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Paddington |
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Western Australia, WA, Australia |
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Au
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Super Porphyry Cu and Au
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The Paddington gold deposit is located in the Broad Arrow gold field, 5 km south of Broad Arrow and some 34 km north of Kalgoorlie in Western Australia. It lies within the Kalgoorlie Terrane of the Eastern Goldfields Superterrane, in the Yilgarn Craton (#Location: 30° 29' 20"S, 121° 20' 39"E).
Between 1897 to 1901, the area now within the Paddington pits and surrounds produced 1.7 t of gold from 0.12358 Mt of ore @ 14 g/t Au until easily worked high grade ore at shallow depths was exhausted. Despite a number of attempts no significant mining took place until modern exploration commenced in the 1970s. By 1982, sufficient resources had been outlined to commence mining two lode systems, Paddington I and Paddington II in1985, extracting ore from two open pits until 2002. A hiatus followed when the titles and plant changed ownership. Since ore has been sourced from a series of deposits within a 40 km radius to feed the Paddington Mill. These have included Mount Pleasant, including the Homestead underground deposit 18 km SW of the Paddington mill which was exploited from 2009. Ore is also sourced from the open cut Enterprise deposit at Ora Banda, 38 km to the NW of the treatment plant supplemented by the small Wattlebird open cut mine. Ore has also been mined from the Bullant underground mine, 40 km by road west of the Paddington Mill. The Janet Ivy open cut mine is located 33 km south of the Paddington Mill and 10 km west of Kalgoorlie. Resources are available at the Tuart cluster of deposits near the Homestead mine, and at Federal in the Woodcutters Goldfield 12 km NE of the Paddington mill.
For detail of the regional setting of the Kalgoorlie Terrane, see the Yilgarn Craton record.
The Paddington gold deposits occur on the eastern limb of a narrow NNW trending structure, the Bardoc-Broad Arrow syncline within the Bardoc Tectonic Zone. In this zone, the sequence comprises highly deformed fault slice lenses of intercalated Archaean mafic and ultramafic volcanics and metasediments, and is a very similar succession to that on the Golden Mile at at Kalgoorlie.
The gold at Paddington is mainly within a granophyric quartz dolerite, the Paddington Dolerite, intruding and crosscutting a basic volcanic unit, the high Mg tholeiitic basalt of the Paddington Volcanics. It is flanked to the east by a thick sequence of altered mafics, ultramafics and sediments of the Mt Colac ultramafics which form the Footwall to the lodes. To the west it is bounded by the Black Flag Beds consisting of basal graphitic shales grading upwards into acidic tuffs and metapelites. The district strike trends north-south and dips sub-vertically.
The main mineralisation extends over a strike length of 1.6 km, averaging 30 to 40 m in width. The deposit comprises two main lenses, Paddington I, which persists to at least 250 m below surface, and Paddington II, which is separated by an ENE cross shear and has been tested to a depth of 90 m.
Within the lodes, mineralisation is present as a series of dilatant sheeted quartz veins which are generally 1 to 5 cm thick, but may be up to 30 cm. In the more intensely mineralised areas these veins are repeated every 10 to 20 cm. They comprise quartz, lesser dolomite/ankerite and albite with minor sulphides, and where rich in gold have a bleached selvage (quartz-chlorite- sericite-carbonate) and contain abundant pyrite and arsenpyrite. As the degree of veining and alteration increases, the selvages merge to form pervasive alteration with disseminated sulphide. In these zones, sulphides are up to 10 vol.% of the ore, consisting of arsenopyite, pyrite and marcasite. Specks of gold up to 1 mm across occur as dendritic films and grains in quartz veins, and blebs within arsenopyrite and carbonate pseudomorphs. Overall, gold is fine grained and shows a preference for quartz and arsenopyrite, particularly along arsenopyrite microfractures, as blebs on grain boundaries and as exsolutions along growth zones in the arsenopyrite.
The deposit also has a strong vertical zonation related to weathering and leaching in the oxidised zones to around 30 m, although nuggets are found in the upper 5 to 10 m of the 'residual zone' which is not as intensely leached as the succeeding 20 of more metres. From 30 to 60 m, in the moderately weathered zone, a distinctive supergene enriched zone has been developed, with gold upgraded by a factor of 1.5 to 2. This enriched interval decreases in grade with depth to the base of oxidation at 70 m and the top of the primary sulphide zone.
Within the oxide zone, supergene gold associated with goethite-limonite. Trace chalcopyrite, sphalerite, galena, native silver are also found with arsenical and iron sulphides. Pyrrhotite is the dominant sulphide below 180 m.
The total geological in situ resource at the commencement of mining in 1985 was - 8.4 Mt @ 3.2 g/t Au amounting to 27 t Au. This was in the two lodes, Paddington I with 5.6 Mt @ 3.3 g/t Au and Paddington II with 2.8 Mt @ 3.0 g/t Au.
Resources available at each of the external deposits supplying or planned to supply the Paddington Mill are as follows (Norton Goldfields website, 2019; and Quarterly Report, 2015 for Homestead):
Bullant - Measured + Indicated + Inferred Mineral Resource of 2.68 Mt @ 5.35 g/t Au for 14.4 t of contained gold;
Tuart has Indicated + Inferred Mineral Resources of 1.71 Mt @ 1.65 g/t Au Open Cut and 2.55 Mt @ 5.92 g/t Au Underground;
Federal - Indicated + Inferred Mineral Resource of 3.81 Mt @ 1.50 g/t Au Open Cut and 0.42 Mt @ 6.187 g/t Au Underground;
Janet Ivy - Indicated + Inferred Mineral Resource of 19.5 Mt @ 0.89 g/t Au, including 0.3 Mt @ 1.00 g/t Au (0.6 g/t cut-off).
Homestead - in 2015 remaining resources were 0.238 Mt @ 18.79 g/t Au, with resources mined continuing to be replaced by discovery.
Enterprise - Indicated + Inferred Resource 2013 - 22.5 Mt @ 1.69 g/t Au (Mining Technology website, 2019);
Current JORC compliant Ore Reserves and Mineral Resources available to the Paddington Mill in these and other deposits are as follows as at 30 June, 2017 (Norton Goldfields website, 2019):
Proven + Probable Ore Reserves - 17.3 Mt @ 1.6 g/t Au for 28 t of contained gold (included in Resources);
Measured + Indicated + Inferred Mineral Resources - 267 Mt @ 1.28 g/t Au for 340 t of contained gold;
of this resource, 118 Mt @ 1.35 g/t Au for 159 t of gold is Inferred.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2017.
Record last updated: 4/9/2019
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.
Paddington
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Selected References:
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Hancock M C, Robertson I G, Booth G W 1990 - Paddington Gold deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v1 pp 395-400
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Morey, A.A., Weinberg, R.F., Bierlein, F.P. and Davidson, G.J., 2007 - Gold deposits of the Bardoc Tectonic Zone: a distinct style of orogenic gold in the Archaean Eastern Goldfields Province, Yilgarn Craton, Western Australia : in Australian J. of Earth Sciences v.54, pp. 783-800.
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Weinberg R F, Van der Borgh P, Bateman R J and Groves D I, 2005 - Kinematic History of the Boulder-Lefroy Shear Zone System and Controls on Associated Gold Mineralization, Yilgarn Craton, Western Australia : in Econ. Geol. v100 pp 1407-1426
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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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