"Broken Hill 1:250000 metallogenic special and revised metamorphic facies-isograd maps". Dr Joel Fitzherbert, Senior Geoscientist, Geological Survey of New South Wales

1. Broken
Hill
1:250
000
metallogenic
special
&
Refined
metamorphic
facies-­‐isograd
maps
Joel Fitzherbert
Peter
Downes,
Phil
Blevin
and
David
Forster

2. This
talk
• Current
series
of
GSNSW
metallogenic
maps
• Broken
Hill
1:250
000
– Concept
and
components
• Refined
metamorphic
facies/isograd
maps
• ApplicaEon
of
isograd
maps
to
mineral
systems
• Current
and
future
GSNSW
work
in
the
Broken
Hill

3. Current
metallogenic
map
series
Each
map
to
highlight
key
aspects
of
the
geology
relevant
to
that
area.
e.g.
Bathurst
–
Ord
volcanism
Review
data
on
individual
deposits
to
beNer
classify
them.
New
data
acquired
and
integrated
into
the
deposit
datasets
Mineral
deposits
classified
according
to
the
mineral
systems
of
New
South
Wales
Updated
Eme
space
plot
that
includes
the
main
mineralising
events
Back
of
the
map
to
highlight
mining
history
and
geology

4. Broken
Hill
1:250
000
Concept
and
components

5. Broken
Hill
1:250
000
Concept
Detailed
mapping,
but
lack
of
a
summary
map
Recent
daEng/straEgraphic
relaEons
in
posters/papers

6. Broken
Hill
1:250
000
Concept
DiagrammaEc
representaEon
ReproducEon
of
Phillips
(1978)

7. • Complex
geology
at
1:250
000
– Highlights
the
Purnamoota
Subgroup
• Hores
Gneiss
• Silver
King
Metadolerites
• Olarian
intrusive
phases
removed
• Simplified
version
of:
– Broken
Hill
StraEgraphic.
Willis
(1989)
– InterpretaEon
of
Broken
Hill
1:25
000
map
series
Stevens
(2009)
– 1:100
000
scale
interpreEve
Proterozoic
geology
GSNSW
(2009)
– Includes
undercover
interpretaEon
– Cover
sequences
GA
1
million
• Transparent,
sEppled
Broken
Hill
1:250
000
components

8. • First
complete
Eme-­‐space
plot
• Updated
geology
and
daEng
– Stevens
(2008)
– Dutch
et
al
(2006)
– GSNSW
(2009)
• AddiEon
of
mineral
deposits
against
Eme
• AddiEon
of
tectonic
interpretaEon
against
Eme
Broken
Hill
1:250
000
components

9. • Two
1:500
000
scale
insets
for
Olarian
and
Delamerian
Isograd/
facies
maps
• Commodity
plots
for
mineral
occurrences
interpreted
to
be
associated
with
each
orogenic
event
• Olarian
inset
includes
• Olarian
intrusive
phases
• Delamerian
– Post
Olarian
dykes
and
intrusions
– Delamerian
structure
Broken
Hill
1:250
000
components

10. Broken
Hill
1:250
000
components

11. Broken
Hill
1:250
000
SupporEng
info

12. Metamorphic
facies/isograd
maps
Olarian
c.
1600
Ma
Delamerian
c.500
Ma
Isograds/facies
broadly
parallel
to
straEgraphy
In
a
broad
sense
isograds
are
rotated
around
regional
F2
structures.
Higher-­‐T
zones
broadly
reflect
higher-­‐T
zones
in
the
Olarian
Isograds
crosscut
straEgraphy
Mineral
zones:
Staurolite
Staurolite
+chloritoid
Chloritoid
Facies
maps:
Upper-­‐greenschist
Amphibolite
Granulite
Isograds:
BioEte
Sillimanite
Sillimanite+Kspar
Othopyroxene
Key
aspects

13. Drill
Core
Metamorphic
facies/isograd
maps
ConstrucEon
Field
Traverses
Petrographic
re-­‐evaluaEon
Previous
work
Petrographic
database

14. Polymetamorphism/deformaIon
• MulEply
deformed
terrane
– At
least
2
peak
and
2
retrograde
events
• MulEple
thermal
highs
– Up
to
four
generaEons
of
aluminosilicate
• MulEple
retrograde
events
– At
least
two
at
similar
P-­‐T
condiEons
Stratabound
nature
of
the
field
gradient
&
composiIonal
heterogeneity
• Increased
grade
ocen
corresponds
with
changing
mineralogy
• Group-­‐scale
heterogeneity
– albite
rocks,
pelite,
psammite,
granite,
dolerite,
felsic
volcanic,
carbonaceous
• Within-­‐group
heterogeneity
– Example
of
basic
rocks
• EvoluEon
to
high
FeO-­‐type
• Control
on
index
minerals
Metamorphic
facies/isograd
maps
ConstrucEon
issues

15. Orthopyroxene
isograd
(metabasite
composiEon)
High
FeO
Broken
Hill
Group
High
MgO+CaO
Thackaringa
Group
VariaEon
between
two
main
composiEonal
types
Metamorphic
facies/isograd
maps

16. Metamorphic
facies/isograd
maps
(Sillimanite
+
K-­‐feldspar
isograd)
Hardest
isograd
to
map
Phillips
(1978)
Sillimanite+K-­‐feldspar
Burton
(2001)
Sillimanite+parEal
melt

17. Applying
facies/isograd
maps
to
mineral
systems
Commodity
Versus
Metamorphic
grade
Commodity
over
metamorphic
grade
AddiEon
of
Olarian
intrusive
phases
-­‐
PegmaEte
(D1)
-­‐
Mundi
Mundi
granite
AssociaEon
with
metamorphic
facies
zones
and
isograds
-­‐
Amphibolite
facies
-­‐
Between
orthopyroxene
and
sillimanite-­‐K-­‐feldspar
isograds
Apparent
straEgraphic
control
on
pegmaEte
-­‐
Stevens
(1978)
But….

18. Applying
facies/isograd
maps
to
mineral
systems
An
example:
Hores-­‐type
W
and
Waukeroo-­‐type
Sn
Yanco
Glen
(W)
Waukeroo
(Sn)
Euriowie
(Sn)
Kantappa
(Sn)
PegmaEte/quartz
vein
hosted
Stratabound
W
Hores
Gneiss
Sn
Paragon
Euriowie
1582
+/-­‐
16
Ma
(Cassiterite)

19. Applying
facies/isograd
maps
to
mineral
systems
An
example:
Hores-­‐type
W
and
Waukeroo-­‐type
Sn
Stevens
(2006)
Sill/dyke
complex
in
amphibolite
facies
Yanco
Glen
(W)
Waukeroo
(Sn)
Euriowie
(Sn)
Kantappa
(Sn)
Upper
pegmaEte
field
(upper
greenschist
facies)
Metamorphic
field
gradient
is
essenIally
stratabound
Intrusive
phases
are
essenIally
stratabound
Pooled
at/close
to
the
wet
solidus
Syn
to
post
D1

20. Applying
facies/isograd
maps
to
mineral
systems
An
example:
Hores-­‐type
W
and
Waukeroo-­‐type
Sn
Sawyer
(1998)
Fitzherbert
(1998)
Pooling
small
volume
melt
batches
at
or
below
solidus.
Level
of
the
Hores
Gneiss
Small
fracEonated
melt
batches,
enriched
in
fluxing
elements
(F,
Li,
B)
Amblygonite
(Li,
F)
FlouroapaEte
(F)
Lepidolite
(Li)
Tourmaline
(B)
Depressed
solidus
rises
considerably
higher
levels
in
the
Paragon
Group

21. Applying
facies/isograd
maps
to
mineral
systems
An
example:
Hores-­‐type
W
and
Waukeroo-­‐type
Sn

22. Applying
facies/isograd
maps
to
mineral
systems
An
example:
Hores-­‐type
W
and
Waukeroo-­‐type
Sn
Blevin
(1998)

23. Applying
facies/isograd
maps
to
mineral
systems
Further
applicaEon
Mundi
Mundi
Suite
(1590-­‐1580
Ma)
Equivalents
of
Bimbowrie
Supersuite
rocks
Iron
Duke
Type
breccias
Fe
+/-­‐
U
Amphibolite
facies
and
shallower
Larger
plutons
greenschist
facies
In
Broken
Hill,
just
see
the
eastern
edge
of
the
extensive
late
syn-­‐
to
post-­‐Olarian
magmaEc
event
(1590-­‐1580
Ma).

24. Applying
facies/isograd
maps
to
mineral
systems
Curnamona
wide
Isograds
of
Webb
and
Crooks
(2005)
Mundi
equivalent
Bimbowrie
Supersuite
Located
in
the
amphibolite
facies
and
above.
Main
zone
straddles
the
andalusite
sillimanite
isograd
IOCG
associaEon

25. Applying
facies/isograd
maps
to
mineral
systems
What’s
lec?
Other
possibiliEes
Melts
and
volaEle
phase
separaEon,
prograde
metamorphic
fluids,
retrograde
metamorphic
fluids
ParEal
melEng
DehydraEon
Retrograde
H2O
addiEon

26. Applying
facies/isograd
maps
to
mineral
systems
Retrograde
isograds
• ExhumaEon
of
Palaeoproterozoic
• Weathering
• Focused
hydraEon
along
pre-­‐exisEng
faults/shears
OR
Neoproterozoic
basinal
faults
• ?Neoproterozoic
burial
metamorphism
– Under
as
much
as
?15
km
of
Neoproterozoic.
– Isogads
developed
– Dutch,
Hand,
Clark,
Raimondo
et
al…
– Staurolite
isograd
~500oC
• Delamerian
Orogeny
– ReacEvaEon
of
hydrous
zones
as
schist
zones.
– Further
shortening
– ExhumaEon?
Dutch
et
al
(2006)

27. Applying
facies/isograd
maps
to
mineral
systems
Example:
Moderate-­‐T
retrograde
fluids
Retrograde
fluids?
Appear
to
be
replacement
of
a
granulite
facies
fabric

28. Applying
facies/isograd
maps
to
mineral
systems
Low
–T
retrograde
(Thackaringa)
CommodiEes
over
Delamerian
isograds.
Thackaringa
Type
siderite-­‐quartz
veins
Arcuate
zone
of
shear
zone
hosted
veins
centered
around
Broken
Hill
Broadly
parallel,
but
transgress
Delamerian
field
gradient
to
south
AlteraEon
and
fluid
inclusions
150-­‐200°C
(Dong
et
al
(1987)
Reid
et
al
(2009).
Not
stratabound
–
low
metamorphic
grade

29. Aim:
-­‐ Characterise
the
thermal
response
of
medium-­‐
to
high-­‐grade
regional
metamorphism.
-­‐ BeNer
characterise
mineralisaEon
and
alteraEon
in
the
Broken
Hill
area.
SelecIon
criteria:
-­‐ Cover
all
of
peak
Olarian
metamorphic
zones
-­‐ Focus
on
short
holes
that
have
similar,
but
variable
rock
types.
-­‐ Cover
the
straEgraphic
variaEon.
-­‐
Represent
or
sample
areas
of
known
mineralisaEon
-­‐ Sample
the
Delamerian
retrograde
schist
zones.
Current
&
future
studies
in
Broken
Hill
GSNSW
Broken
Hill
core
hylogger
project

30. Visible
and
near
infrared
(VNIR)
400
-­‐
1000
nm
Iron
oxides
e.g.
hemaEte,
goethite,
jarosite
REE
oxide
minerals
Shortwave
Infrared
(SWIR)
1000
-­‐
2500
nm
OH
bearing
minerals
Clays,
phyllosilicates,
amphiboles,
sulphates
Carbonates
Mid
or
Thermal
Infrared
(MIR
or
TIR)
8000
-­‐
12000
nm
Silicates
e.g.
quartz,
feldspar,
garnet,
pyroxene
Spectral
regions
relevant
to
geology
(&
Hylogger)
Thermal (TIR)
Broken
Hill
required
addiEon
of
new
minerals
to
the
spectral
library
e.g.
kyanite,
sillimanite,
staurolite
Current
&
future
studies
in
Broken
Hill
GSNSW
Broken
Hill
core
hylogger
project

31. 5000m
of
core
has
been
hylogged
and
will
be
complimented
by
a
petrographic
study
including
mineral
chemistry:
-­‐
Style
of
mineralisaEon/alteraEon
-­‐
Timing
of
mineralisaEon/alteraEon
-­‐
RelaEonship
to
metamorphism?
If
not
can
we
see
through
the
effects
of
metamorphism?
Black
Prince
Current
&
future
studies
in
Broken
Hill
GSNSW
Broken
Hill
hylogger
project

32. Future
Work
Pb/S
Isotopes
• CollecEon
of
samples
from
areas
peripheral
to
the
main
line
• Any
well
located
samples
would
be
appreciated
DaEng
• DaEng
of
metamorphism/
alteraEon/mineralisaEon
• Early
metamorphic
assemblages