Download Potential for Rare-Earth Element (REE) Deposits in Northern

Potential for Rare-Earth Element (REE)
Deposits in Northern Labrador
and Québec: Lessons from Strange
Lake and even stranger places
Andrew Kerr1, Steve Amor2, Derek Wilton1
1Dept.
of Earth Sciences, Memorial University
2Geological Survey of Newfoundland-Labrador
St. John’s, NL, Canada
Some Grateful Acknowledgements
Merci de l’invitation de présenter ici. Je voudrais
remercier aussi…….
Red Wine Mountains, August 2010
Randy Miller (once with GSNL, now with Search Minerals), Tyson
Birkett and Steve Zajac (originally with IOC in the 1980s). Pat
Collins and Jeanette Walsh (Quest Rare Metals), Anthony
Williams-Jones (McGill University), Robert Banville (Midland
Exploration), and the
for support
TheNunatsiavut
spectacular southGovernment
coast of Newfoundland
(photo by here.
Andy Kerr)
Strange Lake - Essential Facts
the “B-Zone” Deposit (approximate location)
The Strange Lake area contains world-class
deposits of the REE, highly enriched in heavy
(critical) REE. They are in many respects unique,
and other potential REE deposits also occur in
this part of Labrador and Quebec. Our purpose
is to discuss geology and exploration methods.
High-grade region of
the “Main Zone” deposit
QC
LB
Bulk sample site, Zone 1 Lens, Strange Lake Main Zone Deposit.
The B-Zone (Quest Minerals) is located in the background.
Coarse-grained eudialyte (Eu), nepheline (Ne) and pyroxene (Px) from the
Red Wine Mountains area, central Labrador. Deposits also rich in HREE.
Eu
Px
Ne
Strange Lake is the best known – but not the only one. These
deposits are diverse in character, mineralogy and potential.
Eudialyte: Na4(Ca, light REE)2(FeII, Mn, Y, heavy REE) ZrSi8O22(OH, Cl)2
Presentation Outline
• Some Regional Context: General geology and Mesoproterozoic “anorogenic” magmatism in northern
Labrador, Québec and related regions.
• Strange Lake: The discovery and wider context, and
characteristics of the the REE resource. Summary of
key geological and geochemical attributes, and the
contrasting (but not contradictory?) models.
• Other REE Deposit Types: A brief listing of other
areas and deposit types in this region – with
emphasis on the diversity of styles and chemistry.
• Exploration Methodology: The roles of regional to
local surficial geochemistry, geophysics and “new”
methods using indicator minerals.
Regional Context
SL – Strange Lake
ML- Misery Lake
FR- Flowers River
RW- Red Wine
PHS – Port Hope Simpson
SL
ML
FR
• The Churchill Province is
RW
PHS
REE
• Much of the region of
interest is within the
Churchill Province, with
some deposits in adjacent
blocks such as the Nain.
underlain by reworked
Archean crust, and it has a
long and complex Paleoproterozoic history.
• All REE Mineralization is
linked to younger Mesoproterozoic igneous suites
(from 1460 to 1240 Ma)
GREENLAND CONNECTIONS
• Prior to the opening of the
Labrador Sea in the Eocene,
Labrador was joined to SW
Greenland.
•Something to illustrate •the
Gardar
This region includes the
Gardar Province – A well
•Connections to Greenland
GREENLAND
u
Ch
il
rch
lP
(Nain)
Anorogenic
Magmatic Suites
of Labrador
v.
ro
Ketilidian
SL
Grenville
Makkovik
known region of alkaline
igneous activity with many
potential REE deposits. These
rocks are younger than North
American examples.
• The Gardar region and the
Mesoproterozoic igneous
rocks of Labrador are likely
part of the same plume event.
Alkaline Intrusive rocks
of the Gardar Province
http://sp.lyellcollection.org/content/318/1/193/F19.large.jpg
Strange Lake – An Abbreviated History
• The deposit was found through a uranium exploration
program – during an unplanned field ‘rest stop’.
• Exploration (1979-84) proved a Zr-Y-Nb resource, but
development plans failed due to the recession.
• After Voisey’s Bay discovery, claimed as Inuit Land.
• Interest in uranium (2008) grew in adjacent Quebec….
Then the REE suddenly become more strategic.
• A ‘new’ deposit was defined a few km inside Québec
(the B-zone) and is now in feasibility assessment.
• Strange Lake is notable for high relative contents of
the heavy REE – it contains some unique rocks, and is
of much interest for research work. Plus, it is a world
class resource of the REE (+ Zr, Nb, Hf…).
Aplite-pegmatite-rich zones contain the high-grade material
“exotic-rich granite”
Inclusion-rich
“exotic granite”
The “exotic-rich granite” may itself constitute low-grade ore
The “ore” at the Strange Lake
Deposit is a physical mixture of
variably-enriched granite and highly
enriched aplite-pegmatite zones.
NW-SE Cross-section
from part of the new B-Zone deposit in Québec,
TRANSVERSE
CROSS-SECTION
drawn from
Rare Minerals. The geology is essentially the same.
Source:
QuestQuest
Rare Minerals
)
iched
r
n
e
(
te
gmati
e
p
y
l
Large
Inclusion-rich
“exotic granite”
(with variable
Hematite alteration )
After Quest Minerals, 2010
• Like the original discovery in Labrador, the ”B-Zone” is a mixture of highgrade pegmatite zones, and lower-grade host granite; the bulk grade is
largely a function of pegmatite density and thickness.
Latest B-Zone Indicated Resource Estimates (2013)
278 Mt at 0.93% TREO*, 1.92% ZrO2, 0.18% Nb2O5
(includes 20 Mt at 1.44% TREO* for actual mining resource)
An additional 214 Mt at 0.85% TREO* is inferred at depth in “granite”
The original Strange Lake discovery from the 1980s has a non-compliant
resource of some 58 Mt at ~0.9% TREO*, but the drilling is very shallow.
The Exploration Camp at Lac Brisson, Québec
The REE, Zr and Nb are preferentially hosted in
pegmatitic and aplitic zones that cut the host granite.
These contain unusual Zr- and REE-bearing minerals,
also found in disseminated form in many granites.
2 cm (approx)
`
Strange Lake – Bulk Rare Earth Distributions
Note consistent patterns
and negative Eu anomalies:
extensive fractionation
Source: GSNL analyses
• REE Patterns from within the Strange Lake Deposit and its host
rocks are very consistent, although the individual units overlap.
• The most enriched granites are of interest as REE sources, with
average grades of ~ 0.6% TREO*. This material was generally not
included in any historical resource estimates.
Important Mineralogical Factors
Gittinsite
• Strange Lake is a “treasure trove”house of
unusual minerals, and it is likely that many
new species remain to be described.
• Unusual alkali and calcium zirconosilicates such
as elpidite and narsarsukite are present as
early ‘phenocryst’ phases in some of the
granites and melanocratic inclusions. The most
important Zr source is gittinsite – named for
Ernest Gittins (U of Toronto petrologist).
Kainosite
Galena
Elpidite?
• Important Ca (Na) – Y – REE silicates include
gerenite, kainosite and gadolinite. Importantly,
these are amenable to acid leaching extraction.
• Lots of fluorite and other mineral species;
some common, some still to be documented.
REE/chondrite
• The REE patterns of the
various units at Strange
Lake show systematic
variation that is best
explained through igneous
fractionation processes.
• The country rocks have
steeper REE patterns and
are lower in total REE.
(Country rocks}
(Country rocks}
• Granites show increasing
HREE content that could
record removal of LREE by
minerals or by loss of LREE
to hydrothermal fluids as
the magmas crystallized.
• REE patterns of high-grade
zones are very distinctive
and HREE- enriched.
Strange Lake Main Zone – Relative HREE Contents
Pegmatites/Aplites
1.71% TREO*
Y
43%
Source: GSNL analyses
• The heavy REE are relatively enriched, representing some 17% to
24% of the total REE budget.
• Pegmatite and aplite units (high-grade) generally have higher
heavy REE and Y proportions – notably the latter.
• The B-Zone mineralization has essentially the same features and
chemistry, although the relative HREE contents are somewhat lower.
Strange Lake – Other Key Attributes
• The ring complex is surrounded by a fluorite-rich
magmatic breccia zone likely representing an
arcuate fault – but this has no REE enrichment.
• Many (but not all) granites contain dark inclusions
with relict zirconosilicate phenocrysts; textures are
very like those attributed to mafic-felsic mixing.
• Nd isotope data do not match country rocks or
likely Archean basement – a significant proportion
of the REE were sourced in the mantle ~ 1240 Ma.
• Mixed mantle-crust heritage is most likely origin.
• A wide range of incompatible elements other than
REE are strongly enriched – e.g., U, Th, Be, Rb, Pb,
Sn. Negative correlations between these and Ca.
B-Zone
Main Zone
•
•
•
Model partly after R. R. Miller, 1986
1. Emplacement of latest, most
evolved granite magma along contact
between older units.
2. Crystallization causes accumulation
of residual melt and volatiles near the
roof of the unit, forming pegmatite and
aplite units. The latter cross-cut the
contacts of granite units.
3. Main Zone and B-Zone may
represent deeper and shallower levels
of a magmatic-hydrothermal system.
Strange Lake – Genetic Mysteries
• The deposit and associated granitic rocks are to a
large extent unique – the relative HREE-Y enrichment particularly unusual. How did this happen?
• Initial ideas (1980s) invoked largely magmatic
processes to enrich REE, but an alternative ‘hydrothermal’ explanation was favoured by others; fluid
mixing proposed as mechanism for REE deposition.
• This debate is not over – new models for the B-Zone
propose mixing of magmatic and meteoric fluids.
• The two deposits are similar, although there is
more hematite alteration in the B-Zone, and
perhaps a dominance of pegmatite over aplite.
• Different levels of a common magmatic system?
2 cm
Fine-grained “exotic-rich”
peralkaline granite unit
• Highly-enriched inclusion-free unit
associated with Labrador mineralization
• Less-enriched inclusion-bearing unit
that is the dominant host at the B-Zone.
“Exotic”granite unit with
fine-grained inclusions
• Mineralized pegmatite
with gittinsite and other Zr
and REE minerals – this is
where much of the grade
resides. Some pegmatites
have zonation suggesting
igneous processes.
• <<<<<<<<<<<
Homogeneous, highlyenriched granite that was
encountered in the deepest
holes beneath the B-Zone.
This resembles the host
granite seen in Labrador –
possibly beneath deposit?
>>>>>>>>>>>>>>
How can we make a Strange Lake magma?
• Evolved granites are considered by some as crustal
melts, but this cannot come from known basement.
• Crustal melting gives steep REE patterns – not seen!
• Isotopic data suggest that a mantle component or a
crustal precursor with a very short residence time –
Could a two stage process be involved?
• One possibility lies within a little-known group of
evolved intermediate rocks associated with
anorthosite-granite suites – ‘ferrodiorites’
• Protracted fractionation seems to have formed the
most enriched magmas, but there has been some
hydrothermal compositional disturbance also. But
magmatic processes are way more important.
Exploration from 2009 to 2012 was
focused mostly in north-central Labrador,
and adjacent regions of Québec. The area
to the north along the border saw less
activity, largely because no major
Mesoproterozoic igneous suites were
identified through earlier mapping.
Misery Lake
These are the main areas of recent
exploration, but other smaller
prospects have been identified in both
provinces, and partially explored.
Other Areas of REE Interest in the Area
• Flowers River Complex: Closest analogue to the
Strange Lake host rocks, partly volcanic, ~ 1290 Ma
• Letitia Lake: Distinctive LREE-Be rich zones
associated with ~ 1330 Ma peralkaline volcanic
rocks on the northern edge of the Grenville Prov.
• Red Wine Mountains: Undersaturated ~ 1330 Ma
metaplutonic suite noted for the presence of
eudialyte – a mineral enriched in HREE but no U,Th
• Misery Lake (QC): Well-defined ca. 1410 Ma ringcomplex with known REE zones; now also of current
interest for scandium (Sc) – rare but valuable.
• Ytterby: Magmatic LREE concentrations in late
(~1420 Ma) granites in the Mistastin Batholith.
Critical REE Abundances in Labrador/Québec Mineralization
UZ
LZ
Lower Zone
Upper Zone
Nechelacho
After V. Sederin et al.
• It has proven useful to classify REE mineralization using the relationships
between ”Critical”, ”Surplus” and ”Total” REE. On this basis, areas in the top
right of the charts are the most economically encouraging.
• Enrichment is clear for Strange Lake, Red Wine and Flowers River – note
that these have higher critical REE values than Nechelacho (NWT) area.
Exploration Methods for REE Deposits
• In many cases, peralkaline igneous suites are small,
and may not be well exposed; Strange Lake is a
good example, as there are very few outcrops.
• Regional radiometric surveys have proved useful,
and this is how many were first detected. High Th/U
ratios are typical. Radiometry is also useful for
prospecting – as REE minerals are often cryptic.
• Aeromagnetic surveys may reveal patterns of ringcomplexes, but not all deposits will reveal these.
• Surficial geochemical methods have great potential,
especially if linked with indicator mineral studies.
The latter can also tell us something about the
mineralogy of a target – this is very important!
STRANGE LAKE
Radiometric (Th) anomaly over the
Strange Lake Intrusion- highest zones
are seen over the Main Zone 1 Lens in
Labrador.
(GSC data, figure from Zajac et al.,
in press, Canadian Mineralogist)
B-Zone
Main Zone
Note that the B-Zone has little
response – due to a blanket of
material derived from the west.
MISTASTIN BATHOLITH AREA
Radiometric data also give a good
indication of the inner red granite
at Y2. These are data for Th-related
radioactivity – reflecting the Thenriched nature of such rocks and
related mineralization. (from
Midland Exploration)
The clear definition of intrusive bodies
by high-resolution aeromagnetics
is truly remarkable – This survey in 2009
in part led to definition of the Misery Lake
Complex within the Mistastin Batholith.
This is now an active exploration Project.
Diabase dykes
(Harp dykes?
(GSC total field; assistance by G. Kilfoil at GSNL)
Misery Lake
Complex and
REE prospects
QUEBEC
Intrusive “edge” of the
Mistastin Batholith
Diabase dykes
(Harp dykes?
25 km
LABRADOR
???
Ytterby 3
p
???
H
ar
D
yk
e
ML1
p
ML2
???
H
ar
~ 12 km
D
yk
e
Mistastin Batholith (S)
Ring-complexes and other
intrusions (?) defined by new
aeromagnetic (1vd) data
ML3
GSC Data, assisted by G. Kilfoil, GSNL
A border area located to the
northwest of the Mistastin
Batholith: Can you find the
expression of Strange Lake?
GSC Data, assistance by G. Kilfoil, GSNL
First vertical derivative (1vd)
Labrador
Québec
Napeu Kainut Intrusion
(age unknown)
Mistastin
Batholith
The use of surficial geochemistry
as an exploration tool on various scales
“North River
Anomalies”
Strange Lake
Image: Fluoride in lake waters,
Northern Labrador
(Fluoride in lake waters seems
to be one of the most effective
regional indicator elements….)
Regional Surficial Geochemistry – Summary
• Most of the known REE deposits have expression in
surficial geochemistry, and not only from REE.
• Strange Lake has a well-developed dispersion train.
• Extensive lake sediment database for both sides of
the border, but the element suites vary, with limited
REE analyses in Québec. Recent reanalysis work under
GEM-2 now allows easier merging of these data.
• This is a valuable database, although some aspects
remain puzzling. There are challenges in separating
mineralization signatures from the other factors
which can create regional zones of enrichment.
• These new data give enhanced definition of the
dispersion train from Strange Lake….and much more.
Thorium
(Th)
Incompatible elements such
as Th and Cs do provide some
definition for known REE
prospects, but these are not
easily discriminated from
wider regional patterns.
Th is associated with
wider granitic areas,
with lows on areas
of anorthosites. Cs is
not a clear pattern.
REE Deposit
Strange
Lake
Flowers
River
Red Wine /
Letitia Lake
Cesium
(Cs)
INAA Data;
NGR
samples
(GSNL)
Samarium
(Sm)
The REE form more useful
surficial indicators of known
mineralization, but in general
the light REE are more widely
dispersed than the heavy
REE, which work better.
Note the marked
unexplained area
of enrichment NE
of Strange Lake,
and also SL train.
REE Deposit
Strange
Lake
Flowers
River
Red Wine /
Letitia Lake
Ytterbium
(Yb)
INAA Data;
NGR
samples
(GSNL)
“NORTH RIVER”
The geochemical
anomaly known as
North River still has
not been fully
explored. It is very
interesting that
regional magnetic
data reveal some
ring-like patterns in
here……
•
SYMBOLS
Fluoride in Water
(scaled for value)
Yttrium
(Y)
(smoothed)
MERGED LB/QC DATA
• Y and La are the only REE
available. Y is a good
proxy for the heavy REE,
but the regional pattern
is once again diffuse.
• Interestingly, it seems to
define other areas in
northern Labrador not
revealed by LREE data.
Data from NGR
(GSC) and MRNF
samples, ICP-MS
Merged, and
smoothed.
Amor et al., 2016,
In “Explore”
• The representation of
data and scaling are of
great importance if the
objective is to highlight
smaller areas of the
strongest enrichment.
• What you get out of data
depends on treatment.
Yttrium
(Y)
(rescaled,
Smoothed)
MERGED LB/QC DATA
• These are the same
data as in the previous
slide, but rescaled to
show only the highest
values, and leave most
other variation unseen.
• This gives much clearer
definition of the
Strange Lake dispersion
train, and other areas
of possible interest in
both provinces, but
mostly in Labrador.
Data from NGR
(GSC) and MRNF
samples, ICP-MS
Merged, and
smoothed.
Amor et al., 2016,
“Explore”
• A good illustration of
the potential of these
data given further
manipulation and
processing.
Tin
(Sn)
(smoothed)
SL Train
Data from NGR
(GSC) and MRNF
samples, ICP-MS
Merged, and
smoothed.
Amor et al., 2016,
“Explore”
MERGED LB/QC DATA
• One of the interesting
results was the very
good definition of the
Strange Lake dispersal
train by Sn – This is also
enriched in the rocks at
Strange Lake.
• Sn also highlights the
areas in northern
Labrador noted for the
heavy REE, and also the
Letitia and Red Wine
areas in Labrador.
• Broad anomalies west
of the border do not
have obvious causes –
but they may vanish
with scale adjustment.
Gittinsite – located about
140 km from its source!
Strange Lake
Voisey’s Bay Area
• Investigations into MLA-SEM
methods by Derek Wilton and Altius
Minerals led to the discovery of
gittinsite in tills on the Labrador coast.
This must have come all the way from
Strange Lake – there is no other known
source closer than Kipawa, W. Québec.
SEM/MLA Photos from Derek Wilton
A Role for Indicator Mineral Surveys?
• Looking for distinctive indicator minerals is a
promising method, and also a way to distinguish
true anomalies from broad regional patterns.
• A new project using Mineral Liberation Analyzer
(MLA) and Scanning Electron Microscope (SEM) is
under way at Memorial, initially for Strange Lake.
• What questions might this project answer?
• How far do minerals survive transportation?
• Can they be detected even where bulk geochemical
anomalies are absent or extremely subtle?
• Can a reference library for these minerals be
assembled for application to other project areas?
CREAIT Labs, MUN
Photos – D. Wilton
• SEM/MLA – ”Scanning Electron Microscope / Mineral
Liberation Analyzer ” is a method of investigating rock samples
or mineral separates using automatic imaging and analysis. It is
a variant of the QEMSCAN technique used in geometallurgy.
• Reference libraries are used for spectral identification – so the
first step is to develop these libraries.
• The method can be used to screen processed till samples,
looking for rare grains of indicator minerals – which also give
an indication of what the undiscovered target might be.
Mineralized “aplite” containing
poikilitic gittinsite (CaZrSi2O7)
High-grade pegmatite, with
fluorite and “exotics”
• Information from MLA-SEM work will also help to understand the
myriad complexities of the rocks at Strange Lake.
• Information from mineralized rocks will provide material for
reference libraries. So this is very much a two-way street.
• Typical scenery in the area
of the Strange Lake
dispersion train. I think you
can see why surficial
techniques would be a
valuable method for
prospecting!
• <<<<<<<<<<<
Sampling tills down-ice
from Strange Lake,
summer of 2016. The
project involves funding
from RDC, and also the
Nunatsiavut Government
(photos from Derek
Wilton).
>>>>>>>>>>>>
LB
QC
LB
QC
Thank You.
Merci beaucoup.
Nakkumek.
Is this the shape of things to come?
Source: Financial Post, business section, Nov 21, 2016
(website www.business.financialpost.com)
• The recent article about the use of ‘blimps’ for development
of Strange Lake (and possibly concentrate transportation)
underlines an important point – the remoteness of the region
and lack of infrastructure raises the economic threshold for any
discovery. Should something like this ultimately prove feasible,
it has implications for other types of projects, notably gold.