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Girilambone District - Tritton, Murrawombie, Larsens East, Hartmans, Great Hermidale, Budgery, Bonnie Dundee, Avoca Tank |
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New South Wales, NSW, Australia |
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Cu Au Ag
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Super Porphyry Cu and Au
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The Girilambone District contains at least eight copper deposits, including Girilambone North (Larsens East, North East, Double Tanks and Hartmans), Girilambone (Murrawombie) and Girilambone Deeps, Avoca Tank, Tritton, Budgerygar, Great Hermidale, Bonnie Dundee and Budgery (#Location: Girilambone - 31° 15' 31"S, 146° 52' 9"E; Tritton - 31° 23' 39"S, 146° 43' 11"E) .
These deposits are distributed over a strike length of around 60 km. Individual deposits range from 1 up to 14 Mt @ 2.7% Cu, 0.3 g/t Au in the largest, the blind Tritton orebody. The original Girilambone deposit is located 45 km north-west of Nyngan and 105 km ENE of Cobar in central-western New South Wales, Australia, whilst Tritton is 10 km to the SW.
The Girilambone deposits are located in the western section of the Palaeozoic Lachlan Fold Belt of the Tasman Orogen in eastern Australia. They are hosted by the Ordovician Girilambone Group flysch sequence which is largely composed of medium grained quartz-wackes which have been regionally metamorphosed to quartz-chlorite-sericite schist. This sequence extends from as far south as Wagga Wagga, and extends to the north of Girilambone. In the Girilambone district 'basement' semi-pelitic and mafic schists of this succession are unconformably overlain by mafic schists and quartz-greywacke of the Caro schist and by the Tritton Formation quartz-wacke, sandstone and phyllite. Near Girilambone the 'basement schists' are intruded by syn- and post-tectonic granitoids, intermediate, mafic and ultramafic Alaskan-type intrusive rocks. Only some of the younger of these intrude the Caro Schist and Tritton Formation.
For more background on the regional stratigraphy see Geological Setting section of the Cobar Mineral Field record. The Girilambone Group is basement to the Cobar Basin and represents the oldest known rocks in this part of the Lachlan Fold Belt.
The stratigraphy in the Girilambone district comprises, from the base:
Girilambone Beds - basement schists, composed of quartz-chlorite-sericite schist;
Unconformity
Caro schists - laminated quartz-mica schist and laminated quartzwacke;
Tritton Formation:
Quartzwacke with minor pelite;
Budgery Sandstone;
Massive phyllite;
Ballast Beds - Weltie Formation.
The significant massive sulphide deposits of the district occur within the Caro schist near the base of the greywacke succession and is associated with intervals of chloritisation, siderite and epidote alteration, thin magnetite lenses, hematite alteration and intense silicification. Not all of these features are recognised at all deposits. Complexly folded quartzite ridges extend discontinuously over a strike length of up to 150 km and consist of intensely silicified greywacke. All of the known deposits are located close to such ridges.
Pink quartzite of these ridges, including red jasper with disseminated pyrite within mafic schists occur adjacent to some large ultramafic and mafic intrusives and are developed throughout the region at different stratigraphic positions, indicating the quartzite is not a stratigraphic unit, but rather is of low temperature hydrothermal origin.
The mineralisation in the Girilambone district is polymetallic, comprising pyrite, chalcopyrite, chalcocite, sphalerite and galena, with <0.5 g/t Au and <20 g/t Ag. Ore occurs within steep dipping, WNW striking shears within quartz-chlorite-sericite schist and psammitic turbidites of the Caro schist.
The geology of the individual deposits of the district are discussed below.
Girilambone (Murrawombie) - Copper carbonate and phosphates, supergene chalcocite and primary chalcopyrite are found in steeply dipping shear zones which strike at 300°. The Main Lode consisted of lenses of massive sulphides within crypto-crystalline quartz that have been complexly folded and faulted. The massive sulphides are predominantly chalcocite within laminations and as lenses in cryptocrystalline pink quartz. Some grains within the pink quartzite are rounded and detrital, although the majority is very fine grained with no diagnostic characteristics. Within the pit, the Main Lode had a strike length of 120 m and was 10 m thick.
Stringers of pyrite and chalcopyrite were found as a discrete zone in the footwall of the Main lode, within chlorite-sericite schist hosts.
Mineralisation also occurs, predominantly as disseminated pyrite within chlorite-sericite schist. Associated alteration takes the form of chlorite with epidote, siderite and magnetite lenses.
The original reserve at Girilambone was 8 Mt @ 1.4% Cu as leachable chalcocite. An inferred resource of 3.4 Mt @ 0.96% Cu remains below the Murrawomble pit (1998).
Girilambone North - comprises the Larsens East, Northeast, Hartmans and Double Tank massive sulphides for a total proved + probable reserve of 5.38 Mt @ 0.78% Cu as leachable copper in 1998.
The Larsens massive sulphide was 250 m long, 46 m true width, 300° strike and dip of 20 to 45° and was composed of massive pyrite-chalcopyrite lenses within weakly silicified semi-pelitic schist accompanied by minor mafic components. It contained a reserve of 1.915 Mt @ 1.04% Cu which was leachable.
The Northeast massive sulphide lens is mostly chalcopyrite, striking at 330°, dips 60°E, has a 200 m strike length and true width of 14 m. In 1998 it had a reserve of 0.988 Mt @ 0.82% Cu.
The Hartmans comprises a massive gossanous zone within a wide halo of limonite, and is believed to be after secondary chalcocite, with enriched Au values. The underlying primary ore is composed of thin lenses of massive pyrite-chalcopyrite within a halo of disseminated pyrite. Reserves in oxide, transition and chalcocite ore totalled 2.502 Mt @ 0.57% Cu in 1998.
The Double Tanks mineralisation occurs as thin lenses of massive pyrite-chalcopyrite in semi-pelitic schists, trending at 330° over a strike length of 150 m and true width of 6 m, dipping at 65°E.
The Bonnie Dundee and Budgerygar lodes are generally contain <0.4% Cu, except in zones of supergene enrichment and are part of a 2.5 km interval of fault offset, en echelon lode development, which include the Tritton deposit. As with all of the Girilambone and Girilambone deposits listed above, these are delimited by NW trending faults. These lodes are on the same NW-SE trend immediately to the north of Tritton. Tritton is ~20 km SW of Murrawomble/Girilambone.
Tritton is the largest of the deposits in the district. It is hosted by Ordovician quartz sandstones (quartzites) and meta-pelites (mica schists) which have been metamorphosed to greenschist facies through at least four major deformation events. The first three of these events developed the pre-mineralisation architecture that controlled the internal geometry of the ore deposit. The last major deformation was critical to the control of the overall geometry and the location of the ore deposit and initiating the faults that were synchronous with the mineralisation.
The Tritton ore body is controlled by both fault and fold structures. On a deposit scale, domains are defined by major (district scale) steeply dipping northwest trending faults which are responsible for the overall NW-SE trend of the deposit. The overall south-east plunge of the ore body is a result of the east to ESE dip of bedding and a bedding parallel fault which lies between the north west striking faults.
The ore deposit a regular, tabular, body which consists of two zones, the upper (UOZ) and lower ore zone (LOZ), each approximately 400 m long, which strike at 28°, dip 20 to 70°E and pitch towards 130°.
The UOZ is un-weathered and is hosted by quartzite with only minor schist. It varies from massive banded pyrite and chalcopyrite to bands of sulphide interlaminated with silicified schist and contains the highest chalcopyrite:pyrite ratios, the highest gold and silver values, minor bornite and tennantite and is characterised by more numerous lenses of hematite+magnetite+silica alteration.
The LOZ is composed of massive and banded pyrite+chalcopyrite lenses in chloritic semipelitic schist, and immediately overlies carbonate+epidote+magnetite altered mafic schist. The orebody is cut by narrow, sub-vertical mafic dykes.
The Tritton orebody is part of a larger mineralised system that covers several square kilometres. The main Tritton ore body, which is blind, is hosted within the north east trending, south east dipping, bedding parallel structure, the Tritton lode. The sub parallel Budgerygar and Bonnie Dundee lodes structures have been mapped on surface and have strike lengths in excess of 800 m. Each has been the focus of intense silica-sericite alteration while sulphide mineralisation is found along the entire length of these structures, concentrated in high grade shoots.
The host metasediments underwent an initial stage of replacement style alteration that is zoned from proximal (adjacent to the main fluid channels) laterally outward to more distal settings as: i). quartz+magnetite+carbonate to ii). stipnomelane+quartz+biotite±magnetite to iii). Fe-chlorite+carbonate±biotite±quartz±sulphides. These zoned replacement assemblages are syn-deformation but mainly postdate the formation of metamorphic quartz±albite veins. The quartz+magnetite+carbonate assemblage may be restricted to shallow levels in the UOZ.
A subsequent series of open space/depositional events in dilatant fractures and local breccias illustrate the following succession of events (from Erceg and Hooper):
i). hematite+Fe-chlorite at very shallow levels;
ii). Fe-sulphide+quartz+Mg-chlorite. Fe-sulphide minerals comprise zoned pyrrhotite+pyrite to pyrite to pyrite+arsenopyrite/arsenean pyrite at progressively shallow levels. The quartz ranges from strained to ribbon clear and unstrained in progressively later events indicating a change from compressional to extensional regimes during the mineralisation events. At very shallow levels, pyrite has botryoidal colloform banded texture indicative of very rapid cooling conditions.
iii). Base metal sulphides+carbonates. Copper sulphides are zoned from chalcopyrite to chalcopyrite+bornite to tennantite+chalcopyrite at progressively shallow levels. Sphalerite and galena are associated with copper mineralisation in the late stages of the base metal event and in settings distal from major structures. The sphalerite is Fe-rich and zoned from deeper to shallower levels, while galena abundance increases at progressively shallow levels. Gold mineralisation took place during the late stages of the base metal event, with minute 2 to 15 µm native gold inclusions in tennantite. In contrast, silver rich electrum inclusions occur in late stage galena+sphalerite+chalcopyrite+pyrite veins. The carbonates grade from ankerite to Fe/Mn rich carbonates (siderite, Mn-siderite and rhodocroisite) at progressively shallower and later stages of the base metal event.
iv). Siderite±pyrite/chalcopyrite veinlets cross cut all other assemblages and extend for tens of metres into the wall rock schist and quartzite units.
Erceg and Hooper observe that spatial and temporal zonation of alteration and mineralisation indicate that hot (>250 to 300°C) mineralised fluids were channelled into significantly cooler areas (particularly at very shallow levels in the orebody) during a change from compressional to extensional regimes. The cooling of the mineralised fluid resulted in base and precious metal mineralisation. This produced a pattern exhibiting an overall change from quartz+oxide (magnetite to hematite), to sulphide minerals (pyrite/pyrrhotite to copper sulphides to lead+zinc sulphides), to late stage carbonate deposition.
Avoca Tank is a relatively small, high-grade deposit located 5 kilometres to the north of Murrawombie. The deposit is hosted in psammitic to pelitic metasedimentary rocks interlayered with dolerite sills, overlain by a coarse-grained sandstone hanging wall sequence. Mineralisation is found as narrow shear-hosted massive magnetite-pyrite-chalcopyrite-sphalerite ±pyrrhotite occurring as elongated, flattened pipe-like bodies.
The host sequence is dominantly composed of variably foliated medium- to thick-bedded, medium-grained meta-sandstone of the Narrama Formation. The meta-sandstone generally has a bimodal grainsize distribution, comprising ~0.5 to 1 mm quartz and albite grains set in a fine-grained matrix that is often recrystallised, and is quartz-rich. Individual beds have well developed grading. Close-spaced, foliated lamellae of white mica ± chlorite are characteristic of this suite. These have been interpreted as an evolved, spaced, crenulation cleavage or differentiated layering. Interbedded, fine-grained pelitic schist typically has a continuous cleavage defined by white mica and chlorite. Meta-dolerite sills are generally metres to tens of metres in thickness with doleritic textures preserved in the core of the sills and strongly foliated margins. These sills are typically composed of chlorite-albite-actinolite-epidote-titanite-carbonate reflecting the complete recrystallisation of primary mineralogy during metamorphism and hydrothermal alteration. As a consequence, these sills have a low magnetic susceptibility and are not easily distinguished from geophysical data.
The dominent structural fabric in the deposit area is S2, which occurs as a closely spaced, bedding parallel cleavage that is often expressed as a well-developed differentiated layering in meta-sandstone beds. A poorly preserved S1 foliation, where present, has been overprinted by the S2 fabric (Fergusson and Henderson 2015). In pelitic horizons, S2 is expressed as a continuous slaty to fine-grained schistose cleavage, crosscut by a more widely spaced array of D3 shears that are typically developed at a high angle to S2. These D3 shears are characteristically narrow and generally external to the mineralised interval, but become noticeably wider and more closely spaced as mineralisation is approached. Where closely spaced, D3 shear arrays locally resemble S2 proximal to mineralisation. Mineralisation at Avoca Tank is restricted to these D3 shear zones, although foliation partings parallel to S2 has locally facilitated mineralisation parallel to S2 and bedding, often within hinge zones (similar to saddle reefs). Chloritic or carbonate alteration can invade the host rock along foliation parallel zones for a short distances outward from mineralised shears. D3 shears have a very uniform orientation with a consistent normal shear sense. Drag folding of S2 is prominent around the margins of the D3 shears. The latter characteristically only have a weak internal deformation, although brecciation foliation development parallel to S3 is locally evident. D4 folds locally rotate both the S2 foliation and D3 shear zones, and are particularly evident where refolding D3 quartz carbonate veins (Murphy and Cox 2019). D4 folds are open with a weak, spaced axial planar foliation peripheral to the mineralised zone, whilst within that zone, they locally display a higher strain, and may be responsible for tight to isoclinal folding of S3 within wide chloritic D4 shear zones. Chalcopyrite may be remobilised into higher strain D4 shear zones.
The development of S2 in the region is interpreted to have taken place at 440 to 435 Ma (muscovite and whole rock Ar-Ar; Fergusson and Henderson 2015), consistent with the late stage Benambran Orogeny. Hydrothermal titanite from a mineralised D3 shear zone at Avoca Tank gave a robust age of 430 ±6 Ma (U-Pb dating; Fitzherbert and Huang 2019), which is consistent with termination of the Benambran Orogeny, collapse of the Girilambone terrane and the onset of Siluro-Devonian back arc spreading. D4 remains undated but is consistent with deformation related to the ca. 390 to 380 Ma Tabberabberan Orogeny in the region.
Mineralisation hosted by D3 shearing within metasedimentary sequences at Avoca Tank is composed of a consistent early oxide, grading to sulphide-rich paragenesis. External to mineralisation, D3 shear zones have an associated mineralogy dominated by Fe-rich chlorite, white mica with local magnetite and fine-grained titanite/allanite concentrations, with locally abundant fine-grained spessartine garnet that may be associated with the magnetite. D3 shear zones within the mineralised zone, preserve an initial 'oxide phase' assemblage which is rich in magnetite, Fe-rich chlorite and quartz, with locally abundant allanite and titanite. The subsequent, overprinting 'sulphide phase' is initially reflected by the crystallisation and partial replacement of magnetite by pyrite and then by chalcopyrite within the earlier formed shears. Fine blebs of pyrite and chalcopyrite are often found within partially replaced magnetite and pyrite grains. Relict anhedral and recrystallised 'oxide phase' magnetite is found within the ore grade shears, while magnetite in equilibrium with the 'sulphide phase' is smaller and euhedral. Chalcopyrite ±pyrrhotite and low-Fe sphalerite may be locally abundant and interstitial to, and partially replacing magnetite and pyrite. The sulphide phase gangue mineralogy is dominated by Fe-chlorite, carbonate (including siderite), quartz and stilpnomelane. Siderite predominantly occurs as a partial replacement magnetite in association with the sulphide phase. Albite, K feldspar and white mica are locally abundant within the ore zone. Alteration peripheral to mineralised D3 shears falls off over a short distance of generally ≤10 m, and often comprises centimetre to decimetre scale Fe-rich chlorite, fine-grained magnetite and carbonate within S2 cleavage in the wall rocks. Narrow magnetite-bearing but sulphide barren D3 shears may also be abundant over a width of ~10 m within the wall rock peripheral to the mineralised D3 shears. The dolerite sills contain little mineralisation, although intense D3 shearing around their margins has associated strong epidote and carbonate alteration within both the mafic bodies themselves and the adjacent metasedimentary rocks.
According to Simpson et al., 2024, the current resource at Avoca Tank is - 0.7 Mt at 2.5% Cu, 0.8 g/t Au.
Budgery is part of the Budgery geological complex, close to Hermidale township, ~20 km south of the Tritton processing plant.
Mineral Resources and Ore Reserves
The resource at Tritton in 2003 totalled 14 Mt @t 2.7% Cu, 0.3g/t Au, 12g/t Ag (at a 1% Cu cutoff).
Remaining Measured + Indicated + Inferred Mineral Resources at the end of the 2018 financial year were (Aeris Resources Annual Report, 2018):
Tritton underground - 10.3 Mt @ 1.4% Cu, 0.11 g/t Au, 4.5 g/t Ag (includes 4 Mt of Inferred resources);
Tritton pillars (recoverable) - 0.42 Mt @ 2.6% Cu, 0.22 g/t Au, 9.6 g/t Ag (all indicated);
Murrawombie - 5.4 Mt @ 1.5% Cu, 0.29 g/t Au, 5.9 g/t Ag (comprises 4.6 Mt of Indicated and 0.8 Mt Inferred Resources);
Avoca Tank - 0.9 Mt @ 2.6% Cu, 0.77 g/t Au, 13.8 g/t Ag (comprises 0.77 Mt of Indicated and 0.1 Mt Inferred Resources);
Budgerygar - 1.6 Mt @ 1.5% Cu, 0.11 g/t Au (all Inferred Resources);
Budgery - 2.0 Mt @ 1.1% Cu, 0.13 g/t Au (comprises 1.7 Mt of Indicated and 0.3 Mt Inferred Resources);
Stockpiles - 0.03 Mt @ 2.1% Cu (Measured Resources);
TOTAL - 20.7 Mt @ 1.5% Cu, 0.19 g/t Au.
Ore Reserves for the same group of deposits at the end of the 2018 financial year were (Aeris Resources Annual Report, 2018):
TOTAL - 8.4 Mt @ 1.5% Cu, comprising 3.1 Mt @ 1.7% Cu Proved and 7.4 Mt @ 1.4% Cu Probable Ore Reserves.
The most recent source geological information used to prepare this decription was dated: 2024.
Record last updated: 30/1/2024
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Girilambone Tritton
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Selected References:
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Ackerman, B.R. and Chivas, A.R., 2004 - Tritton copper deposit, Girilambone district, NSW: in CRC LEME online, http://crcleme.org.au/RegExpOre/Tritton.pdf, 3p.
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Downes, P.M., Raymond, C. and Fitzherbert, J.A., 2017 - Girilambone Copper District: in Phillips, G.N., (Ed.), 2017 Australian Ore Deposits, The Australasian Institute of Mining and Metallurgy, Mono 32, pp. 473-478.
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Fogarty J M, 1998 - Girilambone district copper deposits: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp 593-600
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Simpson, B., Fitzherbert, J., Moltzen, J., Baillie, I., Cox, B. and Huang, H., 2024 - Magnetite trace element characteristics and their use as a proximity indicator to the Avoca Tank Cu‑Au prospect, Girilambone copper province, New South Wales, Australia: in Mineralium Deposita v.59, pp. 169-187. doi.org/10.1007/s00126-023-01204-9.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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