joke, page-73

re: grades? For those intersested see :
http://www.minerals.nsw.gov.au/explorationNsw2/exploration_nsw_projects/koonenberrryMapping

Reprint of pdf file:

FEATURE
30 www.minerals.nsw.gov.au Minfo 68, 2000
Recent advances in mapping and understanding
of the Koonenberry Belt
The Koonenberry Belt defines the
eastern margin of the Curnamona
Craton. The exposed older rocks in the
Belt consist of Late Proterozoic and
Cambrian sedimentary and volcanic
rocks deposited on the eastern margin
of continental Australia during and
following the Rodinian break-up. The
main structural trends in the Belt were
defined by tight folding and thrusting
that occurred during the Late Cambrian
Mootwingee Stage of the Delamerian
Orogeny at about 500 million years ago.
Further mapping in the
Koonenberry Belt (figures 1 and 4 show
the mapping area) has confirmed the
lithological/stratigraphic subdivision of
the basement rocks into Kara,
Teltawongee and Ponto beds and Gnalta
Group. Most of
t h e e x p o s e d
c o n t a c t s
between these
units appear to
be early thrust
faults. Closer
g e o l o g i c a l
mapping and
f u r t h e r
g e o p h y s i c a l
interpretation
has enabled
subdivision of
the units. The
Ponto beds have
been subdivided
d u r i n g
G e o l o g i c a l
1600 Ma metamorphic events. Apparent
ages of 1610 Ma to 1640 Ma and older,
revealed in SHRIMP age profiles in
Thorndale Composite Gneiss zircons,
are interpreted as ages that have been
incompletely reset.
Correlations with northern
Australia
The improved geochronological
framework for the Willyama
Supergroup invites closer comparison
with other Palaeoproterozoic
sequences, such as the Mount Isa Inlier
and McArthur Basin in northern
Australia. The 1700 Ma to 1710 Ma
magmatic event, previously recognised
in the OD and now in the BHD, is
considered an early phase of an
intracratonic rift setting for the
Willyama Supergroup. This appears to
be the same age as a major extensional
episode (Calvert period) in the
McArthur Basin and Lawn Hill
Platform [near the top of the Big
Supersequence (R.W. Page, M.J.
Jackson and A.A. Krassay, 2000)], and
may represent a tectonic analogue of
this widespread magmatic event.
Rocks of Broken Hill Group age are
not widely documented in northern
Australia. An erosional/depositional
break may be present in the Willyama
Supergroup or, as considered by
George Gibson, part of the section may
have been tectonically excised. In the
OD, geochronological and stratigraphic
evidence suggest at least two breaks. In
the BHD, an age gap of several million
years might be present between the top
of the Broken Hill Group and the
Sundown Group, and a gap of up to 10,
or even 20, million years, may be
present between the Sundown Group
and Bijerkerno Metasediments. Until
there are better age constraints for the
Sundown Group and basal Paragon
Group, these suggestions remain as
possibilities.
A readily acceptable correlation
with northern Australian sequences can
be established from close age
comparisons of the Bijerkerno
Metasediments (1656±5 Ma) and a
‘pelite suite’ at Mount Howden in the
OD (1648±6 Ma) with tuff ages
(1654±5 Ma, 1656±4 Ma, 1652±7 Ma)
in the Urquhart Shale — mineralised
host of the Mount Isa and Hilton
orebodies. Furthermore, the new age of
the Dalnit Bore Metasediments
(1642±5 Ma) cannot be distinguished
from a number of ~1640 Ma
stratigraphic ages determined in the
middle McArthur Group (at the HYC
deposit), in the Fickling Group (Walford
deposit), and in the middle McNamara
Group (Riversleigh Formation).
Significance
Confirmation that the Paragon Group
is stratigraphically contemporaneous
with mineralised sequences in northern
Australia is an important outcome of
t h i s g e o c h r o n o l o g i c a l s t u d y.
Specifically, there is now a definite age
correlation basis for considering a
refocus of some Curnamona Province
exploration efforts into the Paragon
Group in the BHD and equivalents in
the OD. This consequence, and other
ramifications of the new age dates,
provide a robust geological framework
against which more advanced basin
analysis and metallogenic models can
be examined.
This article has been extensively
edited from a paper by R.W. Page
(who kindly provided the text),
B.P.J. Stevens, G.M. Gibson and
C.H.H. Conor — to concentrate on
Broken Hill results. The paper was
published in AGSO Record 2000/10.
For more information contact
Rod Page on (02) 6249 4261, e-mail:
R o d . P a g e @ a g s o . g o v. a u o r
Barney Stevens on (08) 8080 0629,
f a x ( 0 8 ) 8 0 8 7 8 0 0 5 e - m a i l :
[email protected]
or George Gibson on (02) 6249 9727,
f a x ( 0 2 ) 6 2 4 9 9 9 6 5 , e - m a i l :
[email protected]
(continued from previous page)
View of Mount Lynn, northern end of Turkaro range,
Marrapina station showing Ravendale Formation (Late
Devonian), with Kara beds (Neoproterozoic) forming
lower foreground. The view is looking south from a
silcrete hill.
Photograph by Kingsley Mills
(text continued opposite)
FEATURE
Minfo 68, 2000 www.minerals.nsw.gov.au 31
Broken Hill
SH/54-7
MILPARINKA
SH/54-8
URISINO
AREA O
AREA B
AREA A
SI/54-4
MANARA
SH/54-16
WILCANNIA
SI/54-3
MENINDEE
SH/54-15
BROKEN HILL
SH/54-12
WHITE CLIFFS
SH/54-11
COBHAM LAKE
50 km
Mapping
Koonenberry
South Australia
23566
0
northwest) in Teltawongee beds, several
zones of secondary folding of those
structural trends, and a northeasttrending
set of moderately magnetised
cross-cutting dykes.
In 1999 a deep seismic line was
commissioned by AGSO–DMR to cross
the Bancannia Trough and the
Koonenberry Belt from the Euriowie
inlier to Yancannia. That survey
revealed the sedimentary structure
within a 6 km thick Devonian and
Mesozoic section of the Bancannia
Trough. Correlations with the Winduck,
Snake Cave and Ravendale seismic
intervals of the Darling Basin can be
made, and steep reverse faults bring
basement rocks up and over the Trough
to the west and east. Faulting can be
seen within the deep structure of the
Koonenberry Belt, with suggestions that
shears associated with both the
Koonenberry and Olepeloko faults may
dip at moderate angles to the west.
The strong magnetic stripes that
characterise the regional response of the
Ponto beds and some of the Teltawongee
beds have been proved to be due to
magnetite-bearing quartz–mica phyllite
units and, to a lesser extent, altered
metavolcanic units. Some patches of
surficial maghemite obscure the
magnetic response of deeper features.
A better understanding of the Mount
Arrowsmith Volcanics, an alkali basaltic
suite with associated intrusions, has
been revealed through detailed mapping
(by Ian Cooper) in the Nundora–
Packsaddle–Milpa area. It appears that
several independent extrusive volcanic
centres were active on a shallow marine
shelf in late Proterozoic time. There was
apparent brief emergence of volcanic
edifices above sea level and then
submergence in a shallow marine
environment. Some extrusive and
tuffaceous units have become strongly
differentiated towards more silicic
quartzofeldspathic trachytic
compositions. Beneath the volcanic
piles intrusive gabbroic sills show
crystal settling differentiation with some
peridotitic lower sections. Above the
volcanic piles, dolomitic siltstones and
sandstones have been intruded by small
plutons of syenitic and dioritic
compositions that may form part of the
Mount Arrowsmith Volcanics episode.
Figure 4. The area of the Koonenberry mapping
project (this figure is part of figure 1, p. 24)
Survey mapping into a number of
sequences and formations either by
detailed mapping (Peter Buckley in the
Grasmere map sheet area) or by the
interpretation of magnetic and
radiometric patterns coupled with field
knowledge (Barney Stevens and
Kingsley Mills). Results of that work are
available in the new Grasmere
geological map and in the new
Koonenberry geological interpretation
maps.
Zircon dating of units in the Ponto
beds have yielded dates as old as 516
million years. While the results may be
subject to interpretation, they do suggest
that the Ponto beds are probably Middle
Cambrian in age, and younger than first
thought. There is a geochemical
progression from calc-alkaline
volcanism (525 Ma) in the Gnalta Group
in the west, through the alkaline Mount
Arrowsmith Volcanics (586 Ma) in the
Kara beds, to tholeiitic volcanism in the
Ponto beds (516 Ma) in the east.That
variation may reflect differing thickness
of the Earth’s crust which was
undergoing extension at different times
of volcanism.
Despite close study, no evidence has
been revealed to suggest microcontinent,
island arc or collision zones.
Sedimentary environments can be
interpreted as a shallow passive
continental shelf for
the latest Proterozoic
to earliest Cambrian
Kara beds and
nearshore for the
early Cambrian
Gnalta Group;
turbiditic slope
deposits for the
Early to Middle
C a m b r i a n
Teltawongee beds;
or distal shelf and
slope deposits for
the Middle
Cambrian Ponto
beds.
Recognition of
basic volcanic units
in late Proterozoic
(Adelaidean) rocks
on the western side
of the Bancannia
Trough near
Fowlers Gap suggests a possible
correlation with the Mount Arrowsmith
Volcanics and the Kara beds. There may
be continuity of basement from the
Broken Hill Block to the Koonenberry
Belt beneath the Bancannia Trough.
The Koonenberry Fault and its
subsidiary splays appear to be
characterised by dominant dip-slip
motion. East–west, and northwesttrending,
faults appear to indicate latestage
sinistral strike slip motion.
New discoveries and advances
in understanding of the
Koonenberry geology
A low-level geophysical survey was
carried out in 1999 to cover an area to
the north and northeast of the previous
1995 survey. The survey covered an
area from White Cliffs to Yancannia to
Mount Arrowsmith to Milparinka. As
well as covering some areas of known
bedrock exposure, the survey revealed
some interesting features beneath
shallow Mesozoic cover at the southern
margin of the Eromanga Basin. In the
Kayrunnera 1:100 000 map sheet area,
the new survey showed subtle basement
features beneath a cover estimated to be
less than 60 m on the basis of mapped
geology and water bore information.
Magnetic features include weak
basement structural trends (southeast–
FEATURE
32 www.minerals.nsw.gov.au Minfo 68, 2000
Several small granitic intrusions
have now been recognised within the
magnetically quiet and strongly
deformed turbidite facies sequence
(Teltawongee beds) to the east of the
Koonenberry Fault. These rocks are
fine-grained and foliated, but show
country rock xenoliths. Several bodies
in the Williams Peak area appear to be
associated with gold in the base of the
overlying Mesozoic sequence.
Re-interpretation of the geological
and geophysical features (close to the
Barrier Highway) suggests that two
large caldera-like ring structures may
explain some of the unusual rock
relationships there. Younger Late
Cambrian to Devonian units are
preserved within the rings, while an
exposure of highly deformed older
phyllite on Churinga and a nest of
weakly deformed ?Carboniferous basic
intrusions appear related to the ring
margins.
Pointers to further mineral
exploration
Historical mineral occurrences and
small mining operations are known
throughout the Koonenberry Belt but
the area is very much a greenfields area
for exploration. Until recently the
geology was poorly understood.
However, key focal points for
geological investigation and mineral
exploration may now be recognisable.
The Milparinka–Mount Browne–
Tibooburra region in the north is well
known for its significant gold
occurrences, both in quartz veins and
in alluvial units in basal conglomerate
beds of the Mesozoic cover sequence.
Smaller occurrences of gold have been
worked near Williams Peak
(Kayrunnera map area) as alluvial gold
in the base of the Mesozoic cover,
Koonenberry Gap (carbonate-bearing
quartz veins), and Cawkers Well (in
quartz–chlorite–siderite veins).
Anomalous gold values are also
widespread in association with ankeritic
carbonate in breccia and shear zones
associated with the larger faults. The
more quartzofeldspathic rocks derived
from the differentiation of the alkaline
Mount Arrowsmith Volcanics also
contain anomalous gold values.
Traces of
c o p p e r
carbonates are
often seen
associated with
fractures in basic
volcanic rocks in
the region,
e s p e c i a l l y
tholeiitic units
within the Ponto
beds and near the
Koonenberry
Fault zone.
H i s t o r i c a l l y,
copper has been
mined from the
Grasmere and
Ponto quartzose
lode horizons
that have been
interpreted as syngenetic deposits. The
oxidised zones of numerous lodes have
been worked in the Wertago copper
field. These are within Carboniferous
fault zones and along the Koonenberry
Fault. There is also a spatial
relationship with andesitic lava flows
and intrusions into the Siluro-Devonian
Mount Daubeny Formation red-bed
sequence.
Rich silver values were obtained
from the Noonthorangie silver field
(Wertago map area) at the turn of the
twentieth century where argentiferous
galena occurs in narrow quartz–siderite
veins along fault zones over a deep
magnetic anomaly.
The new high-resolution
geophysical coverage has revealed
numerous bullseye magnetic anomalies
(both positive and negative) and many
do not appear to have been adequately
tested. There are also curious magnetic
anomalies and areas of disturbance of
regular magnetic trends that deserve
closer investigation. Large areas of the
north and northeast appear to have only
a shallow cover and, with the aid of the
new generation geophysics, are
amenable to mineral exploration.
Progress in mapping
The Koonenberry region was
(regionally) mapped at 1:250 000 scale
in the 1960s. The new generation of
geological mapping at 1:100 000 scale
commenced in 1995 immediately
following a high resolution magnetic
and radiometric survey carried out as
part of the Discovery 2000 program. At
least 12 map sheet areas at this scale
contain mappable older rock units.
Mapping has commenced in those map
areas containing the most extensive
exposure of Palaeozoic rocks.
The Bunda, Grasmere and
Kayrunnera 1:100 000 geological map
sheets are now available in full colour.
The Wonnaminta and parts of the
Bancannia and Mount Arrowsmith map
sheets are currently being mapped and
compiled. Nuchea will be mapped in
the second half of this year. The
Koonenberry pre-Permian geological
map at 1:250 000 scale gives an
overview of the central and southern
parts of the Koonenberry Belt. The
Koonenberry Geological Interpretation
Map at 1:250 000 scale, and the four
component 1:100 000 map sheets,
present a compilation of current
geological and geophysical knowledge
of the central and southern parts of the
belt.
Photograph by Kingsley Mills
Basal section of the Snake Cave Sandstone (Middle
to Late Devonian) with Teltawongee beds (Early to
Middle Cambrian) forming subdued lower slopes and
background.
This article is based on a paper
presented by Kingsley Mills and
Michael Hicks at the 2000 BHEI
Conference, with an abstract published
in AGSO Record 2000/10. For further
information contact Kingsley Mills on
(08) 8080 0621, or fax (08) 8087 8005,
e-mail [email protected]