Koonenberry Geological Mapping Project
Finalisation of the Koonenberry Project in the far northwest of NSW is a focus of the New Frontiers initiative. Second edition geological mapping has now been completed following the acquisition of high resolution magnetic, radiometric and gravity data, deep seismic reflection data, isotopic studies, whole rock geochemistry, and regolith studies in conjunction with the former CRC LEME.
Products
Map products (Figure 1) are in the final editing and map production process and include:
- Twelve 1:100 000 geology maps;
- Four 1:25 000 geology maps;
- Four 1:100 000 regolith maps;
- Two 1:250 000 solid geology maps.
Explanatory notes that describe detailed unit descriptions, geological history and mineral system interpretations are also nearing completion.
A GIS data package on DVD is being developed that will include the geophysical/geological interpretation maps completed for the Cobham Lake and Milparinka 1:250 000 scale map sheet areas. This DVD data package will update the Koonenberry CD digital data package that was released in 2002. This package will incorporate GIS data, databases and publications, and will include geographical information, Landsat imagery, geological and geophysical coverage, detailed interpretation of the basement geology, public access point data sets related to exploration, mineral occurrences and tenement information.
Geological history
The Koonenberry Belt wraps around and defines the eastern margin of the Curnamona Craton and includes parts of the Delamerian and Thomson Orogens (Figure 2). The Koonenberry Fault is a long-lived, deep tapping feature that forms a prominent feature in both imagery and the field.
Intracontintental rifting associated with the breakup of the Rodinia supercontinent in the Neoproterozoic resulted in deposition of the shelf to slope sediments of the Kara Formation and alkali-basalts of the Mount Arrowsmith Volcanics. These units, of the Grey Range Group, are time and tectonic setting equivalents of the Adelaidean units that crop out to the west of the Bancannia Trough.
Sag or drift in the Cambrian led to further deposition of sediments along the then continental margin resulting in the shelf deposits of the Gnalta Group, slope and turbidite sequences of the Teltawongee Group and foot of slope to deep water sediments of the Ponto Group. The Ponto Group also contains exhalative horizons.
Calc-alkaline andesites and pyroclastic rocks of the Mount Wright Volcanics are intercalated with the Gnalta Group and are present as airfall tuffs in the Ponto Group. The tholeiitic basalts of the Bittles Tank Suite have a MORB affinity and occur as extrusive lavas and intrusives in the Ponto Group and as intrusives in the Teltawongee Group.
The late Cambrian Delamerian Orogeny involved tight folding, thrusting, and cleavage formation accompanying low grade regional metamorphism at about 500 Ma. Oroclinal folding of the Neoproterozoic to Cambrian sequence in the Delamerian Orogeny resulted in the distinctive shape of the Koonenberry Belt and the Grasmere Knee Zone. A late sinistral transpressional regime led to half-graben formation on splays on the eastern margin of the Koonenberry Belt.
Relaxation after the Delamerian Orogeny and opening of the Larapintine Seaway across northern Australia resulted in shallow marine sedimentation (Mutawintji, Pimbilla Tank and Kayrunnera groups). Deeper water turbidite sequences are represented by the Warratta Group in the Tibooburra-Milparinka area.
Further deformation occurred in a late Ordovician to Early Silurian cleavage forming event, correlated to the Benambran Orogeny in the Lachlan Orogen to the east. I-type granite intrusion in the Early Silurian included the Tibooburra Suite in the north and the Allambie Woolshed Granite in the south. Dextral strike-slip movement in the late Benambran opened the pull-apart Mount Daubeny Basin leading to deposition of a red-bed sequence of clastic sediments (Mount Daubeny Formation) accompanied by andesitic volcanism and later rhyolitic dykes of the Wertago Suite.
Widespread fluvial to deltaic deposition of quartzose sediments of the Wana Karnu Group in the Late-Middle Devonian was temporarily halted by the Tabberabberan Orogeny before being unconformably overlain by further quartzose sandstones of the Ravendale Formation.
Further deformation including shearing, brecciation and fluid remobilization occurred in the Carboniferous Kanimblan-Alice Springs Orogeny. Emplacement of several ultramafic bodies (including Cliffs Tank Complex, Macs Tank Ultramafic) are interpreted to have been related to fault movements in this event.
The Yanna Tank formation in the south is interpreted to represent glacial processes in the Permian. Numerous diatreme pipes intruded the region in the late Permian to early Triassic. Clusters of diatremes occur in the Cobham Kink Zone and in the Kayrunnera area.
Further erosion and deposition in fluvial to marine environments occurred through the Mesozoic, forming thick accumulations of sediment in the Eromanga Basin. Sea level fluctuations are represented by marine and terrestrial fossil assemblages. The Namur Sandstone is the basal unit of the Mesozoic sequence, overlain by the Cadna-owie Formation and the Rolling Downs Group.
A wetter climate in the Palaeogene led to extensive leaching of silica and subsequent silicification (e.g. Eyre Formation). Ferricretes also represent induration and are common throughout the Koonenberry Belt.
In contrast to the Cretaceous and Tertiary, the Koonenberry Belt endured an arid environment in the Quaternary comprising modern drainage systems, aeolian dunes, salt lakes and gibber plains. Neotectonism is apparent in the Koonenberry Belt and is represented by young faults scars and recent seismic activity.
Mineral systems of the Koonenberry Belt
The Koonenberry Belt is prospective for a variety of mineral commodities in a range of styles. The prospective lithologies have been identified and highlighted in a prospectivity map shown in Figure 3. The Koonenberry Belt also has major deep tapping structures that have undergone multiple deformation, providing structural complexity and the potential for upgrading mineralisation. The Koonenberry Fault and related splays, the Grasmere Knee Zone and Cobham Kink Zone are all major structural features that have undergone a complex history of reactivation and fluid infiltration (Fig. 3). The Koonenberry Belt is under explored by modern exploration methods.
Orthomagmatic Ni-Cu-PGE
Primary sulphides (pyrite-chalcopyrite-pyrrhotite) and violarite (ex-pentlandite) have been intersected in the drilling of rift associated alkali-basalts and associated ultramafics of the Neoproterozoic Mount Arrowsmith Volcanics.
Mississippi Valley/stratabound Pb-Zn-Ag
Manganese-rich exhalative and dolomitic units are common in the shelf to slope sedimentary rocks of the Kara Formation. These units were deposited in an intracontinental rift setting, and are equivalent to the Adelaidean Farnell Group to the west that has been a focus for Mississippi Valley type exploration on the Mundi Mundi Plain.
Little modern exploration for base metal mineralisation in the Neoproterozoic Kara Formation has taken place, despite stream sediment assays indicating an elevated copper and zinc background in the Kara Formation.
Volcanic Massive Sulphide Cu-Zn-Ag-Au
Besshi-style mineralisation has been identified at Grasmere, Cymbric Vale and Ponto. These deposits are hosted by the Ponto Group, a mid to late Cambrian package of ocean floor phyllites with sandstone lenses, exhalative horizons (quartz-magnetite units), tuffs from the Mount Wright Volcanics and extrusive basalts and mafic intrusives of the MORB-affinity Bittles Tank Suite. Thrust repeats, folding and truncation of sequences by later faulting has resulted in approximately 50 km of strike length remaining untested for continuation of mineralisation, particularly in areas of shallow (<100m) cover.
Turbidite hosted orogenic Au
The eastern margin of the Koonenberry Belt is prospective for orogenic Au where late-Ordovician to early Silurian deformation correlated with the Benambran Orogeny has resulted in cleavage parallel, crack-seal quartz veins, and reverse faults producing hanging wall anticlines. Orogenic gold has been identified in the Warratta Inlier, near Tibooburra and at Cawkers Well and near Williams Peak.
At Warratta, historic mining of the Pioneer-Phoenix reef system in the late 1880s averaged ~25g/t Au. Gold is associated with pyrite and arsenopyrite. Strike-extensive carbonate-sericite 'bleached' zones correlate with magnetic lows (zones of magnetite destruction) and narrow halos of phengite-chlorite-pyrite-carbonate alteration. Drilling in 2006 confirmed the continuation of gold mineralisation at depth.
Epithermal Ag-Pb-Cu
Epithermal mineralisation has been identified near the northern end of the Mount Daubeny Basin in Cambrian basement units (Ponto and Teltawongee groups) and the Siluro-Devonian Mount Daubeny Formation. This epithermal event is related to opening of the pull-apart Mount Daubeny Basin and associated andesitic volcanism.
Epithermal mineralisation is interpreted to overprint early Thackaringa-style Ag-Pb veins of the Nuntherungie Silverfield. However, it is possible that mineralisation is related to thermal zonation with Cu-rich deposits of the Wertago Copperfield proximal to the volcanic pile and the Ag-Pb rich deposits of the Nuntherungie Silverfield distal. It is interpreted that remobilisation of cupriferous fluids around the Wertago area has also occurred during the Kanimblan-Alice Springs Orogeny.
Diatreme-hosted diamonds
The Turkey Creek diatreme and associated diatremes in the Kayrunnera pipe cluster contain kimberlitic and high-pressure indicator minerals suggesting the area has major potential for diamonds. No diamonds, however, have yet been discovered in the area.
In the south of the Koonenberry Belt in the Dolo Hills area, recovery of one macrodiamond and six microdiamonds in the 1990s, and nearby kimberlitic chromite shedding basaltic intrusives suggest a local source of diamond.
Placer gold
Placer gold deposits are responsible for most of the historical gold production in the region. Fossil placer-gold occurs in the Namur Sandstone, the basal Mesozoic unit, throughout the Koonenberry Belt, but especially around the Tibooburra, Warrratta and Mount Browne Inliers. Reworking of the Cretaceous units has resulted in recent placer-gold within Quaternary and modern day alluvial systems.
Precious opal
Opal in the White Cliffs area occurs as thin layers within the sedimentary rocks of the Early Cretaceous Doncaster Member of the Wallumbilla Formation of the Rolling Downs Group.
Selected references
looking southwest from
Big Wallaby Tank on Morden Station
- Buckley, P.M. 2001. Grasmere 1:100 000 sheet, home to a few surprises. In: Graves, K., editor, Minfo No. 70 New South Wales Mining and Exploration Quarterly, NSW Department of Mineral Resources, 2001.
- Buckley, P.M. 2003. The MDB: A mineralised late Silurian to early Devonian pull-apart structure. In Peljo M., comp., 2003. Broken Hill Exploration Initiative: Abstracts from the July 2003 conference. Geoscience Australia Record 2003/13.
- Buckley, P.M. and Mills, K.J. 2006. Excursion Guide for the Koonenberry Belt Field Trip. Broken Hill Exploration Initiative conference.
- Gilmore, P.G., Greenfield, J.E., Reid, W.J. and Mills, K.J. 2007. The metallogenesis of the Koonenberry Belt. In: Lewis, P.C. 2007, Mines and Wines 2007. Extended Abstracts, Bulletin 46, Australian Institute of Geoscientists.
- Greenfield, J.E. and Reid, W.J. 2006. Orogenic gold in the Tibooburra area of northwestern NSW - a ~440Ma ore system with comparison to the Victorian goldfields. Australian Earth Sciences Convention 2006.
- Mills, K.J. and David, V. 2004. The Koonenberry Deep Seismic Reflection Line and Geological Modelling of the Koonenberry Region, in Western New South Wales. Geological Survey of NSW, GS 2004/185.
- Musgrave, R.J., Greenfield, J.E. and Dick, S. 2008. Geophysical and geological expression of a Neoproterozoic to Cambrian rifted arc setting in south-eastern Australia; analysis and interpretation through potential field inversion and 3D modelling. Abstract for 33rd International Geological Congress, Oslo.
For more information on the mapping project please contact the Geological Mapping Team.
(Last updated on 24/02/2009)