Download Uranium Transport and Deposition and Uranium Deposits

Uranium Transport and Deposition
and Uranium Deposits
Stephen J. Piercey + Jonathan Cloutier
HYDROTHERMAL SOLUBILITY OF U
•
Uranium occurs in crustal environments in two valence
states:
1. U4+ (uranous Ion)
2. U6+ (uranyl Ion)
HYDROTHERMAL SOLUBILITY OF U
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In magmatic (silicate melt) environments U exists as
U4+ making it a highly (melt) incompatible element, so:
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U resides only in a few “accessory” minerals
⇨ e.g., zircon, monazite, apatite, titanite, allanite
•
U thus becomes highly concentrated in residual
melts & late-crystallizing minerals such as those
above
From Kyser, 2014
HYDROTHERMAL SOLUBILITY OF U
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In hydrothermal environments it is readily oxidized to U6+
commonly forming soluble complexes with:
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fluoride
(pH <4)
Acid
chloride
(T > 100 °C, low pH)
Acid
phosphate (5 < pH < 7.5)
Near Neutral
carbonate (pH > 8)
Alkaline
From Kyser (2014)
Precipitation of Uranium
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To form uranium minerals (e.g., uraninite - UO2) we need to
cause soluble uranium to precipitate.
This is generally a redox reaction where a soluble uranium
form in an oxidized solution reacts with some reactant that is
reducing (i.e., the fluid is reduced leading to precipitation).
Reductants such as:
•
organic matter;
•
reduced sulfur (H2S or HS-);
•
sometimes, ferrous iron (Fe2+);
•
or another fluid (with lower fO2)
Examples of Uranium Precipitation
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At high temperatures, uranous minerals (e.g., U4+O2 uraninite) are often associated with ferric oxides or
hydroxides, implying REDOX reactions such as :
U6+O2(CO3)34-(aq) + 2Fe2+O (rock)+ H2O
U4+O2(Uraninite) + 2Fe3+O(OH)(goethite) + 3CO2(g) + O2(g)
Examples of Uranium Precipitation
OR ☞ ,
U6+O2(CO3)34-(aq) + 2Fe2+O (rock)
Hematite
+ H 2O
U4+O2(uraninite) +
Illite
Fe23+O3(Hematite) + 3CO2(g) +
O2(g)
Millennium deposit - Athabasca Basin
Unconformity-related U
HYDROTHERMAL SOLUBILITY OF U
•
At low temperatures, the most important complexes are
likely to be:
•
•
•
UO22+(aq)
UO2(CO3)n2-2n(aq)
Most effective precipitation mechanisms are still redox
reactions, with reductants such as Fe-bearing minerals,
reduced sulfur and organic carbon.
ORE PRECIPITATION OF U
•
In these lower T environments
U precipitation is often
hypothesized as linked to U-bearing fluids encountering
reduced S, producing redox reactions such as:
4U6+O2 (CO3)34-(aq) + HS- (aq) + 15H+ + 2Fe2+ + H2O
4U4+O2 (uraninite) + SO42-(aq) + 12CO2(g) + 8H2O + ½O2(g)
ORE PRECIPITATION OF U
•
Many deposits formed by low T processes in sedimentary
sequences show textural evidence of U minerals directly
replacing organic matter
•
e.g., sandstone-hosted deposits in Colorado Plateau
district
direct replacement of coalified fossil plants
(including entire tree logs) by uraninite and coffinite
Uranium deposits are formed
after sandstone deposition by
U-bearing hydrothermal fluids
that replace original plant
material with U-minerals.
Uraninite Petrified Wood,
Coconino Cty, AZ
Foos, 1999
galleries.com
Uranium Deposits of the Colorado Plateau
MAIN URANIUM MINERALS
“UNOXIDIZED” ORES
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Uraninite
UO2
Isometric
Full solid solution with
Thorianite
ThO2
Isometric to hexagonal
“Pitchblende”: A varietal name for poorly crystalline (often
colloform) uraninite
Brannerite
(U,Ca,Y,Ce)(Ti,Fe2+)O6
Monoclinic
Coffinite
(U,Th)[(OH)4x|(SiO4)1-x]
Tetragonal
Uranothorite (Th,U)SiO4
Tetragonal
All these minerals generally (brownish-)black – except thoriteuranothorite is brownish-yellow
URANIUM MINERALS
“SUPERGENE” ORES & WEATHERING PRODUCTS
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Uranophane Ca(UO2)2[HSiO4]2•5H2O
Monoclinic
Autunite
Ca(UO2)2(PO4)2•[10-12]H2O Tetragonal
Carnotite
K2(UO2)2[VO4]2•3H2O
Monoclinic
Carnotite
⇨ Generally bright greenish-yellow
⇨ Commonly formed by simple surface weathering
of uraninite or other primary U minerals
⇨ This can produce a valuable indicator “gossan”
S. Wolfsried
Typical yellow gossan on pitchblende ore in granite
D. Wilton
Deposit types
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
(Source: Kyser and Cuney, 2008)
Uranium resource
By Country
By deposit type
(Source: Kyser, 2014)
Uranium resource
(Source: Wikipedia, 2014)
World U3O8 Production 2004 (T)
Source: Globe&Mail 11/02/06)
WORLD RESOURCES OF U
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Unconformity-Type U Deposits
in Canada and Australia
currently contain >33% of
World Resources
Olympic Dam MesoProterozoic
IOCG Deposit contains >31%
(but @ 0.03% U)
30,500
Younger sandstone-hosted
deposits in US, Kazhakstan &
Niger contain ~18%
after Jefferson et al, 2007
(Source: Kyser,2014)
PRODUCTION OF U
(Source: Kyser, and Cuney 2008)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
* Average crust: 1.7 ppm *
(Source: Kyser and Cuney, 2008)
Misra, 2002
From Cuney (2010)
U Deposits - AGE SIGNIFICANCE
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QPC-hosted Paleoplacers formed 2.8 - 2.2 Ga
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Paleosurface-related unconformity-type deposits most
abundant 2.0 - 1.5 Ga
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Base of Proterozoic sedimentary basins
Uraniferous black shales peak Cambrian-Devonian
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U persistent in surface placers due to more reducing
ocean and atmosphere conditions
Only a potential resource (≤100 ppm U3O8)
Sandstone-type (e.g., Southwest USA) are generally < 400Ma
RECOMMENDED READING
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Unconformity Associated U Deposits of the Athabasca
Basin; Jefferson et al. 2007, Kyser and Cuney 2008, Kyser
2014
Suppl_QPC&U-Solubility
Suppl_OlympicDam
(Source: Kyser and Cuney, 2008)
Conglomerate-Hosted “PaleoPlacer”
Conglomerate-Hosted “PaleoPlacer”
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Hosted by quartz-pebble Conglomerates (QPC) of L.
Archean - E. Proterozoic
⇨ Most are > 2.2 Ga
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Up to 0.2 % U3O8 – although virtually U-free, Au-bearing
examples exist (e.g., Jacobina, Brazil)
Typical host-conglomerate represents fluvial braided
stream deposit
Conglomerate-Hosted “PaleoPlacer”
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Conglomerate Matrix Mineralogy includes:
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quartz
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zircon, monazite, chromite, rutile, leucoxene (after
primary Ti-minerals)
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sericite, chlorite, chloritoid (after primary detrital
minerals)
Conglomerate-Hosted “PaleoPlacer”
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Typical Ore Mineralogy includes:
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uraninite, uranothorite
brannerite (Ti-association, authigenic)
pyrite (up to 20% of Conglomerate Matrix)
native gold
(Source: Kyser and Cuney, 2008)
Note Pyrite-rich
interstices between
pebbles. These also contain
U-minerals
“Paleoplacer” U in quartz pebble conglomerate.
Denison Mine, Eliot Lake, ON. GSC 1995-200A
Autoradiograph
“Paleoplacer” U in quartz pebble conglomerate.
Denison Mine, Eliot Lake, ON. GSC 1995-200A
Conglomerate-Hosted “PaleoPlacer”
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Only substantial U production has been from Elliot Lake &
Witswatersrand deposits
Witswatersrand deposits produce U at 0.03 % U3O8 as a
byproduct of mining 10 g/T Au
Much of it from ore horizons of only 0.1m to 1m thickness
Elliot Lake was a primary U producer with historical grade
~0.1% U3O8
‘Goldfields’ are Fluvial Fan
successions containing one or
more ‘Reefs’ - Basal
Conglomerate horizons with
economic concentrations of Au
Since 1886,Witswatersrand
Basin has produced 48,000
Tonnes of Au –
~ 35% of all Au ever produced
by Mankind
Major Goldfields (Vertical Bar Pattern) Hosted
by Witswatersrand Supergroup
Misra, 2002
Conglomerate-Hosted “PaleoPlacer”
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Interesting feature at Witwatersrand is the common
association of Au concentration with biogenic carbon at
the bottom contact of individual ore horizons
Interpreted as evidence of Au concentration by algal mats
at > 2.7Ga
“Carbon Leader Gold Ore” from Blyvooruitzicht Gold Mine, Carletonville Goldfield, West
Witwatersrand , South Africa. The Carbon Leader (aka Carbon Leader Reef or Carbon Leader Seam), is a carbonaceous
(kerogen + bitumen) interval (interpreted by some workers as stromatolitic) containing both
native gold and uraninite.
[Long dimension of photo is 2.1 cm]
photo: James St. John OSU-Newark
In addition to Au -Blyvooruitzicht
Mine also contains estimated
reserves of 251.2 Mt grading
0.025% U.
("Uranium in South Africa“,
wise-uranium.org. 2012)
Au and U Paleoplacers
READ Suppl-QPC&U-Solubility:
3.9.3 QPC-hosted Au Deposits (p 195-197)
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This is essentially a short summary by Robb (2005) of why
some workers believe that later hydrothermal processes
(similar to those for GQC Deposits) led to further Auenrichment at Witswatersrand
Bear in mind, however, that the initial enrichment in both
Au (Witwatersrand) and/or U (e.g., Eliot Lake) was almost
certainly due to a paleoplacer process
Edward Burtynsky, Uranium Tailings, No.12, Elliot Lake 1995
UNCONFORMITY-RELATED U DEPOSITS
Spatially associated with Unconformities between:
1. Proterozoic Siliciclastic Basins
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Relatively flat-lying, un-metamorphosed, and undeformed,
Late PaleoProterozoic to Mesoproterozoic, fluvial strata
Clastic sediments uncomformably deposited over highly
weathered Basement, in large Intracratonic Basins
2. Metamorphic Basement
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Tectonically interleaved Paleoproterozoic
metasedimentary & Archean-Proterozoic granitoid rocks
after Jefferson et al, 2007
DEFINITIVE CHARACTERISTICS
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U mineralization commonly associated with intersections
between unconformity & faults, shear zones and fracture
zones
Mineralization accompanied by alteration
⇨ Illite, Kaolinite/Dickite, Chlorite and Dravite (Na-Mg-rich
tourmaline)
after Ruzicka, 1996
MINERALIZATION
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Massive pods, veins & disseminations of uraninite
2 subtypes:
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Complex type (A.K.A. Sandstone-hosted, Monometallic, Claybounded, and Egress-type)
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Simple type (A.K.A. Basement-hosted, Polymetallic, Fracturecontrolled, and Ingress-type)
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Principally uraninite
Include Ni-Co-As minerals (+ trace Au, Pt, Cu) & base metal
sulphides, in addition to uraninite
Complex and simple refer mostly to the source of the fluids and metal
assemblages. Host rocks can be different. This is the main designator
of the complexity or simplicity of the deposits.
Summary of Key Features of U Deposits – Eastern Athabasca Basin
Jefferson et al,
2007
Unconformity-related
districts in Canada
Jefferson et al, 2007
ATHABASCA BASIN DEPOSITS
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Great majority of mines & prospects located where
Athabasca Group sediments unconformably overly
basement Western Wollaston & Wollaston-Mudjatik
Transition Domains (Eastern Margin)
Significant mined deposits & prospects in the Carswell
Structure (Cluff Lake Camp) - and new drill intersections
at Maybelle R. and Shea Ck. - demonstrate the potential
for deposits in the Western Athabasca Basin
after Jefferson et al, 2007
Regional Geology of the Athabasca Region
Kyser, 2014
478
Ma
Known Impact Structures in Saskatchewan
100 Ma
210 Ma
Although the Carswell impact occurred
well after primary ore formation, the
post-impact rebound/uplift of the
structure enhanced surface proximity of
several U deposits, including the Cluff
Lake District
Sask. Industry & Resources
Summary of some Athabasca Basin Deposits – by Depth
Deposits are found at, or near, the unconformity between: Athabasca
“sandstones” (<1.7 Ga) and crystalline basement (2.7 – 1.7 Ga)
(Source: Areva Resources Inc)
Manitou Falls Formation
McArthur River, SK
Basement rocks
McArthur River, SK
Mineralization
McArthur River, SK
ATHABASCA BASIN DEPOSITS
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Basin sediments have an extremely long history of
diagenetic and hydrothermal alteration
Main episodes of U mineralization occurred ca. 1.6 Ga
from migration of highly saline, oxidizing basinal brines at
180 – 240 °C
Several stage of U remobilization during far-field tectonic
events (e.i., Grenville Orogeny at ca. 1Ga, Assembly of
Rodinia at ca. 800Ma)
At least one later stage of U mineralization (fracture filling)
is attributed to the circulation of cool, dilute meteoric
waters (<50°C) at < 400 Ma
after Wasyliuk, 2006
Wasyliuk, 2006
Remobilization of U mineralization
Millennium Deposit
(Source: Cloutier et al., 2009)
Primary deposition
at 1590Ma
Style 1
(+”Perched Ore”
in overlying MF)
Complex Type
Style 2
Simple type
Dielmann (Key Lake) includes both
Basement-hosted and Unconformity Ore
Jefferson et al,
2007
Simple
type
Alteration Haloes
provide a valuable
exploration tool for
Simple Type Deposits
However Complex Type
shows no distinct
alteration halo in
overlying “Sandstone”
Complex
type
Note inversion of
alteration zoning
between the two styles
Simple- vs Complex Type Deposits in the Athabasca Basin
Jefferson et al,
2007
Current Unconformity-Related Models
Complex Type
Oxidizing
Basinal fluids
U
Complex type
+ As, Ag, Co, Cu, Mo,
Ni, Pb, Pt, Se
and Zn
Reducing
Basement fluids
Modified after Wilson and Kyser (1987), Kotzer and Kyser (1995) and Fayek and Kyser (1997)
Simple Type
Oxidizing
Basinal fluids
Oxidizing
Basinal fluids
U
Oxidizing
Basinal fluids
+ Ca
+ Mg, Fe
Modified after Alexandre et al. (2005)
+U
+U
Modified after Hecht and Cuney (2000), Derome et al. (2005)
ALTERATION MINERALOGY
Clay & Alteration Minerals (Athabasca Gp)
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Illite
K(Al,Mg,Fe)2(Si,Al)4O10(OH)2
Kaolin Group
[ Al4Si4O10(OH)8 Polytypes ]
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Chlorite Group
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Kaolinite, S-Kaolinite, Dickite
Mg-Chlorite, Fe-Chlorite
Sudoite
(Mg,Fe2+ )2Al3(Si,Al)4O10(OH)8
Tourmaline Group
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Dravite
NaMg3Al6B3Si6O27(OH)4
Magnesiofoitite Mg2(Al,Fe3+)Al6B3Si6O27(OH)4
ALTERATION MINERALOGY
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Portable SWIR (short-wave infrared reflectance
spectroscopy) instruments are now available for fieldmapping of alteration mineralogy
Capable of rapidly distinguishing the common clay minerals
of the Athabasca Basin – including the polytypes of the
kaolin group (dickite, kaolinite)
Spectral International
Inc.
Jefferson et al,
2007
Earle & Sopuck, 1989
Left hand map: alteration zones in
surficial material & Outcrop of the
Athabasca Group
Right hand map: % of samples with
illite/(illite+kaolinite) > 60% from
U/C+10m to top of Athabasca
Group
Regional illite, chlorite & dravite (B) Anomalies – SE Athabasca Basin
Wasyliuk, 2006
Alteration Zones Cross-Section – Cigar Lake
Wasyliuk, 2006
Alteration Zones Cross-Section – Deilmann (Key Lake)
Wasyliuk, 2006
Alteration Zones Cross-Section – McArthur R. (P2 North)
Generalized alteration models for
subtypes of simple deposits
These detailed cross sectional observations can be compiled in to
two end-member alteration models for simple type deposits.
1. Quartz dissolution type model
Jefferson et al,
2. Silicification type model
2007
Sandstone-Hosted U Deposits
If you get involved with Sandstone-Hosted Type U Deposits it is
worth reading:
3.11.2 Sandstone-Hosted Uranium Deposits (p210-214) in
Suppl_QPC&U-Solubility
But, for now, I am saving the details of this type, including the
important class of “Roll Front” U deposits, for the 4th Year
Class
Wardle, 2005
LABRADOR U DEPOSITS
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The most developed U prospects lie in the eastern part of
the Central Mineral Belt (CMB), in and around the
Makkovik Province terrane
These include the Kitts and Michelin Deposits, discovered
in 1956 and 1968, respectively.
BRINEX developed these two prospects, and developed a
plan in 1978-79 to mine them as a combined operation …..
then U prices collapsed.
after Wardle, 2005
Figure 2. Uranium occurrences of the Central Mineral Belt and surrounding region, highlighting examples discussed in this
report. Geological base map modified from Wardle et al. (1997).
where they were reworked by Paleoproterozoic deformation
and metamorphism. These reworked Archean rocks likely
form the basement to much of the Makkovik Province and
Sparks and Kerr
(2009)
sive suite, and older units, are in turn cut by fresh diabase
dykes known as Kikkertavak dykes, which are dated precisely at ca. 2230 Ma (Cadman et al., 1993).
G.W. SPARKES AND A. KERR
bolites within the Makkovik Province, but locally retain
their original discordance with Archean host rocks (Ryan et
al., 1983). Deformed and metamorphosed supracrustal
rocks, likely equivalent to the Post Hill Group also occur
Group sits unconformably upon Archean basement rocks,
but the more strongly deformed and metamorphosed Post
Sparks and Kerr
Hill group is in tectonic contact with these older rocks. The
Post Hill group is strongly deformed and disrupted
by shear
(2009)
Principal U Deposits of Labrador Central Mineral Belt
Wardle, 2005
A recent exploration boom
•
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During mid- to late-2000s (2004-2009) there was a major
staking rush and exploration boom for U.
Resulted in numerous new discoveries and associated
research.
•
•
Jacques Lake, Two Time.
Expansion of existing resources at Moran Lake and
Michelin.
Figure 2. Uranium occurrences of the Central Mineral Belt and surrounding region, highlighting examples discussed in this
report. Geological base map modified from Wardle et al. (1997).
where they were reworked by Paleoproterozoic deformation
and metamorphism. These reworked Archean rocks likely
form the basement to much of the Makkovik Province and
Sparks and Kerr
(2009)
sive suite, and older units, are in turn cut by fresh diabase
dykes known as Kikkertavak dykes, which are dated precisely at ca. 2230 Ma (Cadman et al., 1993).
LABRADOR U DEPOSITS
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Michelin (and Burnt Lake & Rainbow) are hosted by
rhyolitic ash-flow tuffs of the Aillik Group
At Michelin, uraninite mineralization is associated with
widespread Na-metasomatism and localized hematization
of these host rocks.
At Jacques Lake similar mineralization style is hosted in
volcanic conglomerates with andesitic compositions.
Sparks and
Kerr (2009)
Michelin, Labrador
Michelin, Labrador
Jacques Lake, Labrador
LABRADOR U DEPOSITS
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The Kitts-Post Hill Belt contains the rocks of the Post Hill
Group
Uranium mineralization is found throughout the belt
adjacent to major dissecting shear zones
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Occurs as veinlets & shear-fillings in reduced units
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Kitts, Inda, Gear and Nash deposits
Po-rich graphitic argillite, iron formation & mafic
metavolcanics
Uraninite occurs associated with pyrite, minor base metal
sulphides & hematite alteration.
after Wardle, 2005
Figure 2. Uranium occurrences of the Central Mineral Belt and surrounding region, highlighting examples discussed in this
report. Geological base map modified from Wardle et al. (1997).
where they were reworked by Paleoproterozoic deformation
and metamorphism. These reworked Archean rocks likely
form the basement to much of the Makkovik Province and
Sparks and Kerr
(2009)
sive suite, and older units, are in turn cut by fresh diabase
dykes known as Kikkertavak dykes, which are dated precisely at ca. 2230 Ma (Cadman et al., 1993).
Sparks and
Kerr (2009)
Figure 5. Generalized plan view and northwest-southeast cross-sections through the Kitts deposit, illustrating the general
geometry of the mineralization and presence of post-mineralization intrusive rocks; based on work in the 1970s, modified from
Moran Lake
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Occurs in both Bruce River and Moran Lake groups.
Hosted predominantly in conglomerates parallel to Bruce
River Group - Moran Lake Group unconformity.
Hosted by “reduced” zones in the conglomerates. Also
get uraninite-carbonate veins.
Also get brecciated basaltic units with hematite alteration
and uraninite (Moran Lake C Zone).
Associated with V2O5.
Figure 2. Uranium occurrences of the Central Mineral Belt and surrounding region, highlighting examples discussed in this
report. Geological base map modified from Wardle et al. (1997).
where they were reworked by Paleoproterozoic deformation
and metamorphism. These reworked Archean rocks likely
form the basement to much of the Makkovik Province and
Sparks and Kerr
(2009)
sive suite, and older units, are in turn cut by fresh diabase
dykes known as Kikkertavak dykes, which are dated precisely at ca. 2230 Ma (Cadman et al., 1993).
Moran Lake
CURRENT RESEARCH, REPORT 08-1
Figure 6. Partly schematic cross-section through the area of the Moran Lake C-Zone uranium deposits, showing thrusts
inferred to repeat the basal contact of the Bruce River Group above the Moran Lake Group; modified after diagrams released
on the Crosshair Exploration and Mining website.
Radioactivity is reported from quartzite and conglomerate of the Seal Lake Group at the Stormy Lake showing, a
Sparks and
that are characterized by possible iron-rich alteration and
Kerr (2009)
metasomatism. The host rocks at these prospects are dis-
Moran Lake
G.W. SPARKES AND A. KERR
Plate 6. Representative photographs of mineralization hosted by sedimentary rocks of the Bruce River Group. A) Host rocks
to the Moran Lake Lower C-Zone deposit, showing oxidized (red) and reduced (grey-green) areas; uranium mineralization is
associated mostly with the latter, as indicated. B) Mineralized chlorite–sericite-rich shear zone cutting the sandstone host
rocks of the Moran Lake Lower C-Zone deposit, indicating local remobilization of uranium. C) Discrete zones of uranium mineralization associated with strong hematization of medium- to coarse-grained sandstone, Moran Lake B-Zone prospect. D)
Strongly sheared pebble conglomerate hosting uranium mineralization associated with sericite-pyrite alteration, Moran Lake
A-Zone prospect.
ated within a thrust sheet that is dominated by mafic pillow
lavas of the Moran Lake Group (Joe Pond Formation), with
lesser amounts of argillitic sedimentary rocks (Warren
Creek Formation). This contrasts with the previous interpre-
Sparks and
Kerr (2009)
and deep-red, intensely hematized rocks that appear essentially featureless. LaCroix and Cook (2007) describe these
as "jasper and chert", but their gradational boundaries with
recognizable basalts are also consistent with them being the
CURRENT RESEARCH, REPORT 08-1
Moran Lake
Plate 7. Representative photographs of uranium mineralization and associated breccia textures at the Moran Lake Upper CZone deposit. A) Mineralized material, showing intense hematite alteration and early brecciation cut by later zones of brecciation associated with chalcopyrite. The exact location of the uranium mineralization in this sample is not presently known.
B) Hematite-rich mineralized breccia cut by a later fracture that contains high-grade uranium mineralization. Note also
extensive carbonate that postdates the hematite alteration. C) Spectacular breccia zone with hematite and carbonate-rich
matrix surrounding strongly altered fragments of uncertain protolith. The fragments appear to have been "milled", suggesting mechanical erosion during interaction with hydrothermal fluids. D) Unbrecciated and locally mineralized host rocks from
the Moran Lake Upper C-Zone deposit, which are in part of volcanic origin. Localized hematite alteration in the upper part
of photo is not associated with strong radioactivity, but the intensely hematitic material in the lower part contains high-grade
mineralization.
mafic rocks, but the full extent of such alteration remains to
Sparks and
Ag over 1.0 m. Individual assays contain up to 0.63% CuKerr (2009)
Two Time Zone
•
•
•
Mineralization in brecciated granites of the Archean Nain
Province.
Get uranium mineralization with hematite alteration.
Also get chlorite and quartz alteration.
Figure 2. Uranium occurrences of the Central Mineral Belt and surrounding region, highlighting examples discussed in this
report. Geological base map modified from Wardle et al. (1997).
where they were reworked by Paleoproterozoic deformation
and metamorphism. These reworked Archean rocks likely
form the basement to much of the Makkovik Province and
Sparks and Kerr
(2009)
sive suite, and older units, are in turn cut by fresh diabase
dykes known as Kikkertavak dykes, which are dated precisely at ca. 2230 Ma (Cadman et al., 1993).
Two Time Zone
CURRENT RESEARCH, REPORT 08-1
Plate 8. Representative photographs of uranium mineralization at the Two-Time Zone. A) Outcrop of well-developed, mineralized hydrothermal breccia, reminiscent of "tuffisite" textures developed in some high-level plutonic rocks. B) Pervasive fracturing and localized brecciation developed within granitoid rocks of the Kanairiktok intrusive suite, marginal to a mineralized zone. C) More extensive brecciation associated with higher grade mineralization, showing fragments of altered granitoid
rocks in a chlorite–hematite-rich matrix. D) Contact of a post-mineralization mafic dyke (dark material); intense hematization and elevated radioactivity at the dyke contact is considered to reflect local remobilization of uranium from the surrounding mineralized granitoid rocks.
This short section summarizes existing geochronologi-
which these were based. The oldest near-concordant U-Pb
CURRENT RESEARCH, REPORT 08-1
Sparks and Kerr
Figure 3. Schematic chart showing the stratigraphic setting of uranium mineralization in the Central Mineral Belt
of
(2009)
OLYMPIC DAM Cu-Au-U DEPOSIT
“IOCG/Breccia” type
Location of Olympic Dam Deposit
Supergiant Cu-Au-U Deposit
Middle Proterozoic Host Rocks
Gawler Craton, South Australia
Reynolds, 2000
Olympic Dam Deposit
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Supergiant Cu-Au-U-Ag Deposit
~ 1.59 Ga based on Host Rock Age
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Stuart Shelf Province of South Australia
Hosted in large hydrothermal breccia complex wholly
within Proterozoic Roxby Downs Granite (Hiltaba Suite
Intrusions)
Complex multi-stage hydrothermal alteration
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hematite + sericite
+ (chlorite + siderite + quartz)
Olympic Dam Deposit
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Mineralization intimately associated with hematite
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( & with magnetite at outer margins of breccia
complex)
Hypogene ore zonation (laterally & vertically within breccia
complex)
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Cpy (on margins) ⇨ Bornite ⇨ Chalcocite ⇨
Barren Core Zone (Hematite-Qz Breccia)
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Au & Ag associated with Cu sulphides
Pitchblende disseminated throughout hematitic breccia
zones
Ore-hosting Lithology
Simplified Subsurface Geology of Olympic Dam Deposit
Robb, 2005; after Haynes et al,
1995
Presence of overlying basalt and
volcanic complex in this model of
Hynes et al (1995) are speculative –
all that remains after erosion is the
breccia complex within the Roxby
Downs Granite (+ minor vestiges of
largely felsic volcaniclastic rocks).
To date, there a number of competing
models for the genesis of this rather
unique deposit.
Robb, 2005
McPhie et al. (2011)
Olympic Dam Deposit
READ SupplOlympicDam:
Box 3.1 Olympic Dam
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(p157-158) - posted online.
A decent short description of the deposit
Bear in mind that he presents only the Haynes et al (1995)
model – which is just one of many existing hypotheses for
Olympic Dam
Olympic Dam Deposit
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Reserves + resources (WMC, 1999):
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2,320 Mt
1.3 % Cu
0.03% U
0.5 g/T Au, 2.9 g/T Ag
By any measure, a super-giant deposit
“Olympic Dam-type deposit” therefore represents an
extremely attractive exploration target
Olympic Dam Deposit
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Olympic Dam is considered the flagship example of an
IOCG deposit……………
What is an IOCG Deposit?
IOCG DEPOSITS
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IOCG: Iron Oxide Copper-Gold
“This class ……. does not represent a single style or a
common genetic model, but rather a family of loosely
related ores that share a pool of common characteristics.
The principal feature they have in common is the
abundance of iron oxides that accompany the
ore…………..”*
*T.M. Porter, 2000 in the introductory chapter to “Hydrothermal
Iron-Oxide Copper-Gold and Related Ore Deposits: A Global
Perspective”, Australian Mineral Foundation, Adelaide, 2000
From Williams et al. (2005)
IOA Deposits
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Cousins of IOCG but have iron oxides with apatite, with or
without Cu-Au-Ag and U.
Sometimes have REE.
Type examples are Kiruna, Sweden and Adirondacks,
USA.
IOA Deposits
From Jonnson et al. (2013)
Olympic Dam Mine Complex
Western Mining Corp