C O M M O N W E A L T H OF A U S T R A L I A
DEPARTMENT
OF NATIONAL
BUREAU OF MINERAL RESOURCES,
DEVELOPMENT
GEOLOGY
A N D
GEOPHYSICS
REPORT No. 114
Geology of the Mount Woodcock 1-mile Sheet Area, Tennant Creek, N.T. BY
D . DUNNET AND R . R . HARDING
Issued under the A uthority of the Hon. David Fairbairn Minister for National 1967
S55< R
EP
9A) 6
BMR
Development
COMMONWEALTH
OF A U S T R A L I A
DEPARTMENT OF NATIONAL DEVELOPMENT BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS
REPORT No. 114
Geology of the Mount Woodcock 1-mile Sheet Area, Tennant Creek, N.T. BY
D. DUNNET AND R. R. HARDING
Issued under the A uthority of the Hon. David Minister for National 1967
Development
Fairbairn
C O M M O N W E A L T H
D E P A R T M E N T
O F
A U S T R A L I A
O F N A T I O N A L
D E V E L O P M E N T
MINISTER: T H E HON. D A V I D FAIRBAIRN, D . F . C . ,
M.P.
SECRETARY: R . W \ B O S WELL
B U R E A U O F M I N E R A L
RESOURCES,
G E O L O G Y A N D
D I R E C T O R : J. M .
GEOPHYSICS
RAYNER
THIS R E P O R T W A S P R E P A R E D IN T H E G E O L O G I C A L B R A N C H ASSISTANT DIRECTOR: N .
Published
H.
by the Bureau of Mineral Resources, Canberra
A.C.T.
FISHER
Geology and
Geophysics
CONTENTS
Page SUMMARY
o.
INTRODUCTION
..
..
..
1
„.
3
Location
3 o*
Access Previous Investigations
„,
H i s t o r y of M i n i n g a n d P r o d u c t i o n Physiography STRATIGRAPHY ARCHAEAN PROTEROZOIC
.„
<»• ,
••
3
.
<,.
4
0
4
0
„.
..
.•
..
5
..
..
. •.
.
..
7
..
e o
Warramunga Group
7
..
C o r r e l a t i o n in t h e W a r r a m u n g a G r o u p Bernborough-Whippet Sequence
„.
..
5
..
.
.
.
,
8 9 9
Bernborough Formation
..
10
Sequences overlying the Bernborough F o r m a t i o n
„.
12
..
13
••
15
Orlando Sequence
8 8
Porphyroidal Rocks Northern Star Sequence
14 o a
C o r r e l a t i o n of t h e W a r r a m u n g a G r o u p S e q u e n c e s
. . 1 7
S t r a t i g r a p h y of t h e M a r i o n R o s s S h e e t A r e a Tomkinson Creek Beds PALAEOZOIC
„.
19 ••
19 o.
„.
21
Cambrian CAINOZOIC
21 ..
a o
..
IGNEOUS ROCKS
22 23
Granitic Rocks and Porphyries
».
23
P o r p h y r i e s of t h e B e r n b o r o u g h M i n e A r e a
.„
24
Schorl Rock
„•
..
24
Gabbro and Dolerite
..
..
24
ROCKS ASSOCIATED WITH GOLD AND C O P P E R MINERALIZATION Ironstones
a
.
Jaspers
9
.
Quartz Veins
n
.
.. ..
26 • • 2 6
..
27 27
iv Page STRUCTURAL GEOLOGY
28
PHASE 1 FOLDING
..
PHASE 2 FOLDING
..
„.
31
PHASE 3 FOLDING
..
o c
Quartz Hill Subarea
29
..
32
..
, . 3 2
Fold Styles
36
Orlando Subarea
0
.
36
Q u e e n of S h e b a S u b a r e a
o a
Northern Star Subarea
a o
Whippet Subarea
..
37 . . 3 7
..
DISCUSSION AND T E C T O N I C D E V E L O P M E N T
39 ..
39
C O R R E L A T I O N O F S T R U C T U R E , S T R A T I G R A P H Y , AND M A G N E T I C P A T T E R N S 40 GEOCHEMISTRY Sampling
..
..
..
..
.. ..
42
Analysis
. . 4 2
Results
.o
..
««,
42
S t a t i s t i c a l T r e a t m e n t of I r o n s t o n e R e s u l t s
. . 4 3
Second O r d e r Anomalies
..
„.
Soil S a m p l e A n o m a l i e s
..
..
Discussion
..
ECONOMIC GEOLOGY
«.
48 48
..
..
48
Northern Star Mine
.. ..
..
..
Q u e e n of S h e b a M i n e
..
..
„.
Other Mines
„
RECOMMENDATIONS
..
.»
48 49 . , 4 9
«.
8
REFERENCES ..
45
..
Orlando Mine
APPENDIX 1
41
..
49
.
50
..
51
..
..
53
TABLES Page 1.
Stratigraphy, Tennant Creek area
2.
Stratigraphy, Warramunga Group
3.
Stratigraphy, Bernborough-Whippet Sequence
4.
Type section, Bernborough Formation
5.
Stratigraphy, Orlando Sequence
ot>
„.
6 .
„
.«, c
.
9 9
.
11
..
, . 1 3
v PLATES Page P l a t e 1, fig.
fig.
Typical topography in the Orlando Mine a r e a
,.
..
54
Group, Butchers Creek area P l a t e 2, fig.
L o a d c a s t s o n b a s e of f i n e - g r a i n e d g r e y w a c k e b e d , G o l d e n Slipper Mine a r e a
fig-
55
S m a l l h e m a t i t e d y k e i n a n S^ s h e a r - p l a n e , 1 m i l e n o r t h of Orlando Mine
P l a t e 3 , fig. fig.
55
P h a s e 2 folds in a s i l t s t o n e / s h a l e s e q u e n c e a t the Klondyke M i n e T e c t o n i c c o n g l o m e r a t e f o r m e d by s h e a r i n g p a r a l l e l to S S'.
P l a t e 4, f i g .
..
56
C r e n u l a t i o n c l e a v a g e (S^) i n a t h i n l y b e d d e d s e q u e n c e , Q u a r t z 57
Tight chevron style p h a s e 3 folds with one s h e a r e d limb, Orlando subarea
57
Geological m a p , Mount Woodcock Sheet a r e a , s c a l e :
Plate 5
56
and
Hill s u b a r e a fig.
54
T y p i c a l i n t e r b e d d e d f l a g g y g r e y w a c k e a n d s h a l e of t h e W a r r a m u n g a
1 : 6 3 , 3 6 0 A t b a c k of R e p o r t
FIGURES 1.
C o r r e l a t i o n of t h e W a r r a m u n g a G r o u p s e q u e n c e s
18
2.
S t r u c t u r a l g e o m e t r y of t h e M o u n t W o o d c o c k S h e e t a r e a
30
3.
P h a s e 3 fold s t y l e s
33
4.
G e o m e t r y of p h a s e 3
34
5.
Mount Woodcock/Tennant C r e e k , structural
6.
G e o m e t r y of t h e M o u n t W o o d c o c k 1 - m i l e S h e e t a r e a
..
38
7.
Bishop Creek/Mount Woodcock, regional geochemistry
44
8a.
C u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n of c o p p e r , c o b a l t , a n d z i n c i n
subareas
35
Tennant Creek ironstones 8b.
C u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n of l e a d , m o l y b d e n u m , a n d b i s m u t h in Tennant C r e e k i r o n s t o n e s
8c.
ironstones 8d.
46
F r e q u e n c y d i s t r i b u t i o n p o p u l a t i o n s of c o p p e r i n T e n n a n t C r e e k ..
..
F r e q u e n c y d i s t r i b u t i o n c u r v e c o m p o n e n t s for c o p p e r , T e n n a n t Creek ironstones
9a.
C u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n of c o p p e r , c o b a l t , a n d z i n c in Tennant C r e e k soil s a m p l e s
9b.
C u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n of l e a d , m o l y b d e n u m , and bismuth in Tennant C r e e k soil samples
47
SUMMARY T h e M o u n t W o o d c o c k 1 - m i l e S h e e t a r e a l i e s i m m e d i a t e l y n o r t h of t h e T e n n a n t Creek
1-mile
Sheet
area
(Crohn
& Oldershaw,
w e a t h e r i n g r a n g e s f r o m 200 t o 700 f e e t .
1965).
O u t c r o p i s p o o r a n d t h e d e p t h of
T h e t o p o g r a p h i c r e l i e f i s 300 feet.
The area contains Proterozoic,
Palaeozoic, and Cainozoic rocks.
The Proter-
ozoic rocks comprise the Warramunga Group (Lower Proterozoic) and the Tomkinson Creek B e d s (probably Carpentarian).
T h e W a r r a m u n g a G r o u p i s probably about 12,000 feet thick:
it
c o n s i s t s of s h a l e , g r e y w a c k e , s a n d s t o n e , v o l c a n i c s , s i l t s t o n e , p o r p h y r o i d a l r o c k s , a n d h e m a tite shale.
T h r e e s e q u e n c e s , s e p a r a t e d by faults, h a v e b e e n m a p p e d on the Mount Woodcock
Sheet a r e a , and c o r r e l a t i o n between them is tentative.
T h e m o s t likely c o r r e l a t i o n indicates
that the r o c k s a r e partly older than and partly equivalent to the s e q u e n c e in the Tennant C r e e k Sheet a r e a . The Bernborough F o r m a t i o n , c o m p r i s i n g greywacke,shale, siltstone, and volcanics, a n d t h e W h i p p e t S a n d s t o n e M e m b e r a r e n e w u n i t s w h i c h o c c u r n e a r t h e b a s e of t h e s e q u e n c e . The
T o m k i n s o n C r e e k B e d s ( f o r m e r l y t h e A s h b u r t o n Sandstone) r e s t u n c o n f o r m a b l y on t h e
Warramunga
Group.
T h e y c o n s i s t of c o n g l o m e r a t e , s a n d s t o n e , f e l d s p a t h i c s a n d s t o n e , a n d
s i l t s t o n e , a n d a r e t e n t a t i v e l y c o r r e l a t e d with t h e H a t c h e s C r e e k G r o u p in t h e D a v e n p o r t R a n g e s and
the
Tawallah
Group
in the C a r p e n t a r i a B a s i n .
A s e q u e n c e of t h i n C a m b r i a n b r e c c i a ,
v o l c a n i c s , g r i t , a n d s i l t s t o n e r e s t s u n c o n f o r m a b l y on W a r r a m u n g a G r o u p in t h e e a s t . two-thirds
of t h e S h e e t a r e a
About
i s c o v e r e d by a fine y e l l o w - b r o w n , b r o w n , o r r e d - b r o w n dust,
and alluvial sand and silt.
part;
it
The
Tennant
includes
four
even-grained,
Creek
main
and aplitic.
A
Granite
Complex
extends
into
the central and southern
t y p e s of g r a n i t e - g n e i s s i c p o r p h y r i t i c , m a s s i v e p o r p h y r i t i c , smaller
complex
near
the Bernborough Mine includes four
i n t r u s i o n s r a n g i n g from q u a r t z - h o r n b l e n d e - f e l d s p a r p o r p h y r y to flow-banded q u a r t z p o r p h y r y . A q u a r t z - t o u r m a l i n e r o c k i s f o u n d s o u t h - w e s t of t h e W h i p p e t M i n e .
Gabbro and dolerite crop
out n e a r the boundary between the W a r r a m u n g a Group and Tomkinson Creek B e d s , and a s m a l l b o d y of d o l e r i t e o c c u r s n e a r O r l a n d o ; tectonic.
the basic rocks a r e either late paratectonic or post-
T h r e e t y p e s of i r o n s t o n e h a v e b e e n o b s e r v e d :
m a s s i v e lodes, banded and textured
r e p l a c e m e n t b o d i e s , a n d b o d i e s of h y d r a t e d s u p e r g e n e o x i d e s a n d l a t e h y d r o t h e r m a l hematite.
Rarely is one type present exclusively.
specular
T h e l o c a t i o n of m o s t of t h e l o d e s h a s b e e n
controlled by local s t r u c t u r e s . The
s t r u c t u r e of t h e a r e a h a s b e e n i n v e s t i g a t e d o n a r e c o n n a i s s a n c e s c a l e b y
s t r u c t u r a l a n a l y s i s t e c h n i q u e s . T h e r e s u l t s s u g g e s t t h a t t h e r e a r e t h r e e p h a s e s of d e f o r m a t i o n , the
first
of w h i c h
antedates
the
deposition
of t h e T o m k i n s o n C r e e k B e d s , a n d i s b r o a d l y
s y n c h r o n o u s w i t h t h e e m p l a c e m e n t of t h e g r a n i t e s . T h e s e c o n d a n d t h i r d p h a s e s a r e s y m m e t r i cally
related,
and
represent
the
same
stress
field
under different physical conditions.
T h e r e i s no d i r e c t c o r r e l a t i o n between the m a g n e t i c a n o m a l i e s and the geological structures.
T h e p r e s e n c e of f a v o u r a b l e b e d s a n d f a v o u r a b l e s t r u c t u r e s ( s h e a r z o n e s ) h a v e
b e e n i m p o r t a n t f a c t o r s c o n t r o l l i n g t h e f o r m a t i o n of t h e i r o n s t o n e s . S a m p l e s of i r o n s t o n e , s t r e a m s e d i m e n t , a n d c o l l u v i u m w e r e c o l l e c t e d a n d a n a l y s e d for c o p p e r , cobalt, lead, zinc, b i s m u t h , and molybdenum.
S t a t i s t i c a l a n a l y s i s of t h e r e s u l t s
indicates that the e l e m e n t s a r e distributed in the i r o n s t o n e s in two populations, the u p p e r one of w h i c h i s r e l a t e d t o e c o n o m i c c o n c e n t r a t i o n s of c o p p e r . T h e i r o n s t o n e s in the Black E y e , G r e a t W e s t e r n , and Bishop C r e e k a r e a s and two m a g n e t i c a n o m a l i e s on favourable s t r u c t u r a l features a r e r e c o m m e n d e d for further gation. 1
investi
INTRODUCTION
T h e M o u n t W o o d c o c k 1 - m i l e S h e e t a r e a w a s m a p p e d b y t h e B u r e a u of M i n e r a l R e s o u r c e s in 1964. 1-mile
T h i s R e p o r t i s c o m p l e m e n t a r y t o t h e d e s c r i p t i o n s of t h e T e n n a n t C r e e k
S h e e t a r e a by C r o h n & O l d e r s h a w (1965) a n d t h e T e n n a n t C r e e k G o l d f i e l d b y I v a n a c
( 1 9 5 4 ) , i n w h i c h t h e g o l d a n d c o p p e r m i n e r a l i z a t i o n a n d t h e d e v e l o p m e n t of t h e v a r i o u s m i n e s are
discussed.
Crohn
& O l d e r s h a w h a v e a l s o d i s c u s s e d t h e i g n e o u s r o c k s of t h e T e n n a n t
C r e e k S h e e t a n d d e s c r i b e d p a r t s of t h e a r e a i n d e t a i l .
T h e r o c k t y p e s in the Mount Woodcock
S h e e t a r e s i m i l a r to t h o s e in t h e T e n n a n t C r e e k S h e e t , T h i s R e p o r t d e s c r i b e s t h e s t r a t i g r a p h y of t h e W a r r a m u n g a G r o u p , t h e d e f o r m a t i o n a l h i s t o r y of t h e a r e a , a n d t h e s t r a t i g r a p h i c a n d s t r u c t u r a l c o n t r o l s of t h e g o l d a n d c o p p e r mineralization. T h e m a p p i n g w a s c a r r i e d out with 1:12,000 s c a l e a i r - p h o t o g r a p h s m a d e a v a i l a b l e b y c o u r t e s y of P e k o - W a l l s e n d photographs Mapping. data.
and
plotted
Drainage
and
on
Pty Ltd.
1:46,000
cultural
T h e g e o l o g i c a l d a t a w e r e r e d u c e d to 1:46,000 s c a l e
scale
features
base maps
s u p p l i e d b y t h e D i v i s i o n of N a t i o n a l
were
t o c o n t r o l t h e p l o t t i n g of g e o l o g i c a l
used
T h e c o m p i l a t i o n w a s s u b s e q u e n t l y r e d u c e d p h o t o g r a p h i c a l l y to 1:63,360 s c a l e . A
geochemical
survey
was
made
of
the
stream
sediments, ironstones, and
l a t e r i t i c c a p p i n g s on t h e b a s i c r o c k s a s s o c i a t e d with t h e T o m k i n s o n C r e e k and W a r r a m u n g a Group
B e d s in the Mount Woodcock, H a y w a r d C r e e k , M a r i o n R o s s , and 5/217 1 - m i l e Sheet
areas.
The
survey
was
a c o n t i n u a t i o n of w o r k c o m m e n c e d b y M c M i l l a n & D e b n a m ( 1 9 6 1 )
w i t h t h e o b j e c t of d e l i m i t i n g a r e a s of c o p p e r m i n e r a l i z a t i o n b y r e g i o n a l g e o c h e m i c a l
sampling.
T w o d e t a i l e d d r i l l i n g p r o g r a m m e s u n d e r t a k e n b y t h e B u r e a u of M i n e r a l R e s o u r c e s i n 1 9 6 4 h a v e b e e n d i s c u s s e d b y D u n n e t (1965) a n d H a r d i n g ( 1 9 6 5 ) . Location ,
,
The Mount Woodcock 1-mile Sheet i s bounded by latitudes 1 9 ° 1 5 S . and 1 9 ° 3 0 S . ,
,
and longitudes 134°00 E. and 134°30 E. Access The Alice
Springs
in
Stuart the
and
south,
Barkly and
Highways
Mount
Isa
provide
in the e a s t .
access
from
D a r w i n in the n o r t h ,
T h e t o w n s h i p of T e n n a n t C r e e k i s
s i t u a t e d 1 1 m i l e s s o u t h of t h e s o u t h e r n b o u n d a r y of t h e S h e e t . W i t h i n t h e S h e e t a r e a t h e r e i s a l a r g e n u m b e r of t r a c k s s u i t a b l e f o r 4 - w h e e l d r i v e v e h i c l e s except for s h o r t p e r i o d s after heavy r a i n . One cattle station, Phillip C r e e k , is situated within the Sheet a r e a .
The T h r e e -
w a y s r o a d h o u s e , w i t h p o s t o f f i c e a n d g a r a g e f a c i l i t i e s , i s s i t u a t e d a t t h e j u n c t i o n of t h e S t u a r t and
Barkly
Orlando,
in
Highways. the
The
only
other
permanent
settlement is the mining community at
s o u t h - w e s t c o r n e r , w h i c h h a s a p o p u l a t i o n of a b o u t 2 0 0 . I t i s c o n n e c t e d t o
T e n n a n t C r e e k township by a s e a l e d r o a d .
A few p r o s p e c t o r s a n d m i n e r s o p e r a t e in t h e a r e a ,
and r o a d metal is quarried close to the Barkly Highway. 3
Previous Investigations Ivanac
(1954)
p r e p a r e d a p r e l i m i n a r y r e g i o n a l g e o l o g i c a l m a p of t h e T e n n a n t
C r e e k G o l d f i e l d a n d s u m m a r i z e d t h e r e s u l t s of p r e v i o u s i n v e s t i g a t i o n s . (1965)
mapped
report
includes
and described a
the geology
comprehensive
account
Crohn & Oldershaw
of t h e T e n n a n t C r e e k 1 - m i l e S h e e t a r e a . of t h e T e n n a n t
Their
Creek Granite Complex and the
s t r a t i g r a p h y of t h e W a r r a m u n g a G r o u p . In
1955-57
a
Bureau
of M i n e r a l
Resources
geochemical
party (McMillan &
D e b n a m , 1961) s a m p l e d t h e i r o n s t o n e s c r o p p i n g o u t in t h e T e n n a n t C r e e k 1 - m i l e Sheet a r e a a n d s e v e r a l of t h e i r o n s t o n e s i n t h e M o u n t W o o d c o c k S h e e t a r e a .
The samples were analysed
f o r c o p p e r , a n d t h e i r o n s t o n e s i n t h e N o r t h e r n S t a r a n d O r l a n d o a r e a s w e r e found t o b e a n o m alous.
T h e Orlando Mine h a s since been opened up to produce copper and gold. D a l y ( 1 9 5 7 ) s u m m a r i z e d t h e r e s u l t s of t h e p r e - w a r m a g n e t i c p r o s p e c t i n g b y t h e
A e r i a l , G e o l o g i c a l , a n d G e o p h y s i c a l S u r v e y of N o r t h e r n A u s t r a l i a in t h e T e n n a n t C r e e k F i e l d , a n d d i s c u s s e d t h e r e s u l t s i n t h e l i g h t of s u b s e q u e n t d e v e l o p m e n t s . T h e O r l a n d o M i n e h a s b e e n i n v e s t i g a t e d b y P e k o M i n e s N , L . , t h e Q u e e n of S h e b a l e a s e by National Lead Co., and N o r t h e r n Star L e a s e by Peko Mines N . L . and Metals E x p l o r ation N.L.
H i s t o r y of M i n i n g a n d P r o d u c t i o n T h e e a r l y h i s t o r y of t h e g o l d f i e l d a n d p r o d u c t i o n u p t o J u n e 1 9 6 3 h a v e b e e n d i s c u s s e d b y I v a n a c (1954) a n d C r o h n & O l d e r s h a w (1965).
T h e only m a j o r d e v e l o p m e n t s i n c e
1 9 6 3 i s t h e c o m m e n c e m e n t of p r o d u c t i o n f r o m t h e I v a n h o e M i n e i n 1 9 6 4 . The m i n e s and prospects in the Mount Woodcock Sheet a r e a include: Carramon,
Edna
Beryl,
Golden
Slipper,
Havelock,
Klondyke,
Marion
Bernborough,
Ross, North Star,
N o r t h e r n S t a r , O l i v e W o o d , O r l a n d o , Q u e e n of S h e b a , a n d W h i p p e t . Recent production figures for these m i n e s a r e :
Orlando:
M a y 1961 - J u n e 1 9 6 3 : 37,300 o z g o l d a n d 745 tons c o p p e r c o n c e n t r a t e
from
8 9 , 1 0 0 t o n s of o r e . J u n e 1963 - J u n e 1964: 18,278 oz gold, 4072 oz s i l v e r and 488 tons copper c o n c e n t r a t e f r o m 5 2 , 8 3 3 t o n s of o r e . Reserves:
1 8 0 , 0 0 0 t o n s w i t h a n e s t i m a t e d g r a d e of 9 d w t g o l d a n d 1 p e r c e n t
copper. Edna
Beryl:
Whippet: Marion
Ross:
October
1958 - S e p t e m b e r 1959:
179 o z g o l d f r o m a b o u t 530 t o n s of o r e .
January
1957 - S e p t e m b e r 1 9 6 1 :
6 2 5 o z g o l d f r o m a b o u t 7 0 0 t o n s of o r e .
December
1958 -
October
1960: 4
1 8 o z g o l d f r o m a b o u t 1 4 0 t o n s of o r e .
Following diamond drilling by M e t a l s Exploration N . L . and the M i n e s B r a n c h , N o r t h e r n T e r r i t o r y Administration, and drilling and geochemical
s u r v e y s b y t h e B u r e a u of
M i n e r a l R e s o u r c e s (Dunnet, 1965), the N o r t h e r n Star l e a s e s have b e e n t a k e n u p a s a p r o s p e c t for c o p p e r and gold by M e t a l s Exploration N . L , Several p r o s p e c t o r s and syndicates a r e active in the a r e a , a n d the M a r i o n R o s s Mine w a s worked sporadically during 1964. Physiography
T h e p h y s i o g r a p h y of t h e M o u n t W o o d c o c k 1 - m i l e S h e e t a r e a i s s i m i l a r t o t h a t of the Tennant C r e e k 1-mile Sheet a r e a (Crohn & O l d e r s h a w , 1965). T h e W a r r a m u n g a G r o u p r o c k s g e n e r a l l y c r o p o u t i n g r o u p s of f l a t - t o p p e d r i d g e s , t r e n d i n g e a s t - s o u t h - e a s t , s e p a r a t e d by low-lying a r e a s 2 to 3 m i l e s a c r o s s .
In t h e s o u t h , t h e
g r a n i t e s g e n e r a l l y c r o p out a s t o r s , b u t in t h e B e r n b o r o u g h a r e a t h e g r a n i t e p o r p h y r i e s low blocky outcrops. broad
or
form
The Tomkinson Creek Beds c r o p out a s long strike ridges separated by
narrow V-shaped valleys;
t h e s l o p e s a r e g e n e r a l l y c o v e r e d b y a n g u l a r b l o c k s of
silicified sandstone. The C a m b r i a n sediments form distinctive rounded hills with m i n o r along the m o r e resistant beds.
scarps
S o m e of t h e l a r g e r q u a r t z r e e f s f o r m r a z o r b a c k r i d g e s ( e . g .
near Bernborough). Vein-quartz talus is commonly extensive over Warramunga sediments, and as
residual
gravel
after
scarp
retreat
and differential
t r a n s p o r t of t h e p e d i m e n t t a l u s .
W e s t of t h e S t u a r t H i g h w a y r e l i e f i s a b o u t 3 0 0 f e e t , b u t t o t h e e a s t of t h e h i g h w a y and
south
of t h e
T o m k i n s o n C r e e k B e d s the topography i s flat o r slightly undulating.
h i g h e s t p o i n t i s M o u n t A r g o , w i t h a n e l e v a t i o n of 1 2 8 4 f e e t .
The
M a n y of t h e r i d g e s i n t h e W a r r a
m u n g a G r o u p a r e r e m n a n t s of a n o l d l a n d s u r f a c e , w i t h a z o n e of i r o n e n r i c h m e n t , u p t o 1 5 feet thick, underlain by a m u c h thicker leached zone.
No t r u e l a t e r i t e i s p r e s e n t .
The steep-
s i d e d p r o f i l e s of t h e r i d g e s h a v e b e e n d e v e l o p e d b y t h e u n d e r c u t t i n g of t h e i r o n - e n r i c h e d z o n e d u r i n g t h e c u r r e n t c y c l e of e r o s i o n .
The C a m b r i a n b r e c c i a s and volcanics cropping out in the
e a s t a r e e n r i c h e d i n i r o n t o w a r d s t h e t o p of t h e w e a t h e r e d z o n e , b u t t h e e q u i v a l e n t h o r i z o n s i n t h e w e a t h e r i n g p r o f i l e of t h e C a m b r i a n
'quartzites' and sandstones in the Tomkinson C r e e k
B e d s a r e indurated with silica. The low-lying a r e a s between the ridges formed by the W a r r a m u n g a Group a r e remarkably
flat,
probably
a
r e s u l t of t h e s p o r a d i c h e a v y r a i n a n d f l a s h f l o o d s .
alluvium occurs around Phillip Creek and Butchers Creek;
Extensive
t h i c k n e s s e s of u p t o 1 5 f e e t a r e
e x p o s e d in t h e c r e e k s . The mine workings and diamond d r i l l - c o r e s indicate that the W a r r a m u n g a Group r o c k s a r e g e n e r a l l y f r e s h a t d e p t h s b e l o w 200 feet, b u t in s h e a r z o n e s a n d n e a r s u l p h i d e b o d i e s t h e r o c k s m a y b e o x i d i z e d down to 700 feet (e.g., O r l a n d o M i n e 600 feet;
Northern Star Mine
700 feet). A t t h e N o r t h e r n S t a r M i n e t h e w a t e r - t a b l e in t h e shaft i s 270 f e e t d e e p ; a t t h e O r l a n d o Mine it fluctuates down to about 400 feet. STRATIGRAPHY T h e m a i n r o c k units in the Tennant C r e e k a r e a h a v e b e e n d e s c r i b e d by Ivanac (1954) a n d C r o h n & O l d e r s h a w (1965), a n d a r e s e t o u t in T a b l e 1 . 5
T A B L E 1; STRATIGRAPHY, TENNANT CREEK AREA Age
Lithology
Rock Unit
Remarks
A l l u v i u m , c r e e k g r a v e l s , b u l l d u s t,
Recent
etc. Tertiary
Unconsolidated andpoorly con solidated sand, clay, grit, gravel (in p a r t l a t e r i t i z e d ) UNCONFORMITY
Lower Middle
Gum Ridge
Calcareous sandstone, shale,
Cambrian
Formation
chert
Lower
Helen
Lavas andpyroclastic rocks
Cambrian(?)
Springs
(including Cabbage
Gum
Basin Sediments) Gentle warping and e r o s i o n
Volcanics UNCONFORMITY Dolerite, gabbro, diorite,
Gold a n d copper
lamprophyre, quartz veins,
ization
quartz-magnetite and quartz-
ally related to the gabbro
hematite lodes.
and dolerite
Gold a n d
mineral
probably
genetic
sulphides Gold a n d copper ization major
mineral
associated
with
orogeny and meta-
morphism,
phases
2, 3 ,
Rising Sun
Conglomerate, quartzite
Tennant Creek
Formation
sandstone, shale
Sheet a r e a
1-mile
HATCHES CREEK GROUP
MIDDLE PROTEROZOIC
and 4
basic volcanics
Tomkinson
Quartz sandstone, feldspathic
Mount
Creek Beds
quartz sandstone, grit, con
R o s s , Hay w a r d C r e e k , a n d
glomerate
5/217 Sheet a r e a s
Quartzite, sandstone, shale,
Crops
greywacke pebble conglomer
Ranges
ate, siltstone, acid volcanics,
& S m i t h , 1961)
out in
Davenport
(Smith,
Woodcock,
Stewart,
Marion
UNCONFORMITY Granite, adamellite, porphyry,
Contact
quartz veins
Warramunga Group. Phase
m e t a m o r p h i s m of
1 deformation.
6
TABLE 1;
Rock Unit
Age
(CONT'D)
Lithology
Remarks
Blw 3
Sandstone, shale, and siltstone
Blw 2
Greywacke, minor shale and hematite shale, pebble beds
LOWER PROTEROZOIC
WARR;\MUNGA GROUP
Blw 1
Shale, some greywacke, porphyroidal
rocks
Undiffer Shale, siltstone, hematite shale, entiated
In p a r t B l w 1
greywacke, quartz greywacke, quartz sandstone, chert, turbidite
Bern
A c i d v o l c a n i c f l o w s , tuff,
borough
greywacke, turbidite, shale,
Form
siltstone
ation Bwb
Quartz sandstone, feldspathic
Whippet
quartz sandstone, quartz-pebble
Sand
conglomerate
stone Member UNCONFORMITY ARCHAEAN
Quartz-feldspar-garnet
gneiss,
magnetite schist, amphibolite
F r o m diamond
drill-hole
i n t e r s e c t i o n s only
ARCHAEAN No A r c h a e a n
rocks
crop
out in t h e Mount Woodcock Sheet a r e a , b u t q u a r t z -
e l d s p a r - g a r n e t g n e i s s , m a g n e t i t e s c h i s t , a n d a m p h i b o l i t e of i n f e r r e d A r c h a e a n a g e h a v e b e e n ecorded
in a diamond drill-hole (Australian Development N . L . , drill log,B M R Technical
'ile N T / S E / 5 3 / 1 4 ) , in t h e T e n n a n t C r e e k Sheet a r e a .
PROTEROZOIC T h e P r o t e r o z o i c r o c k s a r e of l o w e r m e t a m o r p h i c g r a d e t h a n t h e A r c h a e a n r o c k s , on which they probably r e s t unconformably.
They include the Lower Proterozoic W a r r a m u n g a
G r o u p a n d t h e T o m k i n s o n C r e e k B e d s ( A s h b u r t o n S a n d s t o n e ) of p r o b a b l e C a r p e n t a r i a n a g e . 7
Warramunga Group T h e W a r r a m u n g a G r o u p c r o p s out o r u n d e r l i e s C a m b r i a n o r R e c e n t s e d i m e n t s over
most
of
the Sheet area.
Murchison Ranges;
T h e g r o u p e x t e n d s s o u t h w a r d s t o t h e n o r t h e r n m a r g i n of t h e
in t h e w e s t , it e x t e n d s a c r o s s the M a r i o n R o s s 1 - m i l e Sheet a r e a , w h e r e
it i s overlain unconformably by the Tomkinson C r e e k B e d s ;
in t h e e a s t , it i s i n t r u d e d by t h e
T e n n a n t C r e e k G r a n i t e C o m p l e x a n d o v e r l a i n b y a t h i n c o v e r of C a m b r i a n s e d i m e n t s ;
in t h e
n o r t h , the u n c o n f o r m a b l e and faulted contact with the T o m k i n s o n C r e e k B e d s extends along the m a r g i n of t h e S h e e t a r e a . The
Warramunga Group is
assumed
to
r e s t unconformably
g n e i s s e s i n t e r s e c t e d i n t h e d r i l l - h o l e s t o t h e s o u t h - w e s t of T e n n a n t C r e e k .
on the
Archaean
The monotonous
l i t h o l o g y , l a c k of o u t c r o p , a n d p o s s i b l e r e p e t i t i o n b y f o l d i n g a n d f a u l t i n g m a k e i t d i f f i c u l t t o m e a s u r e t h e t h i c k n e s s of t h e G r o u p , b u t t h e m a x i m u m t h i c k n e s s i s e s t i m a t e d t o b e a b o u t 1 2 , 0 0 0 feet, although it m a y b e m u c h g r e a t e r . T h e W a r r a m u n g a G r o u p i s c o n s i d e r e d to b e L o w e r P r o t e r o z o i c in a g e .
It i s o l d e r
that the Tomkinson C r e e k B e d s and H a t c h e s Creek Group, which a r e tentatively c o r r e l a t e d with t h e C a r p e n t a r i a n T a w a l l a h G r o u p in t h e C a r p e n t a r i a B a s i n . K/Ar
isotopic age determinations on g r a n i t e s intruding the W a r r a m u n g a Group
i n d i c a t e p r o v i s i o n a l a g e s of 1 6 3 0 , 1 5 1 0 , a n d 1 4 0 0 m . y , ( H u r l e y e t a l . , 1 9 6 1 ) .
T h e t r u e a g e of
t h e g r a n i t e i s p r o b a b l y 1 6 3 0 m . y . , a n d t h e o t h e r d a t e s p r o b a b l y r e p r e s e n t p e r i o d s of m e t a m o r phism. The W a r r a m u n g a Group occupies a broad anticline plunging west at a low angle; t h e a x i a l p l a n e l i e s a p p r o x i m a t e l y a l o n g t h e l i n e of t h e B a r k l y H i g h w a y .
The group consists
of s h a l e , s i l t s t o n e , g r e y w a c k e , a n d q u a r t z g r e y w a c k e , w i t h m i n o r c h e r t , h e m a t i t e s h a l e , s a n d stone, conglomerate, acid volcanics, and feldspathic greywacke and associated rocks derived from the acid volcanics. T h e m a i n lithological f e a t u r e s have b e e n d e s c r i b e d by C r o h n & O l d e r s h a w (1965), T h e s u c c e s s i o n in the Mount Woodcock Sheet a r e a i s p a r t l y o l d e r and p a r t l y equivalent to the sequence in the Tennant C r e e k Sheet a r e a , Lithology is m o r e v a r i e d and deformation l e s s than in the Tennant C r e e k Sheet a r e a , and s e v e r a l additional subdivisions have been established. H o w e v e r , it i s difficult to elucidate the s t r a t i g r a p h y on the Mount Woodcock Sheet a r e a b e c a u s e of t h e p a u c i t y o f o u t c r o p a n d t h e p r o b a b l y p r e s e n c e of l a r g e f a u l t s . T h e b a s e of t h e g r o u p i s n o t e x p o s e d . T h e o l d e s t k n o w n r o c k s a r e t h e g r e y w a c k e a n d s h a l e b e l o w t h e W h i p p e t S a n d s t o n e M e m b e r of t h e B e r n b o r o u g h F o r m a t i o n ; t o t h e e a s t of t h e S t u a r t H i g h w a y a s l o w h i l l s of r u b b l e . m o r p h o s e d by the adjacent granite, north-west
corner
of
the
A s i m i l a r o u t c r o p n o r t h of t h e B a r k l y H i g h w a y n e a r t h e
Warramunga
dipping n o r t h a t about 40 .
they crop out
S o m e of t h e r o c k s h a v e b e e n m e t a
A b o r i g i n a l R e s e r v e c o n s i s t s of s h a l e a n d s i l t s t o n e
The beds contain cordierite and andalusite spots formed by con
tact m e t a m o r p h i s m , and granite is probably present at a relatively shallow depth. Most
of
the sediments w e r e deposited in a miogeosynclinal environment, and
load c a s t s , sole m a r k i n g s , small slump s t r u c t u r e s , graded bedding, and s m a l l - s c a l e c r o s s bedding
are
common.
The
rocks
are
generally
thinly bedded, flaggy, and poorly s o r t e d ;
greywacke and quartz greywacke a r e the dominant lithological types. 8
T h e t h i c k s e q u e n c e s of
m a s s i v e greywacke and volcanic greywacke were probably formed by turbidity c u r r e n t s or mudflows. C o r r e l a t i o n in t h e W a r r a m u n g a G r o u p T h e p a u c i t y of o u t c r o p s , t h e m o n o t o n o u s l i t h o l o g y , t h e p r o b a b l e v a r i a t i o n of l i t h o l o g y a l o n g t h e s t r i k e , a n d t h e i n f e r r e d p r e s e n c e of l a r g e f a u l t s m a k e i t d i f f i c u l t t o e l u c i d a t e the stratigraphy.
T h e W a r r a m u n g a G r o u p in t h e T e n n a n t C r e e k 1 - m i l e S h e e t a r e a w a s s u b
divided
& Oldershaw
by C r o h n
(1965)
into t h r e e f o r m a t i o n s (Blw^, Blw^,
a n (
* Blw^).
The
l i t h o l o g y of t h e s e u n i t s i s s u m m a r i z e d i n T a b l e 2 a n d t h e t h i c k n e s s e s h a v e b e e n a d j u s t e d i n a c c o r d a n c e with t h e s e c t i o n s m e a s u r e d in t h e Mount Woodcock S h e e t a r e a . T A B L E 2: S T R A T I G R A P H Y , W A R R A M U N G A G R O U P Lithology
Thickness
Unit
(ft) 3000
Blw„
Relatively clean quartz sandstone, shale, and siltstone. Possibly partly equivalent to Blw^
3000(?)
Greywacke, minor shale and siltstone, hematite shale, and pebble beds
Blw^
Mainly shale and siltstone, m i n o r greywacke.
Probably over
Lenses
of p o r p h y r o i d a l r o c k s n e a r b a s e
6000
In t h e M o u n t W o o d c o c k S h e e t a r e a , t h r e e s e p a r a t e s e q u e n c e s h a v e b e e n m a p p e d . T h e sequences cannot be directly c o r r e l a t e d a s they a r e bounded by faults. Bernborough-Whippet Sequence The
Bernborough-Whippet
Warramunga Group;
sequence
includes
the lowest
e x p o s e d p a r t of t h e
i t c r o p s o u t i n a b r o a d a n t i c l i n e e x t e n d i n g f r o m e a s t of t h e W h i p p e t M i n e ,
s o u t h - w e s t w a r d s t h r o u g h t h e B e r n b o r o u g h M i n e a r e a t o t h e Q u e e n of S h e b a M i n e , a n d s o u t h eastwards
to the B i s h o p
Creek
Bore area.
T h e s t r a t i g r a p h y of t h e B e r n b o r o u g h - W h i p p e t
s e q u e n c e i s a s shown in T a b l e 3. TABLE 3: STRATIGRAPHY, BERNBOROUGH-WHIPPET Thickness
SEQUENCE
Lithology
Unit
(ft) 1000+
U n n a m e d (good o u t c r o p )
Well-bedded,
interbedded greywacke and shale,
minor siltstone, and some 4000-6000
U n n a m e d (poor outcrop)
Siltstone,
shale, and some
conglomerate 'hematite
shale';
minor greywacke 3000-3600
Bernborough Formation
A c i d v o l c a n i c f l o w s , g r e y w a c k e , tuff, a n d s i l t stone and shale l e n s e s
Whippet
Cross-bedded, r i p p l e - m a r k e d quartz sandstone, feldspathic and clayey quartz sandstone, con glomerate, and minor volcanics
Sandstone Member Greywacke, quartz greywacke, shale, and silt stone Unknown
Unnamed 9
The middle
complete
sequence
unit i s not exposed.
is
not
e x p o s e d i n a n y o n e a r e a , a n d m u c h of t h e s o f t
T h e m o s t c o m p l e t e s e c t i o n s a r e in the F l y n n M e m o r i a l / B e r n -
borough Mine and Whippet Mine a r e a s . E a s t of t h e S t u a r t H i g h w a y a n d n o r t h of t h e B a r k l y H i g h w a y , t h e s c a t t e r e d o u t crops
of
greywacke
underlie
the Bernborough Formation,
r e p r e s e n t t h e l o w e s t e x p o s e d p a r t of t h e W a r r a m u n g a G r o u p .
They a r e intruded and meta
morphosed
and
shale,
which
apparently
b y t h e g r a n i t e s of t h e T e n n a n t C r e e k G r a n i t e C o m p l e x , a n d i n t h e e a s t t h e y a r e
o v e r l a i n b y t h e C a m b r i a n r o c k s of t h e B a r k l y T a b l e l a n d . Bernborough tuff,
Formation.
rents.
The coarse-grained
a n d fine tuffaceous r o c k s . The the
T h e B e r n b o r o u g h F o r m a t i o n c o n s i s t s of a c i d l a v a ,
and slumped and m a s s i v e tuffaceous
poorly dips
exposed
steepen
B e d d i n g i s g e n e r a l l y p o o r e x c e p t in t h e s h a l e s .
formation
coarse-grained in
away
c r o p s o u t a s a s e r i e s of l o w c u e s t a s i n t h e B e r n b o r o u g h a r e a ;
rocks the
greywacke formed by mudflows or turbidity c u r
r o c k s a r e interbedded with shale and siltstone, m i n o r a s h s t o n e ,
generally
back
from
form
the
dip
slopes,
and the shale and siltstone a r e
slopes and intervening valleys.
the
axis
of
the
In t h e W h i p p e t M i n e a r e a , t h e
a n t i c l i n e , a n d t h e b e d s a r e p o o r l y e x p o s e d in low
rubble-covered hills. The the
formation,
north-east,
and
which r a n g e s in t h i c k n e s s f r o m
3000 t o 3600 f e e t , t h i c k e n s to
t h e p r o p o r t i o n of v o l c a n i c r o c k s d e c r e a s e s ;
in the Whippet Mine a r e a
v o l c a n o l i t h i c g r e y w a c k e p r e d o m i n a t e s , a n d t h e s o u r c e of t h e v o l c a n i c s w a s p r o b a b l y i n t h e s o u t h - w e s t o r w e s t of t h e S h e e t a r e a . The Formation. near
the
Member
Whippet
Sandstone
M e m b e r o c c u r s i n t h e l o w e r p a r t of t h e B e r n b o r o u g h
T h e m e m b e r i s u n d e r l a i n locally by volcanic r o c k s and is interbedded with t h e m Stuart
Highway,
4
miles
north
of t h e F l y n n M e m o r i a l .
The Whippet Sandstone
i s n o t c o n t i n u o u s , a n d s o u t h of t h e E d n a B e r y l M i n e i t c o n s i s t s of s e v e r a l s a n d s t o n e
i n t e r b e d s in the B e r n b o r o u g h
Formation.
T h e t y p e s e c t i o n i s n e a r t h e W h i p p e t T r i g . S t a t i o n , w h e r e a b o u t 6 0 0 f e e t of c l e a n medium-grained north. ence
thinly
b e d d e d t o b l o c k y q u a r t z s a n d s t o n e i s e x p o s e d , d i p p i n g a t 70
T h i n b e d s r i c h i n h e m a t i t e a n d e p i d o t e a r e p r e s e n t i n p a r t of t h e s e q u e n c e . of
well-developed
ripple m a r k s indicates a shallow-water environment.
to the
The p r e s The ripples
a r e p a r t l y a s y m m e t r i c a l , a n d t h e s t e e p s l o p e s to t h e w e s t s u g g e s t a c u r r e n t d i r e c t i o n f r o m the east.
T h e r o c k s a r e orthoquartzite with very little feldspar.
They a r e underlain by shale
and siltstone,. and a r e o v e r l a i n by shale and tuffaceous greywacke; r o c k s of t h e B e r n b o r o u g h On is
represented
above these a r e volcanic
Formation.
the t r a c k f r o m the Flynn M e m o r i a l to the B e r n b o r o u g h Mine, the m e m b e r by
poorly
bedded
clayey and feldspathic quartz sandstone with pebbles, up
t o 3 i n c h e s a c r o s s , of q u a r t z , q u a r t z i t e , a n d a f e w a c i d p o r p h y r i t i c r o c k s .
The acid porphy
r i t i c p e b b l e s m a y h a v e b e e n d e r i v e d b y c o n t e m p o r a n e o u s e r o s i o n of t h e v o l c a n i c s . T h e Whippet Sandstone, w h e r e v e r it is exposed, i s c l o s e to the T e n n a n t C r e e k G r a n i t e C o m p l e x , and a p p e a r s a t f i r s t sight to be a b a s a l sandstone lying unconformably on it. However, the granite intrudes typical W a r r a m u n g a shale and siltstone that underlie the Sand s t o n e , a n d t h e M e m b e r i s a c o n f o r m a b l e p a r t of t h e W a r r a m u n g a G r o u p , 10
Lithologically the
Member
s o m e w h a t r e s e m b l e s the Blw^ unit in the Tennant C r e e k 1 - m i l e Sheet a r e a , but the
two a r e not correlated The
type
stratigraphically. section
of
t h e u p p e r p a r t of t h e B e r n b o r o u g h F o r m a t i o n i s s i t u a t e d
e a s t of t h e B e r n b o r o u g h M i n e ( T a b l e 4 ) .
TABLE 4:
TYPE SECTION, BERNBOROUGH
Thickness
FORMATION
Lithology
(ft) 600
Soft
purple
f r i a b l e tuff o r m u d f l o w g r e y w a c k e ,
unbedded,
con
t a i n i n g p h e n o c r y s t s of q u a r t z a n d e p i d o t i z e d f e l d s p a r 300
Fine-grained to
pink
and
white clayey quartz sanstone. mauve
siltstone,
thinly
Poorly exposed red
bedded.
Poorly exposed
m a s s i v e fawn s i l t s t o n e 600
F l o w o r g l a s s y c r y s t a l tuff, c o n t a i n i n g q u a r t z , f e l d s p a r , a n d g l a s s y rock
fragments
in a
red
glassy
matrix;
f l o w - b a n d e d in p a r t .
M i n o r tuff Massive dote 100
glassy
purple volcanic rock, containing quartz and epi-
'phenocrysts'.
Well-bedded
T w o - f o o t b e d of r e d c h e r t y m u d s t o n e a t b a s e
thinly bedded
r e d to pink siltstone and m a s s i v e r e d
m u d s t o n e with 1 to 2 inch fine-grained white clayey quartz s a n d stone interbeds. Massive
tuffaceous
feldspar
and
Strongly
structureless
rock fragments.
Minor ash beds. 600
Thins to north porphyritic
rocks,
containing
Veined with r e d cherty m a t e r i a l .
No q u a r t z p h e n o c r y s t s
contorted
slumped
often
thinly bedded tuffaceous
rocks
with s h e a r e d and flattened chloritic and epidotic augen 400
Thinly bedded siltstone and shale, v e r y poorly exposed Whippet Sandstone M e m b e r
400
M a s s i v e to blocky and flaggy, bedded q u a r t z s a n d s t o n e and f e l d s pathic quartz
sandstone
Intrusive porphyry
This
is
the best-exposed
s e c t i o n of t h e B e r n b o r o u g h F o r m a t i o n ;
t h r e e volcanic m e m b e r s , and three shale/siltstone m e m b e r s .
it includes
T h e soft m i d d l e unit t h i n s out
n o r t h w a r d s , a n d in t h e E d n a B e r y l / W h i p p e t M i n e a r e a only two v o l c a n i c m e m b e r s a r e p r e s e n t . 11 2021 '67—2
The westwards steeply
and
are
south-west. the
Bernborough
to n e a r
Formation
crops
the Bishop Creek Bore. partly
overturned
o u t f r o m t h e Q u e e n of S h e b a M i n e s o u t h -
A r o u n d t h e Q u e e n of S h e b a M i n e , t h e b e d s d i p
to t h e
east;
f a r t h e r s o u t h , t h e b e d s d i p a t 60
to the
T h e f o r m a t i o n h a s b e e n displaced along a m a j o r n o r t h - w e s t e r l y fault between
Bernborough
and
Queen
of S h e b a M i n e s ;
t h e o v e r t u r n i n g of t h e b e d s s u g g e s t s t h a t t h e
fault h a s a dextral m o v e m e n t .
Only lower m e m b e r grey
cherty
consists Bishop a
rock
of
with
siltstone
Creek
contorted. and
two volcanic
members
crop
o u t i n t h e Q u e e n of S h e b a M i n e a r e a .
is well banded and possibly flow-banded;
Bore
large with
area,
quartz
and feldspar
5 percent these
rock
crystals.
Elsewhere the s a m e horizon
of c o a r s e
f r a g m e n t s of q u a r t z a n d f e l d s p a r .
types
well bedded, and a r e c o m m o n l y strongly
are
T h e u p p e r m e m b e r i s c o m p o s e d of p u r p l e a s h - f l o w tuff o r t u f f a c e o u s
finely
bedded
shaly
rock.
underlying
and overlying beds.
Most by
of t h e t u f f a c e o u s
mudflows
w a t e r - l a i d tuffs.
or
greywacke,
turbidity
they c o m m o n l y p r o j e c t into
T h e r o c k i s p r o b a b l y a w a t e r - l a i d tuff, a n d t h e c o a r s e
f r a g m e n t s w e r e introduced by explosive volcanic activity.
deposited
In t h e
T h e f i n e l y b e d d e d r o c k c o n t a i n s f r a g m e n t s of r o c k a n d
feldspar, up to 5 m m a c r o s s , oriented parallel to the cleavage; the
The
i t c o n s i s t s p a r t l y of a f i n e - g r a i n e d
rocks
Quartz is uncommon.
in t h e B e r n b o r o u g h
currents
Formation were probably
and the detritus was probably derived from
Lava flows a r e subordinate.
T o t h e s o u t h of B e r n b o r o u g h l i e s a l a r g e p i p e o r v e n t , a t l e a s t 3 s q u a r e m i l e s i n a r e a , w h i c h i s f i l l e d w i t h i g n i m b r i t e , r h y o l i t e p o r p h y r y , a n d r h y o l i t e (W. O l d e r s h a w , B M R , pers.
comm.).
The vent
cuts
the Bernborough Formation.
c o a r s e r than the flows in t h e B e r n b o r o u g h F o r m a t i o n ; and predominantly blue-grey.
The vent r o c k s a r e generally
they a r e rich in quartz phenocrysts,
T h e v e n t m a y b e t h e s o u r c e of t h e B e r n b o r o u g h v o l c a n i c s , b u t
it i s m o r e probable that it is r e l a t e d to the Tennant C r e e k G r a n i t e Complex and the p o r p h y r i e s in the Tennant C r e e k 1 - m i l e Sheet a r e a (Crohn & O l d e r s h a w , 1965).
Sequences overlying the Bernborough Formation. is
overlain
by
The Bernborough
Formation
a s e q u e n c e of s i l t s t o n e a n d s h a l e , w h i c h i s g e n e r a l l y p o o r l y e x p o s e d .
Near
B e r n b o r o u g h a n d t o w a r d s t h e N o r t h e r n S t a r M i n e t h e r e a r e s e v e r a l p o o r o u t c r o p s of t h i n l y b e d d e d buff s i l t s t o n e , b a n d e d r e d a n d b r o w n s i l t s t o n e , a n d h e m a t i t e - r i c h s h a l e .
Pink siltstone
a n d m i n o r g r e y w a c k e a r e f o u n d i n t h e Q u e e n of S h e b a a n d G o l d e n S l i p p e r M i n e a r e a s . Near the Edna B e r y l and Whippet Mines, the sequence also consists predominantly of s i l t s t o n e , w i t h s o m e s h a l e a n d a t l e a s t 200 f e e t of t h i n l y b e d d e d h e m a t i t e - r i c h s i l t s t o n e a n d shale. The
shale/siltstone
sequence
is
at least
4000
feet thick in the Bernborough
a r e a , a n d possibly up to 6000 feet in the n o r t h - e a s t . Above the shale/siltstone north
of
the
Queen
Butchers Waterhole.
of
Sheba
Mine,
sequence, interbedded greywacke- and shale crop out i n t h e W h i p p e t / E d n a B e r y l M i n e s a r e a , a n d s o u t h of
T o t h e n o r t h a n d n o r t h - w e s t of t h e Q u e e n of S h e b a M i n e , t h e g r e y w a c k e ,
quartz greywacke, shale, and siltstone dip mainly north-west. a
The graded bedding indicates
n o r t h - w e s t facing, and n e a r t h e Golden Slipper Mine the s e q u e n c e probably o v e r l i e s pink
siltstone, quartz siltstone, and minor greywacke. 12
In t h e W h i p p e t / E d n a B e r y l M i n e s a r e a , t h e i n t e r b e d d e d g r e y w a c k e / s h a l e
sequence
i s r e p r e s e n t e d b y a s u c c e s s i o n of g r e y w a c k e a n d q u a r t z g r e y w a c k e , w i t h m i n o r i n t e r b e d s of shale
and
siltstone.
medium-grained quartz thickness
Towards
the
t o p of t h e e x p o s e d s e q u e n c e t h e r e a r e s e v e r a l b e d s of
s a n d s t o n e , g r a n u l e s a n d s t o n e , and pebble c o n g l o m e r a t e , with a total
of a b o u t 1 0 0 f e e t .
T h e b e d s can be t r a c e d discontinuously to the e a s t for a l m o s t
4 miles. S o u t h of B u t c h e r s W a t e r h o l e t h e r e i s a s i m i l a r s e q u e n c e of w e l l b e d d e d g r a d e d g r e y w a c k e an.d q u a r t z g r e y w a c k e , i n t e r b e d d e d w i t h s h a l e a n d s i l t s t o n e , w h i c h d i p s a t 6 0 the
north-east.
The
trend
of t h e b e d d i n g
to
and the lithology indicate that t h e s e b e d s a r e
e q u i v a l e n t t o t h e u p p e r p a r t of t h e s e q u e n c e w h i c h c r o p s o u t w e s t of t h e G o l d e n S l i p p e r M i n e . The Butchers Waterhole greywacke/shale
s e q u e n c e i s o v e r l a i n b y a s e q u e n c e of p o o r l y e x
posed shale, siltstone, and hematite shale which is commonly lateritized; a
dark
pattern
on the
air-photographs.
the sequence
forms
T h i s u n i t i s t h e h i g h e s t p a r t of t h e B e r n b o r o u g h /
Whippet sequence. The Bernborough/Whippet west-trending
sequence is bounded to the south-west by the n o r t h
Q u a r t z Hill F a u l t and to the n o r t h - w e s t by the n o r t h - e a s t - t r e n d i n g
Northern
Star Shear Zone. Orlando Sequence T h e O r l a n d o s e q u e n c e c r o p s o u t s o u t h of t h e Q u a r t z H i l l F a u l t . c o n s i s t s m a i n l y of g r e y w a c k e a n d s h a l e d i p p i n g s o u t h - w e s t a t 6 0
The sequence
t o 90 „ A s s u m i n g t h a t t h e
s e q u e n c e i s not r e p e a t e d , it i s about 10,000 feet thick. The s e q u e n c e i s a s shown in T a b l e 5.
T A B L E 5: STRATIGRAPHY, ORLANDO SEQUENCE Thickness
Lithology
(ft) B l w ^ (only on T e n n a n t C r e e k 1 - m i l e S h e e t a r e a ) Maximum
Shale,
6500
minor
siltstone,
tuff,
and a
few b e d s
of c o n g l o m e r a t e .
L e n s e s of p o r p h y r o i d a l r o c k s ( t u f f a c e o u s g r e y w a c k e s e t c . ) . alent
to
lower
part
of
Blw^
in t h e
Equiv
Tennant C r e e k Sheet a r e a
( Tuffaceous greywacke and greywacke, minor
conglomerate
( ( Pink s i l t s t o n e , m a s s i v e , unbedded, a n d often silicified;
probably
( volcanic in origin Maximum 7000
( ( Greywacke, quartz greywacke, minor shale and siltstone. Massive, ( p r o b a b l y p a r t l y deposited by turbidity c u r r e n t s G r e y w a c k e and shale with s o m e sandstone and g r a n u l e sandstone Q u a r t z Hill F a u l t 13
The an
upper
unit
sequence
c o n s i s t s of a l o w e r c o a r s e - g r a i n e d g r e y w a c k e u n i t o v e r l a i n b y
predominantly
of s h a l e .
The boundary between the lower and upper units is
transitional. T h e l o w e r u n i t c o n s i s t s m a i n l y of g r e y w a c k e a n d q u a r t z - g r e y w a c k e , w i t h m i n o r shale.
N e a r t h e b a s e of t h e s e q u e n c e a b o u t 1 0 0 f e e t of c l e a n m e d i u m - g r a i n e d q u a r t z s a n d s t o n e
a n d g r a n u l e s a n d s t o n e c r o p s o u t i n t h e c o r e of a n e a s t - p l u n g i n g f o l d . t o t h e n o r t h , t h e p r o p o r t i o n of g r e y w a c k e i s m u c h h i g h e r .
Near Butchers Waterhole
T h e two l o c a l i t i e s a r e s e p a r a t e d
by the Q u a r t z Hill F a u l t , and the b e d s cannot be c o r r e l a t e d a c r o s s the fault. T h e u p p e r p a r t of t h e l o w e r u n i t i n c l u d e s a c o n s i d e r a b l e t h i c k n e s s of m a s s i v e pink partly silicified fine-grained
rhyolitic ash which w e a t h e r s green.
The rock is probably
c o m p o s e d l a r g e l y of v o l c a n i c a s h , b u t i t h a s a c h e r t y a p p e a r a n c e w h e r e s i l i c i f i e d .
The pink
r h y o l i t i c a s h e x t e n d s on to the M a r i o n R o s s 1 - m i l e Sheet a r e a to the w e s t , w h e r e it f o r m s a useful m a r k e r unit. greywacke (at
the
It i s o v e r l a i n b y c o a r s e g r e y w a c k e a n d p e b b l e g r e y w a c k e .
Black
Angel
Mine),
which
is
regarded
a s i g n e o u s by C r o h n & O l d e r s h a w (1965).
T h e u p p e r u n i t of t h e O r l a n d o s e q u e n c e c o n s i s t s m a i n l y of s h a l e . the Tennant C r e e k 1-mile Sheet a r e a at
least
The pebble
b e d s a r e v e r y c o a r s e - g r a i n e d and locally r e s e m b l e the 'Black Angel P o r p h y r y '
6000
feet,
with
shale
and
( B l w ^ of C r o h n & O l d e r s h a w , 1 9 6 5 ) . siltstone predominating.
It e x t e n d s into
The thickness is
T h i n b e d s of g r e y w a c k e , tuff,
a n d a s h s t o n e o c c u r i n t h e l o w e r p a r t of t h e u n i t p a r t i c u l a r l y a t , a n d t o t h e n o r t h of, t h e O r l a n d o Mine.
T h e y a r e c o m m o n l y l e s s t h a n 10 feet thick, b u t s o m e d i s c o n t i n u o u s g r e y w a c k e b e d s ,
u p t o 20 f e e t t h i c k , h a v e b e e n n o t e d .
A r o u n d the O r l a n d o M i n e , thin flaggy f i n e - g r a i n e d and
p a r t l y silicified q u a r t z s a n d s t o n e s have b e e n s h e a r e d , and now c r o p out a s ates.
pseudo-conglomer
C o a r s e - g r a i n e d q u a r t z o s e b e d s f o r m boudins in the p s e u d o - c o n g l o m e r a t e s ; saucer-shaped
tectonic
inclusions
in the
less
they a r e
roughly
equidimensional
competent shale
matrix.
S e v e r a l b e d s of p y r i t i c s h a l e a n d s i l t s t o n e a r e a s s o c i a t e d w i t h t h e f l a g g y b e d s ;
the
pyrite c r y s t a l s a r e euhedral and up to 8 m m a c r o s s . T h r e e l a r g e b o d i e s of t u f f a c e o u s and feldspar,
r o c k , w i t h s c a t t e r e d l a r g e c r y s t a l s of q u a r t z
c r o p out within this shale sequence.
They a r e the A r g o and Olive Wood l e n s e s
a n d a n u n n a m e d l e n s n e a r t h e Q u a r t z H i l l r o a d a b o u t 2 m i l e s s o u t h - e a s t of t h e M a r i o n R o s s Mine (discussed below). S o u t h of t h e O r l a n d o M i n e , t h e b e d s a b o v e t h e O r l a n d o p a r t of t h e s e q u e n c e a r e poorly exposed; and shale.
t h e y i n c l u d e l o w l a t e r i t i z e d h i l l s of t u f f a c e o u s s i l t s t o n e , t a l c o s e s i l t s t o n e ,
T h e y r e p r e s e n t t h e h i g h e s t p a r t of t h e W a r r a m u n g a G r o u p e x p o s e d o n t h e M o u n t
Woodcock Sheet a r e a . R o c k s c o n t a i n i n g l a r g e c r y s t a l s of q u a r t z a n d f e l d s p a r , a n d f r a g m e n t s of r o c k
('Porphyroidal
Rocks') T h e A r g o and Olive Wood l e n s e s , and t h e u n n a m e d l e n s n e a r Q u a r t z Hill r o a d , in and
t h e O r l a n d o s e q u e n c e , h a v e b e e n d e s c r i b e d b y I v a n a c (1954) a s i n t r u s i v e d y k e s a n d s i l l s extrusive
conglomerates
volcanic and
flows.
J. Elliston (pers. comm.) considers that they a r e mud-flow
r o c k s p r o d u c e d by c r y s t a l l i z a t i o n f r o m a colloidal s t a t e .
about 2 m i l e s long a n d f r o m 600 to 1000 feet thick.
E a c h body i s
They a r e markedly inequigranular rocks,
r e s e m b l i n g p o r p h y r i e s , a n d c o n s i s t of ' p h e n o c r y s t s ' of q u a r t z a n d f e l d s p a r a n d f r a g m e n t s of r o c k set in a fine-grained
matrix.
They form m a s s i v e blocky outcrops, and a r e commonly 14
lateritized. and
The texture varies laterally and vertically.
the original
structure
has been
t h e r e i s n o e v i d e n c e of c h i l l i n g . greywacke.
partly
All t h r e e l e n s e s have been s h e a r e d
obliterated.
The lenses may be intrusive, but
In p l a c e s t h e c o n t a c t s a p p e a r t o b e g r a d a t i o n a l i n t o s h a l e o r
Some apophyses from the l e n s e s appear to intrude the country rock, but the r e
l a t i o n s h i p s c a n a l s o b e e x p l a i n e d b y s l i p f o l d i n g a n d l o c a l t r a n s p o s i t i o n of b e d d i n g . T h e O l i v e W o o d l e n s i s 2 1/4 m i l e s l o n g a n d 6 0 0 f e e t t h i c k . it r a n g e s from c o a r s e porphyritic q u a r t z - f e l d s p a r to
tuff.
The greywacke
contains
crystals
F r o m e a s t to west,
rock to m a s s i v e tuffaceous
of q u a r t z u p t o 4 m m i n d i a m e t e r .
greywacke(?) The lateral
v a r i a t i o n in t e x t u r e i s a c c o m p a n i e d by a d e c r e a s e in t h e t h i c k n e s s which s u g g e s t s a s o u r c e to the e a s t . T h e M o u n t A r g o l e n s a n d t h e u n n a m e d l e n s s o u t h - e a s t of t h e M a r i o n R o s s M i n e are
both
antiform
intensely
north-west. feldspar The
cleaved.
The Argo
a g a i n s t t h e Q u a r t z Hill F a u l t .
lens
o c c u p i e s t h e c o r e of a t i g h t s t e e p l y p l u n g i n g
I t c o n s i s t s of t w o s e p a r a t e u n i t s w h i c h d i v e r g e t o t h e
T h e s o u t h e r n u n i t i s m o s t l y c o a r s e - g r a i n e d w i t h f r a g m e n t s of r o c k , q u a r t z , a n d
from
northern
6 to unit
8 mm is
across;
more
massive
s o m e b e d s of s h a l e a n d f i n e - g r a i n e d tuff a r e p r e s e n t . and m o r e
variable laterally than the southern unit.
B a n d s of t a l c o s e tuff a r e c o m m o n , a n d t h e p h e n o c r y s t s a r e g e n e r a l l y m u c h s m a l l e r t h a n i n t h e southern unit.
T h e t e x t u r e of t h e s o u t h e r n u n i t i s s i m i l a r t o t h a t of t h e O l i v e W o o d l e n s , w h i l e
t h e n o r t h e r n u n i t r e s e m b l e s t h e l e n s s o u t h - e a s t of t h e M a r i o n R o s s M i n e . I n a d d i t i o n t o t h e t h r e e m a i n l e n s e s , t h i n b e d s of s i m i l a r r o c k t y p e s o c c u r t h r o u g h out
the basal
s h a l e s e q u e n c e , together with tuffaceous
exposed example is the sheared talcose inequigranular
g r e y w a c k e , tuff, a n d a s h s t o n e . ('porphyroidaP)
One
rock in the Orlando
M i n e w h i c h d e f i n e s a n o v e r t u r n e d w e s t - p l u n g i n g s y n c l i n e a n d a n t i c l i n e t o t h e e a s t of t h e m i n e . T h e c e n t r a l l i m b of t h e s t r u c t u r e h a s b e e n s h e a r e d o u t a n d a p p e a r s t o c o n t r o l t h e m i n e r a l ization. A t t h e b a s e of t h e s h a l e s 1 m i l e w e s t of t h e M a r i o n R o s s M i n e , t h e r e a r e s e v e r a l beds
of a c o a r s e - g r a i n e d
quartz
with
concentrically
r o c k c o n t a i n i n g q u a r t z p h e n o c r y s t s , l a r g e r o u n d e d a g g r e g a t e s of arranged
inclusions
of c h l o r i t e ,
and quartzite pebbles;
they
r e s e m b l e quartz p e b b l e s in the Black Angel p o r p h y r y . The
origin
of t h e s e r o c k s i s u n c e r t a i n ,
that they a r e f i n e - g r a i n e d 'phenocrysts'
J . Elliston (Geopeko N.L.) c o n s i d e r s
s e d i m e n t s f o r m e d by turbidity c u r r e n t s o r m u d flows and that t h e
w e r e f o r m e d a u t h i g e n i c a l l y i n a c o l l o i d a l s u s p e n s i o n of fine s e d i m e n t ( E l l i s t o n ,
1964).
S o m e of t h e p h e n o c r y s t s m a y h a v e o r i g i n a t e d i n t h i s w a y - s u c h a s t h o s e f o u n d n e a r
Marion
Ross,
origin.
The
turbidity
currents.
and in the Black Angel porphyry; rocks
b u t m o s t of t h e m a p p e a r t o b e v o l c a n i c i n
m a y have been deposited a s a s h flows o r m u d flows, o r r e d e p o s i t e d by T h e m a s s i v e n a t u r e of t h e m a i n l e n s e s , t h e p r e s e n c e of l a p i l l i , a n d of
embayed and r e s o r b e d quartz and feldspar and bipyramidal quartz, and the eutaxitic texture, suggest
that
they
are
a s h flows
or
lahars,
r e s t r i c t e d in distribution (Ross & Smith, 1961). tures,
but pyroclastic flow-rocks a r e not usually so Deformation h a s obliterated diagnostic tex
b u t t h e r o c k s a r e m a i n l y of e x t r u s i v e o r i g i n , a n d i n t r u s i v e q u a r t z - f e l d s p a r
porphyry
d y k e s , c o m p a r a b l e w i t h t h o s e of t h e T e n n a n t C r e e k a r e a , a r e s u b o r d i n a t e . Northern Star Sequence Although the structure is complex, and the stratigraphy i s uncertain, the Northern Star
s e q u e n c e p r o b a b l y c o n s i s t s of a l o w e r u n i t of g r e y w a c k e a n d s h a l e , o v e r l a i n b y s h a l e , 15
siltstone, and hematite shale.
The outcrop f o r m s a n a r r o w zone trending e a s t - w e s t from the
w e s t e r n m a r g i n of t h e S h e e t , s o u t h of M o u n t W o o d c o c k , t o t h e N o r t h e r n S t a r M i n e a n d a c r o s s to
the
Zone,
Stuart
Highway.
The s e q u e n c e is bounded to the south by the N o r t h e r n Star Shear
a n d by t h e o v e r l y i n g T o m k i n s o n C r e e k B e d s to t h e n o r t h .
small-scale
folds,
dips range from
but
30
apgear
to
form
The beds contain complex
a continuous s e q u e n c e dipping south to s o u t h - e a s t ;
t o 80 , w i t h o c c a s i o n a l o v e r t u r n i n g t o t h e n o r t h .
In t h e w e s t t h e s t r a t i
g r a p h y i s u n k n o w n , b u t t h e s c a t t e r e d o u t c r o p s n o r t h - w e s t of B u t c h e r s W a t e r h o l e a p p a r e n t l y f o r m p a r t of a l a r g e a n t i f o r m p l u n g i n g s t e e p l y t o t h e w e s t . T h e e a s t e r n p a r t of t h e a r e a a r o u n d t h e N o r t h e r n S t a r M i n e h a s b e e n i n v e s t i g a t e d in detail by d r i l l i n g and g e o c h e m i c a l s u r v e y s (Dunnet, 1965), W e s t of t h e m i n e , g r e y w a c k e a n d s h a l e c r o p o u t i n B u t c h e r s C r e e k n e a r i t s j u n c tion with Phillip C r e e k (185500, 2578000). and
south-east,
and
probably
The greywacke and shale dip predominantly e a s t
u n d e r l i e the fine-grained pink siltstone, shale, and h e m a t i t e
shale at the Northern Star Mine.
T h e r o c k s a t t h e m i n e a r e i n t e n s e l y f o l d e d , w i t h a s y s t e m of o l a t e r f o l d s s u p e r i m p o s e d o n a n e a r l i e r s y n c l i n e . T h e e n v e l o p i n g s u r f a c e d i p s s o u t h a t 30 t o 60 .
Chloritic shale has been r e c o r d e d in diamond d r i l l - c o r e s . A r i d g e c o m p o s e d of q u a r t z - h e m a t i t e a n d W a r r a m u n g a G r o u p r o c k s c r o p s o u t
1 m i l e s o u t h of t h e N o r t h e r n S t a r M i n e , a l o n g t h e N o r t h e r n S t a r S h e a r Z o n e . similar
The beds are
to t h o s e a t the N o r t h e r n S t a r Mine, and include s h a l e , pink siltstone, and h e m a t i t e
s h a l e w i t h m i n o r b e d s of g r e y w a c k e ;
t h e y d i p a t a b o u t 50
south-east towards the Northern
Star Shear Zone. T h e l o w o u t c r o p of h e m a t i t e s h a l e a n d s h a l e a q u a r t e r of a m i l e e a s t of t h e N o r t h e r n S t a r M i n e (188000, 2578000) d i p s s o u t h - e a s t a t 50 . shales
known to o c c u r 3 m i l e s s o u t h - w e s t (182000, 2575000). inches
T h e white silicified r u b b l e on the
c o u l d b e s i l i c i f i e d c a r b o n a t e r o c k s , a s l e n s e s of d o l o m i t e a n d d o l o m i t i c s i l t s t o n e a r e thick,
and
siltstone,
and
Northern
Star
are
dip
at
associated
Crystalline carbonate
lodes
rocks
50
south-east; with
carbonate
(DDH
probably
the sedimentary dolomites
T h e l e n s e s a r e up to 2 feet long and 6
they a r e interbedded with leached yellow to pink
shale, hematite shale, siltstone, and minor greywacke. rocks
were
a l s o i n t e r s e c t e d about 1000 feet b e l o w the
15, Mines Branch, N.T. Administration, unpubl. r e c o r d s ) . represent
recrystallized
to the s o u t h - w e s t .
sediments,
and
may
The
b e e q u i v a l e n t to
It i s p o s s i b l e , h o w e v e r , t h a t t h e y w e r e f o r m e d
d u r i n g t h e g o l d a n d c o p p e r m i n e r a l i z a t i o n of t h e N o r t h e r n S t a r a r e a . Between
the
Northern
Star
Mine
and
the
Stuart
Highway t h e r e a r e
several
s m a l l l o w o u t c r o p s of s h a l e , s i l t s t o n e , a n d m i n o r h e m a t i t e s h a l e d i p p i n g m a i n l y s o u t h - e a s t a t 40
t o 60 .
T h e o u t c r o p s f o r m t h e e a s t e r n l i m i t s of t h e N o r t h e r n S t a r s e q u e n c e .
South
e a s t of t h e N o r t h e r n S t a r S h e a r Z o n e , t h e B e r n b o r o u g h - W h i p p e t s e q u e n c e d i p s n o r t h a n d n o r t h west;
this is c o n s i s t e n t with the h y p o t h e s i s that the N o r t h e r n Star Shear Zone is a faulted
synclinal trough. A b o u t 3 m i l e s n o r t h - n o r t h - e a s t of B u t c h e r s W a t e r h o l e , s m a l l h i l l s of i n t e r b e d d e d greywacke,
quartz
s o u t h a t 40
t o 70 , r i g h t w a y u p .
greywacke,
and
shale,
with well developed bedding and load c a s t s , dip
A s s u m i n g that the succession is continuous, the b e d s p r o b
a b l y u n d e r l i e t h e d o l o m i t e s in t h e N o r t h e r n S t a r s e q u e n c e . extends
west
The greywacke-shale
sequence
(between 176000, 2576000, and 171000, 2577000) with m i n o r q u a r t z s a n d s t o n e 16
and granule quartz sandstone beds. is
unknown.
Dips r a n g e from s t e e p north to s t e e p south, and the facing
T h e q u a r t z s a n d s t o n e u n i t a t 1 7 6 0 0 0 , 2 5 7 6 0 0 0 , d i p s 70
south, probably on the
s o u t h e r n l i m b of a s t e e p w e s t - p l u n g i n g a n t i f o r m . T h e fold c a n b e t r a c e d o n t h e a i r - p h o t o g r a p h s , but
w a s not l o c a t e d in the field.
c r o p out in s c a t t e r e d m e s a s ; structure
probably
In t h e w e s t ( a r o u n d 1 7 1 0 0 0 , 2 5 7 6 0 0 0 ) g r e y w a c k e a n d s h a l e
d i p s r a n g e f r o m 70
n o r t h , t h r o u g h 60
w e s t t o 70
c o n s i s t s of a l a r g e a n t i f o r m p l u n g i n g t o t h e n o r t h - w e s t .
south;
Farther
the
south
(around 172000, 2573000), the interbedded shale, quartz g r e y w a c k e , and quartz sandstone dip m a i n l y t o t h e s o u t h - w e s t i n a s e r i e s of f o l d s p l u n g i n g g e n t l y w e s t ;
t h e s e n s e of m o v e m e n t i s
c o n s i s t e n t w i t h t h e p r e s e n c e of a m a j o r a n t i c l i n e t o t h e n o r t h - w e s t . A l o w l a t e r i t i z e d h i l l of W a r r a m u n g a G r o u p r o c k s o c c u r s a t 1 7 2 0 0 0 , 2 5 7 5 0 0 0 ; it
consists
of
shale
and
h e m a t i t e - s h a l e (?)
rubble and shows a p a t t e r n on a i r - p h o t o g r a p h s
s i m i l a r t o t h a t of t h e N o r t h e r n S t a r s e q u e n c e . If t h e b e d s c a n b e c o r r e l a t e d w i t h t h e N o r t h e r n Star
sequence,
it
The Northern
Star
west
the
and
photographs
a p p e a r s that they have b e e n i n v e r t e d in a n o v e r t u r n e d plunging s y n c l i n e . t r e n d a n d l i t h o l o g y of t h e b e d s i n t h e w e s t s u g g e s t t h a t t h e y b e l o n g t o t h e
s e q u e n c e , and t h a t t h e r e i s no s t r u c t u r a l c o n n e c t i o n b e t w e e n the b e d s in the sequence
at
177000,
to
the
south
2577000
of B u t c h e r s W a t e r h o l e .
trend
north-west;
The l i n e a m e n t s on the a e r i a l
t h e y a p p e a r t o b e a c o n t i n u a t i o n of t h e
B e r n b o r o u g h F a u l t , and m a y d i s p l a c e the N o r t h e r n Star s e q u e n c e , in which c a s e it would not b e p o s s i b l e to c o r r e l a t e the s e q u e n c e s in the e a s t and w e s t . C o r r e l a t i o n of t h e W a r r a m u n g a G r o u p S e q u e n c e s A t e n t a t i v e c o r r e l a t i o n of t h e t h r e e W a r r a m u n g a G r o u p s e q u e n c e s o n t h e M o u n t W o o d c o c k and T e n n a n t C r e e k S h e e t a r e a s i s given in F i g u r e 1, i s g i v e n in t h e ' R o c k R e l a t i o n s h i p D i a g r a m * on P l a t e 5,
The m o s t likely c o r r e l a t i o n
This correlation involves the direct
e q u a t i n g of t h e g r e y w a c k e u n i t s (Bwg) a n d s h a l e ( B w s ) i n e a c h s e q u e n c e . T h e c o r r e l a t i o n of t h e g r e y w a c k e - s h a l e u n i t s i n t h e B e r n b o r o u g h - W h i p p e t a n d N o r t h e r n S t a r s e q u e n c e s i s b a s e d o n t h e s i m i l a r i t y of t h e g r e y w a c k e s . interbedded
l e n s e s i n t h e l o w e r p a r t of e a c h u n i t . siltstone
They a r e well bedded,
with s h a l e s , and a s s o c i a t e d with clean quartz sandstone and granule sandstone
unit
Both sequences a r e o v e r l a i n by a s h a l e / h e m a t i t e s h a l e /
which is poorly exposed and h a s a d a r k p a t t e r n on the a i r - p h o t o g r a p h s .
c o r r e l a t i o n of t h e s e r o c k t y p e s w i t h t h e O r l a n d o s e q u e n c e i s u n c e r t a i n . unit
of
the
consists
Orlando
of
sequence
tuffaceous
has
greywacke
a h i g h p r o p o r t i o n of g r e y w a c k e t o s h a l e a n d i n p l a c e s i t rather
than quartz greywacke;
it a l s o includes the pink
c h e r t o r r h y o l i t i c a s h s t o n e w h i c h i s unknown in t h e o t h e r t w o s e q u e n c e s . unit,
unlike
includes
the
the
other
sequences,
porphyroidal
rocks
The
The lower greywacke
is
well exposed;
The overlying shale
it d o e s not c o n t a i n h e m a t i t e s h a l e , but
at Olive Wood and Mount A r g o .
Dolomite is known in the
O r l a n d o M i n e in a s s o c i a t i o n with c h l o r i t i c s l a t e . T h e d o l o m i t e m a y b e e q u a t e d with t h e N o r t h ern
Star
dolomite, although J. Elliston (Geopeko, p e r s . c o m m . ) c o n s i d e r s that the Orlando
d o l o m i t e i s a n e p i g e n e t i c d e p o s i t f o r m e d b y r e p l a c e m e n t of b r e c c i a d u r i n g t h e g o l d - c o p p e r mineralization. Another p o s s i b l e c o r r e l a t i o n equates the B e r n b o r o u g h - W h i p p e t and N o r t h e r n Star s e q u e n c e s , but the g r e y w a c k e - s h a l e unit in t h e s e s e q u e n c e s i s equated with the g r e y w a c k e s h a l e u n i t of B l w ^ i n t h e T e n n a n t C r e e k S h e e t a r e a . tuffaceous
This correlation equates the greywacke and
g r e y w a c k e in t h e l o w e r O r l a n d o s e q u e n c e a n d t h e pink c h e r t with t h e B e r n b o r o u g h
F o r m a t i o n , a n d i n t e r p r e t s t h e M o u n t A r g o a n d O l i v e W o o d r o c k s a s t h e u p p e r p a r t of t h e B e r n borough Formation.
T h e O r l a n d o S h a l e s e q u e n c e (Blw^ = B w s ) i s t h e n e q u a t e d w i t h t h e s i l t -
s t o n e s and s h a l e s which o v e r l i e the B e r n b o r o u g h F o r m a t i o n . H o w e v e r , pink s i l t s t o n e , c o m m o n 17
Tennant Creek 1-mile Sheet
Bernborough Sequence
Orlando Sequence
Northern Star Sequence
I Elw2 Greywacke/shale Hematite shale Ew 3
Elw 2 A Ew 1
Predominantly shale Shale
1 1 1
1
1
1
1
1
1
1
1
siltstone
Shale
siltstone
1
Shale
siltstone
1 1 1 1
Porphyroidal rocks
Hematite shale
Hematite shale
Greywacke and shale
Greywacke and shale 1
Greywacke and shale t
Shale/siltstone
I
1
I I
Hematite shale
1 !
Bernborough Formation
Whippet Sandstone Member
Undifferentiated sediments I I 1
F i g . 1 : C o r r e l a t i o n of W a r r a m u n g a G r o u p s e q u e n c e s ( S e e a l s o A p p e n d i x 1)
18
c
in
the
Bernborough-Whippet
sequence,
w a s not o b s e r v e d in t h e O r l a n d o s e q u e n c e ;
it a l s o
s e e m s unlikely that the B e r n b o r o u g h F o r m a t i o n would change its c h a r a c t e r o v e r a distance of 3 t o 4 m i l e s , a n d t h e f i r s t c o r r e l a t i o n t h e r e f o r e s e e m s t h e m o r e p r o b a b l e .
S t r a t i g r a p h y of t h e M a r i o n R o s s S h e e t A r e a A g e o l o g i c a l r e c o n n a i s s a n c e of t h e e a s t e r n p a r t of t h e M a r i o n R o s s S h e e t a r e a was
undertaken
munga Mine.
Group
concurrently
crops
out
w i t h t h e m a p p i n g of t h e M o u n t W o o d c o c k S h e e t .
The W a r r a
in a b r o a d c u r v e between the Black Angel Mine and the L a s t Hope
T h e s u c c e s s i o n c o n s i s t s of a h o m o g e n e o u s s e q u e n c e of i n t e r b e d d e d g r e y w a c k e a n d s h a l e ,
overlain
of
pink s i l t s t o n e , c h e r t , fine tuffaceous s a n d s t o n e , a c i d v o l c a n i c s ,
and subordinate greywacke.
by
a
sequence
T h e pink r o c k s closely r e s e m b l e the pink c h e r t and a s h s t o n e in
the Orlando s e q u e n c e , but they a p p e a r to b e thicker and to contain m o r e volcanic m a t e r i a l . The
thickness
of
the
greywacke-shale
p r o b a b l y o v e r 1000 feet t h i c k .
unit
is
3000
to 4000 feet, and the pink siltstone i s
In the s o u t h , a r o u n d 162000, 2566000, the pink s i l t s t o n e unit
c r o p s o u t i n t h e c o r e of a w e s t - p l u n g i n g s y n c l i n e a n d c o n t a i n s a c o n s i d e r a b l e p r o p o r t i o n of volcanic r o c k s n e a r the b a s e , including s o m e pink and purple r h y o l i t e s , f r o m 1 to 5 feet thick, rhyolitic ashstone, tuffaceous
g r e y w a c k e , and pink to m a u v e feldspathic g r e y w a c k e .
These
r o c k s g r a d e u p i n t o p i n k s i l t s t o n e a n d a s h s t o n e a t t h e t o p of t h e e x p o s e d s e q u e n c e . In the n o r t h , a l o n g a n e a s t - w e s t line f r o m 165000, 2573000 to 161000, 2573000, t h e pink siltstone s e q u e n c e is r e p e a t e d with a n o r t h e r l y d i p , a p p a r e n t l y on the n o r t h e r n l i m b of a n a n t i c l i n e .
P i n k s i l t s t o n e a n d c h e r t c r o p o u t i n t h e e a s t e r n p a r t of t h i s a r e a , b u t f a r t h e r
w e s t t h e s e q u e n c e c o n s i s t s of f i n e p i n k f e l d s p a t h i c s a n d s t o n e a n d s i l t s t o n e .
Ross
Sheet
shallow area
The
structure
area
includes
plunge
to
the
of
the
rocks
of
the W a r r a m u n g a G r o u p in the e a s t e r n M a r i o n
a
s y n c l i n e in the south and an a n t i c l i n e in t h e n o r t h , b o t h with a
west.
This attitude indicates a major structural b r e a k between this
and the adjacent Orlando a r e a to the east.
The b r e a k i s defined by two l i n e a m e n t s on
t h e a i r - p h o t o g r a p h s - t h e e x t e n s i o n of t h e N o r t h e r n S t a r S h e a r Z o n e a n d a w i d e
north-westerly
s h e a r zone which p a s s e s between the G r e a t W e s t e r n and Orlando M i n e s . An interbedded
s e q u e n c e of g r e y w a c k e a n d s h a l e e x t e n d s f r o m t h e B l a c k A n g e l
Mine to the G r e a t W e s t e r n Mine;
it i s o v e r l a i n by pink s i l t s t o n e and tuffaceous s i l t s t o n e
and
a p p a r e n t l y u n d e r l a i n by a c i d v o l c a n i c s (164000, 2558000). T h e s e q u e n c e i s i n t r u d e d by c o a r s e acid porphyritic Creek part,
dykes,
probably
1-mile Sheet a r e a before
the
related
to
the
quartz-feldspar
(Crohn & O l d e r s h a w , 1965).
cleavage
p o r p h y r y in the T e n n a n t
The dykes w e r e intruded, at l e a s t in
folding ( g h a s e 2), and a r e s h e a r e d a n d folded.
r o c k s d i p n o r t h - w e s t t o n o r t h a t 20
The sedimentary
t o 60 , a n d t h e y f o r m t h e s o u t h e r n l i m b of t h e s y n c l i n e
a t 162000, 2566000, T h e r e l a t i o n s h i p of t h e M a r i o n R o s s s e q u e n c e t o t h e M o u n t W o o d c o c k s e q u e n c e is uncertain, but the two pink volcanic s e q u e n c e s can probably be c o r r e l a t e d .
Tomkinson Creek Beds The
Tomkinson
(Noakes & T r a v e s , 1949; necessitates
the
renaming
Creek
Beds
were
originally named the Ashburton Sandstone
Ivanac, 1954), but p r i o r u s a g e for a W e s t e r n A u s t r a l i a n r o c k unit of
the unit.
M o r e c o m p l e t e s e c t i o n s a r e found 60 m i l e s to t h e
n o r t h i n t h e a r e a of T o m k i n s o n C r e e k ( R a n d a l l , B r o w n , & D o u t c h , 1 9 6 6 ) . 19
T h e T o m k i n s o n C r e e k B e d s a r e f o u n d a l o n g t h e n o r t h e r n m a r g i n of t h e M o u n t Woodcock 5/217
Sheet
1-mile
area
Sheet
and extensively areas.
The
on the adjacent
Tomkinson
Creek
Hayward Creek, Marion Ross, and B e d s have not been m a p p e d in detail
and will probably be r e v i s e d to group status later.
In t h e
Mount Woodcock Sheet a r e a , the relationship between the W a r r a m u n g a
G r o u p and Tomkinson C r e e k B e d s i s uncertain, a s the contact i s either faulted o r obscured by soil.
I n t h e w e s t e r n p a r t of t h e M a r i o n R o s s S h e e t a r e a , t h e t r e n d o f t h e T o m k i n s o n C r e e k
Beds changes from
e a s t - w e s t to n o r t h - s o u t h , with low dips to the w e s t .
beds
pronounced
rest
rocks. phase
.with
a
Farther of t h e
angular
unconformity
In p l a c e s , the b a s a l
on the steeply dipping W a r r a m u n g a
south, they r e s t on s h e a r e d porphyritic granite s i m i l a r to the porphyritic
Tennant C r e e k G r a n i t e Complex in the Quartz Hill a r e a (Crohn & Oldershaw,
1965).
Parts
of t h e
Tomkinson
Creek
B e d s a r e overlain with angular unconformity
by the C a m b r i a n Helen Springs Volcanics and G u m Ridge F o r m a t i o n .
The Beds a r e assigned
a C a r p e n t a r i a n a g e a n d a r e t e n t a t i v e l y c o r r e l a t e d w i t h t h e a r e n a c e o u s T a w a l l a h G r o u p of t h e C a r p e n t a r i a B a s i n , a n d t h e H a t c h e s C r e e k G r o u p , 80 m i l e s s o u t h of T e n n a n t C r e e k t o w n s h i p in the D a v e n p o r t R a n g e s (Smith, S t e w a r t , & Smith, 1961), The Tomkinson Creek Beds trend predominantly east-west, and dip steeply north o r a r e overturned steeply south along their southern m a r g i n .
F a r t h e r n o r t h , they a r e folded
i n l a r g e s t e e p - p l u n g i n g c h e v r o n - t y p e f o l d s , p r o b a b l y a s a r e s u l t of t h e p h a s e 3 d e f o r m a t i o n . They and
include minor
quartz
shale
pebble conglomerate, quartz sandstone, feldspathic quartz sandstone,
and siltstone.
T h e a r e n i t e s a r e m u c h c l e a n e r than t h e g r e y w a c k e s in the
W a r r a m u n g a Group, although g r e e n quartz greywacke and some feldspathic greywacke around Mount Woodcock.
cross-bedding and ripple m a r k s a r e common. few
pebbles
Although quartz pebble c o n g l o m e r a t e s , with a
of g r e y t o g r e e n q u a r t z i t e a n d c h e r t , a r e c o m m o n t h r o u g h o u t t h e s e q u e n c e , n o
basal conglomerate has been observed. are
occur
They a r e usually well bedded, and r a n g e f r o m flaggy to m a s s i v e ;
M o s t of t h e p e b b l e s c o n s i s t of w h i t e r e e f q u a r t z ;
well rounded and r a n g e f r o m half an inch to 4 inches a c r o s s .
they
O n e p e b b l e of u n s h e a r e d
quartz-feldspar porphyry was noted. A Creek,
in
t r a v e r s e a c r o s s t h e T o m k i n s o n C r e e k B e d s in t h e u p p e r r e a c h e s of G i b s o n
the Hayward
Creek
1-mile
Sheet
area,
i n c l u d e s a b o u t 1 0 , 0 0 0 f e e t of a r e n i t e s ,
f a u l t e d a t t h e b a s e , w h i c h a r e c o n f o r m a b l y o v e r l a i n b y a t l e a s t 1 5 0 0 f e e t of f i n e - g r a i n e d v e r y thin-bedded quartz
sandstone, micaceous siltstone, and clayey micaceous quartz sandstone.
Ivanac
(1954)
has
suggested
that
there
is
a
gradation from sandy shale and
s a n d s t o n e w i t h a r g i l l a c e o u s c e m e n t of t h e W a r r a m u n g a G r o u p t o s i l i c e o u s s a n d s t o n e , q u a r t z i t e , a n d c o n g l o m e r a t e of t h e T o m k i n s o n C r e e k B e d s b e t w e e n t h e B l a c k A n g e l M i n e a n d t h e northern
edge
of
t h e g o l d f i e l d , b u t t h e r e c o n n a i s s a n c e m a p p i n g of t h e M a r i o n R o s s 1 - m i l e
S h e e t i n d i c a t e s t h a t t h e a p p a r e n t t r a n s i t i o n i s d u e t o t h e j u x t a p o s i t i o n of t h e a r e n a c e o u s b e d s i n t h e u p p e r p a r t of t h e W a r r a m u n g a G r o u p w i t h t h e T o m k i n s o n C r e e k B e d s . The
southern
margin
of t h e T o m k i n s o n C r e e k B e d s l i e s a d j a c e n t t o d i f f e r e n t
s t r a t i g r a p h i c l e v e l s of t h e W a r r a m u n g a G r o u p ;
this i s caused by the angular
unconformity
i n t h e M a r i o n R o s s S h e e t a r e a , a n d b y f a u l t i n g m o v e m e n t b e i n g of a d e c o l l e m e n t t y p e b e c a u s e o f t h e m a r k e d l y d i f f e r e n t c o m p e t e n c e s of t h e t w o u n i t s . 20
The T o m k i n s o n C r e e k B e d s a r e intruded by gabbro and d o l e r i t e .
The association
of t h e B e d s w i t h b a s i c i n t r u s i o n s i s s i m i l a r t o t h a t i n t h e H a t c h e s C r e e k G r o u p i n t h e D a v e n p o r t Ranges
where
w o l f r a m , b i s m u t h , c o p p e r , and gold have b e e n found.
In a d d i t i o n , t h e
gold-
c o p p e r m i n e r a l i z a t i o n of t h e W a r r a m u n g a G r o u p m a y p o s t d a t e t h e d e p o s i t i o n of t h e T o m k i n s o n Creek Beds.
They t h e r e f o r e w a r r a n t detailed mapping and m i n e r a l exploration.
PALAEOZOIC T h e only P a l a e o z o i c volcanics
overlain
by
r o c k s i n t h e T e n n a n t C r e e k a r e a a r e a t h i n s e r i e s of b a s i c
fossiliferous
chert,
dolomitic
siltstone, and dolomite.
T h e y a r e of
C a m b r i a n age and f o r m a discontinuous link between the L o w e r P a l a e o z o i c s e d i m e n t s in the Wiso Basin and Barkly Tableland. Cambrian T h e C a m b r i a n Helen Springs Volcanics and G u m Ridge F o r m a t i o n in the Mount Woodcock Sheet a r e a have been mapped a s a single unit.
They a r e c o n s i d e r e d to b e L o w e r and
Middle C a m b r i a n in a g e (Ivanac, 1954). C a m b r i a n r o c k s c r o p o u t s p o r a d i c a l l y i n t h e e a s t e r n h a l f of t h e M o u n t W o o d c o c k Sheet a r e a .
T h e y c o n s i s t of b r e c c i a , g r i t s , s i l t s t o n e , a n d l a v a s a n d t u f f a c e o u s r o c k s w h i c h
show considerable lateral variation.
The best sections a r e exposed near the Tennant Creek
G r a n i t e C o m p l e x , s o u t h of t h e B a r k l y H i g h w a y .
The general sequence is a s follows:
Thickness (ft) (minium) 50
Silicified
s h e l l g r i t ( c o a r s e c a l c a r e n i t e ) , in b e d s u p t o 1 foot t h i c k , i n t e r b e d d e d
with c a l c a r e o u s 30 4
siltstones
Breccia Massive
n o d u l a r - w e a t h e r i n g a n d e s i t e o r b a s a l t , with hexagonal c r a c k s on the
nodules 2
Grit, volcanic ash
4
Andesite or basalt, amygdaloidal and vesicular
4
B r e c c i a and silicified quartz grit
flows
UNCONFORMITY Warramunga Group The Cambrian
Tennant Creek Granite Complex s e d i m e n t s and volcanics w e r e deposited on a n undulating e r o s i o n
s u r f a c e on P r o t e r o z o i c r o c k s .
They show considerable lateral v a r i a t i o n s , and within a s m a l l
a r e a , the l o w e r b r e c c i a , t h e v o l c a n i c s , o r t h e u p p e r b r e c c i a m a y r e s t d i r e c t l y on W a r r a m u n g a Group.
The lower and upper b r e c c i a s a r e indistinguishable lithologically; 21
t h e y c o n s i s t of
angular and rounded fragments 4
inches
across,
set
rounded pebbles.
of c h e r t , s i l i c i f i e d s a n d s t o n e , a n d s i l i c i f i e d l i m e s t o n e , u p t o
in a d a r k b r o w n m a t r i x .
A b o u t 1 p e r c e n t of t h e f r a g m e n t s c o n s i s t of
The b r e c c i a s probably represent fossil
soils and local basal
conglomer
ates.
The Helen Springs Volcanics include amygdaloidal and vesicular basic o r i n t e r mediate
flows;
the
amygdales
a r e filled with z e o l i t e s , o r h e m a t i t e , l i m o n i t e , and q u a r t z ,
a n d f o r m u p t o 1 5 p e r c e n t of t h e r o c k .
T w o t y p e s of f l o w a r e e q u a l l y c o m m o n :
in one z e o l i t e s
a n d c a l c i t e have c r y s t a l l i z e d in t h e g r o u n d m a s s and the r o c k h a s a fine s p e c k l e d a p p e a r a n c e ; in t h e o t h e r t h e l a t e m i n e r a l s h a v e c r y s t a l l i z e d in v e i n s a n d v e s i c l e s up to 1 c m a c r o s s . one
section
the
amygdaloidal
flows
are
In
s e p a r a t e d f r o m a m a s s i v e d a r k f i n e - g r a i n e d flow
b y 2 f e e t of p o o r l y s o r t e d a r e n a c e o u s a n d t u f f a c e o u s
material.
T h e m o s t c o m p l e t e s e c t i o n of t h e G u m R i d g e F o r m a t i o n c r o p s o u t i n t h e n o r t h e a s t e r n p a r t of t h e S h e e t a r e a ; siltstone. beds.
The
probably
i t i n c l u d e s a b o u t 50 f e e t of s i l i c i f i e d s h e l l g r i t a n d c a l c a r e o u s
B e d s of c o a r s e m a t e r i a l , u p t o 1 f o o t t h i c k , a r e i n t e r l e a v e d w i t h t h i n n e r residual
represents
hyolithids
and
fossiliferous the
same
brachiopods,
horizon.
and
some
A t 219000, 2557000, the r u b b l e c o n t a i n s abundant trilobites.
A
single trilobite (Redlichea sp.) was
found a t 226000, 2567000 in t h e silicified r u b b l e in the Owen H i l l s . with
coarse
Highway;
angular
fragments
fine-grained
r u b b l e f o u n d i n t h e s o u t h - e a s t e r n p a r t of t h e S h e e t a r e a
of
quartz
overlies
A m a s s i v e silicified grit
t h e g r a n i t e o n b o t h s i d e s of t h e B a r k l y
i t i s n o t m o r e t h a n 10 f e e t t h i c k .
CAINOZOIC
A b o u t t w o - t h i r d s of t h e S h e e t a r e a i s c o v e r e d b y t h i c k C a i n o z o i c s a n d a n d d u s t . They
range
origin.
from
red
to yellow-brown,
and
are
r i c h i n q u a r t z , a n d a r e m a i n l y of a e o l i a n
At Peko M i n e s E x p l o r e r V P r o s p e c t in the M a r i o n R o s s Sheet a r e a , the sand and dust
w e r e found to b e o v e r 100 f e e t t h i c k .
M o s t of t h e p e n e p l a i n s a n d p l a t e a u x a r e s u r r o u n d e d by gently s l o p i n g p e d i m e n t deposits
of
gravel
and
reef
quartz
derived
f r o m t h e W a r r a m u n g a G r o u p , a n d m o s t of t h e
plains a r e littered with quartz.
M a n y of t h e s t r e a m s a r e l o s t in wide d i s t r i b u t a r i e s w h e r e t h e y e n t e r t h e p l a i n s , a n d h a v e d e p o s i t e d s a n d a n d s i l t u p t o a t l e a s t 10 f e e t t h i c k .
In the
north-east,
the
Cambrian
rocks
are
covered
b y a t h i n s h e e t of w h i t e
quartz sand, derived from the Tomkinson C r e e k Beds. T h e whole Sheet a r e a i s d e e p l y w e a t h e r e d , with a f e r r u g i n o u s a n d , in s o m e c a s e s , a
silicified layer, overlying a leached layer.
of
the
rock
has
been
In t h e w e a t h e r i n g p r o f i l e t h e o r i g i n a l t e x t u r e
o b l i t e r a t e d , p a r t i c u l a r l y in d o l e r i t e and s i l t s t o n e .
Where the nature
of t h e o r i g i n a l r o c k i s u n c e r t a i n t h e o u t c r o p h a s b e e n m a p p e d a s l a t e r i t e ( C z l ) . itic
bodies
in
the
upper
Phillip
The later-
C r e e k a r e a , o n t h e m a r g i n of t h e T o m k i n s o n C r e e k B e d s ,
probably represent lateritized dolerite dykes. 22
IGNEOUS ROCKS Granitic Rocks and Porphyries T h e Tennant C r e e k G r a n i t e C o m p l e x extends into the Mount Woodcock 1 - m i l e Sheet
area.
The
grained,
and
contains
numerous
complex
aplitic
includes
granites small
gneissic
porphyritic,
massive porphyritic, medium-
T h e c o m p l e x i s cut by q u a r t z v e i n s a n d d o l e r i t e d y k e s , a n d
c
xenoliths
and
some
infaulted
wedges
of s e d i m e n t a r y
material
(Crohn & O l d e r s h a w , 1965).
Porphyritic Fault.
The
fine-grained developed the
earliest granite
east-west
long
axes
of
and
phase
fine-grained
granite
crop
out
north-east
of t h e Q u a r t z H i l l
i s a m a s s i v e r e d p o r p h y r i t i c g r a n i t e , which i s i n t r u d e d by r e d
and probably by a l a t e r pale g r e y m e d i u m - g r a i n e d g r a n i t e . foliation
the
is
sporadic
present
A poorly
in the porphyritic and fine-grained r e d g r a n i t e s ;
hornblende-rich
f i n e - g r a i n e d x e n o l i t h s a r e o r i e n t e d in t h i s
plane.
T h e p o r p h y r i t i c g r a n i t e c o n t a i n s p h e n o c r y s t s of f e l d s p a r ,
quartz, and p s e u d o -
m o r p h s of c h l o r i t e a f t e r h o r n b l e n d e s e t i n a f i n e - g r a i n e d r e d g r a n i t i c m a t r i x . pink
feldspars
range
up
to
The subhedral
1 c m a c r o s s , a n d e n c l o s e s m a l l w h i t e c r y s t a l s of p l a g i o c l a s e ;
the large quartz grains a r e rounded. V e i n s of f i n e - g r a i n e d r e d g r a n i t e c u t t h e r e d p o r p h y r i t i c g r a n i t e , b u t n o t t h e p a l e grey type. and
are
They a r e m o s t c o m m o n near the boundary between the r e d and pale g r e y g r a n i t e s , randomly oriented;
farther
n o r t h they t r e n d a b o u t 175
and dip steeply.
The pale
g r e y p o r p h y r i t i c g r a n i t e c o n s i s t s of r o u n d e d f e l d s p a r a n d q u a r t z c r y s t a l s , u p t o 1 c m a c r o s s , in a m e d i u m - g r a i n e d g r a n i t i c g r o u n d m a s s ;
mica is the dominant mafic mineral.
The grain-
s i z e of t h e g r e y p o r p h y r i t i c g r a n i t e d e c r e a s e s t o w a r d s t h e c o n t a c t w i t h t h e r e d p o r p h y r i t i c granite
and
the
presence
of
this chilled m a r g i n indicates that the pale grey granite is the
younger. I n t h e e a s t e r n p a r t of t h e c o m p l e x , t h e d o m i n a n t r o c k t y p e i s a p i n k p o r p h y r i t i c g r a n i t e c o n s i s t i n g of p o t a s h f e l d s p a r , p l a g i o c l a s e , q u a r t z , b i o t i t e , a n d h o r n b l e n d e ; r e l a t i v e l y l o w h i l l s o r m o u n d s of r e s i d u a l b o u l d e r s . of p a l e p i n k , b r o w n , o r w h i t e g r a n i t e c r o p s o u t . hematite; silicified.
in p l a c e s it c o n t a i n s f e l d s p a r The
it f o r m s
At a higher level a subhorizontal
sheet
I t i s c o m p o s e d of f e l d s p a r , q u a r t z , a n d a l i t t l e
p h e n o c r y s t s , up to 1 c m a c r o s s , and i s extensively
s h e e t i s u p t o 40 f e e t t h i c k a n d i s d i v i d e d p a r a l l e l t o i t s b a s e b y a z o n e of
c r u s h e d r o c k in w h i c h a u g e n s t r u c t u r e s a r e w e l l d e v e l o p e d .
Although the lower contact with
t h e p i n k p o r p h y r i t i c g r a n i t e w a s n o t s e e n , t h e t r a n s i t i o n t a k e s p l a c e o v e r a d i s t a n c e of a f e w inches; pink
the upper contact is not exposed.
T h e s h e e t of l e u c o g r a n i t e m a y b e i n t r u d e d i n t o t h e
p o r p h y r i t i c g r a n i t e , b u t i t i s p o s s i b l e t h a t i t r e p r e s e n t s a z o n e of t h e p i n k p o r p h y r i t i c
g r a n i t e which h a s been leached and silicified. A d y k e of g r a n i t e w i t h f e l d s p a r p h e n o c r y s t s i n t r u d e s t h e p i n k p o r p h y r i t i c g r a n i t e n e a r its northern margin;
i t i s 25 t o 30 f e e t t h i c k , t r e n d s 0 9 5 , a n d d i p s s t e e p l y .
The three
t y p e s of g r a n i t e i n t h e n o r t h e r n p a r t of t h e c o m p l e x a r e a l l c l e a v e d , i n p l a c e s i n t e n s e l y ; c l e a v a g e t r e n d s a t 090
t o 100
and dips steeply.
The shale, siltstone, and volcanic(?)
of t h e W a r r a m u n g a G r o u p a r o u n d t h e g r a n i t e s h a v e b e e n h o r n f e l s e d , b u t t h e y o u n g e r s e d i m e n t s and volcanics have not been affected. 23
the
rocks
Cambrian
P o r p h y r i e s S o u t h of t h e B e r n b o r o u g h M i n e T h r e e o r f o u r p o r p h y r y i n t r u s i o n s o c c u r a b o u t 2 m i l e s s o u t h of t h e B e r n b o r o u g h Mine.
T h e m o s t e x t e n s i v e i s a d a r k b l u e - m a r o o n f i n e - g r a i n e d r o c k w i t h p h e n o c r y s t s of q u a r t z
a n d f e l d s p a r a n d a g g r e g a t e s of h e m a t i t e ; t h e g r a i n s i z e of t h e g r o u n d m a s s a n d t h e p r o p o r t i o n of p h e n o c r y s t s a r e v a r i a b l e , and it i s p o s s i b l e that two s e p a r a t e i n t r u s i o n s a r e p r e s e n t . i s w e l l d e v e l o p e d c l o s e t o a n d p a r a l l e l t o t h e s o u t h e r n m a r g i n of t h e p o r p h y r y ; i s a b o u t 50 f e e t t h i c k a n d s t e e p l y i n c l i n e d .
Banding
the banded zone
S m a l l z o n e s of b a n d i n g a r e p r e s e n t i n t h e s o u t h -
c e n t r a l p a r t of t h e i n t r u s i o n , a n d t h e p o r p h y r y h a s b e e n c l e a v e d a n d f o l d e d a b o u t a x e s t r e n d i n g 088
a n d p l u n g i n g a t 10
dominantly fine-grained,
west.
T o t h e e a s t of t h i s z o n e of s p o r a d i c b a n d i n g t h e p o r p h y r y i s
and to the w e s t it is dominantly m e d i u m - g r a i n e d .
The banding may
r e p r e s e n t t h e b o u n d a r y of a c h i l l e d m a r g i n o r t h e m a r g i n of a s l i g h t l y l a t e r c e n t r a l i n t r u s i o n . C r e a m q u a r t z p o r p h y r y , a n d a s m a l l b o d y of p o r p h y r y w i t h p h e n o c r y s t s of f e l d s p a r , h o r n b l e n d e , a n d q u a r t z , c r o p o u t a t t h e s o u t h - e a s t c o r n e r of t h e c o m p l e x . of t h e q u a r t z - h o r n b l e n d e - f e l d s p a r range
up to 5 m m a c r o s s .
The groundmass
p o r p h y r y i s fine t o m e d i u m - g r a i n e d , a n d t h e p h e n o c r y s t s
T h e c r e a m q u a r t z p o r p h y r y b e c o m e s finer in g r a i n t o w a r d s the
contact with the q u a r t z - h o r n b l e n d e - f e l d s p a r porphyry, and close to the contact the rock is flowbanded and v a r i a b l e in texture. T h e o r d e r of e v e n t s i s p o s s i b l y a s f o l l o w s : 5.
Folding and cleaving
4.
Cream
3.
Coarser
quartz
porphyry,
grained
partly flow-banded
porphyry
similar
around
the
e d g e of t h e i n t r u s i o n
in c o m p o s i t i o n to 2, with flow-banding for
about 40 feet round the edge 2.
F i n e - g r a i n e d d a r k b l u e - m a r o o n p o r p h y r y , p o s s i b l y a vent filling
1.
A s m a l l b o d y of q u a r t z - h o r n b l e n d e - f e l d s p a r
porphyry.
Schorl Rock The
dyke-like
b o d y of q u a r t z - t o u r m a l i n e r o c k e a s t of t h e S t u a r t H i g h w a y a n d
s o u t h - w e s t of t h e W h i p p e t M i n e i s p r o b a b l y i n t r u s i v e i n t o t h e n o r t h - d i p p i n g v o l c a n i c s a n d s h a l e of t h e B e r n b o r o u g h F o r m a t i o n . tends
070 ,
hematite, epidote, and sericite. grains,
T h e d y k e i s a b o u t 1800 f e e t l o n g , f r o m 6 t o 15 f e e t t h i c k , a n d
T h e r o c k i s c o m p o s e d m a i n l y of q u a r t z a n d t o u r m a l i n e , w i t h a l i t t l e f e l d s p a r ,
fringed
T h e r o c k c o n t a i n s a b o u t 5 p e r c e n t of l a r g e e m b a y e d q u a r t z
b y r a d i a l a g g r e g a t e s of q u a r t z .
The tourmaline is zoned, and r a n g e s from
c o l o u r l e s s to b l u e - g r e e n to g r e e n to b r o w n (from c o r e to r i m ) .
In p l a c e s , t h e t e x t u r e s u g g e s t s
t h a t t h e t o u r m a l i n e h a s b e e n f o r m e d b y t h e r e p l a c e m e n t of f e l d s p a r . Gabbro and Dolerite S m a l l i n t r u s i o n s of g a b b r o a n d d o l e r i t e c r o p o u t a l o n g t h e c o n t a c t b e t w e e n t h e T o m k i n s o n C r e e k B e d s a n d t h e W a r r a m u n g a G r o u p . In t h e u p p e r P h i l l i p C r e e k a r e a t h e y i n t r u d e t h e W a r r a m u n g a G r o u p , and b a s i c d y k e s and s i l l s a r e c o m m o n in the T o m k i n s o n C r e e k B e d s . T h e y a r e g e n e r a l l y p o o r l y e x p o s e d and s t r o n g l y l a t e r i t i z e d , a n d a r e difficult to d i s t i n g u i s h f r o m lateritized Cambrian and Warramunga Group siltstones. 24
N e a r the L a s t Hope Gold Mine, on the Marion R o s s Sheet a r e a , a e o a r s e
gabbro
c r o p s o u t o v e r a n a r e a of a b o u t 2 s q u a r e m i l e s a l o n g t h e b a s e of t h e T o m k i n s o n C r e e k B e d s . T h e g a b b r o h a s a c h i l l e d m a r g i n a g a i n s t t h e s a n d s t o n e , a n d s e v e r a l d y k e s of a m i c a l a m p r o p h y r e ( ? ) intrude the adjoining W a r r a m u n g a Group s e d i m e n t s .
To the e a s t , the g a b b r o n a r r o w s along the
contact between the W a r r a m u n g a Group and the Tomkinson C r e e k B e d s , and dies out a s h o r t d i s t a n c e b e y o n d t h e w e s t e r n b o u n d a r y of t h e M o u n t W o o d c o c k S h e e t . zone
of
magnetic
anomalies
Farther east, there is a
a l o n g t h e c o n t a c t of t h e T o m k i n s o n C r e e k B e d s w h i c h s u g g e s t s
t h a t t h e g a b b r o c o n t i n u e s in depth into
the Mount Woodcock Sheet a r e a .
O c c a s i o n a l d y k e s of
d o l e r i t e a n d a r e a s of d a r k l a t e r i t e , w i t h r e l i c s of d o l e r i t i c t e x t u r e , i n t h e h e a d w a t e r s of P h i l l i p C r e e k o c c u r in the s a m e z o n e .
S a m p l e s f r o m t h i s z o n e w e r e f o u n d t o c o n t a i n b e t w e e n 25 a n d
70 p p m of c o p p e r , a n d s a m p l e s f r o m t h e B h o r i z o n m a t e r i a l w e r e f o u n d t o c o n t a i n : Sample
Cu
Co
Pb
Zn
053421
15
7
2
80
053422
60
1
5
053423
30
1
053424
10
No.
^1
Mo
Bi
40
5
1
7
25
3
1
8
20
^ 1
<1
A t t h e h e a d of t h e n o r t h e r n b r a n c h of P h i l l i p C r e e k , a d a r k g o s s a n o u s r o c k o u t for a l m o s t 500 f e e t .
crops
P r e l i m i n a r y s a m p l i n g yielded s e v e r a l high c o p p e r v a l u e s , and it w a s
r e s a m p l e d to d e t e r m i n e t h e possibility that it r e p r e s e n t s a g o s s a n a b o v e a sulphide body, but the results were inconclusive.
T h e copper, cobalt, lead, and zinc v a l u e s a r e higher than
from known lateritized d o l e r i t e s , but they a r e m u c h lower than those obtained from the
those
Northern
Star and Orlando ironstones. The g a b b r o and dolerite a r e too deeply w e a t h e r e d to b e studied in thin
section.
The dolerite dykes extend at least a s far a s the Stuart Highway, and s e v e r a l gossanous lateritic b o d i e s w e r e o b s e r v e d a r o u n d t h e c o n f l u e n c e of G i b s o n a n d P h i l l i p C r e e k o n t h e H a y w a r d C r e e k Sheet a r e a . sequence.
A n i s o l a t e d d o l e r i t e i n t r u d e s t h e p i n k c h e r t a n d a c i d v o l c a n i c u n i t of t h e O r l a n d o The
d o l e r i t e i s not deeply l a t e r i t i z e d , and c r o p s out in a c r e e k a s a s h e a r e d and
b r e c c i a t e d body along a n e a s t - w e s t s h e a r zone. T h e g a b b r o and d o l e r i t e m a y b e a s s o c i a t e d with the gold and c o p p e r of t h e W a r r a m u n g a G r o u p , o r t h e y m a y b e y o u n g e r .
r o c k s in t h e D a v e n p o r t R a n g e s a n d H a t c h e s C r e e k a r e a . spread wolfram,
mineralization
They m a y be c o m a g m a t i c with the b a s i c R y a n (1961) c o n s i d e r e d t h a t t h e w i d e
c o p p e r , gold, a n d b i s m u t h m i n e r a l i z a t i o n in t h e
Davenport Ranges/Hatches
C r e e k a r e a i s r e l a t e d t o a g r a n i t i c s o u r c e , b u t m o r e r e c e n t i n v e s t i g a t i o n s b y S. Y e a m a n & I . Pontifex ( p e r s . comm.) s u g g e s t s that the mineralization may b e r e l a t e d to the gabbro, dolerite, and basalt. T h e d i a m o n d d r i l l h o l e s put down by A u s t r a l i a n D e v e l o p m e n t N . L . a t B u r e a u M i n e r a l R e s o u r c e s a r e a N o . 3 , s o u t h - w e s t of T e n n a n t C r e e k , i n t e r s e c t e d p r e s u m e d basement rocks, including quartz-feldspar-garnet
of
Archaean
gneiss, amphibolite, and magnetite
gneiss.
T h e s e a r e a p p a r e n t l y i n t r u d e d b y a ' l a t e ' d o l e r i t e w h i c h c a r r i e s t r a c e s of p y r i t e a n d c h a l c o p y r i t e . T h e a s s o c i a t i o n of m a g n e t i t e w i t h t h e c o p p e r s u l p h i d e s , c o b a l t , b i s m u t h , a n d suggest
that the Tennant Creek mineralization
is also related to the b a s i c
gold
rocks.Thebasic
r o c k s a r e thought to b e a p p r o x i m a t e l y c o n t e m p o r a n e o u s with the m i n e r a l i z a t i o n in the T e n n a n t 25
Creek
Gold
F i e l d , a n d C . W e g n e r , f o r m e r l y of A u s t r a l i a n D e v e l o p m e n t N . L . , c o n s i d e r s t h a t
the mineralization was associated with the basic r o c k s . Oldershaw
(1965)
concluded
that
the
H o w e v e r , I v a n a c (1954) a n d C r o h n &
gold and c o p p e r - b e a r i n g q u a r t z - h e m a t i t e and q u a r t z -
magnetite lodes a r e related to the granites and porphyry intrusions.
ROCKS ASSOCIATED WITH GOLD AND C O P P E R
MINERALIZATION
Ironstones The
ironstones
at
C r o h n & O l d e r s h a w (1965).
Tennant
Creek
have
been
described
b y I v a n a c (1954)
T h e y c o n s i s t m a i n l y of q u a r t z , h e m a t i t e , m a g n e t i t e , a n d
and
jasper.
T h e m a g n e t i t e c o n t e n t i n c r e a s e s r a p i d l y b e l o w t h e w a t e r - t a b l e , a n d m o s t of t h e h e m a t i t e h a s been formed
in
the
oxidized
zone
above
the water-table.
I n m o s t of t h e i r o n s t o n e l o d e s t h e
p r o p o r t i o n of q u a r t z a n d j a s p e r i s s m a l l , a n d h e m a t i t e i s t h e c h i e f c o n s t i t u e n t o f t h e l o d e s a t the surface.
Three intrusive lodes in
composed
origin.
two.
types
of
The
three
the
two
been
recognized;
m a s s i v e lodes which
are
but
of
lode
c o m m o n l y o c c u r in close a s s o c i a t i o n , and one type is r a r e l y
I n t h e N o r t h e r n S t a r a r e a , f i v e t y p e s of i r o n s t o n e h a v e b e e n d i s t i n g u i s h e d
t y p e s of r e p l a c e m e n t o r a l t e r a t i o n ( D u n n e t , 1 9 6 5 ) , a n d i n t h e Q u e e n of S h e b a
r e l a t i v e l y m a s s i v e t y p e s of i r o n s t o n e c a n b e d i s t i n g u i s h e d b y t h e d i f f e r e n c e i n
proportion
quartz,
have
hydrated oxides and specular hematite which a r e probably hydrothermal
types
by t h e i r different the
ironstone
The third type is m o r e commonly associated with talc and chlorite than the other
present exclusively. area
of
into the s e d i m e n t a r y r o c k s , banded i r o n s t o n e s f o r m e d , mainly by r e p l a c e m e n t , and
of
quartz.
T h e T e n n a n t C r e e k i r o n s t o n e s g e n e r a l l y c o n t a i n a b o u t 10 p e r c e n t
t h e p r o p o r t i o n v a r i e s c o n s i d e r a b l y in individual l o d e s .
The Northern Star iron
s t o n e s b e a r a n u n u s u a l l y h i g h c o n t e n t of m a n g a n e s e .
A l m o s t a l l t h e i r o n s t o n e l o d e s a r e l o c a l i z e d i n s h e a r - z o n e s o r z o n e s of but in s o m e c a s e s t h e r e p l a c e m e n t i s r e s t r i c t e d to one o r m o r e favourable b e d s .
breccia,
The quartz-
h e m a t i t e - j a s p e r l o d e s a t t h e K l o n d y k e M i n e a n d t o t h e s o u t h of N o r t h e r n S t a r M i n e a r e g e n e r a l l y c o n f i n e d t o t h e c r e s t of a f o l d , a n d t h e l o d e s h a v e a s a d d l e - s h a p e d s t r u c t u r e .
The c o m b i n e d s t r u c t u r a l and lithological c o n t r o l s have r e s u l t e d in the
formation
of a s e r i e s of e n - e c h e l o n l o d e s p l u n g i n g p a r a l l e l t o t h e i n t e r s e c t i o n of t h e f a v o u r a b l e b e d a n d the
controlling structure.
a t a low angle p a r a l l e l to p steeply S/S^
parallel
intersection
to does
and not
The ironstones controlled by the S , and those controlled by the S p^. exceed
and
s h e a r zones generally plunge s t r u c t u r e s generally plunge
A r o u n d t h e N o r t h e r n £>tar M i n e , h o w e v e r , t h e p l u n g e of t h e 50 .
T h e s a m e f a c t o r s a r e probably r e s p o n s i b l e for the
s t e e p a t t i t u d e of t h e P e k o l o d e , c o n t r o l l e d b y t h e l i t h o l o g y a n d t h e S^ P e k o S h e a r .
In s o m e c a s e s t h e i r o n s t o n e s a p p e a r t o h a v e b e e n c o n t r o l l e d only b y t h e limb
of a
Northern
fold a s i n t h e E d n a B e r y l a n d W h i p p e t M i n e s .
sheared
S o m e of t h e i r o n s t o n e s s o u t h of t h e
Star Mine and at the Golden Slipper Mine c r o p out in b r e c c i a z o n e s ;
flat and t a b u l a r , and a r e elongated p a r a l l e l to the b r e c c i a z o n e s .
the lodes a r e
T h e f o r m a n d a t t i t u d e of a l l
t h e i r o n s t o n e l o d e s c a n b e r e l a t e d t o t h e d e g r e e of l i t h o l o g i c a l c o n t r o l a n d t h e a t t i t u d e of t h e controlling structures. 26
Jaspers T h e j a s p e r s c o n s i s t of c r y p t o c r y s t a l l i n e
silica with a pink to b r i g h t r e d
d u e t o t h e p r e s e n c e of v a r y i n g p r o p o r t i o n s of h e m a t i t e . have
been
formed
replacement
by
silicification
of h e m a t i t e s h a l e .
siderable distances.
and
the c e l l u l a r banded h e m a t i t e lodes by
O n e 6 - f o o t b e d of j a s p e r f o l l o w s t h e s a m e b e d r o u n d a t i g h t f o l d i n
w h i c h t h e p l u n g e c h a n g e s f r o m 10
The
siltstone,
In m a n y c a s e s t h e j a s p e r i s r e s t r i c t e d t o o n e b e d o v e r c o n
T h e m o s t favourable b e d s for r e p l a c e m e n t a r e the pink and r e d siltstone
and micaceous siltstone.
structures.
of
colour
At the Northern Star Mine the j a s p e r s
jaspers
t o 50
along the Northern Star Shear Zone.
a r e c o m m o n l y f o r m e d a t t h e i n t e r s e c t i o n of f a v o u r a b l e b e d s
and
I n t h e O r l a n d o M i n e a r e a , i s o l a t e d e n - e c h e l o n p o d s of j a s p e r w i t h m i n o r h e m a t i t e
a r e found w h e r e a n S
shear intersects a siltstone bed.
o
I v a n a c (1954) a n d C r o h n & O l d e r s h a w (1965) h a v e s u g g e s t e d t h a t t h e r e i s a
genet
ic a s s o c i a t i o n b e t w e e n t h e j a s p e r and p o r p h y r i e s , but t h i s h a s not b e e n o b s e r v e d in t h e Mount Woodcock
Sheet
porphyry.
area,
where
most
of
the
jaspers
and ironstones
postdate the granite and
A n u m b e r of t h e i r o n s t o n e s a l o n g t h e u p p e r c o n t a c t of t h e B e r n b o r o u g h
Volcanics
a r e p r o b a b l y l o c a l i z e d t h e r e b e c a u s e of t h e p r e s e n c e of a f a v o u r a b l e b e d .
The ironstones and j a s p e r s a r e commonly sheared or brecciated and b y v e i n l e t s of q u a r t z a n d s p e c u l a r h e m a t i t e .
recemented
A l t h o u g h i n c l u s i o n s of j a s p e r h a v e b e e n n o t e d i n
s o m e of t h e i r o n s t o n e s , t h e y a r e t h o u g h t t o b e b r o a d l y c o n t e m p o r a n e o u s , a n d t h e f o r m a t i o n of both
types
this
is
of l o d e i s t h o u g h t t o b e s y n c h r o n o u s w i t h , o r
the
case,
the
hydrothermal
solutions
could
p o s t d a t e , t h e w a n i n g of p h a s e 3 .
If
have been derived from the gabbro and
dolerite.
Quartz Veins Quartz Field, the
particularly
veins
slaty
have
cleavage
veins
are
common
i n a l l t h e P r o t e r o z o i c r o c k s of t h e
in the W a r r a m u n g a G r o u p ,
Tennant
T h e y a r e of s e v e r a l d i f f e r e n t a g e s .
Creek
S o m e of
b e e n folded by t h e e a s t - w e s t s l a t y c l e a v a g e (S^); m a n y a r e y o u n g e r t h a n t h e but
older than the phase 3 deformation, and even m o r e a r e
contemporaneous
w i t h o r y o u n g e r t h a n p h a s e 3 . M a n y of t h e q u a r t z v e i n s t r e n d n o r t h - w e s t a l o n g t h e S^ c l e a v a g e a n d faults, and n o r t h - e a s t in the S
direction. 4
The veins range from thin s t r i n g e r s parallel to the bedding and S ages,
to
large
discontinuous
pods,
up
to
50
a n d S^
cleav
feet wide and s e v e r a l h u n d r e d i e e t long, in the
n o r t h - w e s t - t r e n d i n g Q u a r t z Hill and B e r n b o r o u g h F a u l t s . The and
q u a r t z v e i n s g e n e r a l l y c o n t a i n o n l y m i n o r a m o u n t s of h e m a t i t e ,
tourmaline.
Auriferous
quartz
veins
are
almost
chlorite,
unknown in the Tennant C r e e k Gold
F i e l d e x c e p t a t t h e L a s t Hope Gold Mine in t h e M a r i o n R o s s S h e e t a r e a , w h e r e t h e y r a n g e up to 4 feet wide, t r e n d 310 , and a r e p r o b a b l y r e l a t e d to the a d j a c e n t d o l e r i t e and g a b b r o . blebs
and
crystals
in
the
Tennant
in
the
border
of
pyrite
C r e e k 1 - m i l e S h e e t a r e a , a n e t w o r k of s m a l l a u r i f e r o u s q u a r t z v e i n s o c c u r s zone
of
a
quartz porphyry intrusion.
no pyrite.
2021/67—3
Scattered
a r e a l s o p r e s e n t in t h e v e i n s ( I v a n a c , 1954). A t t h e P u p M i n e ,
27
The veins contain a little hematite, but
STRUCTURAL GEOLOGY T h e s t r u c t u r e of t h e a r e a w a s i n v e s t i g a t e d u s i n g a s t r u c t u r a l a n a l y s i s s i m i l a r to that u s e d by W e i s s
(1959) a n d T u r n e r & W e i s s (1963).
technique
The method i s suitable for
a r e a s of m u l t i p l e d e f o r m a t i o n , s u c h a s t h e T e n n a n t C r e e k F i e l d , w h e r e c o n v e n t i o n a l t e c h n i q u e s cannot
be
used
relationships
because
deduced
of
from
the this
poor
exposures
analysis
a n d l a c k of m a r k e r b e d s .
The structural
p a r t l y c o n t r a d i c t t h e c o n c l u s i o n s of I v a n a c ( 1 9 5 4 )
a n d C r o h n & O l d e r s h a w (1965). M a n y of t h e r e l a t i o n s h i p s h a v e b e e n e s t a b l i s h e d b y c o m p a r i s o n of similar
features
originate
in
isolated
localities.
The
method
a s t h e r e s u l t of a s i n g l e s t r e s s f i e l d ;
symmetrically
a s s u m e s that these isolated features
this may
oversimplify the tectonic history,
but i s generally supported by the o b s e r v e d r e l a t i o n s h i p s . The Phase the
1 is
Tennant
unconformable
Beds.
Creek
area
has
b e e n s u b j e c t e d t o t h r e e p h a s e s of
deformation.
i n f e r r e d f r o m t h e g e o m e t r i c a l r e l a t i o n s h i p s of p h a s e 2 s t r u c t u r a l e l e m e n t s , a n d relationship
between
the
Warramunga
Group
and
the Tomkinson Creek
A c o n s i d e r a b l e t i m e b r e a k i s p o s t u l a t e d b e t w e e n p h a s e s 1 and 2, to a l l o w t i m e for the
i n t r u s i o n of t h e g r a n i t e ( s y n c h r o n o u s w i t h p h a s e 1 ? ) , e r o s i o n t o e x p o s e t h e g r a n i t e , a n d d e p o s i t i o n of t h e T o m k i n s o n C r e e k B e d s . P h a s e 2 i s t h e m a i n p e r i o d of d e f o r m a t i o n ; regional
metamorphism
and
it is broadly synchronous with
the
i s c h a r a c t e r i z e d b y a s l a t y c l e a v a g e (S^) w h i c h i s d e v e l o p e d t o
s o m e e x t e n t in a l l t h e r o c k s , i n c l u d i n g t h e T o m k i n s o n C r e e k B e d s , Phase faults,
fracture
crenulation
3 c o n s i s t s of t w o c o n j u g a t e s t r u c t u r a l e l e m e n t s ;
cleavage,
cleavage
contradictory
time
and
(S^).
north-west-trending
c r e n u l a t i o n c l e a v a g e (S^), a n d n o r t h - e a s t - t r e n d i n g f a u l t s and
T h e s e two s e t s m a y have r e s u l t e d f r o m s e p a r a t e p h a s e s , but the
relationships
indicate
that
they
are
probably
synchronous and form a
conjugate set. In elements
have
accordance been
with
modern
designated
practice
(Turner
i n t e r s e c t i o n of t w o p e n e t r a t i v e s u r f a c e s , a n d ' B ' f o r a f o l d a x i s ; the phase with which they a r e a s s o c i a t e d .
& W e i s s , 1963), the
structural
' S ' f o r a p e n e t r a t i v e s u r f a c e , * p' f o r t h e a x i s of
by l e t t e r s .
subscripts a r e used to designate
C o r r e l a t i o n of s t r u c t u r a l e l e m e n t s f r o m o n e a r e a
t o a n o t h e r i s b y c o m p a r i s o n of f o l d s t y l e , f a b r i c , o r i e n t a t i o n , s y m m e t r y , a n d t i m e r e l a t i o n s h i p s . T h e following s t r u c t u r a l e l e m e n t s have b e e n r e c o g n i z e d in the M o u n t
Woodcock
Sheet a r e a : S
Bedding
S^
Axial plane cleavage a s s o c i a t e d with phase 1 folds.
B^
F o l d a x e s of p h a s e 1 f o l d s
p^
C o z o n a l a x i s of b e d d i n g a s s o c i a t e d with p h a s e 1 f o l d s
S
Axial
plane
slaty
(and
perhaps
crenulation)
Not developed
cleavage
associated
with phase
2 folds p^
I n t e r s e c t i o n of S a n d
S
Crenulation
or
a n d c o z o n a l a x i s of b e d d i n g f o l d e d b y p h a s e 2
fracture
cleavage associated with phase 3.
Trend north-west
? Sg
Contemporaneously
pg
Intersection S
of
developed
S and
crenulation
cleavage
with
similar trend to S
S , a n d c o z o n a l a x i s of b e d d i n g f o l d e d b y p h a s e 3 , w i t h
axial phase 28
C o z o n a l a x i s of S Crenulation
and intersection S
g
and
fracture
g
and S
c l e a v a g e , p r o b a b l y a s s o c i a t e d with p h a s e 3 .
Trend
n o r t h - e a s t and probably conjugate to Intersection
of
S and
S^,
and
cozonal
a x i s of b e d d i n g f o l d e d b y p h a s e 3
with
as axial plane Equals B^ D e s i g n a t e s the pole o r n o r m a l to a s u r f a c e i.e. T T S i s the n o r m a l to a b e d d i n g p l a n e s t e r e o g r a p h i c p r o j e c t i o n s a r e plotted on the l o w e r h e m i s p h e r e . PHASE 1 FOLDING T h e r e i s s o m e e v i d e n c e to s u g g e s t that the W a r r a m u n g a G r o u p w a s folded the
Tomkinson
Creek
Beds
were
laid
down
and
before
b e f o r e t h e m a i n fold m o v e m e n t which w a s
a s s o c i a t e d w i t h t h e r e g i o n a l m e t a m o r p h i s m a n d t h e d e v e l o p m e n t of t h e e a s t - w e s t s l a t y c l e a v a g e . T h e e a r l y f o l d m o v e m e n t i s t e r m e d p h a s e 1 ; t h e fold a x e s a r e s u b h o r i z o n t a l a n d t r e n d n o r t h west, with steep axial planes. d i p s p r o b a b l y d i d n o t e x c e e d 50
T h e f o l d i n g w a s n o t i n t e n s e a n d no a x i a l c l e a v a g e w a s f o r m e d ; and the regional plunge w a s probably n o r t h - w e s t .
of t h e T e n n a n t C r e e k G r a n i t e C o m p l e x p r o b a b l y t o o k p l a c e d u r i n g t h i s p h a s e .
The intrusion In t h e w e s t e r n
p a r t of t h e M a r i o n R o s s 1 - m i l e S h e e t a r e a , t h e T o m k i n s o n C r e e k B e d s r e s t u n c o n f o r m a b l y o n the T e n n a n t C r e e k G r a n i t e C o m p l e x and on the v e r t i c a l W a r r a m u n g a G r o u p s h a l e s , h e m a t i t e shales, and quartz greywackes. Tomkinson
Creek
Warramunga
The g r a n i t e and W a r r a m u n g a G r o u p a r e both cleaved, but the
B e d s a r e not c l e a v e d , possibly b e c a u s e they a r e m o r e c o m p e t e n t than the
Rocks.
T o t h e n o r t h of t h e M o u n t W o o d c o c k S h e e t a r e a , t h e T o m k i n s o n C r e e k
B e d s h a v e a n incipient e a s t - w e s t c l e a v a g e , and dip steeply n o r t h o r a r e p a r t l y o v e r t u r n e d to t h e s o u t h . T h e s e s t r u c t u r e s w e r e p r o b a b l y f o r m e d d u r i n g t h e m a i n p h a s e 2 folding, a n d the folding m u s t t h e r e f o r e be younger than the Tomkinson Creek B e d s .
T h e g r a n i t e s commonly have an e a s t - w e s t foliation, which was probably d u r i n g t h e s e c o n d p h a s e of d e f o r m a t i o n . part
of
the
formed
S o m e of t h e s p o t t e d c o n t a c t h o r n f e l s e s i n t h e e a s t e r n
Mount Woodcock Sheet a r e a a r e cut and r e t r o g r e s s i v e l y a l t e r e d by an e a s t - w e s t
s l a t y c l e a v a g e (S^).
T h u s , t h e r e is little doubt that the granite was intruded either before or
d u r i n g t h e e a r l y p a r t of t h e m a i n fold p e r i o d , a n d i t s r e l a t i o n s h i p s w i t h t h e T o m k i n s o n C r e e k B e d s in t h e w e s t s u g g e s t t h a t it w a s e m p l a c e d d u r i n g p h a s e 1. Evidence geometry
of
the
for
the
Warramunga
existence
of
phase
Group sediments.
1 deformation can be deduced from
the
T h e n o r m a l s to the bedding throughout the
M o u n t W o o d c o c k a n d M a r i o n R o s s S h e e t a r e a s p l o t o n t h e l o w e r h e m i s p h e r e of a s t e r e o g r a p h i c projection
as
a
widely
scattered
pattern,
dominated
by
two m a x i m a .
These maxima are
s y m m e t r i c a l l y d i s p o s e d a b o u t a h o r i z o n t a l n o r t h - w e s t a x i s which i s not p a r a l l e l to t h e p h a s e 2
or
phase
3 fold
axes,
and
they
a r e thought to r e p r e s e n t r e l i c bedding attitudes from the
p h a s e 1 folding ( s e e F i g . 2). In t h e T e n n a n t C r e e k G o l d F i e l d , s o m e f o l d s a s s o c i a t e d w i t h p h a s e 2, i . e .
with
a s l a t y c l e a v a g e a s a x i a l p l a n e , c h a n g e t h e i r p l u n g e r a p i d l y a n d m a r k e d l y in a r e a s w h e r e t h e attitude
of
the
slaty
cleavage
is
constant.
This indicates that the slaty cleavage has been
s u p e r i m p o s e d o n a n e a r l i e r f o l d e d s u r f a c e , a n d t h u s t h e p l u n g e of t h e b e d d i n g / c l e a v a g e i n t e r section
is
not
constant.
T h e p h a s e 1 f o l d s in t h e M o u n t W o o d c o c k S h e e t a r e a p l u n g e n o r t h
w e s t , e x c e p t f o r o n e fold i n t h e c e n t r e , w h i c h p l u n g e s s o u t h - w e s t ( s u b a r e a 2, P I . 5 ) .
Granite
i s p r e s e n t i n t h e c o r e of t h i s fold a n d m a y b e r e s p o n s i b l e f o r t h e c h a n g e in d i r e c t i o n of p l u n g e . 29
S y n o p t i c 7TS
diagram : 254
to bedding ( S ) . Contoured and
folding
Synoptic d i a g r a m : 125 per 1 % a r e a . T w o and
S3
cleavage
of
does not
bedding axes
equal
S y n o p t i c d i a g r a m : 106
1,3,5,10 and 15% maxima
maxima
and fold a x e s . N o t e
6 per 1 % area
r e a d i n g s . Contoured Sj
Statistical
poles 1,2,4
Contoured
1,3,5
and
fold
position of main B j and positions
F i g . 2 : S t r u c t u r a l g e o m e t r y of t h e W o o d c o c k S h e e t a r e a . 30
S
axes
2
axes.
1 0 % per 1 %
area. Spread of maxima
reflect
cleavages
of
B
reflect B
5
Near
the^ Black
c o n s t a n t l y a t a b o u t 30 but
where
the
sympathy. 15
Angel
north-west.
bedding
steepens
Mine
in
the Marion Ross Sheet a r e a , the bedding
T h e S ^ c l e a v a g e g i v e s p ^ i n t e r s e c t i o n s a t a b o u t 20 the
rotation
axis
is not p a r a l l e l to p ^ , and p
dips west,
s t e e p e n s in
The O r l a n d o s u b a r e a a l s o i n c l u d e s p h a s e 2 folds in which the plunge c h a n g e s f r o m
e a s t to 45
w e s t w i t h i n a f e w h u n d r e d f e e t a l o n g t h e s t r i k e of t h e S ^ c l e a v a g e .
PHASE 2 FOLDING
The formed
m a i n s t r u c t u r a l e l e m e n t of t h e p h a s e 2 d e f o r m a t i o n i s t h e s l a t y
during the regional m e t a m o r p h i s m ;
m i c a and chlorite plates.
T h e c l e a v a g e i s not e x t r e m e l y p e n e t r a t i v e b u t c a n b e s e e n in o u t c r o p
i n a l l of t h e r o c k t y p e s , e x c e p t s o m e of t h e m a s s i v e g r e y w a c k e s .
I t s t r i k e s a t 260
e x c e p t w h e r e i t h a s b e e n m o d i f i e d b y l a t e r f o l d i n g , a n d d i p s b e t w e e n 70 ( s e e F i g . 6).
cleavage
i t i s c o m m o n l y d e f i n e d b y t h e p a r a l l e l g r o w t h of
T h e m o s t c o m m o n d i p i s a b o u t 80
to the north.
t o 290
s o u t h a n d 70
,
north
The cleavage coincides with
the
a x i a l p l a n e s of a l l t h e f o l d s , b u t m e s o s c o p i c f o l d s a r e n o t c o m m o n , a n d a r e o n l y d e v e l o p e d i n thinly bedded or incompetent r o c k s . ation (P ),
w
n
i
c
n
i
2
s
T h e i n t e r s e c t i o n of b e d d i n g a n d c l e a v a g e p r o d u c e s a l i n e -
c o m m o n l y v i s i b l e a s b e d d i n g t r a c e s on the c l e a v a g e p l a n e s ;
in s o m e p e l i t i c
s e q u e n c e s t h e r e i s a l s o a fine m i c a r u m p l e p a r a l l e l to t h e bedding t r a c e . C o l o u r banding a l s o v i s i b l e o n t h e S ^ c l e a v a g e i n m a n y p a r t s of t h e g o l d f i e l d ;
is
this feature superficially resembles
t h e l i n e a t i o n { $ ^ , b u t t h e b a n d i n g i s a p r o d u c t of l a t e r i t i c w e a t h e r i n g . I n t h e f o l d s w i t h S ^ a x i a l c l e a v a g e t h e fold a x e s (B^) a r e a l w a y s p a r a l l e l t o adjacent
B
intersections.
p a r a l l e l t o fiie a x i a l p l a n e s of t h e f o l d s i n t h e p e l i t i c b e d s , b u t d i v e r g e s l i g h t l y i n t h e beds.
the
In a d j a c e n t g r e y w a c k e a n d s h a l e b e d s , t h e c l e a v a g e (S^) m a y b e
T h e a x i s of d i v e r g e n c e of t h e S
psammitic
c l e a v a g e i s r o u g h l y p a r a l l e l t o t h e f o l d a x i s (B ) , a n d
t h e p l u n g e s of t h e m i n o r f o l d s i n b o t h r o c k t y p e s a r e p a r a l l e l . T h e p l u n g e s of t h e
lineation and the m e s o s c o p i c B ^ folds a r e not
a n d t h e y m a y v a r y r a p i d l y b y a s m u c h a s 90 . v a r i a t i o n of p deformation. 45
and B
constant,
S^ i s s t a t i s t i c a l l y p l a n a r in t h e s e a r e a s , a n d t h e
a r e t h o u g h t t o b e t h e r e s u l t of f o l d i n g of t h e b e d d i n g b e f o r e t h e p h a s e 2
In t h e O r l a n d o M i n e a r e a , t i g h t m e s o s c o p i c f o l d s g e n e r a l l y p l u n g e f r o m 1 5
n o r t h - w e s t ; h o w e v e r o n e f o l d w a s o b s e r v e d t o c h a n g e i n p l u n g e f r o m 15
e a s t to 45
to
west
i n s e v e r a l h u n d r e d f e e t of a x i a l l e n g t h . M u l l i o n s , r o d s , and m i n e r a l lineation a r e not g e n e r a l l y a s s o c i a t e d with the 2 s t r u c t u r e s . In the O r l a n d o M i n e a r e a the thinly b e d d e d fine c h e r t y s a n d s t o n e - s i l t s t o n e
phase
sequence
h a s b e e n s h e a r e d by m o v e m e n t on S ^ a t a n a c u t e angle to t h e b e d d i n g to f o r m a t e c t o n i c p s e u d o conglomerate
(Amos, 1962);
i t c o n s i s t s of f l a t t e c t o n i c i n c l u s i o n s i n a s h a l e - s i l t s t o n e m a t r i x .
T h e i n c l u s i o n s a r e f l a t t e n e d in t h e c l e a v a g e , a n d a r e e l o n g a t e d in t h e B ^ fold a x i s in t h e r a t i o of a p p r o x i m a t e l y 2 : 1 . T h i s i s i n c o n t r a s t t o t h e d e f o r m a t i o n of a m y g d a l e s a n d c h l o r i t i c f r a g m e n t s in t h e B e r n b o r o u g h V o l c a n i c s , w h i c h a r e f l a t t e n e d in t h e c l e a v a g e b u t h a v e a d o w n d i p
elongation
s u b n o r m a l to B^o T h e B ^ f o l d s a r e g e n e r a l l y a s y m m e t r i c a l a n d t h e e n v e l o p i n g s u r f a c e of t h e is
t h o u g h t t o r e f l e c t t h e i n i t i a l d i p of t h e b e d d i n g .
Sheet is a good e x a m p l e :
the p h a s e 1 m o v e m e n t gave r i s e to a n o r t h - w e s t - d i p p i n g s e q u e n c e ,
b u t l a t e r p h a s e 2 m o v e m e n t p r o d u c e d a s e r i e s of m i n o r w e s t - p l u n g i n g f o l d s . the
folds
T h e B l a c k Angel a r e a in the M a r i o n R o s s
c r e s t s of t h e f o l d s ( t h e e n v e l o p i n g s u r f a c e )
beds. 31
The plane joining
s t i l l r e f l e c t s t h e i n i t i a l n o r t h - w e s t d i p of t h e
Throughout the goldfield and p a r t i c u l a r l y in the Orlando Mine a r e a , t h e r e z o n e s of feet
tarecciation
wide
and
parallel to the
may
extend
for
cleavage.
hundreds
are
They range from s e v e r a l inches to a hundred
of f e e t a l o n g s t r i k e .
N e a r the O r l a n d o Mine they
t r a n s g r e s s p h a s e 3 s t r u c t u r e s and a r e thought to r e p r e s e n t a late m o v e m e n t on e a r l i e r p h a s e 2 features.
They f o r m favourable z o n e s for r e p l a c e m e n t and a r e c o m m o n l y filled with q u a r t z ,
hematite, or jasper.
I n o t h e r a r e a s , z o n e s of i n t e n s e s l a t y c l e a v a g e h a v e b e e n n o t e d .
t h e s e z o n e s o c c u r i n t h e l i m b s of B apparently unrelated to folds. t h e m i d d l e l i m b of a
In p l a c e s ,
folds, a s at the Orlando Mine, but s o m e s h e a r - z o n e s a r e
T h e Orlando Mine i s situated on a s h e a r - z o n e which s h e a r s out
s y n c l i n e a n d a n t i c l i n e p l u n g i n g a t 25
to the west.
PHASE 3 FOLDING T h e t h i r d p h a s e of d e f o r m a t i o n i s r e p r e s e n t e d b y t w o c o n j u g a t e s e t s of
shears,
w h i c h p r o b a b l y b e g a n t o d e v e l o p a t t h e c l o s e of p h a s e 2 . I n t h e s o u t h e r n p a r t of t h e a r e a l o c a l z o n e s of n o r t h - w e s t - t r e n d i n g f r a c t u r e a n d c r e n u l a t i o n c l e a v a g e s ( R i c k a r d , 1 9 6 1 ) - h e r e t e r m e d Sg - e x h i b i t a c o n s t a n t s e n s e of m o v e m e n t i n i n d i v i d u a l z o n e s . there The
is
In t h e N o r t h e r n S t a r Mine a r e a
a c r e n u l a t i o n c l e a v a g e (S ) t r e n d i n g n o r t h - e a s t w i t h a c o n s t a n t s e n s e of m o v e m e n t .
north-west
cleavage
i s b e s t d e v e l o p e d a l o n g t h e l i n e of t h e Q u a r t z H i l l F a u l t a n d i n t h e
Orlando Mine a r e a to the west. The Bernborough Fault, which trends north-west, also belongs to phase 3.
The
f a u l t a p p e a r s t o d i s p l a c e t h e N o r t h e r n S t a r S h e a r Z o n e , b u t f a r t h e r w e s t t h e c o n t i n u a t i o n of t h e shear-zone apparently displaces a north-west fault-zone.
These contradictory time relation
s h i p s a n d t h e s i m i l a r i t y in s t r u c t u r a l style s u g g e s t that t h e two s h e a r d i r e c t i o n s f o r m a c o m plementary
conjugate
shear
system,
but
in one p l a c e ,
one system is always predominant.
Quartz Hill Subarea T h e p h a s e 3 d e f o r m a t i o n i s m o s t intensely developed in t h e Q u a r t z Hill
subarea,
w h i c h e x t e n d s f r o m Q u a r t z H i l l t o t h e M a r i o n R o s s M i n e , a n d n o r t h w a r d s t o w a r d s t h e Q u e e n of Sheba
Mine.
quartz
reefs
south
T h e Q u a r t z H i l l F a u l t i s m a r k e d b y a z o n e of i n t e n s e S extending from
of B u t c h e r s W a t e r h o l e ;
a d i s t a n c e of o v e r 36 m i l e s .
T h e m a i n m o v e m e n t on the fault
a p p e a r s t o b e d e x t r a l , b u t z o n e s of s i n i s t r a l m o v e m e n t a r e c o m m o n , c o n s i d e r that in t h e T e n n a n t C r e e k intensity
c l e a v a g e a n d a l i n e of
Rocky R a n g e in the T e n n a n t C r e e k 1 - m i l e Sheet a r e a to a point C r o h n & O l d e r s h a w (1965)
1-mile Sheet a r e a the main movement w a s vertical.
The
of c l e a v a g e i n d i f f e r e n t p a r t s of t h e a r e a d e p e n d s p a r t l y o n t h e l i t h o l o g y a n d p a r t l y
o n t h e d e v e l o p m e n t of s h e a r d o m a i n s . T h e s e d o m a i n s r a n g e f r o m s e v e r a l f e e t t o a t l e a s t a m i l e a c r o s s , and can usually be t r a c e d for considerable distances along the s t r i k e .
In any one d o m a i n
t h e i n t e n s i t y a n d s t y l e of c l e a v a g e a n d t h e s e n s e of m o v e m e n t a r e c o n s t a n t .
The cleavage may
b e a n open f r a c t u r e c l e a v a g e , but in m o s t c a s e s is a crenulation cleavage which h a s completely or partly obliterated the earlier east-west slaty cleavage.
C o m p l e t e t r a n s p o s i t i o n of e a r l i e r S
s u r f a c e s i s evident in the Mount A r g o a r e a . T h e s t r i k e o f t h e S^ c l e a v a g e r a n g e s f r o m 2 4 0 ° t o 0 1 0 ° a n d t h e d i o f r o m 6 0 °
q
w e s t t o 70
north-west.
dips (Fig. 4). common.
a n d 320 , with
south
subvertical
320 - s t r i k e direction, p a r a l l e l to the m a i n Quartz Hill Fault; i s the m o s t
T h e 300 - s t r i k e d i r e c t i o n c l e a v a g e (S'^) i s e i t h e r a n i n c i p i e n t c r e n u l a t i o n c l e a v a g e
developed similar
The
T h e two m a i n c l e a v a g e d i r e c t i o n s a r e 300
contemporaneously
orientations,
with
S , or
a younger subsidiary cleavage.
S^ a n d S' a r e difficult to d i s t i n g u i s h .
f o u n d , a n d a r e b i s e c t e d b y t h e a x i a l p l a n e of t h e f o l d .
B e c a u s e of t h e i r
In s o m e folds b o t h S
S i m i l a r l y , i n o n e c a s e S^ a n d
a n d S' a r e have oeen
d e v e l o p e d in t h e o n e fold a s a c o n j u g a t e s y s t e m , with t h e a x i a l p l a n e b i s e c t i n g t h e t w o s u r f a c e s (Fig. 3). 32
C
Bruchfalten, associated with S3 fracture
d
cleavage. Note fracture
cleavage developing in core of fold. Orlando
Z o n e of
fracture cleavage with
constant sense of Orlando
Subarea
symmetrically e
movement,
Subarea
oblique to axial
C o n j u g a t e set of kink planes
plane of f o l d . N o t e ,
with orthorhombic
intersection produces pencils
m o v e m e n t . The parallel to S
3
flattening
kink planes are and
S3/S4
plunging 8 0 ° w e s t - i . e . B , but S / S 3
S 4 . Olive
intersection is about
Wood A r e a
i.e. B F i g . 3 : P h a s e 3 fold s t y l e s 33
3
60° west-
does not equal B
3
3
Quartz Hill S u b a r e a : 120
Quartz Hill Subarea: 180 crenulation
bedding
poles TTS showing spread about
and fracture cleavage poles ( T T S 3 )
B3
and relic south-west dip. Contoured
two maxima defining
1,3,7,10 and 1 5 % per 1 % area
Contoured 1,5,8 and 12% per 1 % area
Quartz
Northern Star Subarea: Composite
B
3
S
3
of
Hill S u b a r e a : 70 fold axes
and
B
3
3
initial
bedding
Contoured 1,3,6
3
3
and S
3
.
diagram illustrating bedding ( S ) ,
in girdle spread along
and S . Stronger S
S
crenulation cleavage (S4), and fold
spread result
axes B . Note B
orientation.
4
a n d 10% per 1 % area
4
number of readings
Fig, 4 : G e o m e t r y of p h a s e 3 , 34
spread along
Not contoured because of
small
S4.
F i g . 5: M o u n t W o o d c o c k - T e n n a n t C r e e k s t r u c t u r a l s u b a r e a s .
In t h e Q u a r t z
H i l l s u b a r e a , t h e g e n e r a l a t t i t u d e of b e d d i n g ( S ) a f t e r p h a s e s 1
2 w a s p r o b a b l y t o t h e s o u t h - w e s t a t a b o u t 70
t o 80 .
and
E a r l i e r folds about low-dipping n o r t h -
n o r t h - w e s t a x e s a r e s u g g e s t e d by t h e r e l i c g i r d l e o n t h e T T S d i a g r a m of t h e Q u a r t z H i l l s u b a r e a (Fig.
4).
The
intersection
into
S
transposed
v a r i a b l e plunge (P3 plete
girdle
of
surfaces, 2
).
the
S
a n d S'
T h e a x e s r a n g e f r o m s u b h o r i z o n t a l to s u b v e r t i c a l and s p r e a d in a c o m
along the axial plane directions S
c r e n u l a t i o n folds h a v e s u b v e r t i c a l p l u n g e s . e x p r e s s e d in t h e p
c l e a v a g e s with the bedding, and the b e d d i n g
h a s r e s u l t e d i n trie f o r m a t i o n of c r e n u l a t i o n f o l d s w i t h a x e s of a n d S^ ( F i g . 4 ) . H o w e v e r , t h e m a j o r i t y of t h e
T h e two c l e a v a g e d i r e c t i o n s
a n d S^ a r e
clearly
d i a g r a m b y t h e fold a x e s , w h i c h t e n d t o s p r e a d i n a d o u b l e g i r d l e . 3
Fold Styles The folds r a n g e from
m i c r o s c o p i c t o l a r g e r e g i o n a l s t r u c t u r e s , a n d fold
a r e v a r i a b l e , d e p e n d i n g o n t h e i n t e n s i t y of s h e a r i n g o n S ^ . c h e v r o n - s t y l e folds, which g r a d e into tighter a p p r e s s e d and
limbs
faulted
parallel
parallel to
result from
that
not
does
to
the axial plane.
styles
F r a c t u r e c l e a v a g e r e s u l t s in o p e n
slip folds with 'gleitbrett'
character
In t h e c o r e s of s o m e f o l d s , p e n c i l s t r u c t u r e s
t h e i n t e r s e c t i o n of t h e t w o c l e a v a g e s S
a n d S^.
p a r a l l e l t h e b e d d i n g / c l e a v a g e i n t e r s e c t i o n (Pg)«
There is evidence
Bg is probably a rotation
a x i s and strain a x i s o v e r wide a r e a s . T h e l a r g e s t k n o w n fold i n t h e a r e a i s t h e M o u n t A r g o a n t i f o r m , w h i c h i s by p o r p h y r o i d a l r o c k s .
defined
It h a s a h a l f w a v e l e n g t h of h a l f a m i l e a n d a n a m p l i t u d e of o v e r a m i l e .
I t p l u n g e s n o r t h - w e s t a t a b o u t 60 , a n d t h e n o r t h e r n l i m b i s s h e a r e d o u t a l o n g t h e Q u a r t z H i l l Fault. B e c a u s e of t h e s i m i l a r i t y i n t r e n d o f t h e S ^ , S ^ , a n d S^ c l e a v a g e s a n d t h e
variation
i n i n t e n s i t y of e a c h p h a s e , i t i s d i f f i c u l t t o d e t e r m i n e w h i c h p h a s e i s p r e d o m i n a n t i n i s o l a t e d outcrops. or
T h e p h a s e 3 s t r u c t u r e s c a n g e n e r a l l y b e d i s t i n g u i s h e d b y t h e s t y l e of t h e c r e n u l a t i o n
fracture
cleavage,
t h e c o n s t a n t m o n o c l i n i c s e n s e of m o v e m e n t o v e r l a r g e a r e a s , a n d t h e
s t e e p p l u n g e of t h e S / S , S / S , a n d S / S ' 1
O
m
O
o
intersections.
o
Orlando Subarea In t h e O r l a n d o s u b a r e a , t o t h e n o r t h of a n d i n t h e i m m e d i a t e v i c i n i t y of t h e Mine,
the
subarea.
phase 3 deformation
Orlando
i s n e i t h e r a s i n t e n s e n o r a s p e n e t r a t i v e a s in t h e Q u a r t z H i l l
T h e b o u n d a r y b e t w e e n t h e t w o s u b a r e a s i s t r a n s i t i o n a l , b u t t h e i n t e n s i t y of d e f o r m a t i o n
a p p e a r s t o d e c r e a s e r a p i d l y t o t h e w e s t of t h e O l i v e W o o d M i n e . T h e p h a s e 3 d e f o r m a t i o n i s r e s t r i c t e d t o z o n e s of n o r t h - w e s t - t r e n d i n g cleavage ranging from
10 f e e t t o s e v e r a l h u n d r e d f e e t w i d e .
c l e a v a g e , a n d kink t h e m p r e d o m i n a n t l y in a d e x t r a l s e n s e ; been
noted.
chevrons
at
fracture
T h e zones cut the bedding and S
2
occasional sinistral movements have
T h e r e s u l t a n t f o l d s a r e a l l of t h e c h e v r o n t y p e , b u t r a n g e f r o m s m a l l a m p l i t u d e spacings from
6 i n c h e s t o s e v e r a l f e e t in a r e a s of i n t e n s e f r a c t u r e c l e a v a g e , t o
s i n g l e k i n k s w i t h u p t o s e v e r a l h u n d r e d f e e t b e t w e e n k i n k p l a n e s ( S ^ ) . In s o m e i n s t a n c e s o n l y o n e k i n k p l a n e i s d e v e l o p e d i n a b r u c h f a l t e n fold s t y l e . o T h e s t r i k e of t h e S most
common
c l e a v a g e a n d f a u l t o l a n e s r a n g e s f r o m 280
d i r e c t i o n s a r e 300
and 320
to 340 .
T h e 320 - 3 4 0
T h e fault m o v e m e n t s a r e a l m o s t a l w a y s d e x t r a l . 36
The S
the
set a r e a s s o c i a t e d with
c o n s i d e r a b l e fault m o v e m e n t , a n d a r e c o m m o n l y i n t r u d e d by q u a r t z and m i n o r veins.
o t o 360 , b u t
quartz-hematite
cleavage always dips steeply,
g e n e r a l l y between 80° north and 80° south, and the lowest dip o b s e r v e d was 6 0 ° . the
bedding
ranges from
280
t o 3 0 0 , w i t h d i p s b e t w e e n 60
slaty c l e a v a g e s have a s i m i l a r t r e n d , but a r e subvertical. earlier
structures produces
south-east.
T h e s t r i k e of
a n d 80
to the s o u t h - w e s t ;
The
i n t e r s e c t i o n with t h e s e
the
p^ a x e s w h i c h p l u n g e v e r t i c a l l y o r s t e e p l y t o t h e n o r t h - w e s t o r
T h e s y m m e t r y of t h e O r l a n d o s u b a r e a i s a l m o s t i d e n t i c a l w i t h t h a t of t h e Q u a r t z
Hill s u b a r e a , but the deformation is l e s s intense. A r o u n d t h e O l i v e W o o d M i n e , a c o m p l e x a r r a y of c l e a v a g e s h a s b e e n
developed.
T h e r e a p p e a r t o b e t w o s e t s of n o r t h - w e s t c l e a v a g e s (S ) a n d l o c a l z o n e s of a n o r t h - e a s t c l e a v a g e In s e v e r a l c a s e s t h e y f o r m c o n j u g a t e s e t s , b u t 6\e S
(S^). to
postdate the S
fracture cleavage generally appears
phase. 3
Q u e e n of S h e b a S u b a r e a T h e s t r u c t u r e s in t h e Q u e e n of S h e b a s u b a r e a a r e s i m i l a r t o t h o s e in t h e subarea.
Orlando
T h e S^ c l e a v a g e i s n o t w e l l d e v e l o p e d , b u t f a u l t s s u b p a r a l l e l t o S^ a r e c o m m o n .
In t h e
h i l l s h a l f a m i l e w e s t of t h e G o l d e n S l i p p e r M i n e , a g r o u p of f a u l t s , in p a r t f i l l e d w i t h q u a r t z , trend
at
310
t o 330 , w i t h a n i n c i p i e n t S^ c l e a v a g e a t 3 4 0 . T h e m o v e m e n t o n t h e f a u l t s i s
d e x t r a l a n d i s mainly c o n t r o l l e d by the m o v e m e n t on the B e r n b o r o u g h F a u l t . P
plunge
reversal
between
There is a major
t h e s t e e p n o r t h - w e s t p l u n g e s in t h e n o r t h - w e s t a n d t h e s h a l l o w
s o u t h - e a s t p l u n g e s i n t h e s o u t h - e a s t , p o s s i b l y d u e t o t h e i n t e r s e c t i o n of t h e S^ t r e n d w i t h t h e c r e s t of a p h a s e 2 a n t i c l i n e . Northern Star Subarea T h e N o r t h e r n S t a r s u b a r e a , t o t h e e a s t o f a n d in t h e i m m e d i a t e v i c i n i t y of t h e thern Star Mine, is an important structural domain. A prominent south-west-trending
Nor
lineament,
k n o w n a s t h e N o r t h e r n S t a r S h e a r Z o n e , p a s s e s a b o u t a m i l e s o u t h of t h e N o r t h e r n S t a r M i n e ; it
can
be
traced
from
t h e G o o d n a W a t e r h o l e in t h e n o r t h - e a s t , a l o n g B u t c h e r s C r e e k t o t h e
w e s t e r n b o r d e r of t h e S h e e t a r e a .
T h e l i n e a m e n t d i s p l a c e s t h e Q u a r t z Hill F a u l t , but a p p e a r s
t o b e d i s p l a c e d by t h e B e r n b o r o u g h F a u l t in a d e x t r a l s e n s e .
T h i s s u g g e s t s that the two s e t s
of f a u l t s a r e c o n t e m p o r a n e o u s . N o o u t c r o p s o c c u r a l o n g t h e l i n e of t h e N o r t h e r n S t a r S h e a r Z o n e . The Northern Star subarea is structurally complex.
The rocks at the
Northern
S t a r l e a s e s a r e f o l d e d i n t o a s e r i e s of r e l a t i v e l y o p e n a n t i c l i n e s a n d t i g h t s y n c l i n e s f o r m i n g a b r o a d e a s t - p l u n g i n g synclinoriurn (Ivanac, 1954; Dunnet, 1965).
It p r o b a b l y r e p r e s e n t s a l a r g e
p h a s e 1 o r p h a s e 2 syncline with s u p e r i m p o s e d p h a s e 2 s t r u c t u r e s . a t 260
The main cleavage trends
t o 290 , a n d t h e fold a x e s , a l t h o u g h v a r y i n g c o n s i d e r a b l y in p l u n g e , a r e g e n e r a l l y f l a t .
T h e r e i s s o m e e v i d e n c e f o r t h e p r e s e n c e of c l e a v a g e s of m o r e t h a n o n e a g e . i r o n s t o n e t h e d o m i n a n t c l e a v a g e t r e n d s a t 240
h e m a t i t e - s h a l e b e d s i t f o r m s a c r e n u l a t i o n t y p e of c l e a v a g e . trending
cleavage
to
Around the No. 1
t o 260 , p a r a l l e l t o t h e s h e a r z o n e , a n d in t h e T h e r e l a t i o n s h i p of t h e s o u t h - w e s t -
t h e e a s t - w e s t c l e a v a g e s i s o b s c u r e , b u t b y a n a l o g y w i t h t h e r e s t of t h e
T e n n a n t C r e e k G o l d F i e l d , t h e s o u t h - w e s t - t r e n d i n g c l e a v a g e i s t h o u g h t to b e y o u n g e r . O n e m i l e s o u t h of t h e N o r t h e r n S t a r M i n e , a l i n e of i r o n s t o n e a n d
Warramunga
G r o u p s h a l e a n d s i l t s t o n e c r o p s o u t a l o n g t h e n o r t h e r n m a r g i n of t h e N o r t h e r n S t a r S h e a r Z o n e . In t h i s z o n e t h e d o m i n a n t c r e n u l a t i o n a n d f r a c t u r e c l e a v a g e t r e n d s a b o u t 240 intersect an e a r l i e r e a s t - w e s t slaty cleavage. z o n e ( a r o u n d 1 8 6 9 0 0 , 2 5 7 6 3 0 0 ) w h e r e t h e 240 antiform
a n d a p p e a r s to
T h i s i s m o s t e v i d e n t a t t h e w e s t e r n e n d of t h e
c l e a v a g e (S^) c o i n c i d e s w i t h t h e a x i a l p l a n e of a n
w h i c h h a s b e e n r e p l a c e d a l o n g i t s a x i s by q u a r t z a n d h e m a t i t e . 37
T h e p l u n g e of t h e fold
F i g . 61 G e o m e t r y
of
the
Mount
Woodcock
1-mile
Sheet
area.
o o c l e a v a g e r a n g e s f r o m 15 n o r t h - e a s t t h r o u g h h o r i z o n t a l t o 60 south4 o O n e m i l e t o t h e n o r t h - e a s t , t h e p l u n g e of a fold i n p i n k s i l t s t o n e i n c r e a s e s f r o m 20 t o
a x e s a s s o c i a t e d with the S west, 60
s o u t h - w e s t a l o n g a n a x i a l d i s t a n c e of 30 f e e t .
T h e pink s i l t s t o n e , w h e r e i n v o l v e d in t h i s fold,
h a s b e e n c o m p l e t e l y r e p l a c e d by j a s p e r , but the s u r r o u n d i n g s h a l e s a r e u n a l t e r e d .
The
structure
e a s t of t h e N o r t h e r n S t a r M i n e i s s i m i l a r ;
the bedding dips
a b o u t 60 ^ s o u t h - e a s t a n d t h e f r a c t u r e a n d c r e n u l a t i o n c l e a v a g e t r e n d s a t 2 4 0 o r a t 80
north-west.
t h e p l u n g e (p^)
T h e p l u n g e of t h e f o l d s r a n g e s f r o m 10
h a s probably been controlled by the p r e - S
at
and dips vertically
s o u t h - w e s t to 60
a t t i t u d e of b e d d i n g .
north-east;
In t h e N o r t h e r n
Star s u b a r e a , the v e r t i c a l m o v e m e n t i s always north-block down, and the horizontal component a p p e a r s to be s i n i s t r a l . axis
cannot
both senses.
be
H o w e v e r , two c o n j u g a t e c l e a v a g e s do not o c c u r , s o t h a t a k i n e m a t i c B
determined,
and the r e l a t i v e l y flat
The s y m m e t r y
p^ a x e s a r e c o n s i s t e n t w i t h m o v e m e n t i n
of t h e M o u n t W o o d c o c k a r e a s u p p o r t s t h e p r o b a b i l i t y of s i n i s t r a l
movement. Whippet Subarea
Around
the Edna B e r y l Mine in the Whippet s u b a r e a , the bedding d i p s O
to the north, and the folds plunge e a s t at 5 subvertical.
In t h e f i n e - g r a i n e d
n o r t h - b l o c k down m o v e m e n t .
(
O
t o 20 .
T h e c l e a v a g e t r e n d s a t 260
steeply
J
O
t o 280
and is
r o c k s , the cleavage is a crenulation cleavage with a constant
No e a r l i e r
c l e a v a g e is v i s i b l e and it i s u n c e r t a i n w h e t h e r it i s
a p h a s e 2 o r p h a s e 3 s t r u c t u r e . S i x m i l e s t o t h e e a s t , t h e c r e n u l a t i o n c l e a v a g e e a s t of t h e p e t M i n e t r e n d s a t 220
with the north-block up;
DISCUSSION O F T E C T O N I C D E V E L O P M E N T T h e a t t i t u d e s of t h e S , S ^ , a n d S orthorhombic are
Whip
it probably b e l o n g s to p h a s e 3 .
(Fig. 6). c l e a v a g e s and fault planes f o r m a
s t r u c t u r a l p a t t e r n in the Mount Woodcock Sheet a r e a .
The S
symmetrical
a n d S^ d i r e c t i o n s
b i s e c t e d b y t h e S^ d i r e c t i o n , w h i c h c o i n c i d e s w i t h t h e a x i a l p l a n e of t h e m a j o r
anticlinal
s t r u c t u r e in the Sheet a r e a .
s t r u c t u r e s a r e d o m i n a n t in t h e s o u t h a n d S , s t r u c t u r e s in t h e 3 4 t h e m u t u a l i n t e r f e r e n c e of S^ a n d S^ s t r u c t u r e s s u g g e s t t h a t t h e y a r e s y n c h r o n o u s , a n d
north;
t h e p r e d o m i n a n t s e n s e of m o v e m e n t o n e a c h of t h e m a j o r p h a s e 3 p l a n a r s u r f a c e s s u g g e s t s t h a t they b e l o n g to two r e g i o n a l conjugate s e t s . symmetrical
arrangement
of
the
three
A l t h o u g h b o t h S^ a n d S^ a p p e a r t o p o s t d a t e S ^ , t h e s e t s of s t r u c t u r e s
s u g g e s t s an origin under
similar
s t r e s s conditions. T h e S^ c l e a v a g e d e v e l o p e d s y n c h r o n o u s l y w i t h t h e r e g i o n a l m e t a m o r p h i s m , indicates a maximum compressive
s t r a i n in a n o r t h - s o u t h d i r e c t i o n .
The intermediate
a x i s w a s p r o b a b l y h o r i z o n t a l a n d e a s t - w e s t , p a r a l l e l to t h e m a j o r fold a x i s . by
the
presence
of
cozonal
joints
and
shear-zones
in the g r a n i t e ;
and strain
This is supported
the joints have a sub-
h o r i z o n t a l cozonal a x i s - a k i n e m a t i c £ axis - and their orientation is c o n s i s t e n t with
develop
m e n t d u r i n g p h a s e 2. W i t h t h e w a n i n g of m e t a m o r p h i s m , t h e r o c k s p r o b a b l y f a i l e d a l o n g t h e S t a r S h e a r Z o n e b e c a u s e of t h e c o m p e t e n c e of t h e T o m k i n s o n C r e e k B e d s .
Northern
There was probably
a d e c o l l e m e n t a t t h e b a s e of t h e T o m k i n s o n C r e e k B e d s , a l t h o u g h i t i s n o t v i s i b l e i n t h e f i e l d . T h e f a i l u r e by faulting a n d t h e r e s u l t a n t modification in l o c a l s t r e s s e s r e s u l t e d in t h e d e v e l o p ment
of a c o m p l e m e n t a r y
Q u a r t z Hill F a u l t Z o n e .
s e t of f a u l t s a n d c l e a v a g e i n a n o r t h - w e s t d i r e c t i o n o n s u c h a s t h e
S u b s i d i a r y s u b p a r a l l e l s h e a r s y s t e m s (S / S * ) d e v e l o p e d i n s o m e a r e a s . 39
to
that
of
The
phase
phase
2,
3
deformation
but
the
indicated by the s t e e p k i n e m a t i c was
also
the
intermediate
had
its maximum
intermediate
a x i s of i n t e r s e c t i o n of S
strain
direction
during
r e s u l t f r o m t h e i n i t i a l o r i e n t a t i o n of b e d d i n g . folding e v e n in a r e a s w h e r e
strain axis north-south,
parallel
s t r a i n a x i s a p p e a r s to h a v e b e e n s u b v e r t i c a l , a s phase
and S ' .
It i s p o s s i b l e that t h i s
2, a n d t h a t t h e flat fold a x e s only
T h i s w o u l d e x p l a i n t h e l a c k of s t r o n g c l e a v a g e
is well developed.
If t h e r e w a s a c h a n g e i n t h e d i r e c t i o n of t h e
i n t e r m e d i a t e s t r a i n a x i s , faults f o r m e d in p h a s e 2 would have a dominantly v e r t i c a l m o v e m e n t , while faults f o r m e d in p h a s e 3 would have a dominantly s t r i k e - s l i p m o v e m e n t . on
the
Northern
Star
Shear
The movement
Zone w a s probably largely v e r t i c a l (down-faulted to the north),
a n d the m o v e m e n t on the Q u a r t z Hill F a u l t a p p e a r s to b e s u b h o r i z o n t a l with d e x t r a l s e n s e in the
Mount
Woodcock
Sheet
a r e a , a l t h o u g h t h i s i s n o t i n a c c o r d a n c e w i t h t h e o b s e r v a t i o n s of
C r o h n & O l d e r s h a w (1965) i n t h e T e n n a n t C r e e k S h e e t a r e a
c
C O R R E L A T I O N O F S T R U C T U R E , STRATIGRAPHY, AND MAGNETIC
PATTERNS
The Tennant C r e e k a r e a h a s been investigated by magnetic p r o s p e c t i n g
methods
(Daly, 1957), a n d by a i r b o r n e r e g i o n a l m a g n e t i c s u r v e y s f r o m which 1 inch to 1 m i l e and 1 inch to 2 mile total intensity m a p s w e r e produced. been
undertaken
to
locate
concealed
magnetite
A l a r g e n u m b e r of d e t a i l e d s u r v e y s h a v e a l s o b o d i e s , b e c a u s e of t h e k n o w n a s s o c i a t i o n of
gold and copper mineralization with the ironstones; the s u r v e y s have m e t with varying s u c c e s s . An a t t e m p t h a s b e e n m a d e to r e l a t e the regional magnetic p a t t e r n s to the g r a p h y a n d s t r u c t u r e of t h e a r e a , a n d t h e t o t a l m a g n e t i c i n t e n s i t y m a p of t h e M o u n t
strati
Woodcock
Sheet i s included in P l a t e 5. T h e m a p s h o w s t h a t v a r i a t i o n s i n t h e i n t e n s i t y a n d s t y l e of t h e m a g n e t i c can
be
related
geological area
is
to
the
boundaries
the
pattern
underlying are
of
Tomkinson Creek Beds. intruded
along
the
known.
linear
patterns
r o c k s , but the v a r i a t i o n s can only be i n t e r p r e t e d when the The
m o s t s t r i k i n g f e a t u r e on t h e M o u n t W o o d c o c k Sheet
magnetic
a n o m a l i e s p a r a l l e l t o t h e b e d d i n g a n d c o n t a c t of t h e
T h e s e a n o m a l i e s a r e probably c a u s e d by b a s i c s i l l s which have b e e n
unconformity.
T h e r i d g e s a r e b r o k e n i n t h e v i c i n i t y of 1 7 2 0 0 0 , 2 5 8 1 0 0 0 ,
p r o b a b l y b y t h e e x t e n s i o n of t h e B e r n b o r o u g h F a u l t , a n d i t a p p e a r s t h a t t h e b a s i c s i l l s e i t h e r postdate
the n o r t h - w e s t fault s y s t e m (phase 3), o r w e r e d i s p l a c e d by it. e a s t e r n p a r t of t h e a r e a o c c u p i e d b y t h e T o m k i n s o n C r e e k B e d s ,
north
of G o o d n a W a t e r h o l e , t h e r e i s a n a r r o w m a g n e t i c l o w d i r e c t l y s o u t h of t h e T o m k i n s o n
In t h e
Creek
B e d s , t h e s i g n i f i c a n c e of w h i c h i s u n k n o w n . The two m a i n m i n e s , Orlando and N o r t h e r n Star Mines, have s i m i l a r settings.
Both
mines
are
magnetic
s i t u a t e d a t t h e i n t e r s e c t i o n of a m a j o r s h e a r - z o n e w i t h a z o n e of
s t e e p m a g n e t i c g r a d i e n t e l o n g a t e d p a r a l l e l t o t h e r e g i o n a l t r e n d of t h e b e d d i n g .
At the Northern
Star Mine, the a s s o c i a t i o n i s not c l e a r l y visible on the 1 - m i l e m a g n e t i c m a p , but it h a s b e e n established
by
a
detailed
(Milsom & Finney, 1965).
a e r o m a g n e t i c s u r v e y b y t h e B u r e a u of M i n e r a l R e s o u r c e s i n 1 9 6 4 T h e s u r v e y indicates a s m a l l relatively intense peak within the zone
of s t e e p g r a d i e n t , b u t a t O r l a n d o n o p e a k i s a p p a r e n t . Two tested
by
diamond
magnetic drilling.
anomalies
at
190000,
At the f o r m e r
2562000
and 198000, 2562000 have
host r o c k was encountered, but at the latter an acid porphyry only; porphyries
been
locality a m a g n e t i t e - c h l o r i t e body in a porphyry
t o t h e s o u t h of t h e B e r n b o r o u g h M i n e . 40
it i s p o s s i b l y r e l a t e d to t h e
The two a n o m a l i e s r e s e m b l e the anomaly
at
the
Queen
of S h e b a M i n e i n b o t h m a g n i t u d e a n d t r e n d ;
Mine lies within the Bernborough Co.
Further
t h e a n o m a l y a t t h e Q u e e n of S h e b a
F o r m a t i o n and w a s d r i l l e d unsuccessfully by National L e a d
s t u d y m a y r e v e a l a b r o a d c o r r e l a t i o n b e t w e e n t h e s h a p e of t h e a n o m a l y a n d t h e
t y p e of m a g n e t i c b o d y a n d i t s g e o l o g i c a l s e t t i n g . Both the Tennant C r e e k Granite Complex and the Bernborough F o r m a t i o n a r e c h a r a c t e r i z e d by a n i r r e g u l a r m a g n e t i c p a t t e r n with l a r g e flat p e a k s on a t o t a l m a g n e t i c i n t e n s i t y field w h i c h a v e r a g e s 2700 g a m m a s .
T h i s c o n t r a s t s s t r o n g l y w i t h a n a r e a i n t h e w e s t e r n p a r t of
t h e M a r i o n R o s s S h e e t w h e r e t h e r e i s a f l a t f i e l d of a b o u t 3 0 0 0 g a m m a s , w h i c h i s t h o u g h t t o r e flect a basic intrusion at depth. The major
s h e a r - z o n e s cannot b e identified on the m a g n e t i c m a p s , b u t in s o m e
p l a c e s they s e p a r a t e b r o a d a r e a s with different magnetic p a t t e r n s . similar
to
the
Shear Zone with two m a j o r n o r t h - w e s t s h e a r s . immediately Fault.
Two small magnetic peaks,
N o r t h e r n S t a r a n o m a l y , o c c u r c l o s e t o t h e i n t e r s e c t i o n s of t h e N o r t h e r n S t a r
north
of
the
displaced
T h e e a s t e r n a n o m a l y (at 178000, 2574000) l i e s
Northern Star Shear Zone, adjacent to the Bernborough
T h e a n o m a l y i s thought to b e in a s i m i l a r s t r a t i g r a p h i c p o s i t i o n t o t h e N o r t h e r n S t a r
Mine
and
is
thus
a
favourable
t a r g e t for exploration.
A s i m i l a r anomaly e x i s t s at 169000,
2 5 6 7 0 0 0 o n t h e M a r i o n R o s s S h e e t a r e a , n e a r t h e i n t e r s e c t i o n of t h e N o r t h e r n S t a r S h e a r Z o n e and
a
north-west-trending shear
zone which p a s s e s between the G r e a t W e s t e r n and Orlando
Mine a r e a s . In t h e e a s t e r n p a r t of t h e M o u n t W o o d c o c k S h e e t a r e a , a p r o b a b l e r o o f
pendant
of W a r r a m u n g a G r o u p r o c k s i n g r a n i t e i s i n d i c a t e d a t 2 2 0 0 0 0 , 2 5 7 3 0 0 0 b y a m a g n e t i c r i d g e of o v e r 2 5 0 0 g a m m a s i n t h e o t h e r w i s e f l a t m a g n e t i c p a t t e r n of a b o u t 2 4 0 0 g a m m a s p r o d u c e d b y t h e granite. In g e n e r a l , t h e m a g n e t i c p a t t e r n s c a n n o t b e d i r e c t l y c o r r e l a t e d w i t h g e o l o g i c a l structures.
T h e d i s t r i b u t i o n of m i n e r a l i z a t i o n a t t h e O r l a n d o , N o r t h e r n S t a r , a n d m o s t o t h e r
m i n e s on the Tennant-Creek Field, shows that the important factors controlling the m i n e r a l i z a t i o n a r e t h e p r e s e n c e of f a v o u r a b l e b e d s a n d f a v o u r a b l e s t r u c t u r e s . able
M o s t of t h e l a r g e f a v o u r
s t r u c t u r e s c a n b e r e c o g n i z e d o n t h e 1:80,000- s c a l e a i r - p h o t o g r a p h s , a n d b y c o r r e l a t i n g
t h e s e s t r u c t u r e s with known m a g n e t i c a n o m a l i e s , it i s p o s s i b l e to d e l i m i t favourable targets. this
magnetic
However, t h e s e a r e not n e c e s s a r i l y associated with economic m i n e r a l i z a t i o n , nor does
method
preclude
t h e p o s s i b i l i t y of e c o n o m i c m i n e r a l i z a t i o n i n o t h e r a r e a s .
T h e u s e of
m a g n e t i c p r o s p e c t i n g m e t h o d s at Tennant C r e e k h a s been s t r e s s e d in the p a s t , but the technique m u s t b e c o m p l e m e n t e d by o t h e r g e o p h y s i c a l investigations, g e o c h e m i s t r y , and geological i n t e r pretation. GEOCHEMISTRY Geochemical samples were collected from
the Mount Woodcock, Marion R o s s ,
H a y w a r d C r e e k , and 5/217 Sheet a r e a s (Dunnet & Harding, 1965), and additional s a m p l e s w e r e collected
from
the
Jubilee
Mine
and
Golden
Mile
a r e a s in the T e n n a n t C r e e k Sheet a r e a
(Harding & Dunnet, 1965). Chip gabbros jasper
and lodes.
s a m p l e s w e r e collected from the thick
dolerites,
ferruginous laterites, lateritized
s h e a r e d W a r r a m u n g a Group s e d i m e n t s , and the q u a r t z - h e m a t i t e and
Particular
attention
was
paid
to
t h e i r o n s t o n e s , b e c a u s e of t h e f a v o u r a b l e
r e s u l t s obtained by McMillan & D e b n a m (1961), to d e t e r m i n e w h e t h e r the m i n e r a l i z e d and n o n m i n e r a l i z e d i r o n s t o n e s could be distinguished by their g e o c h e m i s t r y . 41
composed talus.
of
Soil
samples
the
Warramunga
were
collected
Group,
and
from
the
major
from
the
surrounding colluvium and pediment
streams
draining
the
hills
Only a few s a m p l e s w e r e collected f r o m the a e o l i a n d e p o s i t s in the flats. 480 i r o n s t o n e s a m p l e s a n d 715 soil s a m p l e s
were
collected, m o s t l y by
field
assistants. Sampling The parts
of
an
composite
i r o n s t o n e s a m p l e s c o n s i s t of a t l e a s t s i x c h i p s f r o m
different
ironstone body and w e r e c r u s h e d to -80 m e s h .
W h e r e t h e i r o n s t o n e i s o v e r 100
feet long, s e p a r a t e s a m p l e s w e r e taken at 100-foot intervals.
The soil samples w e r e collected
a t a d e p t h of 6 t o 1 2 i n c h e s i n t h e c o l l u v i u m , a n d t h e s t r e a m s a m p l e s a t a b o u t t h e s a m e d e p t h i n t h e c e n t r e of t h e s t r e a m s .
A l l t h e s a m p l e s w e r e s c r e e n e d a n d t h e +80 m e s h m a t e r i a l d i s
carded. Analysis Semi-quantitative
s p e c t r o g r a p h i c a n a l y s e s for copper, cobalt, zinc, lead, m o l y
b d e n u m , and b i s m u t h w e r e c a r r i e d out by the A u s t r a l i a n M i n e r a l D e v e l o p m e n t L a b o r a t o r i e s in Adelaide.
T h e y a r e r e p r o d u c e d i n full i n D u n n e t & H a r d i n g ( 1 9 6 5 ) .
Results F r e q u e n c y distribution d i a g r a m s for the six e l e m e n t s in the i r o n s t o n e and samples
have
been
constructed.
soil
T h e m e d i a n values for the soil and i r o n s t o n e s a m p l e s a r e
a s follows: Element
Soil S a m p l e s (ppm)
(ppm)
Copper
8.5
35
Cobalt
4.0
2
Lead
7.5
6.5
Zinc
^20
Molybdenum
the
5.5
<1
all c a s e s the frequency dispersion
20
<^1
Bismuth In
Ironstone Samples
is
not
<^3
distribution h a s a definite positive s k e w n e s s , which indicates that
logarithmic,
or
that
two p o p u l a t i o n s a r e p r e s e n t .
On t h e a s s u m p t i o n
t h a t t h e c o n c e n t r a t i o n s of t h e e l e m e n t s a r e l o g - n o r m a l l y d i s t r i b u t e d ( S h a w , 1 9 6 0 ) t h e c u m u l a t i v e frequency Dunnet, The
distribution
1965).
ranges
for
All
w a s p l o t t e d on l o g a r i t h m i c p r o b a b i l i t y p a p e r
(Tennant & White, 1961;
t h e s e p l o t s ( F i g s 8 a , b , 9 a , b) i n d i c a t e t h e p r e s e n c e of t w o p o p u l a t i o n s .
t h e p o p u l a t i o n s of t h e s i x e l e m e n t s i n t h e s o i l a n d i r o n s t o n e s a m p l e s a r e a s
follows: 42
SOIL S A M P L E S Element
Lower
IRONSTONE SAMPLES
Upper
Lower
Upper
Population
Population
Population
Population
(ppm)
(ppm)
(ppm)
(ppm)
Copper
0-60
20-500
7-500
Cobalt
0-40
15-50
2-250
30-400
Zinc
20-25
20-40
20-200
100-500
Lead
4-20
7-70
1-50
Molybdenum
0-10
5-40, 25-100
1-70
Bismuth
0-25
5-80
1-5000
200-2000
8-700 3-150 300-10,000
O n t h e a s s u m p t i o n t h a t t h e v a l u e s a b o v e t h e u p p e r l i m i t of t h e l o w e r p o p u l a t i o n are
a n o m a l o u s , a t o t a l g e o c h e m i c a l a n o m a l y m a p h a s b e e n p r e p a r e d ( F i g . 7). T h i s t e c h n i q u e
d o e s n o t i n d i c a t e a l l a n o m a l i e s b e c a u s e of t h e l a r g e o v e r l a p of t h e t w o p o p u l a t i o n s , e s p e c i a l l y in the i r o n s t o n e s .
Two
a r e a s s t a n d o u t o n t h e m a p a n d i n t h e t a b l e s of r e s u l t s :
they contain
the
i r o n s t o n e s around the Orlando and Northern Star Mines, which contain anomalous concentrations of a l l s i x e l e m e n t s .
S t a t i s t i c a l T r e a t m e n t of I r o n s t o n e R e s u l t s
T h e r e s u l t s on the i r o n s t o n e s a m p l e s can b e i n t e r p r e t e d m o r e e a s i l y than t h o s e o n t h e s o i l s a m p l e s a n d t h e y g i v e a d i r e c t i n d i c a t i o n of p o s s i b l e e c o n o m i c d e p o s i t s in t h e i r o n stone lodes.
T h e m e t a l c o n c e n t r a t i o n s a r e m o r e likely to exhibit a l o g n o r m a l d i s t r i b u t i o n in
t h e i r o n s t o n e s t h a n i n t h e s o i l , a n d e x c e p t f o r t h e e f f e c t s of e r r o r s i n s a m p l i n g a n d a n a l y s i s , t h e c o n c e n t r a t i o n s will b e h a v e in the s a m e way a s r o c k e l e m e n t d i s t r i b u t i o n s . been
made
to a n a l y s e
statistically
An a t t e m p t h a s
t h e c o p p e r c o n c e n t r a t i o n s in the i r o n s t o n e s to c h e c k t h e
s i g n i f i c a n c e of t h e t w o a p p a r e n t p o p u l a t i o n s , a n d t o d e t e r m i n e w h e t h e r t h e r e a r e o t h e r a r e a s of e c o n o m i c s i g n i f i c a n c e o n t h e t o t a l g e o c h e m i c a l a n o m a l y m a p .
All
copper
values
o v e r 150 p p m in t h e N o r t h e r n S t a r M i n e a n d O r l a n d o M i n e
a r e a s h a v e b e e n p l o t t e d on a c u m u l a t i v e p e r c e n t f r e q u e n c y d i a g r a m .
The result is a straight
l i n e p l o t w i t h a m e a n of 52u p p m a n d a s t a n d a r d d e v i a t i o n of 0 . 8 1 . T h e r e m a i n d e r of t h e c o p p e r r e s u l t s p l o t t e d a s a s t r a i g h t l i n e w i t h a m e a n of 35 p p m a n d s t a n d a r d d e v i a t i o n of 1.0;
however,
this c u r v e was slightly i r r e g u l a r towards the higher value end.
In o r d e r
to find
out w h e t h e r
the
samples
from the s e c o n d - o r d e r anomalies
(Phillip C r e e k , Bishop C r e e k , Black E y e , G r e a t W e s t e r n , and J u b i l e e a n o m a l i e s ) belonged to a
third
population, of
these
values
were
r e m o v e d from the bulk c u r v e and plotted s e p a r a t e l y .
Both
components
t h e o r i g i n a l c u r v e g a v e s t r a i g h t - l i n e p l o t s , w i t h a s t a n d a r d d e v i a t i o n of
1.0.
T h e m e a n of t h e m a i n s u i t e r e m a i n e d a t 35 p p m w h e r e a s t h e m e a n of t h e
a n o m a l y s u i t e w a s 70 p p m ( F i g . 8 c ) . the
second-order
T h e s i m i l a r s t a n d a r d d e v i a t i o n s u g g e s t s t h a t t h i s s p l i t of
s a m p l e s is not valid, and that the s a m p l e s f r o m the s e c o n d o r d e r anomaly a r e a s , belong
t o t h e u p p e r p a r t of t h e m a i n i r o n s t o n e p o p u l a t i o n .
2021/67-4
43
Reference • 10 • • 50
Ironstone sample Molybdenum (ppm) Copper (ppm) V V V V Bernborough i/olcanics and tuffaceous rocks
F i g , 7: B i s h o p
<— » •
Geological boundary Fault Trend of bedding Plunge of major fold axes Dyke; h -hematite
C r e e k / M o u n t Woodcock regional 44
geochemistry.
T o d e t e r m i n e w h e t h e r c o p p e r i s d i s t r i b u t e d in t w o o r t h r e e d i s c r e t e p o p u l a t i o n s , t h e c o m p o n e n t s m a k i n g u p t h e b u l k c u r v e w e r e o b t a i n e d b y t h e m e t h o d of d i f f e r e n c e s 1959).
(Tanner,
E s t i m a t e s of t h e m e a n s a n d s t a n d a r d d e v i a t i o n s of c o m p o n e n t s , a n d t h e p r o p o r t i o n s in
w h i c h t h e y o c c u r , c a n b e m a d e f r o m t h e f i r s t a n d s e c o n d d i f f e r e n c e s of a n o r d e r l y a r r a y of t h e c o m p o s i t e cumulative distribution. The r e s u l t suggests that the composite cumulative distribution i s m a d e u p of t w o c o m p o n e n t s :
t h e f i r s t c o m p r i s i n g 95 p e r c e n t of t h e t o t a l w i t h a m e a n of 6 8
p p m , a n d t h e s e c o n d f o r m i n g 5 p e r c e n t of t h e t o t a l w i t h a m e a n of 3 0 0 t o 4 5 0 p p m . T h e s e e s t i m a t e s w e r e c h e c k e d by t h e following s t e p s : 1.
A c u m u l a t i v e d i s t r i b u t i o n of t h e f i r s t c o m p o n e n t w a s o b t a i n e d b y d i v i d i n g v a l u e s
of t h e c o m p o s i t e c u m u l a t i v e d i s t r i b u t i o n w h i c h a r e l e s s t h a n 95 p e r c e n t b y 0 . 9 5 . line
of
best
fit'
to
the
The 'straight
r e c a l c u l a t e d v a l u e s ( l i n e 1 , F i g . 8d) p l o t t e d on l o g a r i t h m i c p r o b a b i l i t y
p a p e r was accepted a s the cumulative distribution. 2.
V a l u e s r e a d f r o m t h e ' s t r a i g h t l i n e of b e s t f i t ' w e r e r e c a l c u l a t e d a s p e r c e n t a g e s
of t h e c o m p o s i t e c u m u l a t i v e d i s t r i b u t i o n (by m u l t i p l y i n g b y 0 . 9 5 ) s o t h a t t h e s e c o n d c o m p o n e n t could be obtained by subtraction. 3.
T h e v a l u e s f o r t h e s e c o n d c o m p o n e n t w e r e r e c a l c u l a t e d t o 100 p e r c e n t a n d p l o t t e d
o n l o g a r i t h m i c p r o b a b i l i t y p a p e r ( l i n e 2 , F i g . 8 d ) . T h e v a l i d i t y of t h e e s t i m a t e s of t h e p a r a m e t e r f o r t h e t w o s a m p l e c o m p o n e n t s i s c h e c k e d b y t h e c l o s e n e s s of t h e s e p o i n t s t o t h e l i n e of b e s t fit drawn through them. 4.
T h e p r o c e s s i s r e p e a t e d until, by s u c c e s s i v e a p p r o x i m a t i o n s , c u m u l a t i v e c u r v e s
f o r t h e c o m p o n e n t s , w h i c h c o m b i n e t o f o r m a d i s t r i b u t i o n c l o s e s t t o t h a t of t h e c o m p o s i t e , a r e obtained. T h e r e s u l t of t h e s e m a n i p u l a t i o n s i s t h a t t h e c o m p o s i t e c u m u l a t i v e d i s t r i b u t i o n of t h e g e o c h e m i c a l v a l u e s f o r c o p p e r , in t h e a r e a s s a m p l e d , c a n b e r e p r o d u c e d b y t h e a d d i t i o n of t w o l o g - n o r m a l l y d i s t r i b u t e d c o m p o n e n t s w i t h m e a n s of 4 2 a n d 6 0 0 p p m w i t h s t a n d a r d d e v i a t i o n s of 0 . 9 3 a n d 0 . 6 2 r e s p e c t i v e l y i n t h e r a t i o of 95 t o 5 .
T h e c l o s e a g r e e m e n t of t h e t w o i n d e p e n d e n t
d e t e r m i n a t i o n s s u p p o r t s t h e v a l i d i t y of t w o d i s c r e t e p o p u l a t i o n s , b u t d o e s n o t s u p p o r t t h e s e c o n d o r d e r anomalies a s a d i s c r e t e population. T h u s t h e c o p p e r c o n t e n t of t h e i r o n s t o n e s f r o m t h e O r l a n d o a n d N o r t h e r n M i n e s i s s i g n i f i c a n t l y d i f f e r e n t f r o m t h a t o f t h e r e s t of t h e s u i t e . a n d gold mine and N o r t h e r n Star is a favourable p r o s p e c t . population,
as
i n d i c a t e d on F i g u r e 8d, i s f r o m
Star
Orlando is a producing copper
T h e r a n g e of c o p p e r v a l u e s f o r t h i s
80 t o 3000 p p m , b u t f o r r e a s o n s u n k n o w n a s m a l l
p r o p o r t i o n of t h e s a m p l e s c o n t a i n l e s s t h a n 80 p p m of c o p p e r . Second-Order Anomalies The s e c o n d - o r d e r anomalies include ironstones showing copper concentrations n e a r t h e u p p e r l i m i t of t h e b a c k g r o u n d r a n g e .
T h e r e is s o m e evidence that they include s o m e
i r o n s t o n e s of t h e O r l a n d o / N o r t h e r n S t a r s u i t e , a n d t h i s c o u l d b e c h e c k e d b y f u r t h e r
geochemical
work. It
m a y b e s i g n i f i c a n t t h a t t h i s s u i t e i n c l u d e s s a m p l e s of f e r r u g i n o u s
material
c a p p i n g t h e d o l e r i t e s i l l s , w h i c h s u g g e s t s t h a t t h e c o p p e r c o n t e n t of t h e d o l e r i t e s a n d t h e l o w e r 45
10
20 SO 40 SO
%
CumulotiM
90
99
99 8 99 9
99 99
,
10
Frtqu«ncy
10 SO 40 50 %
90
Cumulolive
Frequency
F i g . 8: C u m u l a t i v e f r e q u e n c y d i s t r i b u t i o n i n T e n n a n t C r e e k i r o n s t o n e s of (a) c o p p e r , c o b a l t , a n d z i n c ; (b) l e a d ,
molybdenum
a n d b i s m u t h ; (c) F r e q u e n c y d i s t r i b u t i o n p o p u l a t i o n s of c o p p e r , (d)
frequency
computed
distribution
c u r v e c o m p o n e n t s for
b y m e t h o d of d i f f e r e n c e s 46
(after
Tanner,
copper, 1959).
FIGURE 9
% Cumulative Fr.qu.ncy
F i g . 9: C u m u l a t i v e
frequency
d i s t r i b u t i o n in T e n n a n t C r e e k
s a m p l e s of (e) c o p p e r , c o b a l t , a n d z i n c ; (f) l e a d ,
soil
molybdenum,
and bismuth. g r a d e i r o n s t o n e s a r e c o m p a r a b l e , and that they may be genetically related.
S a m p l e s 3270 to
3 2 7 3 f r o m a f e r r u g i n o u s c a p o n a d o l e r i t e d y k e i n t h e G i b s o n C r e e k a r e a c o n t a i n 150 p p m c o p p e r a n d u p t o 80 p p m z i n c . 70
S i m i l a r l y , the s a m p l e s from the Phillip C r e e k a n o m a l y , which contain
t o 2 5 0 p p m of c o p p e r a n d 4 0 t o 3 0 0 p p m of z i n c , a r e p r o b a b l y f r o m a d o l e r i t e s i l l , t h o u g h
t h i s c o u l d n o t b e p r o v e d in the field. T h e B i s h o p C r e e k a n o m a l y i n c l u d e s a g r o u p of i r o n s t o n e s , s o m e of w h i c h above-background
concentrations
of c o p p e r a n d m o l y b d e n u m .
contain
O n e of t h e i r o n s t o n e s a m p l e s
(053171) c o n t a i n s 700 p p m lead and 3000 p p m z i n c , and a n e a r b y i r o n s t o n e (053163), which h a s b e e n p r o s p e c t e d f o r g o l d , c o n t a i n s 7 0 0 p p m c o p p e r , 50 p p m m o l y b d e n u m , a n d 2000 p p m b i s m u t h . T h e s e c o n c e n t r a t i o n s i n d i c a t e t h a t t h e y b e l o n g t o t h e i r o n s t o n e s of t h e O r l a n d o / N o r t h e r n S t a r s u i t e , a l t h o u g h m o s t of t h e a d j a c e n t i r o n s t o n e s f a l l in t h e l o w e r - g r a d e g r o u p ( F i g . 7 ) . T h e s t r u c t u r e of t h e a r e a I s a l s o f a v o u r a b l e , a s i t i s s i t u a t e d in t h e n o r t h - w e s t - t r e n d i n g c o r e of a n i n t e n s e s h e a r - z o n e a s s o c i a t e d with the Quartz Hill Fault. T h e G r e a t W e s t e r n and Black Eye a n o m a l i e s a u e p r o b a b l y related.
Their
copper
c o n t e n t s s u g g e s t t h a t t h e y a r e r e l a t e d t o t h e O r l a m d o / N o r t h e r m S t a r s u i t e , a n d t w o of t h e s a m p l e s resemble Two 120
of
ironstones
from
O r l a n d o with high l e a d and zinc c o n c e n t r a t i o n s (053288, 053532).
t h e G r e a t W e s t e r n s a m p l e s a r e a l s o r i c h in m o l y b d e n u m (053527, 100 p p m ;
ppm),
thus showing affinities
053532,
with the Bishop C r e e k and O r l a n d o i r o n s t o n e s .
T h e s e two
N o n e of t h e t h r e e s o u t h e r n s e c o n d - o r d e r a n o m a l i e s i s a s s o c i a t e d w i t h a
magnetic
a r e a s warrant further
investigation.
a n o m a l y , a n d a l t h o u g h g e o c h e m i c a l l y f a v o u r a b l e i r o n s t o n e s o c c u r i n t h e s e a r e a s , t h e y m a y b e of limited extent only.
T h e Phillip C r e e k a n o m a l y c o i n c i d e s with a l i n e a r m a g n e t i c high probably
a s s o c i a t e d with a b a s i c dyke. Of t h e o t h e r a n o m a l o u s i r o n s t o n e s i n d i c a t e d o n t h e t o t a l g e o c h e m i c a l
anomaly
m a p , the w e s t e r n and n o r t h - w e s t e r n i r o n s t o n e s a r e probably r e l a t e d to d o l e r i t e i n t r u s i o n s , and the e a s t e r n i r o n s t o n e s a r e not significant.
T h e q u a r t z - h e m a t i t e s a m p l e (05 3 245) w a s c o l l e c t e d
n e a r a d o l e r i t e d y k e ; t h e c o n c e n t r a t i o n s of c o p p e r (70 p p m ) , l e a d (250 p p m ) , z i n c (70 p p m ) , a n d m o l y b d e n u m (40 p p m ) a r e s i m i l a r t o t h o s e f o u n d in t h e d o l e r i t e a n o m a l i e s . 47
Soil S a m p l e A n o m a l i e s Many
of
the
soil
samples
from the Northern Star Mines a r e a contain
values
b e l o n g i n g t o t h e u p p e r p o p u l a t i o n , a n d s o m e of t h e s a m p l e s f r o m t h e B i s h o p C r e e k a n o m a l y a r e a l s o high.
M o s t of t h e o t h e r s p a t t e r e d s o i l s a m p l e s s h o w i n g a n o m a l o u s v a l u e s c a n b e r e l a t e d t o
nearby s h e a r - z o n e s containing small quartz-hematite veins.
T h e g r o u p of s a m p l e s t o t h e s o u t h
of B u t c h e r s W a t e r h o l e ( 0 5 1 4 0 6 , 0 8 , 1 0 , 1 1 , 1 6 , 27) c o n t a i n h i g h l e a d v a l u e s (15 t o 25 p p m ) ; ironstone explain
occurs
the
in
this
anomaly.
area,
but
the
waterhole
little
is n e a r the Q u a r t z Hill F a u l t , which m a y
O t h e r soil s a m p l e s with a n o m a l o u s v a l u e s o c c u r along the fault in the
Bishop Creek anomaly area. The a second order
radioactive
a n o m a l y in t h e n o r t h e r n p a r t of t h e M a r i o n R o s s S h e e t
area,
scintillograph a n o m a l y , c o r r e s p o n d s roughly with a soil s a m p l e g e o c h e m i c a l
a n o m a l y . T h e a r e a i n c l u d e s a n a r r o w r i d g e of w e a t h e r e d l i m o n i t i c r o c k s i m i l a r t o t h e l a t e r i t i z e d dolerite dykes. further
sampling
Preliminary on
a
s a m p l i n g ( 0 5 1 2 2 4 - 26) i n d i c a t e d a n o m a l o u s b i s m u t h a n d l e a d , b u t
100-foot
grid
gave
anomalous
c o p p e r a n d z i n c in o n l y t w o s a m p l e s .
T h e a n o m a l y m a y b e c a u s e d b y t h e p r e s e n c e of a n u n e x p o s e d d o l e r i t e d y k e . Discussion T h e s t a t i s t i c a l a n a l y s i s of t h e g e o c h e m i s t r y of t h e i r o n s t o n e s a n d t h e
results
of t h e s u r v e y b y M c M i l l a n & D e b n a m (1961) i n d i c a t e t h a t t h e i r o n s t o n e s a s s o c i a t e d w i t h t h e e c o n o m i c c o p p e r s u l p h i d e d e p o s i t s a r e a l s o r i c h in c o p p e r .
T h e c o p p e r c o n t e n t of t h e s e i r o n
s t o n e s i s s t a t i s t i c a l l y d i f f e r e n t f r o m t h a t of t h e n o r m a l i r o n s t o n e s . It i s s t r o n g l y r e c o m m e n d e d that all i r o n s t o n e s i n t e r s e c t e d by d r i l l i n g , p a r t i c u l a r l y w h e r e they do not c r o p out, should be a n a l y s e d for c o p p e r , cobalt, l e a d , z i n c , m o l y b d e n u m , and bismuth. ECONOMIC GEOLOGY T h e e c o n o m i c g e o l o g y of t h e T e n n a n t C r e e k a r e a h a s b e e n d i s c u s s e d b y I v a n a c (1954) a n d C r o h n & O l d e r s h a w ( 1 9 6 5 ) . S e v e r a l n e w c o n s i d e r a t i o n s a r i s i n g f r o m t h i s s u r v e y a r e discussed below. Northern Star Mine T h e i r o n s t o n e s i n t h e N o r t h e r n S t a r a r e a w e r e i n v e s t i g a t e d i n 1964 b y d r i l l i n g and g e o c h e m i c a l s a m p l i n g (Dunnet, 1965).
No. 1 i r o n s t o n e (the m a i n o n e s a r e n u m d e r e d 1 , 2,
a n d 3) h a s b e e n m i n e d f o r g o l d , w h i c h i s a s s o c i a t e d w i t h b i s m u t h c a r b o n a t e s ; 3 a r e low in gold a n d h a v e not b e e n t h o r o u g h l y e x p l o r e d .
ironstones 2 and
E n c o u r a g i n g gold and c o p p e r i n t e r
s e c t i o n s h a v e b e e n m a d e in d i a m o n d d r i l l h o l e s n e a r No. 2 i r o n s t o n e ( M e t a l s E x p l o r a t i o n N . L . ; Mines Branch, Northern Territory Administration;
a n d P e k o M i n e s N . L . ) a t d e p t h s of 800 t o
1000 feet in t h e N o r t h e r n S t a r l e a s e s . T h e sediments at N o r t h e r n Star c o n s i s t o f g r e y w a c k e , s h a l e , siltstone, tuffaceous s a n d s t o n e , a n d h e m a t i t e s h a l e s i m i l a r t o t h e h e m a t i t e s h a l e m a r k e r b e d in t h e M o u n t S a m u e l / E l d o r a d o a r e a (Crohn & O l d e r s h a w , 1965).
D o l o m i t i c s i l t s t o n e a n d s m a l l l e n s e s of d o l o m i t e
c r o p out s e v e r a l m i l e s to the s o u t h - w e s t along the s t r i k e f r o m the N o r t h e r n Star M i n e , and c r y s t a l l i n e d o l o m i t e i s p r e s e n t i n D D H 1 5 a t a b o u t 1000 feet.
The sequences at the Orlando and
Northern Star Mines a r e s i m i l a r , but the carbonate r o c k s at Orlando a r e r e g a r d e d a s epigenetic 48
(J. Elliston, Geopeko, p e r s . c o m m . ) . The copper, gold, b i s m u t h , and m a n g a n e s e - b e a r i n g i r o n s t o n e s h a v e b e e n l a r g e l y f o r m e d b y r e p l a c e m e n t of s u i t a b l e s e d i m e n t s , c o n t r o l l e d b y s h e a r p l a n e s , in anticlinal c r e s t s plunging at a low angle to the e a s t .
On the No. 2 and No. 3 i r o n
s t o n e s , g e o c h e m i c a l s a m p l e s w e r e c o l l e c t e d a t 3 - f o o t i n t e r v a l s i n w a g g o n d r i l l - h o l e s 80 f e e t a p a r t (Dunnet, 1965).
They w e r e a n a l y s e d for c o p p e r , cobalt, lead, zinc, b i s m u t h , and m o l y
bdenum
and a l s o for gold.
copper,
cobalt,
(
zinc,
and
S t a t i s t i c a l a n a l y s i s of t h e r e s u l t s i n d i c a t e s t h r e e p o p u l a t i o n s of molybdenum.
The
d i s t r i b u t i o n of t h e h i g h e s t c o p p e r p o p u l a t i o n
1200 ppm) defines two a n o m a l o u s a r e a s , w h i c h f o r m a d u m b b e l l - s h a p e d a n o m a l y a t d e p t h in
t h e c e n t r e of N o . 2 i r o n s t o n e .
This anomaly is associated with a limonitic cellular h e m a t i t e ,
p r o d u c e d b y r e p l a c e m e n t of h e m a t i t e s h a l e , a n d m a s s i v e m a n g a n i f e r o u s h e m a t i t e .
The cellular
h e m a t i t e m a y r e p r e s e n t t h e l e a c h e d c a p of a m a g n e t i t e - s u l p h i d e o r e b o d y . Up to 1 p e r c e n t c o p p e r i s p r e s e n t in the No. 2 i r o n s t o n e , but t h e r e a r e no signifi c a n t c o n c e n t r a t i o n s in the No. 3 i r o n s t o n e .
The cobalt, and to a l e s s e r d e g r e e zinc and m o l y
b d e n u m , c o n t e n t s v a r y d i r e c t l y w i t h t h e c o n c e n t r a t i o n s of c o p p e r .
The gold a s s a y s r a n g e
from
n i l t o 1.1 d w t p e r t o n , w i t h a m o d e of a b o u t 0 . 2 d w t p e r t o n . T h e g e o c h e m i c a l r e s u l t s s u g g e s t t h e p r e s e n c e of c o p p e r m i n e r a l i z a t i o n a t d e p t h , p r o b a b l y in a s s o c i a t i o n with the body p r o d u c i n g the m a g n e t i c a n o m a l y ( p r i m a r y m a g n e t i t e ) . A company i s c u r r e n t l y c a r r y i n g out f u r t h e r exploration work. Orlando Mine T h e O r l a n d o M i n e i s the only p r o d u c i n g m i n e in t h e Mount Woodcock Sheet a r e a . T h e gold i s mainly a s s o c i a t e d with c h a l c o p y r i t e , p y r i t e , and b i s m u t h i n i t e , in m a g n e t i t e - r i c h , sheared, slaty pseudo-conglomeratic and tuffaceous rocks. The shearing is intense, and f o r m s a b r o a d z o n e a l o n g t h e a t t e n u a t e d s o u t h e r n l i m b of a s y n c l i n e p l u n g i n g a t 25
north-west.
t h e n o r t h e r n l i m b of t h e s y n c l i n e , 6 0 0 f e e t n o r t h - e a s t of t h e m i n e s h a f t , s e v e r a l
quartz-hematite
l e n s e s c r o p out.
On
The q u a r t z - h e m a t i t e l e n s e s and other i r o n s t o n e s extending for a m i l e along
t h e s t r i k e , a r e a n o m a l o u s l y r i c h in c o p p e r , c o b a l t , l e a d , and z i n c . m e t a l s a r e s i m i l a r to t h o s e in the N o r t h e r n Star i r o n s t o n e s .
T h e c o n c e n t r a t i o n s of t h e s e
The siltstone below and possibly
a b o v e t h e m a i n m i n e r a l i z e d s e q u e n c e c o n t a i n s a b u n d a n t p y r i t e w h i c h i s p r o b a b l y s y n g e n e t i c in origin.
In t h e s o u t h e r n w a l l of t h e l o d e a b o d y of c r y s t a l l i n e d o l o m i t i c a n d c h l o r i t i c c a r b o n a t e
r o c k s o c c u r s o n t h e d o w n w a r d e x t e n s i o n of t h e b r e c c i a a n d s h e a r - z o n e w h i c h h a s c o n t r o l l e d t h e mineralization.
T h e c a r b o n a t e r o c k s a r e c o n s i d e r e d t o h a v e b e e n f o r m e d b y r e p l a c e m e n t of
the breccia zone and to be genetically related to the mineralization. C a r b o n a t e r o c k s a r e a l s o a s s o c i a t e d with s e v e r a l other o r e b o d i e s in the Tennant C r e e k a r e a , including the Peko Mine. Q u e e n of S h e b a M i n e T h e Q u e e n of S h e b a M i n e w a s w o r k e d f o r g o l d b e f o r e 1 9 5 2 a n d h a s b e e n i n v e s t i gated by g e o c h e m i c a l s u r v e y s (McMillan & D e b n a m ; surveys
(National Lead Co.).
anomalies without s u c c e s s .
National L e a d Co.) and g r o u n d m a g n e t i c
O n t h e b a s i s of t h i s w o r k t w o h o l e s w e r e d r i l l e d o n m a g n e t i c
T h e c o p p e r c o n c e n t r a t i o n in the i r o n s t o n e s i s not high a n d f u r t h e r
work does not appear to be warranted. Other Mines N o n e of t h e o t h e r m i n e s w a s i n v e s t i g a t e d i n d e t a i l .
T h e p r o s p e c t s o u t h of B i s h o p
C r e e k and t h e G r e a t W e s t e r n and B l a c k E y e i r o n s t o n e s w e r e found to b e a n o m a l o u s in c o p p e r , lead, and zinc. 49
RECOMMENDATIONS Five anomalous a r e a s w a r r a n t further investigation.
T w o of t h e s e a r e m a g n e t i c
a n o m a l i e s in s t r u c t u r a l l y favourable l o c a t i o n s at 178000/2574000 and 169000/256700. T h e o t h e r t h r e e a r e a s n e a r the following m i n e s contain g e o c h e m i c a l l y a n o m a l o u s ironstones related to the Orlando/Northern Star suite: Bishop Creek;
Great Western;
Black
Eye. E a c h of t h e s e five a r e a s d e s e r v e s t o b e e x a m i n e d i n d e t a i l , i n i t i a l l y w i t h a l o w altitude a e r o m a g n e t i c s u r v e y to delimit magnetic drilling t a r g e t s .
50
REFERENCES A M O S , B . J . , 1962 a r e a , Queensland.
S t r u c t u r a l g e o l o g y of t h e P a l a e o z o i c r o c k s , C o o k t o w n 1 : 2 5 0 , 0 0 0 S h e e t B u r . M i n e r . R e s o u r . Aust. R e c . 1962/136 (unpubl.).
B O U M A , A . H . , a n d B R O U W E R , A . , 1 9 6 4 - D E V E L O P M E N T S IN S E D I M E N T O L O G Y .
N.Y.,
Elsevier. C R O H N , P . W . , a n d O L D E R S H A W , W . , 1 9 6 5 - T h e g e o l o g y of t h e T e n n a n t C r e e k 1 - m i l e S h e e t . Bur. Miner. Resour. Aust. Rep. 83. D A L Y , J . , 1957 - M a g n e t i c p r o s p e c t i n g at T e n n a n t C r e e k , 1 9 3 5 - 1 9 3 7 .
Bur. Miner. Resour.
Aust. Bull. 44. DEBNAM,
A.H.,
1956 - G e o c h e m i c a l
C r e e k , N . T . , 1955.
prospecting
for
lead
and
copper
at Peko, Tennant
B u r . M i n e r . R e s o u r . Aust. R e c . 1956/4 (unpubl.).
D U N N , P . G . , and Y E A M A N , W . S . , 1964 - M i n o r m e t a l l i f e r o u s i n v e s t i g a t i o n s - T e n n a n t C r e e k Goldfield DUNNET,
D.,
Creek, N.T.
Northern
Territory.
Bur.
Miner.
Resour.
Aust. R e c . 1964/186 (unpubl.).
1965 - G e o c h e m i c a l i n v e s t i g a t i o n s a t t h e N o r t h e r n S t a r Gold M i n e , T e n n a n t B u r . M i n e r . R e s o u r . Aust. R e c . 1 9 6 5 / 4 8 (unpubl.).
D U N N E T , D . , a n d H A R D I N G , R . R . , 1 9 6 5 - T h e g e o l o g y of t h e M o u n t W o o d c o c k 1 - m i l e S h e e t a r e a , Tennant C r e e k , N.T. Ibid., 1965/168 (unpubl.). ELLISTON,
J.,
1960 - O r e
localization
by
preconsolidation
structure.
P r o c . Aust. Inst.
Min. Metall. N.S. 196, 29-49. E L L I S T O N , J . , 1 9 6 4 - N o t e s o u t l i n i n g t h e r e s u l t s of c u r r e n t r e s e a r c h w o r k o n o r e f o r m a t i o n b y d i a g e n e s i s of m o b i l e s e d i m e n t s .
Geopeko Co. Rep,
(unpubl.).
H A R D I N G , R . R . , 1 9 6 5 - G e o c h e m i c a l i n v e s t i g a t i o n s of a e r o m a g n e t i c r i d g e , T e n n a n t Goldfield, N.T.
Creek
B u r . M i n e r . R e s o u r . Aust. R e c . 1 9 6 5 / 2 7 (unpubl,),
H A R D I N G , R . R . , a n d D U N N E T , D . , 1 9 6 5 - G e o c h e m i c a l s a m p l i n g of t h e G o l d e n M i l e a n d J u b i l e e a r e a s , Tennant Creek, N.T.
Bur. Miner. Resour. Aust. Rec.
1965/143 (unpubl.).
H U R L E Y , P . M . , a n d o t h e r s , 1 9 6 1 - G e o c h r o n o l o g y of P r o t e r o z o i c g r a n i t e s i n t h e N o r t h e r n Territory, Australia. IVANAC,
J.F.,
Bull, geol. Soc. A m e r . , 72, 653-662.
1954 - Geology
a n d m i n e r a l d e p o s i t s of t h e T e n n a n t C r e e k G o l d f i e l d , N . T .
B u r . M i n e r . R e s o u r . Aust. B u l l . 22. MILSOM,
J.S., and
N . T . , 1964.
FINNEY,
W.A.,
1964 - T e n n a n t
Creek detailed aeromagnetic
survey,
B u r . M i n e r . R e s o u r . Aust. R e c . 1964/50 (unpubl.).
M I N E S B R A N C H , N . T . A . - L o g s a n d a s s a y r e s u l t s of c o r e f r o m d i a m o n d d r i l l h o l e s . Star File, Tennant Creek.
51
Northern
McMILLAN,
N.J.,
and
D E B N A M , A . H . , 1961 - G e o c h e m i c a l p r o s p e c t i n g f o r c o p p e r in t h e
Tennant C r e e k Goldfield. NOAKES,
L.C.,
and
B u r . M i n e r . R e s o u r . A u s t . R e c . 1961/101 (unpubl.).
TRAVES,
D.M.,
1954 - Outline
of
the
g e o l o g y of t h e B a r k l y r e g i o n .
Sci. ind. R e s . O r g . M e l b . , L a n d R e s , S e r . 3 , 3 4 - 4 1 . O'CONNOR, M . J . , and DALY, J . , 1958 - R e c o n n a i s s a n c e ground m a g n e t i c s u r v e y o v e r Olive Wood
area,
Tennant
Creek,
N.T.
Bur.
Miner.
R e s o u r . Aust. R e c . 1958/109 (unpubl.).
O'CONNOR, M. J . , and D A L Y , J . , 1962 - T e n n a n t C r e e k g r o u n d m a g n e t i c s u r v e y , 1958.
Ibid.,
1962/148 (unpubl.). O L D E R S H A W , W . , 1961 - T h e h e m a t i t e s h a l e at T e n n a n t C r e e k , N . T .
Bur. Miner. Resour.
Aust. R e c . 1 9 6 1 / 8 (unpubl.). OPIK,
A.A.,
et
al.,
1957
-
Cambrian
geology
of A u s t r a l i a .
Bur. Miner. Resour. Aust.
Bull. 49. OWEN, H . B . , 1942 - Report on Tennant C r e e k Goldfield.
Geol. B r . Dept. Int. Aust. (unpubl,).
RANDAL, M.A., BROWN, M.C., and DOUTCH, H . F , ,1966
-
G e o l o g y of t h e H e l e n S p r i n g s a n d
Miner,
R e s o u r . Aust. 1966/110 (unpubl.).
Beetaloo
1:250,000
Sheet
areas,
N.T.
Bur.
R I C K A R D , M . J . , 1961 - A note on c l e a v a g e s in c r e n u l a t e d r o c k s . ROSS,
C.S.,
and
identification.
SMITH, R . L . , 1961 - Ash-flow tuffs:
Geol. Mag., 98,
P324-32.
their origin, geologic relations and
U.S. geol. Surv. prof. P a p . 366.
R Y A N , G . R . , 1 9 6 1 - T h e g e o l o g y a n d m i n e r a l r e s o u r c e s of t h e H a t c h e s C r e e k W o l f r a m Northern Territory. SHAW,
D.M.,
Field,
B u r . M i n e r . R e s o u r . A u s t , B u l l . 6.
1960 - E l e m e n t
distribution
laws
in
geochemistry.
Geochim.
cosmochim.
Acta, 23, 116-134. SMITH,
K.G.,
STEWART,
J.R.,
and
SMITH,
Davenport and Murchison Ranges, N.T.
J.W.,
1961
-
The
r e g i o n a l g e o l o g y of t h e
B u r . Miner. Resour. Aust. Rep. 58.
S U L L I V A N , C . J . , 1949 - C o n d e n s e d geological r e p o r t B u r . M i n e r . R e s o u r . Aust. R e c . 1 9 4 9 / 9 6 , (unpubl.). i
on
Tennant
Creek
Goldfield, N . T .
T A N N E R , W . F . , 1 9 5 9 - S a m p l e c o m p o n e n t s o b t a i n e d b y t h e m e t h o d of d i f f e r e n c e s . Petrol.
T E N N A N T , C . B . , a n d W H I T E , N . L . , 1959 data.
sediment.
-
S t u d y of t h e d i s t r i b u t i o n of s o m e g e o c h e m i c a l
Econ. Geol., 54, 1281-1290.
TURNER,
F.J.,
TECTONITES. WARD,
J.
29(3), 4 0 8 - 4 1 1 .
H.J.,
and
WEISS,
L.E.,
1963 - S T R U C T U R A L
1964 - R e p o r t
on
OF
METAMORPHIC
a g e o c h e m i c a l s u r v e y of t h e B l a c k A n g e l G r o u p of l e a s e s ,
T e n n a n t C r e e k G o l d f i e l d , N o r t h e r n T e r r i t o r y of A u s t r a l i a . WEISS, L . E . , 1 9 5 8
ANALYSIS
N.Y., McGraw Hill.
-
Co. r e p o r t (unpubl.).
G e o m e t r y of s u p e r i m p o s e d f o l d i n g . B u l l , g e o l . S o c . A m e r , 7 0 ( 1 ) , 9 1 - 1 0 6 .
W E I S S , L . E . , 1 9 5 9 - S t r u c t u r a l a n a l y s i s of t h e b a s e m e n t s y s t e m a t T u r o k a , K e n y a . G e o l . M i n . R e s o u r . , 7.
52
Overseas
Appendix 1 A l t e r n a t i v e C o r r e l a t i o n of W a r r a m u n g a S e q u e n c e s by P . W . C r o h n The
correlations
put
forward
by D u n n e t a n d H a r d i n g ( p a g e s 1 7 - 1 9 and f i g . 1)
a r e b a s e d l a r g e l y on t h e p r o p o r t i o n s of g r e y w a c k e a n d s h a l e in d i f f e r e n t p a r t s of t h e v a r i o u s s e q u e n c e s , a n d t h e r e s u l t s a r e n o t in a c c o r d a n c e w i t h c e r t a i n f i e l d o b s e r v a t i o n s o n t h e T e n n a n t C r e e k O n e - m i l e S h e e t a r e a a s r e c o r d e d by C r o h n a n d O l d e r s h a w ( 1 9 6 5 ) . It i s c o n s i d e r e d , t h e r e f o r e , t h a t a m o r e s a t i s f a c t o r y c o r r e l a t i o n m a y b e e s t a b lished
by u s i n g the h e m a t i t e
s h a l e a s a m a r k e r b e d . On t h e T e n n a n t C r e e k O n e - m i l e S h e e t
a r e a , t h e s t r a t i g r a p h i c e q u i v a l e n c e of a l l m a j o r o c c u r r e n c e s of h e m a t i t e s h a l e , a l t h o u g h i m possible
to p r o v e
regional
s t r a t i g r a p h y , a n d t h e r e i s a m a r k e d s i m i l a r i t y b e t w e e n t h e h e m a t i t e s h a l e b e l t of
the Northern Mount
Star
Samuel
-
conclusively -
because
of
gaps
in
t h e o u t c r o p s , i s s t r o n g l y i n d i c a t e d by
Edna B e r y l - Whippet a r e a with i t s a s s o c i a t e d m i n e r a l i s a t i o n , and the
Eldorado
-
Noble's
Nob
and
the Burnt Shirt - Lone Star - Memsahib -
M a m m o t h b e l t s on the T e n n a n t C r e e k O n e - m i l e Sheet a r e a . A c o r r e l a t i o n b a s e d o n t h e e q u i v a l e n c e of t h e s e h e m a t i t e s h a l e b e l t s t h u s r e s u l t s i n a c o n s i d e r a b l e s i m p l i f i c a t i o n of t h e o v e r - a l l s t r a t i g r a p h y a n d s t r u c t u r e , n o t a b l y in r e s p e c t of t h e f o l l o w i n g : 1. Edna
T h e N o r t h e r n S t a r s e q u e n c e i s c o n t i n u o u s w i t h t h e B e r n b o r o u g h s e q u e n c e in t h e Beryl
2.
area,
and
the N o r t h e r n Star Shear
Z o n e i s a f e a t u r e of o n l y l o c a l i m p o r t a n c e .
T h e g r e a t e r p a r t of t h e B e r n b o r o u g h a n d N o r t h e r n S t a r s e q u e n c e s r e p r e s e n t a n
e x p a n d e d e q u i v a l e n t of t h e B l w ^ u n i t o n t h e T e n n a n t C r e e k O n e - m i l e S h e e t a r e a . 3. Star
T h e W h i p p e t S a n d s t o n e M e m b e r a n d p o s s i b l y t h e q u a r t z s a n d s t o n e s in t h e N o r t h e r n
sequence 4.
dominantly
are
equivalent
to
the Blw^ u n i t on the T e n n a n t C r e e k O n e - m i l e Sheet a r e a .
M o r e o v e r , on t h i s a s s u m p t i o n t h e B e r n b o r o u g h a n d N o r t h e r n S t a r s e q u e n c e s a r e younger
than
t h e O r l a n d o s e q u e n c e , s o t h a t m o v e m e n t on t h e Q u a r t z H i l l F a u l t
w o u l d b e e a s t b l o c k d o w n , c o n s i s t e n t w i t h t h e o b s e r v e d r e l a t i o n on t h e T e n n a n t C r e e k O n e m i l e Sheet a r e a .
53
PLATE 1
F i g . 1 Typical topography in the O r l a n d o Mine o v e r the d i s s e c t e d p e n e p l a i n , and p r e s e n t plain with d e n s e m u l g a on the b u l l d u s t flats.
Wanamunga
Group,
Butchers
C r e e k a r e a . Note the a l m o s t
l a c k of c l e a v a g e . 54
total
PLATE 2
PLATE 3
F i g . 1 P h a s e 2 folds in a s i l t s t o n e / s h a l e s e q u e n c e a t t h e Klondyke M i n e . N o t e t h e c h a n g e in p l u n g e of t h e fold a x e s
56
PLATE 4
Fig.
1 Crenulation cleavage
sequence,
Quartz
s e n s e of m o v e m e n t
Hill
(S^)
in a thinly
bedded
Subarea. Note the constant
F i g . 2 T i g h t c h e v r o n s t y l e p h a s e 3 fold sheared limb, Orlando subarea
with one
M O U N T W O O D C O C K NORTHERN TERRITORY
AUSTRALIA 1:63,360
1 MILE G E O L O G I C A L S E R I E S S H E E T 228
PLATE 5
ZONE 5 Reference Czl
Laterite,
Sand
Cz
PALAEOZOIC
Gum Ridge Formation
gravel,
)
and
ferruginous
soil
alluvium,
Lava, pyroclasts,
(mainly
silt,
lateritized
dolerite)
grave/
calcareous
sandstone,
shale,
chert
Helen Springs Volcanics
CAMBRIAN
Dolerite,
Edl
gabbro
C A R P E N T A R I AN Emt
Tomkinson Creek Beds
\ Quartz
sandstone,
Quartz
feldspathic
- hematite
Quartz -
quartz
-magnetite
sandstone,
-jasper
jasper \
Quartz
Fine
Tennant
to medium-grained
Quartz-feldspar
Creek
G r a n i t e Complex
conglomerate,
Dykes or veins
granite
porphyry
• Pot<
LOWER PROTEROZOIC
Porphyritic,
coarse,
Pink chert
or fine
-Pine, even-grained
granite
Ewe volcanic
ash
Ews
o E
Shale,
siltstone,
hematite
Quartz
greywacke,
minor
shale,
greywacke,
volcanics
Ewg Ewv Bernborough Formation
Volcanolith
greywacke,
Acid
volcanic
flows,
Shale
lenses,
minor
Ewb
Whippet Sandstone Member
greywacke,
Quartz
sandstone,
quartz
sandstone,
tuff
ashstone,
ash-flow ash-flew
tuff,
minor
shale,
f/owsfpj
'porphgr
vo/canolith
ashstone,
volt
yrec
siltstone feldspathic
quartz
sandstone,
quartz-pebble
cc
Bw
Undifferentiated: ^
Subdivision of
based
one or
Geological
more stratigraphic
shale,
units
siltstone,
difference.
in
undetermined
volcanics,
etc.
Each subdivision sequence
boundary
Plunge
of minor
anticline
Plunge
of minor
sgnchne
Plunge of Fault,
greywacke,
purely on lithological
fold
showing
Thrust
relative
horizontal
movement
fault
Shear
zone
Lineament Where location of boundaries, folds, and faults is approximate, line is broken, where inferred, queried, where concealed, boundaries and folds are dotted, faults are shown by short dashes Strike
and
dip of
Vertical
JL-
strata
Horizontal
strata
Overturned
strata
Dip < 15° Dip
A.
strata
15°-45°
Dip
air-photo
< 45°
Trend-
interpretation
lines
Horizontal Strike
strata
and dip of
Prevailing Pitch
strike
of
dip of
in cleavage
cleavage plane
cleavage
Inclined
platy
Vertical Fault
and
lineation
Vertical
cleavage
f/ow
platy
flow
hrec cia.
Macrofossil
locality
Major
mine
Mine,
not
being
worked
*
Prospect Ag
Gold
Pb
Lead
Bismuth
Zn
Zinc
Bi Cu Copper
0
W&ter
£ °T
Magnetic
•^750^=^
bore
Magnetic Low
f^^XCD
Windpump
Contours
1st
Tank
An anomaly occurs where the intens radioactivity is considerably above average intensity of the area in win occurs. An anomaly is graded as 1st, or 3rd order depending on whether t above difference of intensity is Ni> Six or Three times the random variations of intensity
Order
Anomaly
/JWH
Waterhole 2nd
© , Sealed
Order
Anomaly
road
3rd
Order
Anomaly
— —•= = •= Vehicle
track
Telephone Phillip Cr
• Yd G e o l o g y , 1964, by: D D u n n e t , Compiled, 1965, b y : D D u n n e t , Drawn by: F.J.Roberts.
Compiled and published by the Bureau of Mineral Resources, Geology and G e o p h y s i c s , Department of National Development.
Issued under the authority of the
Hon. David F a i r b a i r n , Minister for National D e v e l o p m e n t . B a s e map compiled
I N D E X TO A D J O I N I N G S H E E T S
by the Division of National Mapping,Department of N a t i o n a l Development A e r i a l p h o t o g r a p h y by t h e R o y a l A u s t r a l i a n A i r F o r c e at h 5 0 , 0 0 0 s c a l e a n d
R.R.Harding. R.R.Harding.
H
o
m
e
s
t
e
6
line l
Anomaly
A
Trigonometrical
• 327'
Height
station
feet
GEOLOGICAL RELIABILITY DIAGRAM
S h o w i n g Magnetic D e c l i n a t i o n
:
by A d a s t r a A i r w a y s P t y . L t d . at I 1 2 , 0 0 0 and 1 8 0 , 0 0 0 s c a l e s •, complete v e r t i c a l coverage at I 5 0 , 0 0 0 a n d 1 = 8 0 , 0 0 0 s c a l e s Transverse Mercator Projection MARION ROSS 22? RED B L U F F / 237
HAYWARD BRUNCHILLY CREEK CREEK S T H 218 219 MOUNT WOODCOCK IWARRAMUNGA 229 228
Scale 1 Mile to 1 Inch
SOSSE RIVER 239
TENNANT CREEK 238
TENNANT C R E E K S E 5 3 - 14 5
KILOMETRES
DIAGRAMMATIC REtATIONSHIP OF ROCK UNITS
TECTONIC
B0NNEY
FREW
WELL
SF
SF
53-2
Bi
Sections
RIVER
Detailed reconnaissance —
SKETCH
MAP
numerous traverses
Folding s c h e m a t i c
53-3
C a i n o z o i c sediments omitted from section ANNUAL CHANG, I'E
Scale: ^ = 2 Track
QUARTZ HILL FAULT
BERNBOROiUGH
FAULT — ^
-Track
TERRITORY
r Edl jzws
2000 4000
I
Ew
/
Ews
I
Ewb
'
1|,ewc
E
SPRINGS
i
i
P V
,1
6000 ALICE
i.-i i
7
J
I 1
J
_e<~s \
|
,
-
S-'Z"——I
1
„
Ews
4
Ewb Ews
Track
Phillip
Creek
B I i
Not
i
exposed
.' fv
Ews
WT
Sheet
Edl
Ewb -
area
BERNBOROUGH SEQUENCE
EvMb-t
lfw^>
ORLANDOTENNANT CREEK SEQUENCE
Unconformity
N o t exposed on Mt Woodcock S h e e t a r e a
Track
Butchers
Creek
1
NORTHERN
STAR
Track
STUART
Fault, and
HIGHWAY Tomkinson Creek Beds
Bw
Warramunga Group
-> Plunge \
.Ewb
2000'
H
Edl
|
Ews
/
4000 6000
/
Pwg
£
L
x- Ewb
/ /
\ Ews \
'
— — ~^ P w w
shear zone lineament
s
Thrust Em+
iEmt|
on
Mt. Woodcock
V
Eww/ * V
Track
I
Ews
Ew
71)00
NORTHERN m
NORTHERN STAR SHEAR ZONE
Ew Y
2000'
— 1
4000'
v
6000'
fault of
Trend of
fold bedding
Flight
These symbols indicate a change in average inten of radioactivity in passing from one area to anothe the short hachured lines point to the area with th lower average intensity. The magnitude of the char is Six limes the random variation of intensity of the area with the lower average intensity
^rd
in
Sharp along Line of
d
MT WOODCOCK SHEET 228
ZONE 5
