988) concluded that the 

probable cause of observed oxygen isotopic enrichment was 

crustal contamination of Marcy parental magma near the base 

of the crust.

Peck and others (2010) compiled d18O whole-rock and 

plagioclase values for many Proterozoic anorthosites (fig. 18). 

The d18O isotopic compositions of Nain Complex anorthosite 

are consistent with derivation from a mantle source contaminated by either lower crustal rocks of the Churchill Province 

(d18O = 6.5 to 8.2 ‰) or the Nain Province (d18O = 4 to 7 ‰) 

prior to emplacement (Peck and others, 2010). Many anorthosites from the Grenville allochthonous polycyclic belt, including Havre-Saint-Pierre anorthosite with d18O of about 9.5 ‰ 

and Allard Lake anorthosite with d18O of about 7.9 ‰, have a 

narrow range of d18O values averaging about 7 ‰ suggesting 

mantle derivation with some crustal contamination. Anorthosites in the Grenville allochthonous monocyclic belt, including 

the Marcy Anorthosite, have a higher and broader range (d18O 

= 8 to 11 ‰). Peck and Valley (2000) attributed these higher 

d18O values to low-temperature hydrothermally altered crust, 

perhaps old ocean crust, emplaced into the lower crust and 

subsequently melted and mixed with the parental source of 

these anorthosites. 

Radiogenic Isotope Geochemistry

Radiogenic isotopic characteristics of anorthosite and 

related rocks have been used to determine emplacement age—

although improved U-Pb dating of zircon and baddeleyite now 

provides precise ages for most rocks—and to assess relative 

contributions of mantle and crustal derived components in 

anorthosite sources. Schiellerup and others (2000) summarized Proterozoic massif-type anorthosite radiogenic isotopic 

signatures. They showed that if olivine-bearing anorthosite 

and leucotroctolite are present in an unmetamorphosed massif 

anorthosite suite, those rock types will be characterized by 

the most primitive neodymium (Nd) isotopic compositions, 

thereby providing the closest estimates of parental melt compositions. A wide range of isotopic compositions is thought 

to reflect heterogeneities in the upper mantle. Gleissner and 

others (2011) also pointed out that Sr isotopic compositions 

of individual plagioclase megacrysts are commonly less 

radiogenic than whole-rock analyses of the same rock. This 

suggests that for some anorthosite complexes, secondary (that 

is, metamorphic) processes can affect observed Sr isotopic 

compositions.

In the Kunene anorthosite complex in Namibia, anorthositic rocks range in initial eNd values from +1.1 to +3.0. The eNd

notation represents the deviation of the 143Nd/144Nd ratio in the 

rock sample compared to an evolution line determined by the 

143Nd/144Nd ratio calculated for a chondritic uniform reservoir 

(CHUR) over time (DePaolo and Wasserburg, 1976). An initial 

eNd value compares the sample’s 143Nd/144Nd deviation from 

the CHUR evolution line at the time that the parent magma of 

that rock sample separated from the uniform reservoir, in the 

case for the Kunene anorthosite complex, at around 1371 ± 2.5 

Ma (Mayer and others, 2004). The Kunene anorthositic rocks 

also have initial 87Sr/86Sr ratios of 0.7028 to 0.7041. Unaltered 

related felsic rocks have initial eNd values from +0.4 to +2.2 

and initial 87Sr/86Sr ratios of 0.7025 to 0.7043, calculated for 

a rock age of 1371 Ma. Unaltered related felsic rocks have 

initial eNd values and initial 87Sr/86Sr ratios of 0.7025 to 0.7043, 

whereas altered felsic rocks have initial eNd values from –0.4 

to 2.5 and initial 87Sr/86Sr ratios of 0.7063 to 0.7076 (Drüppel

and others, 2007). The Sr isotopic compositions appear to 

have been more significantly affected by alteration than the Nd 

isotopic compositions.

Anorthositic and noritic samples from three Norwegian massif anorthosites (Egersund-Ogna, Håland-Helleren, 

and Åna-Sira; fig. 3) were analyzed for Sr, Nd, and Pb 

isotopic compositions (Demaiffe and others, 1986). Initial 

87Sr/86Sr ratios vary widely among the three intrusions from 

0.7030 for plagioclase and orthopyroxene megacrysts in the 

WR δ18O (‰ VSMOW)

–6 –4 –2 0 +2 +4 +6 +8 +10

20

0

–20

–40

–60

–80

–100

Present-day

water

WR δD (‰)

Meteoric water line

EXPLANATION

Åna Sira anorthosite

Tellnes orebody

Tellnes dike

BKSK and apophysis

Metamorphic envelope

Figure 17. Whole-rock δD (WR δD) versus δ18O for the ÅnaSira anorthosite, the Tellnes orebody, and norite dike hosting 

the Tellnes orebody; the Bjerkreim-Sokndal layered intrusion 

(BKSK) and apophysis, and the metamorphic envelope of gneiss 

in the Rogaland Anorthosite Province (modified from Wilmart and 

others, 1994). Also shown are the fields for present-day water and 

magmatic hydroxyl (magmatic “water” fixed as hydroxyl radicals 

in silicates under magmatic pressure-temperature conditions; 

gray box on graph). Abbreviations include ‰, per mil; VSMOW, 

Vienna Standard Mean Ocean Water, a primary reference 

water standard for relative oxygen and hydrogen isotopic 

measurements).
30 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

Egersund-Ogna intrusion to 0.7077 for a jotunitic dike. The 

lower part of the Bjerkreim-Sokndal intrusion has an average initial 87Sr/86Sr ratio of about 0.7055, somewhat above a 

typical mantle value of about 0.7030. More acidic rocks have 

initial 87Sr/86Sr ratios as high as 0.7080 suggesting derivation 

either from somewhat contaminated upper mantle magma 

or from partial melting of the lower crust. In contrast, initial 

eNd values for both anorthosite and jotunitic rocks range from 

about +1.8 to +5.5 (Demaiffe and others, 1986) suggesting 

likely derivation from a mantle source. Locally, more acidic 

rocks have less positive to slightly negative initial eNd values 

suggesting progressive contamination of a mantle-derived 

magma with lower crustal melts. 

Lead (Pb) isotopic compositions of various massif anorthositic complexes are internally consistent but vary among 

intrusions (see for example, Weis, 1986). Most Pb isotopic 

linear arrays do not represent isochrons, but rather mixing 

lines. In the Bjerkreim-Sokndal layered intrusion, for example, anorthosite and leuconorite have 206Pb/204Pb ratios from 

17.718 to 17.879, 207Pb/204Pb ratios from 15.518 to 15.540, and 208Pb/204Pb ratios from 37.156 to 37.202 (Weis, 1986; Demaiffe 

and others, 1986). Mangerite and jotunite from the same intrusion have 206Pb/204Pb ratios from 18.001 to 19.033, 207Pb/204Pb 

ratios from 15.548 to 15.642, and 208Pb/204Pb ratios from 

37.240 to 38.097 (Weis, 1986). Based on these three radiogenic isotopic systems, Demaiffe and others (1986) concluded 

that these anorthositic intrusions were derived from depleted 

upper mantle or, possibly, by melting of mafic rocks in the 

lower crust. Progressive contamination of primary magmas 

may have given rise to more acidic rocks in the suites.

Bolle and others (2003) summarized available Sr and 

Nd isotopic data for the Rogaland Province, including data 

for anorthosite, jotunite, and charnockite. More than 200 

initial 87Sr/86Sr ratios have a range of 0.7033 to 0.7227, with 

an average of 0.7066. Anorthosite from the Egersund-Ogna, 

Håland-Helleren, and Åna-Sira massifs have initial 87Sr/86Sr 

ratios of 0.7033 to 0.7063, with an average of 0.7047. Strontium and Nd isotopic compositions in three Norwegian layered 

mafic intrusions, including the Bjerkreim-Sokndal intrusion, 

were used to model the amount of possible crustal contamination that may occur in basaltic and jotunitic magmas. Tegner 

and others (2005) determined that the ratio of mass assimilated to mass crystallized for layered mafic intrusions ranges 

from about 0.1 to about 0.3 in basaltic and jotunitic magmas 

emplaced into the middle crust. Relatively constant Sr and 

Nd isotopic ratios suggested a steady assimilation-fractional 

crystallization process for these intrusions, and modeling suggested that assimilation was not a selective process but one of 

incorporation of large-fraction partial melts.

Osmium (Os) isotopes have been used to establish ages 

for Fe-Ti-oxide deposits and to evaluate the role of the crust, 

particularly the lower crust, in anorthosite magma sources 

(Schiellerup and others, 2000; Hannah and Stein, 2002; 

Gleissner and others, 2012). Rhenium (Re) is fractionated 

very efficiently from Os during mantle melting, resulting in 

significant concentration of Os in the upper mantle compared 

Figure 18. Compilation of d18O whole-rock and plagioclase values for Proterozoic anorthosites (omitting 

bodies partially converted to scapolite) (modified from Peck and others, 2010). The gray band represents 

d18O whole-rock values for modern ocean ridge basalts (MORB). Values in parentheses are the number 

of analyses (n); stars are the average value. In datasets with n larger than 7, the rectangle encloses ± 1 

standard deviation. Archean anorthosites, which as a group have uniform d18O values close to MORB, are 

shown for reference. 

MORB

δ18O (‰ VSMOW)

Roseland, Virginia (11)

San Gabriel, California (19)

Laramie Range, Wyoming (4)

Norway (52)

Nain, Labrador (40)

Grenville allochthonous

 monocyclic belt (217)

Grenville allochthonous

 polycyclic belt (129)

Archean anorthosites (15)

3 4 5 6 7 8 9 10 11 12
Theory of Deposit Formation 31

to lower crust (Schiellerup and others, 2000). Thus, the Re-Os 

isotopic system is an excellent discriminator between mantle 

and crustal components. In the Rogaland Province, Schiellerup and others (2000) analyzed unmineralized anorthosite, 

anorthosite-hosted sulfide deposits, cumulate rocks from the 

Bjerkreim-Sokndal layered intrusion, and two ilmenite-rich 

cumulate dikes. All samples yield well-defined Re-Os and 

Sm-Nd isochrons of 917±22 Ma and 914±35 Ma, respectively, 

which in turn agree well with U-Pb zircon ages of 930–920 

Ma (Schärer and others, 1996). Initial187Os/186Os of the isochron is 0.63± 0.25, with an initial γOs

 = +419, compared to 

an upper mantle γOs of about 0±15 (γOs is the percent deviation of sample 187Os/186Os from average chondritic 187Os/186Os). 

These data suggest that Rogaland anorthosites and related 

deposits were derived from melting of mafic source rocks in 

the lower crust with an age of 1,400 to 1,550 Ma. Based on 

Re-Os isotope characteristics, Gleissner and others (2012) 

determined that two phases of the anorthosite suite in the 

Kunene anorthosite complex, dark anorthosite and white anorthosite, had different (though related) origins. Dark anorthosite 

yielded initial 187Os/186Os ratios from 0.2 to 1.14, with initial 

gOs ranging from 48 to 872, whereas white anorthosite yielded 

initial 187Os/186Os ratios as high as 5, with an initial gOs of 

3,982. Gleissner and others (2012) concluded that dark anorthosite was mainly mantle-derived with crustal contamination 

of less than 10 percent, whereas white anorthosite likely was 

derived from mantle melts with crustal contamination of about 

30 percent.

Radiogenic Nd, Pb, and Sr isotopic compositions of 

unmetamorphosed massif anorthosite complexes commonly 

suggest that these bodies are derived from partial melts of 

the upper mantle (mantle plume model of Ashwal, 1993) and 

(or) partial melting of lower crustal material that has been 

thrust into the mantle (crustal-tongue delamination model of 

Longhi and others, 1999; Gauthier and Chartrand, 2005). The 

Nd and Pb isotopic signatures of the more felsic portions of 

these complexes suggest progressive contamination of mantle 

magmas by lower crustal melts (for example, the Rogaland 

Province). Strontium isotopic compositions are commonly 

affected by secondary metamorphic processes and thus may 

show a broad isotopic variation. In contrast to other isotopic 

systems, Re-Os isotopic determinations of anorthosites and 

associated sulfide fractions typically suggest very significant 

crustal contributions. However, fractionation of Re and Os 

during partial melting of the upper mantle leads to strong partitioning of Re into the crust. Selective assimilation of crustal 

sulfide through partial melting or devolatilization will result in 

high initial gOs values in the anorthositic magma and associated sulfides (Hannah and Stein, 2002). Thus, the variation 

of radiogenic isotopic values among anorthositic complexes 

reflects a wide range of possible processes that contribute 

to the isotopic characteristics of any given anorthosite complex and related mineral deposits (Hannah and Stein, 2002; 

Gauthier and Chartrand, 2005). 

Petrology of Associated Sedimentary 

Rocks

Sedimentary rocks are not genetically related to magmatic Fe-Ti-oxide deposits related to Proterozoic massif 

anorthosite suites.

Petrology of Associated Metamorphic 

Rocks

Metamorphic rocks are not genetically related to magmatic Fe-Ti-oxide deposits related to Proterozoic massif 

anorthosite suites.

Theory of Deposit Formation

Ore Deposit System Affiliation 

Magmatic Fe-Ti-oxide deposits that are economic for 

Ti are produced by complex magmatic processes from Tienriched parental magma in geologic terranes containing Proterozoic massif anorthositic plutonic suites and related rocks.

Sources of Ti-Fe-P-Ore Components

Residual magmas derived from andesine-type anorthosite parental magmas can become enriched in Fe, Ti and P, 

potentially forming economic Fe-Ti-oxide deposits. In the 

underplating mantle-plume model of Ashwal (1993), crystallization of olivine and high-Al orthopyroxene megacrysts in 

a deep magma chamber would enrich residual melts in Fe, Ti, 

and P, producing a composition close to ferrodiorite. In the 

crustal-tongue delamination model (Longhi and others, 1999; 

Duchesne and others, 1999), Fe-Ti-P-enriched magmas are 

produced by direct melting of subducted gabbronorite crustal 

rocks. In either case, Ti-enriched magma will then rise to the 

middle to upper crustal levels entrained in diapiric plagioclaserich mushes. 

Mechanisms that Concentrate Ore

Existence of a primary Fe-Ti-P-rich magma alone is 

insufficient to produce an economic Fe-Ti-oxide deposit, 

as attested by numerous common occurrences of noneconomic Fe-Ti-oxide deposits in anorthositic suites (see for 

example, Hébert and others, 2005; Corriveau and others, 

2007). Ilmenite, the most important ore mineral, has to 

crystalize as discrete grains and be concentrated by physical 

magmatic processes to create an economic Ti orebody. For 

hemo-ilmenite deposits, a critical first step is crystallization 
32 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

of ilmenite, with plagioclase, as an early liquidus mineral, 

as postulated at Tellnes (Wilmart and others, 1989), Lac Tio 

(Charlier and others, 2010), the Bjerkreim-Sokndal layered 

intrusion (Wilson and others, 1996), and the Grader layered 

intrusion (Charlier and others, 2008). A second critical step is 

separation of ilmenite from plagioclase but through a process more efficient than cumulate behavior in a static magma 

chamber, such as the Bjerkreim-Sokndal intrusion, where the 

quantity of plagioclase+ilmenite cumulates is much less than 

the quantity of other cumulates (Wilson and others, 1996). 

One plausible model suggests flushing of oxide-laden magma 

through magma conduits or dike-like systems where dense 

oxide phases are segregated from plagioclase by flow and 

concentrated in traps created by wall-rock/conduit irregularities (for example, Tellnes, Wilmart and others, 1989; Big 

Island dike, Morisset and others, 2010; Lac Tio, Charlier and 

others, 2010). Eight discrete pod and dike-like Fe-Ti-oxide 

deposits in the Saint-Urbain anorthosite may represent keels to 

a large evolving system in which ilmenite collected in cracks 

and fractures in older anorthosite along the base of a chamber, 

whereas plagioclase was transported away by a moving and 

crystallizing magma (Morisset and others, 2010). Charlier and 

others (2006) present a similar argument for Tellnes by which 

the sickle-shape orebody represents the lower part of a larger 

sill deformed into its current shape by gravity-induced subsidence and anorthosite diapirism of the underlying host Åna-Sira 

anorthosite; the upper, more evolved parts of the hypothetical 

sill are not exposed or have been removed.

Summary of the Origin of Magmatic Fe-Ti-Oxide 

Deposits

Magmatic Fe-Ti-oxide deposits that are an economic 

resource for Ti are restricted by both host rock and age 

constraints; these constraints are likely the consequence of a 

particular combination of tectonic circumstances rather than 

any a priori temporal control. The arguments for immiscible 

Fe-Ti-P-rich liquids co-existing with complementary silicate 

liquids (see for example, Philpotts, 1967; Kolker, 1982) have 

been refuted by experimental studies (Lindsley, 2003) and 

field evidence supporting early magmatic crystallization of 

ilmenite (see for example, Duchesne, 1999). The tectonic 

controls required to create abundant free ilmenite, rather than 

titaniferous magnetite from which it is metallurgically difficult 

to separate Ti, include (1) favorable source rocks for melting, 

which are either those related to decompression melting of 

asthenospheric mantle (see for example, Morse, 1981; Corrigan and Hanmer, 1997; Scoates and Mitchell, 2000; Regan 

and others, 2011) or delamination-related melting of lower 

crust underthrust into the mantle (see for example, Longhi and 

others 1999; Duchesne and others, 1999) to create Ti-endowed 

parent magmas; (2) an environment favorable to development 

of andesine-type massif anorthosite rather than labradoritetype anorthosite (see for example, Anderson and Morin, 1969; 

Ashwal, 1993; Hébert and others, 2005); and (3) magmatic 

conditions in the middle to upper crust that would lead to 

crystallization of ilmenite as one of the first liquidus minerals 

and subsequent concentration of that ilmenite into massive 

orebodies. A generalized diagram of possible magmatic evolution paths that could lead to differing oxide concentrations is 

given in figure 19.

The magmatic evolution presented in figure 19 is divided 

into four stages. The first two stages are common for all FeTi-oxide deposits, whereas the latter stages result in unique 

mineral assemblages. Stage 1 consists of magma chambers 

developed at the base of the lithosphere that undergo plagioclase and Fe-Mg silicate fractionation, leading to stage 2, 

which is density separation and diapiric upward migration 

of a plagioclase + Fe- and Ti-enriched crystal-liquid mush. 

Crustal assimilation and further crystallization during ascent 

can influence both oxygen fugacity and silica activity within 

the diapiric mush, driving the system toward two possible 

outcomes. One outcome (stage 3) follows the paths depicted 

on the left part of figure 19, which leads to crystallization of 

ilmenite as an early liquidus phase. A trend of silicate crystallization along the right side of figure 19 (stage 4) concentrates 

Ti-Fe±P into residual melts. Outcomes along stage 3 are represented by massive hemo-ilmenite bodies in host andesinetype anorthosite and cumulate plagioclase+ilmenite in layered 

intrusions. Outcomes along stage 4 result in the occurrence 

of assemblages such as titanomagnetite+ilmenite±apatite, in 

labradorite-type host anorthosite and related mafic rocks or as 

concentrations in layered intrusions typically with olivine as 

an early liquidus mineral. 

Early crystallization of ilmenite in stage 3 is a critical factor for development of a potentially economic hemo-ilmenite 

deposit versus a probably subeconomic titanomagneiteilmenite±apatite deposit. When ilmenite is an early liquidus 

mineral, it invariably has a high hematitic component suggesting that oxygen fugacity is a critical parameter controlling 

oxide-mineral assemblage. Both silica activity and oxygen 

fugacity are controlled by assimilation of continental crust, 

and this control carries through to the oxide-mineral assemblage and plagioclase composition (Morse, 2006; Frost and 

others, 2010). A great variety of rock types in the crust, from 

Archean rocks to more juvenile crust related to subduction 

events, creates a wide range of possible mineral and rock 

assemblages that could contaminate uprising anorthositic magmas. Crustal assimilation of materials that results in higher 

oxygen fugacity and silica activity favors early saturation of 

ilmenite. The dynamic environment of anorthosite emplacement, the persistence of ductile behavior in slowly cooled 

anorthositic plutons (for example, cooling rates of 3–4 °C per 

million years estimated by Morisset and others (2009) for the 

Saint-Urbain anorthosite), and the density contrast between 

plagioclase (≈2.67 grams per cubic centimeter (g/cm3)) and 

ilmenite (≈4.72 g/cm3) will facilitate hydrodynamic sorting 

of dense oxides from plagioclase-rich mushes, concentrating 

oxides into layers and traps.
Ilm

1) Magma from mantle or2) Magma from melting of subducted crustal rocks

Plagioclase

Mg-Fe-silicates

Diapir of 

plagioclase

+

Ti-rich melt

Fe-Ti±P 

residual melt

ASCENT

+

CONTAMINATION by

Si-rich crustal rocks?

ASCENT

+

MINIMAL CONTAMINATION

or CONTAMINATION by

Fe- ±S-rich crustal rocks?

Hemo-ilmenite hosted by 

andesine- type anorthosite

Anorthosite

suite

Titanomagneite + ilmente

± apatite, hosted by

labradorite-type anorthosite

and related mafic rocks

Ilmenite

as liquidus

phase

Higher 

fO2

Lower

fO2

Density

Separation

Plag + Ilm

Plag + Ilm + Opx

Ol ± Plag ± Su

Plag + Ol 

Plag

Plag + Ilm + Opx + Mag

Plag + Ilm + Opx + Cpx

+ Mag + Ap

Plag + Ilm + Opx + Cpx

Ol + Mag + Ap

Plag + Cpx + M

Ilm (± Ol ± O

Plag + Ilm 

Mag + Cpx + Ap 

ANORTHOSITE COMPLEX

for example, Havre-Saint-Pierre

LAYERED INTRUSION

for example, Bjerkreim-Sokndal

cumulate sequence

LAYERED INTRU

for examle, Duluth 

cumulate sequ

Fe-Ti±P-

 enriched liquid

BASE OF

LITHOSPHERE

?

1

2

3

4

Figure 19. Hypothetical model for the magmatic evolution of Fe-Ti-oxide deposits, which is described in detail in the text. The cumulafor the Bjerkreim-Sokndal layered intrusion is adapted from Wilson and others (1996), and the cumulate sequence for the Duluth Compfrom Miller and Ripley (1996). Mineral abbreviations: Plag = plagioclase, Ilm = ilmenite, Mag = magnetite, Ol = olivine, Opx = orthopyroxclinopyroxene, Ap = apatite. fO2, oxygen fugacity; OUI, oxide-bearing ultramafic intrusions.
34 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

The OUIs in the Duluth Complex are late-stage plugs 

and vertical lenses of oxide-bearing ultramafic rocks intruding 

troctolitic rocks. Severson and Hauck (1990) and Severson 

(1994) speculated that OUIs may have formed from assimilation of the underlying Biwabik Iron-Formation, or by possible infiltration metasomatism by late-stage Fe- and Ti-, and 

volatile-rich, intercumulus fluids expelled from crystallizing 

magma chambers. However, the generally low Ti content of 

the Biwabik Iron-Formation and existence of a number of 

oxide bodies where iron-formation is not in the Duluth Complex footwall preclude assimilation as an origin for all bodies, 

and the magma dynamics required to intrude dense, iron-rich 

partial melt high into the Duluth Complex remain speculative 

(Hauck and others, 1997). An origin for OUIs in the Duluth 

Complex continues to be somewhat enigmatic.

Geological Assessment Guides

Attributes Required for Inclusion in Permissive 

Tract at Various Scales

At a regional scale, Proterozoic massif anorthosite 

plutonic suites and related rocks represent a permissive tract. 

Within these regional tracts, ilmenite deposits may be best 

developed in anorthosite bodies intruded along deep-seated 

fracture systems developed at the margins of major tectonic 

provinces and belts. Locally, andesine-type anorthosite plutonic suites less than 1060 Ma are the more favorable rock 

type for the occurrence of deposits with desirable discrete, 

individual ilmenite grains.

Geochemical Considerations

Most Fe-Ti-oxide deposits were discovered by physical exploration and geophysical methods. The occurrence of 

ilmenite in fluvial heavy-mineral deposits may be an efficient 

method for backtracking to source areas prospective for FeTi-oxide deposits in anorthosite and gabbro (Force, 1991; 

Gauthier, 2003). 

Geophysical Attributes

At this time, exploration for ilmenite deposits is not only 

focused on grade and tonnage but also on finding ilmenite suitable for pigment processing (for example, Cr- and Mg-poor 

ilmenite). These criteria depend on relations among magmatic 

evolution, major- and trace-element chemistry, and subsolidus 

re-equilibration. One of the better guides for future prospecting for workable and chemically suitable ilmenite resources 

may rely in part on aeromagnetic signatures of the Fe-Ti 

oxides that record ore microtextures, which can be related 

back to ore chemistry (McEnroe and others, 2000). 

Aeromagnetic maps over favorable terranes may have a 

spectacular range of positive and negative anomalies because 

of highly contrasting rocks and possible deposit types (McEnroe and others, 2001). Concentrations of hemo-ilmenite commonly have distinctive negative magnetic anomalies or mixed 

patterns of positive and negative anomalies. Strong positive 

anomalies related to magnetite content may point toward less 

economically favorable titanomagnetite concentrations. IronTi oxides and their host rocks commonly have higher gravity 

anomalies than surrounding anorthositic, granitic, or gneissic 

country rock, and oxides produce a strong contrast to silicates 

(Gross, 1996). The shape and physical characteristics of OUIs 

in the Duluth Complex create small, round, intense spots of 

gravity and aeromagnetic highs in regional geophysical maps 

that represent obvious exploration targets (Chandler, 2002).

Geoenvironmental Features and 

Anthropogenic Mining Effects

Soil and Sediment Signatures Prior to Mining

Baseline characterization studies surrounding magmatic 

Fe-Ti-oxide deposits hosted by anorthosite complexes are 

absent in the literature. Trace elements in soil and sediment 

would be related to those elements incorporated into Fe-Tioxide structures (for example, Co, Cr, Ni, V, and Zn) or contained in sparse sulfide minerals (for example, Co, Cu, Ni, and 

Zn) (Duchesne and Bologne, 2009). Titanium ore from Tellnes 

has concentrations of about 110-ppm Co, 250-ppm Cr, 430-

ppm Ni, 795-ppm V, and 128-ppm Zn (Wilmart and others, 

1989). Thus, pre-mining sediment and soil signatures could 

include slightly elevated concentrations of Co, Cu, Cr, Fe, Ni, 

Ti, V, or Zn. Because magmatic Fe-Ti-oxide deposits do not 

have related hydrothermal systems, trace-element mobility is 

limited, and thus patterns of anomalously high metal concentrations would be restricted to short distances from oxide 

mineralization.

Secondary Minerals

Alteration and weathering play little role in the development of magmatic Fe-Ti-oxide deposits; thus environmental 

concerns related to secondary minerals are not an issue.

 Drainage Signatures

Acid-mine drainage related to mineralization and mining 

can be a serious concern. The reaction of sulfides, mainly 

pyrite and pyrrhotite, in an aqueous environment with oxygen, 

mediated by bacteria, generates sulfuric acid (Plumlee, 1999; 

Nordstrom and Alpers, 1999). Acid then attacks other metalcontaining minerals, often sulfides, and can release additional 

metals into the environment through aqueous transport.
Geoenvironmental Features and Anthropogenic Mining Effects 35

At near-neutral pH, many metals either precipitate out of 

solution or are adsorbed to amorphous iron hydroxides thus 

becoming relatively immobile (Smith, 1999). However, some 

metals, such as Co, Ni, and Zn, will remain in solution even at 

neutral pH. Drainage water with near-neutral pH and elevated 

concentrations of dissolved metals is termed contaminated 

neutral drainage (CND). Plante and others (2008) addressed 

CND from the Lac Tio mine, Quebec, which sporadically 

contains Ni at levels slightly higher than local regulations 

allow. The source of the Ni was from the weathering of Nibearing sulfides found in small quantities in the ilmenite ore. 

Their research assessed sorption capacities of ore and waste 

rock and indicated that Ni sorption by residual ilmenite and 

plagioclase in waste rock played a significant role in the Ni 

geochemical behavior. Plagioclase is an effective acid neutralizer (Gunsinger and others, 2006; Cook, 1988), and Plante and 

others (2008) determined that any acid generated by sulfides in 

mine waste from Lac Tio was neutralized by silicates. 

The abandoned Storgangen mine in the Rogaland Province produced 8 Mt of tailings. Annual precipitation in the 

area is about 194 cm, and 750,000 m3 of water drains from 

the impoundment annually. This runoff subsequently reaches 

the North Sea, a distance of about 5 km and has a neutral 

pH but a median Ni concentration of 3.2 milligrams per liter 

(mg/L) (n=24) (Ettner, 1999). A passive treatment system was 

designed and tested to remove Ni with variable efficacy over 

time (Ettner, 1999, 2007). 

Climate Effects on Geoenvironmental Signatures

Three climate factors have the most effect on the environmental geology and geochemistry of mineral deposits: temperature, humidity, and precipitation. A cold climate tends to 

inhibit weathering, as does a dry climate and low precipitation, 

whereas a wet climate leads to a shallow water table, which 

tends to preclude deep weathering (Plumlee, 1999). However, 

differences in geologic characteristics have a greater effect on 

pH and metal content in deposit-related waters than do differences in climate for a given deposit type (Plumlee, 1999). 

Past and Future Mining Methods and Ore 

Treatment

Many Fe-Ti-oxide deposits were mined for their Fe 

content before the value of the contained Ti was known (for 

example, the Sanford Hill/South Extension deposit). Early 

exploitation of magmatic Fe-Ti-oxide deposits was often by 

underground mining methods, whereas present-day operations 

at both Tellnes and Lac Tio employ open-pit operations.

There are two main industrial processes used to convert 

ilmenite into TiO2: the sulfate process and the chloride process 

(Mackey, 1994). The sulfate process is the older of the two, 

perfected in 1916 by two Norwegian chemists (Korneliussen and others, 2000). In the sulfate process, finely ground 

ilmenite, or high-TiO2 slag, derived by smelting low-TiO2

hemo-ilmenite feedstock with anthracite coal in an electricarc furnace (Guéguin and Cardarelli, 2007), is digested with 

concentrated sulfuric acid. After initial heating, an exothermic reaction results in formation of a porous cake, which is 

then dissolved in dilute acid and water to yield titanyl sulfate 

(TiOSO4) and iron sulfates (Chernet, 1999). Iron sulfate is 

removed as crystallized ferrous heptahydrate (FeSO4.7H2O), 

also known as copperas. Environmental concerns with the 

sulfate process include neutralization or regeneration of large 

amounts of sulfuric acid and disposition of large quantities of 

copperas. According to Mackey (1994), 3.5 tonnes of waste 

are produced for 1.0 tonne of TiO2 product using the sulfate 

process. Copperas may be used in water-treatment operations, 

for soil enhancement, in animal feed, and for reduction of 

hexavalent chromium (Cr VI) in cement, but production far 

outstrips demand and large quantities of copperas are either 

stockpiled or disposed of as landfill (Filippou and Hudon, 

2009). Accessory Cr in waste material can also be an environmental concern (Korneliussen and others, 2000). 

The chloride process was developed in the 1950s 

(Mackey, 1994). This process requires higher grade TiO2

feedstock, such as rutile from beach sands, Ti-rich slag 

derived from ilmenite, or synthetic rutile derived from leached 

ilmenite. Feed material is calcined with coke and chlorine to 

from gaseous titanium tetrachloride, which is then condensed 

and impurities separated as solids. The liquid is reheated to a 

gaseous state and mixed with hot oxygen to form fine highpurity rutile (white TiO2

 pigment) (Sahu and others, 2006). 

Displaced chlorine gas can be recycled and reused. This 

process produces only 0.2 tonnes of waste per tonne of TiO2

product (Mackey, 1994). As of 1992, the sulfate and chloride 

processes produced about equal amounts of product. However, 

because of a superior TiO2 pigment product and fewer waste 

products, the chloride process has mainly supplanted the sulfate process (Joseph Gambogi, USGS, oral commun., 2012). 

This shift from the sulfate route for TiO2 pigment production 

to the chloride route has increased demand for high-grade TiO2

feedstock. For ilmenite from magmatic deposits to be viable 

for the chloride process, it has to be upgraded to Ti-rich slag. 

A process developed by BHP Billiton, and purchased by Altair 

in 1999, dispenses with the filtration step and utilizes a spray 

hydrolyzer to produce nanoparticles of TiO2 (Verhulst and 

others, 2003).

Metal Mobility from Solid Mine Waste

Placement of mine waste under low-oxygenated water 

is a suggested waste management practice (Plumlee and 

Logsdon, 1999). Mine waste rock from the Tellnes deposit 

was placed in a deep fjord until 1994. Environmental pressures forced the discontinuation of that practice, although no 

deleterious effects had been determined (Olsgard and Hasle, 

1993). Benthic fauna have successfully recolonized the fjord 
36 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

bottom sediment where the tailings had been placed. Waste 

rock is now placed in an open-land deposit where dust and 

metal release due to oxidation of tailings is a concern (Thornhill, 2007). 

Some of the waste rock at the Lac Tio mine is adjacent 

to a lake called Lac Petit Pas. A study conducted by Rio Tinto 

Fer et Titane, the company that operates the Lac Tio mine, 

placed waste material in the lake. It was determined that 

elevated concentrations of some metals are in the first several 

centimeters of sediment within the lake, but that the sediment 

acts as a retention medium (Rio Tinto, 2009).

Pit Lakes

There is sparse reference to pit-lake chemistry related 

to magmatic Fe-Ti-oxide deposits. The McIntyre mine in 

the Sanford Lake district closed in 1982 and is now within 

Adirondack State Park. Country rock is anorthosite and 

olivine metagabbro. One measurement of pit-lake water at 

the McIntyre mine had a pH of 8, and the only trace element 

above the detection limit of an inductively coupled plasma–

atomic emission spectroscopy (ICP–AES) analytical method 

was Zn, at 0.049 mg/L (S. Hollmeyer, University of Vermont, 

unpub. data, 2003). It is possible that pit-lake water from 

magmatic Fe-Ti-oxide mines could contain slightly elevated 

concentrations of Co, Cr, Ni, V, and Zn. 

Volume of Mine Waste and Tailings

The open-pit methods used for Lac Tio and Tellnes produce large volumes of waste rock and tailings. The Storgangen mine operated from 1917 to 1965, producing more than 

10 million tonnes of ore (Schiellerup and others, 2003) and 

more than 8 million tonnes of tailings (Ettner, 1999). Production from the Tellnes open pit is 2 million tonnes of ore and 

1.6 million tonnes of waste rock, yielding 580,000 tonnes of 

ilmenite concentrate (production data current to 1999; data 

after 1999 are withheld) (NGU, 2012). The ratio derived 

from these figures of total rock mined to ore is about 1.8:1. 

Tellnes ore is milled and partially processed near the mine site, 

then shipped to Tyssedal, Norway, where it is processed into 

titanium slag (and iron) and sent on to Fredrikstad where the 

titanium slag is processed into titanium pigment. Nilsen and 

Ballou (2006) report that in recent years total mined material 

has been about 8 million tonnes per year yielding about 3 million tonnes per year of ilmenite (rock to ore ratio of 2.6:1).

Mining of the Lac Tio deposit began in the early 1950s; 

ore is shipped by rail to Sorel-Tracy, Quebec, where it is processed. Waste-rock piles at Lac Tio are estimated at more than 

70 Mt, cover approximately 92 hectares, and are between 20 

and 80 m in height (Plante and others, 2008). 

Smelter Signatures

Information regarding smelter signatures from facilities 

processing magmatic Fe-Ti-oxide ore is limited. Chromium, 

Co, Ni, V, and Zn can occur in some ores at low concentrations; ore beneficiated by roasting before being processed may 

release these metals during that process. Metals contained in 

anthracite coal used in the smelting step of the sulfate process 

may also be released. Leaching of smelter slag can be a concern for some types of deposits (see for example, Plumlee and 

Nash, 1995), but for ilmenite smelting, smelter slag contains 

the TiO2 product and thus is the feedstock used for further 

processing. 

Human Health Issues

Exposure to dust created during mining, transport, and 

processing operations, and to acids and other chemicals used 

in ore beneficiation certainly constitutes some human health 

risk (Kabata-Pendias and Mukherjee, 2007), but human health 

concerns related to titanium mining are minimal.

Acknowledgments

Discussions with Paul Weiblen (emeritus professor at the 

University of Minnesota), Val Chandler (Minnesota Geological Survey), and Mark Severson (Duluth Minerals Section of 

the Natural Resources Research Institute) were very helpful 

for a better understanding of the Duluth Complex in general 

and OUIs in particular. Very helpful reviews were provided 

by Lew Ashwal (University of the Witwatersrand, Johannesburg, South Africa) and Serge Perreault (SOQUEM, Val-d’Or, 

Quebec, Canada). Serge Perreault also provided photographs 

from Lac Tio and from the Rivière-au-Tonnerre Massif of the 

Havre-Saint-Pierre anorthosite suite.
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Appendix
46 A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites

Appendix

The wide variety of rock types related to Fe-Ti-oxide 

deposits and their host rocks includes many unusual characteristic rock compositions. These rocks are referred to in the literature by a number of names including, among many others, 

ferrodiorite, jotunite , monzonorite, nelsonite, or oxide-apatite 

gabbronorite, which can lead to confusion when comparing 

and contrasting compositions across regions (see for example, 

Owens and Dymek, 1992; Vander Auwera and others, 2001). 

The cumulate nature of many of the rock types as well as the 

possibility of highly fractionated rock compositions results in 

excessive labeling of rock types in an attempt to capture the 

specific mineralogical nature of each rock type. Rock names 

used in this report have been fit into a general rock classification scheme (fig. A1) that draws on the International Union 

of Geological Sciences (IUGS) systematics for plutonic rocks 

(Le Bas and Streckeisen, 1991; Streckeisen, 1976), the nomenclature developed by Phinney (1972) for the Duluth Complex, 

and a recent treatment of the problematic nomenclature of the 

charnockite series (Frost and Frost, 2008).

Proterozoic massif anorthosites rarely contain anorthitetype plagioclase (Ashwal, 1993). The plagioclase series 

(Ca,Na)(Al,Si)AlSi2O8 is arbitrarily divided into six subspecies based on the proportion of Na to Ca and related Al-Si 

ordering in the plagioclase mineral structure. Six divisions 

given here are based on the anorthite (An) proportion.

Albite An0 to An10

Oligoclase An10 to An30

Andesine An30 to An50

Labradorite An50 to An70

Bytownite An70 to An90

Anorthite An90 to An100
Appendix 47

Figure A1. Varying rocks types related to Fe-Ti-oxide deposits hosted within Proterozoic anorthositic plutonic suites and related 

layered rocks are classified based on their proportional mineralogy. The traditional Q-A-P (quartz-alkali feldspar-plagioclase) diagram 

is adapted from the International Union of Geological Sciences classification of plutonic rocks of Le Bas and Streckeisen (1991). The 

P-Ol-Px (plagioclase-olivine-pyroxene) triangle is based on rocks from the Duluth Complex (modified from Severson and Hauck, 1990); 

development of the classification for the Duluth Complex is discussed in detail in Miller and others (2002). A subset of the P-Ol-Px 

triangle distinguishing between mafic rocks with clinopyroxene (Cpx) and orthopyroxene (Opx) is modified from Streckeisen(1976). 

Addition of orthopyroxene to rocks in the Q-A-P triangle results in the charnockite series as defined by Frost and Frost (2008). In all 

cases, numbers are percent of each mineral phase.

10 10 cpx norite

plagioclase-bearing pyroxenite

norite

5 95

opx gabbro

gabbronorite gabbro

(from Severson and Hauck, 1990)

(from Streckeisen, 1976)

(from Frost and Frost, 2008)

* iron-rich gabbro and diorite can be termed ferrogabbro and ferrodiorite

**these rocks are also collectively termed leucogabbro or leucotroctolite 

gabbro

Q

A P monzonite

quartz

monzonite

syenite

quartz

syenite

granite

90 90

60 60

20 20

5 5

10 35 65 90

syeno- monzoquartz-rich

granitoids

alkali

feldspar granite

granodiorite

tonalite

diorite*

gabbro*

anorthosite

quartz diorite

quartz gabbro

quartz anorthosite

quartz alkali

feldspar syenite

alkali feldspar

syenite

monzodiorite

monzogabbro

quartz monzodiorite

quartz monzogabbro

P

Ol Px

anorthosite

gabbroic anorthosite** troctolitic

anorthosite**

anorthositic

troctolite** anorthositic gabbro**

90 90

80 80

70 70

20 20

10 10

troctolite

+ Opx

CHARNOCKITE

SERIES

P

Opx Cpx

Rocks in shaded area to right

can be further divided

according to the diagram below.

(from Le Bas and

Streckeisen, 1991)

augite

troctolite

olivine

gabbro

melatroctolite

(picrite)

melagabbro

feldspathic peridotite feldspathic pyroxenite

peridotite pyroxenite

Q

A P

90 90

60 60

20 20

5 5

10 35 65 90

charnockite

quartz

mangerite

mangerite jotunite

diorite*

gabbro*

anorthosite dunite
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Denver Publishing Service Center

For more information concerning this publication, contact:

Center Director, USGS Central Mineral and Environmental Resources 

Science Center

Box 25046, Mail Stop 973

Denver, CO 80225

(303) 236-1562

Or visit the Central Mineral and Environmental Resources Science 

Center Web site at: http://minerals.cr.usgs.gov/
Woodruff and others—A Deposit Model for Magmatic Iron-Titanium-Oxide Deposits —Scientific Investigations Report 2013–5091