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Investigation of the Fe+Ti+REE+Zr+P mineralization in the Raftsund Batholith, Lofoten,

Norway

Donald Maute III

Master of Science Thesis Proposal

Introduction

Iron-titanium-phosphorus rich rocks are found in a variety of localities worldwide. Many

models, based on experimental work, suggest their origins are due to liquid immiscibility

between Si-rich and Fe-rich melts (Philpotts 1967). Others contest the existence of such Fe-rich

immiscible melts due to the unreasonably high temperatures (≥1300oC) required for unmixing to

occur (Lindsley and Epler, 2017. Other models for the genesis of these enriched zones include

hydrothermal fluid enrichment or extreme fractionation and crystal sorting. These types of

enrichment are interesting not only due to their enigmatic petrogenesis, but because they

commonly host economically viable abundances of rare earth elements (REEs), and high-field

strength elements (HFSE) (Tornos et al., 2016; Petrella et al., 2014)

In the Raftsund Batholith, Lofoten, Norway (Figure 1), a number of zones of Fe-Ti-REE-

Zr-P-mineralization have been documented (Ihlen et al., 2014). The mineral assemblage of the

zones consists largely of magnetite + ilmenite + zircon + apatite ± clinopyroxene ±

orthopyroxene ± olivine ± allanite, with secondary biotite and hornblende. A number of these

zones occur as vein-like structures distributed along the south to southeast margin of the island

of Årsteinen. Field observations show the mineralization is located at contacts between texturally

distinct porphyritic monzonite and coarse-grained, equigranular monzonite. These mineralized

zones differ from other nelsonite-like mineralization world-wide due to the presence of

abundant, and large (up to 3 mm) zircon. Classically, nelsonites are characterized by a 2:1 ratio

of magnetite and apatite (Philpotts 1967). The occurrence of the mineral assemblage at the

boundary between porphyritic and coarse-grained monzonitic units introduces the possibility that

a mixing reaction between the two magmas, or between fluids exsolved from the two magmas

may have promoted mineralization.

This research will implement a geochemical, oxygen isotope and textural study of

minerals present in the Årsteinen mineralized zones to distinguish between models of liquid

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immiscibility, hydrothermal fluid enrichment, mineral accumulation or a more complex,

combined origin for the mineralized zones.

Figure 1. A) Map of Norway outlining the location of the Lofoten-Vesterålen

archipelago (Markl 2001). B) Geologic Map of the Lofoten-Vesterålen archipelago,

outlining the Raftsund pluton (Corfu et al., 2004).

Geologic Background

Lofoten-Vesterålen Mangerite Complex (LVMC)

The Lofoten-Vesterålen archipelago is dominated by mangerites, charnockites,

anorthosites, gabbros and granites intruding high-grade Precambrian rocks (Corfu et al., 2004).

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The Lofoten-Vesterålen islands are thought to represent a window into the basement rock

beneath allochthonous Caledonian nappes, which crop out to the east (Corfu et al., 2004). The

intrusive suite on Lofoten-Vesterålen have been described as an anorthosite-charnockite-

mangerite-granite (AMCG) suite. Such intrusive suites are nearly exclusive to the Proterozoic

(Corfu et al., 2004; Bédard, 2009). The widely supported model for the emplacement of

anorthosites in AMCG suites is one of polybaric crystallization – with initial crystallization at

depth in the lower crust (corresponding pressures ~900 MPa), and emplacement at shallower

mid-crustal levels as a crystal-rich mush (~400 MPa) (Markl et al., 1998). The associated

gabbroic to charnokitic rocks on Lofoten-Vesterålen are thought to be related to each other by

crystal fractionation along an Fe-enrichment trend – which intruded at mid-crustal levels like that

of anorthosite emplacement (Markl et al., 1998).

Corfu et al. (2004) proposed a 3-stage model for the Lofoten-Vesterålen AMCG suite that

was initiated with emplacement of the Lodingen and Hopen plutons (1.87-1.86 Ga), which

corresponds with regional contraction and amalgamation of arcs. The dominant and most

voluminous stage of magmatic activity took place between 1.80 and 1.79 Ga and includes the

Raftsund pluton (Corfu et al., 2004). This stage of magmatism encompasses a wide range of rock

types of both crustal and mantle origin. These rocks are proposed to be related by a first-order

process, such as changing plate kinematics at the margin of the Baltic craton (Corfu, et al., 2004)

that may have initiated a large-scale melting event. Between 1.79 and 1.77 Ga magmatic activity

concluded with emplacement of late-stage pegmatites, and includes local hydration and

retrogression (Corfu et al., 2004).

The Raftsund Pluton

The Raftsund pluton, or, due to size, the Raftsund batholith, is centered around

Raftsundet strait and is dated at 1.80-1.79 Ga (U-Pb zircon; Corfu et al., 2004). At 1000 km2, this

intrusion is the largest monzonitic body on the Lofoten-Vesterålen archipelago (Griffin et al.,

1974). On the island of Årsteinen, the Raftsund Batholith is largely composed of two lithologies

with similar compositions, but different macroscopic and microscopic textures: coarse-grained,

equigranular monzonite and a porphyritic monzonite that locally lacks phenocrysts (Figures 2A

and 2B). The mineral assemblage consists of ternary feldspar + clinopyroxene + orthopyroxene +

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hornblende + magnetite + ilmenite + zircon + apatite ± olivine ± pigeonite. The Raftsund

batholith has been previously referred to as a mangerite (Markl et al., 1998; Corfu et al., 2004)

but, will be further referred to as a opx-cpx-fay-monzonite. This allows for a simple, well-

recognized IUGS classification with appropriate prefixes, following Frost and Frost (2008).

Figure 2. A) A contact between the two contrasting textural types of the Raftsund

Batholith, with the porphyritic monzonite and coarse-grained monzonite. Pen is shown

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for scale. Photo courtesy of C.G. Barnes. B) Photograph of a mineralized zone occurring

at the contact between the coarse-grained monzonite and the porphyritic monzonite. Pen

is shown for scale. Photo courtesy of C.G. Barnes.

Fe+Ti+REE+Zr+P mineralization

In the Raftsund Batholith on the south-southeast margin of Årsteinen are zones of Fe-Ti-

REE-Zr-P mineralization. These zones are small vein-like structures that are largely concentrated

at the contacts between the texturally distinct monzonitic units (Figure 2B). The (mineral)

assemblage of the mineralized zones consists of magnetite + ilmenite + olivine + zircon + apatite

± clinopyroxene ± orthopyroxene ± hornblende ± biotite ± allanite (Figures 3A and 3B). The

abundance of zircon greatly exceeds that of apatite, which is not typical for Fe-Ti-P

mineralization world-wide.

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Figure 3. A) Plane-polarize photomicrograph displaying an isolated mineralized zone

near the contact of the two monzonite units consisting of Fe-Ti-oxides, zircon, apatite,

and allanite. Also shown is minor secondary biotite and garnet-orthopyroxene coronas

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around the oxides (determined by Markl, 1998). B) Plane-polarized photomicrograph

displaying common mineral assemblage in the mineralized zone – Fe-Ti-oxides, olivine,

zircon, apatite, clinopyroxene and orthopyroxene.

Proposed Research

The primary aim of this study is to construct a model for the genesis of the Fe-Ti-REE-

Zr-P mineralization in the Raftsund batholith and to provide broader insight into the generation

of Fe-Ti-P ore-forming systems world-wide – which commonly concentrate strategic metals.

Existing models for similar systems are broadly based on one of three mechanisms: liquid

immiscibility (Velasco et al., 2016; He et al., 2016; Chai et al., 2014), hydrothermal enrichment

(Nabatian et al., 2014; Dupuis and Beudoin 2011; Haynes et al., 1995, or crystal accumulation

(She et al., 2015; Charlier et al., 2009; Tollari et al, 2008). The field relationships of the

mineralized zones to their host rocks being concentrated at the lithologic boundary between two

monzonitic units along with preliminary microscopic textures suggest that the Raftsund localities

may be appropriate locations to test liquid immiscibility models in natural systems. Although

liquid immiscibility is commonly cited as a mechanism for Fe-Ti-P mineralization it is also

commonly refuted (Lindsley and Epler, 2017). The occurrence of the mineralization at contacts

between the two texturally contrasting monzonites enables comparison of geochemical, isotopic

and textural features between host rocks and the mineralized zones – which may provide genetic

information to their origins.

The research will consist of 6 components

• Field work

• Petrography – Polarized and reflected light

• Textural analysis – Back Scattered Electron (BSE) and Cathodoluminescence

(CL) imaging

• Major and trace element mineral compositions – Electron Probe Micro Analysis

(EPMA), Energy Dispersive Spectroscopy (EDS) and Laser Ablation-Inductively

Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

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• Oxygen isotope mineral compositions – Secondary Ion Mass Spectrometry

(SIMS)

• Bulk rock geochemistry – X-Ray Fluorescence (XRF) and Laser Ablation-

Inductively Coupled Plasma-Mass Spectrometry

Methods

Sample Collection and Preparation

Samples of the mineralized zones and their host rocks will be collected on the island of

Årsteinen, Lofoten, Norway. Both types of monzonite will be sampled near the enriched zones,

and away from the zones where there was no visible evidence for mineralization. Samples of the

Raftsund monzonite will also be provided by Dr. Nolwenn Coint of the Norwegian Geological

Survey. Samples will be cut into billets and prepared for traditional covered and uncovered

polished thin sections.

Samples for bulk rock will be crushed and powdered by jaw crusher and a shatter box

with a ceramic sample container. Once powdered, the samples were tested for loss on ignition

(LOI) by placing a measured amount of powdered sample into preheated crucibles. The crucibles

were held at 1000°C in an oven for thirty minutes. After cooling in a desiccator, the samples

were weighed to determine the amount of volatiles lost. The LOI powder was fused to create

glass disc by mixing 2.000g ± 0.0010g of LOI powder with 4.0000g ± 0.0020g of a 49.75% Li-

metaborate, 49.75% Li-tetraborate, and 0.5% LiBr fluxing agent. The mixture was placed in a

platinum crucible along with 40 µl of LiI wetting agent, followed by fusing in a Claisse M4

fluxer.

Samples of bulk rock will also be crushed by a jaw crusher for use in mineral separation.

Repeated crushing by an iron mortar and pestle and subsequent sieving will be utilized to

separate zircon and magnetite grains. Heavy liquids and/or magnetic separation will be used if

necessary to further purify the mineral separates.

Petrography

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Optical Petrography

Optical petrography with a polarizing light microscope operating in transmitted and

reflected modes will be conducted to characterize mineral assemblages, inter-mineral

relationships and textures in the mineralized zones and their host rocks.

Scanning Electron Microscopy (SEM)

Mineral zoning and inter-mineral textures will be characterized using BSE and CL

imaging using the Hitachi S-4300 SEM at Texas Tech University. Energy Dispersive

Spectrometry (EDS)-assisted phase identification will complement imaging techniques.

Electron Probe Microanalysis (EPMA)

The JEOL JXA-8200 Superprobe Electron-Probe Micro-Analyzer (EPMA) at Rutgers

University, NJ will be used to characterize the major element compositions of apatite, magnetite

and ilmenite. In addition, the EPMA will be used to collected element distribution maps of

mineral growth and mineral reaction textures identified by optical and SEM petrography.

Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

Trace element compositions of zircon, apatite, magnetite, ilmenite and bulk rock samples

will be collected using LA-ICP-MS in-situ analysis on polished thin sections and polished fused

glass disks using an Agilent 7500CS ICP-MS equipped with a NewWave 213 nm solid-state

laser at Texas Tech University. Trace element data will be reduced using an Excel spreadsheet.

Data for minerals will be reduced with either a measured concentration of SiO2 (zircon), CaO

(apatite) or Fe (magnetite and ilmenite) from the preceding EPMA analysis. Data for bulk rock

samples will be reduced with SiO2 content from preceding XRF analysis.

The data for mineral compositions will be standardized using either the USGS GSD,

USGS GSE, NIST 610 or NIST 612 standards. Repeated analysis of USGS BHVO-2G basaltic

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glass will be utilized to measure precision and accuracy throughout the analytical runs. Durango

apatite will also be added for quality control for apatite.

Energy Dispersive Spectroscopy (EDS)

Major element geochemistry of silicate minerals with a focus on pyroxene and olivine

will be characterized using Energy Dispersive Spectroscopy via the Hitachi S-4300 SEM at

Texas Tech University.

Secondary-Ion Mass Spectrometry (SIMS)

Oxygen isotope ratios of zircon and magnetite will be collected using the Cameca IMS

1280 ion microprobe at the NORDSIM laboratory, Swedish Museum of Natural History,

Stockholm, Sweden. Minerals will be analyzed from the mineralization, the host monzonites, and

magnetite-rich country rock. A 20 kV Cs+ primary beam will be utilized – 10 kV primary, 10 kV

secondary, 1.5 nA and critically focused mode to sputter a 10 micron rastered spot (Pidgeon et

al., 2017).

X-Ray Fluouresence (XRF)

Major element geochemistry of bulk rock samples will be analyzed by XRF at Texas

Tech University using a Thermo Scientific ARL Perform ‘X’ instrument. Elements (ppm) and

oxides (wt%) collected include Al2O3, Ba, CaO, Cr, Cu, Fe2O3(TOT), K2O, MgO, MnO,

Na2O, Ni, P2O5, SiO2, Sr, TiO2, V, Zn, and Zr. Elements were analyzed at 60 kV and 60 mA

except for Al2O3, MgO, Na2O, P2O5, and SiO2 which was analyzed at 30 kV and 120 mA.

Using Data to Address Research Goals

This research will use textural evidence, element, and isotope geochemistry to create a

model for the generation of the Fe-Ti-REE-Zr-P mineralization – by discriminating between

liquid immiscibility, hydrothermal enrichment, or extreme mineral accumulation and crystal

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sorting. The trace element geochemical data will be presented as spidergrams (REE, multi-

element variation diagrams) against chondrite. Major and minor element compositions will be

plotted on binary diagrams (element-element, element-ratio, or ratio-ratio) when necessary to

display correlations in the data or for use in discrimination diagrams for suggested mineral

petrogenesis. Additionally, major and minor element compositions will be presented as chemical

maps to display growth and reaction features. Textural observations will be presented as

photomicrographs, BSE, or CL images as applicable. Oxygen isotopic data will be presented and

normalized to Standard Mean Ocean Water (SMOW), and compared to previous experimental

work (Kyser et al., 1998) and compositions from natural Fe-Ti-P ore-systems. (Westhues et al.,

2017; Tornos et al., 2016; Jonsson et al., 2013; Nyström et al., 2008).

Hydrothermal enrichment is one proposed model for the generation of certain Fe-Ti-P ore

systems and is explained by episodic alteration by magmatic-hydrothermal and/or hydrothermal

fluids rich in Fe and alkalis, commonly accompanied by an alkalic alteration zone in the

surrounding rocks (Westhues et al., 2017). Minerals should preserve evidence of compositional

zoning documenting to the evolution of the mineralizing fluid. Back-scattered electron and CL

images of zircon will be used to distinguish between different domains of zircon and apatite

growth, providing insight into the history of the system. Complex internal textures of zircon in

BSE and CL are known to be representative of hydrothermal zircon – in comparison to magmatic

zircon, which preserves well-developed zoning and euhedral morphologies (Westhues et al.,

2017). Additionally, if zircon textures appear to be “spongy”, due to widespread mineral or fluid

inclusions then this may be suggestive of a hydrothermal origin (Westhues et al., 2017).

Magnetite compositions can also be used to discriminate hydrothermal versus magmatic

origins, through the use of compositional maps and trace element geochemistry (Broughm et al.,

2017). Abundances of Mg, Al, Ti, V, Cr, Mn, Co, Ni, Zn, Ga and Sn in magnetite have been

used to discriminate the petrogenesis of magnetite between different rock types, mineral deposit

types, and in some instances has been used as a relative proxy for temperature (Nadoll et al.

2014). For example, high Ga concentrations (~100 ppm) in magnetite has been suggested

correlate to high-temperature crystallization (Nadoll et al., 2014). Additionally, in silicate

magmas, the Ni/Cr ratios in magnetite are coupled, and are commonly <1 (Dare, et al., 2014). In

hydrothermal systems, Ni/Cr ratios are decoupled and are usually >1, as Ni is generally more

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soluble in fluids (Dare, et al., 2014). Furthermore, if magnetite is observed to have elevated

incompatible element concentrations such as Si and Ca (Dare et al., 2014), then this would

support the hydrothermal enrichment model.

The second major mechanism suggested to generate Fe-Ti-oxide mineralization is liquid-

liquid immiscibility between an Fe-rich and a Si-rich melt. Some have suggested that this

process can occur due to the influence of magma mixing, crystal fractionation, or crustal

contamination (Wilson, 1989, Zhou, et al., 2005). Some of the strongest geologic evidence for

liquid immiscibility is the presence of Fe-rich melt inclusions trapped in minerals contained in

host rocks (Velasco et al., 2016; Jakobsen et al., 2011). If Fe-rich melt inclusions are found

hosted in minerals in the mineralization, or adjacent host rocks, this would be one piece of

evidence supporting the liquid immiscibility model.

In comparison to the Si-rich melt, the conjugate Fe-rich melts have elevated REEs,

HFSEs, P, Ti, high FeO and high CaO/Al2O3 ratios (Veskler et al., 2006). Therefore,

geochemical evidence should be preserved in the minerals that crystallized from an Fe-rich

immiscible liquid. The target minerals (i.e. zircon, apatite, magnetite and ilmenite) are present in

both the mineralized zones and the monzonitic host rocks. Analyzing minerals from the

mineralized zones and their host rocks allow comparisons between mineral compositions to look

for geochemical evidence suggestive of the presence of an Fe-rich melt. If REEs are significantly

enriched in the immiscible Fe-rich melt (Ellison and Hess 1989; Veksler et al., 2006), early

forming phases, such as apatite, should be relatively enriched in their REE content in comparison

to apatite from the host monzonite.

Niobium and tantalum have high affinity for ilmenite, and concentrations are correlated

with abundances in the melt and co-crystallization of other phases (She et al., 2015). The other

phase with strong affinity for these elements that may preferentially partition these elements is

zircon (Nardi et al., 2013). If zircon is not present, and not affecting Nb and Ta concentrations in

ilmenite, and if the ilmenite has elevated Nb and Ta compared to ilmenite in the monzonite, then

this may be evidence for liquid immiscibility (Veksler et al., 2006). In addition, non-chondritic

Ta/Nb values for the Fe-rich liquid have been suggested to be an indicator of liquid immiscibility

(Vicenzi et al., 1994; Veksler et al., 2006).

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Fractionation of oxygen isotopes between an Fe-rich and Si-rich melts may also be used

as evidence for the presence of an Fe-rich immiscible liquid. If δ18O values of magnetite and

zircon between the mineralized zones and the host monzonite are within ~0.6‰, then this may

suggest liquid immiscibility as a responsible process (Kyser et al., 1998). During liquid

immiscibility, 18O has been experimentally determined to slightly fractionate into the Si-rich

melt, compared to the Fe-rich melt (<1‰) (Kyser et al., 1998).

The last of the three suggested processes for generating Fe-Ti-oxide mineralization is a

cumulate origin by gravitational settling and/or crystal sorting. Chromium, vanadium and nickel

are known to be generally compatible with magnetite and ilmenite (Chen et al., 2012). The

concentrations in these minerals correlate with concentrations in the melt, co-precipitating

phases, and mineral/melt partition coefficients (Dare et al., 2014; Nadoll et al., 2014; Charlier et

al., 2007). If the minerals in the mineralized zones have similar or, elevated concentrations of

Cr, V and Ni, in comparison to the host monzonites, then this may be suggestive of early

crystallization and subsequent accumulation. Textural analysis will also be a critical to

identifying cumulate textures by identifying signs of trapped interstitial liquids and documenting

mineral paragenesis. If ore minerals fractionated and accumulated into mineralized zones, then a

correlation between δO18 values of magnetite and zircon in the mineralized zones and the host

rocks should be preserved. On the contrary, if ore-minerals crystallized from a trapped interstitial

liquid, O isotopes of these minerals may have signatures of a more evolved melt.

Timeline

Summer 2017 – Field work and sampling in Lofoten, Norway.

Fall 2017 – Petrography and SEM, grant/fellowship writing.

Spring 2018 – LA-ICP-MS, SEM, preparation for EPMA.

Summer 2018 – EPMA at Rutgers University, NJ. Additional field work and sampling in

Lofoten.

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Fall 2018 – Study abroad at Norwegian University of Science and Technology (NTNU).

Collaboration with Nolwenn Coint and Jacob Keiding at the Norwegian Geological Survey

(NGU). SIMS at NORDSIM laboratory, Stockholm, Sweden. Data synthesis.

Spring 2019 – Collection of more data at Texas Tech University if necessary. Thesis defense.

Funding

Funding for this research will be sourced from:

• GEMMS (GreEn Management of Mineral reSources)

o TBD

• Mineralogy, Geochemistry, Petrology, & Volcanology Division Graduate Student

Research Grant offered by the Geological Society of America

o $2,000

• Texas Tech University Geoscience Society

o $300

Intellectual Merit

This research will provide a better understanding into the mechanisms that concentrate

important strategic metals such as REEs and HFSEs to an economically viable abundance.

Additionally, this will allow for the improvement of models of Fe-Ti-P types of ore-forming

systems. This will enable more accurate prediction of how such mineralization is distributed in

the Earth’s crust, resulting in tactical and sustainable plans for mining operations. Being that the

genesis of these enrichments is not entirely agreed upon, this research will further assist

geoscientists to better understand their behavior.

Broader Impacts

Given the importance of REEs and Zr to the development of modern society, high-tech

advancements, and sustainable energy, this study will provide valuable information for the

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exploration of new resources. This will also be of benefit to government-based mineral

exploration and independent mining companies world-wide by providing the foundation for

improved exploration techniques to be utilized in locating new resources. Additionally, through

the course of the student’s research, he will use a diversity of analytical equipment and acquire

skills to further his progression in his scientific career. The student plans to continue his

involvement with professional scientific organizations and furthermore, to present new,

innovative research on strategic mineral resources using skills and knowledge gained from his

education at Texas Tech University.

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