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Granny Smith, Granny, Goanna, Windich, Wallaby, Childe Harold, Phoenix, Keringal, Jubilee

Western Australia, WA, Australia

Main commodities: Au
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The Granny Smith operation is located ~25 km to the south of Laverton and 240 km NNE of Kalgoorlie in the Eastern Goldfields of WA and 950 km NE of Perth. The operation has mined a series of deposits within 35 km of the central Granny Smith treatment plant. These include, from north to south, the original Goanna, Granny Smith and Windich deposits close to the Granny Smith treatment plant, the small satellite Childe Harold and Phoenix deposits 4 km to the west, the Keringal and Jubilee deposits 14 km SE and 34 km SSE of Granny Smith respectively, the Granny Smith share of the Sunrise Dam deposit, 25 km to the south, and Wallaby 12 km to the WSW.

The Goanna and adjacent Granny Smith deposits were discovered in 1979 by CSR Limited. Placer Pacific acquired a 60% interest in the project in 1988, with the remaining 40% held by Delta Gold NL. Mining commenced in the Granny Smith pit in 1989 and continued concurrent with the development of the Goanna and adjacent Windich pits. Drilling delineated resources at the small Childe Harold and Phoenix deposits 4 km west in 1992 and these were mined in 1993-94 for 1.6 t of gold. In 1992, the Keringal and then the large Sunrise Dam-Cleo deposits 25 km to the south were discovered. The latter straddled the boundary with titles to the remainder of the deposit held by Acacia Resources and later Anglogold Ashanti, and the deposit was mined as a single operation from 1997 with the appropriate share of the ore treated at Granny Smith. The Jubilee deposit was discovered in 1996 and brought into production in March 2000 to produce 5.13 t of gold before being exhausted in February 2002. The Wallaby deposit was discovered in 1998. Barrick acquired Placer Dome in 2006 and inherited its share in the project. The Wallaby open pit was mined from October 2001 until December 2006 and produced 13.6 Mt @ 3.44 g/t Au for 47 t of gold. Underground mining at Wallaby commenced in December 2005 and, to 2018, 15.6 Mt @ 5.71 g/t Au for 89 t of gold has been produced. Gold Fields acquired 100% of the Granny Smith gold mine in late 2013. During all of this period all of the ore from this series of mines has been treated at the central Granny Smith mill.

The main Granny Smith, Goanna and Windich deposits lies within the 10 to 15 km wide Laverton Tectonic Zone which is characterised by a series of anastomosing, semi parallel, major north-south shears and associated faults. The principal structures within the zone in the Granny Smith area are, from west to east, the Childe Harold, Far East, Barnicoat West and Barnicoat East faults. This tectonic zone straddles the broad Ockerbury Fault Zone, the bounding structure that separates the Kurnalpi and Burtville terranes to the west and east respectively, overlapping sections of both. The Burtville Terrane is characterised by fault bounded basalt-ultramafic schist successions and quartzose sedimentary rocks, whilst the Kurnalpi Terrane is dominantly composed of volcaniclastic rocks. The Granny Smith deposits are within the Kurnalpi Terrane section of the Laverton Tectonic Zone.

For detail of the regional context of the Kurnalpi Terrane, see the Yilgarn Craton record.

On a regional scale, the Granny Smith region is dominated by the Mt Margaret granite cored dome (or anticline) >10 km to the NW and the similar Kirgella Dome >20 km the SE. These domes are flanked by what Tully et al. (2017) regard as hornblende hornfels, and what Blewett et al. (2010) suggest are deeper more metamorphosed rocks inferring the domes are D3 metamorphic core complexes. These domes are also flanked to the east and west by NWN striking shear zones, with the central zone between the two domes being dominated by north-south to NNE-striking sigmoidal shear zones. These distinctly different shear zone directions were developed early in the tectonic evolution and produced a favourable architecture for late-stage orogenic gold mineralisation at Wallaby and Granny Smith (Tully et al., 2017).

The host succession in the Granny Smith area is strongly deformed, intruded byt granites and comprises i). a lower suite of tholeiitic mafic and ultramafic volcanic and interflow sedimentary rocks, with sedimentary iron formations and sub-volcanic intrusions; ii). calc-alkaline volcanic rocks, subvolcanic intrusions and associated epiclastic sedimentary sequences, including sedimentary iron formations; These are unconformably overlain by iii). a suite of conglomerates, with both granitic and mafic clasts.

The 3 main Granny Smith deposits are located on the eastern margin of a small, ~1.5 km diameter granitic intrusion, the Granny Smith Granodiorite, between the Childe Harold and Far East faults. Gold is associated with structurally controlled dilatant sites on a major NNW trending, east dipping, brittle-ductile shear zone which is proximal to the contact with the granodiorite and surrounding sedimentary rocks. The weathered profile over this primary mineralisation extends to a depth of 50 to 80 m with gold being significantly depleted in the upper 20 m.

At the Granny-Goanna-Windich string of deposits, mineralisation was continuous over a 3500 m interval, being less intensely developed between the three ore zones. To the north at Goanna, the shear and mineralisation were entirely within oxidised and weathered meta-sediments as a 500 x 50 x 8 m body dipping at 50° to the east. These sedimentary rocks included BIF units which were the focus of mineralisation where they were cut obliquely by sub-parallel shears. Granny is 1500 m further to the south where the shear marks the contact between the overlying sediments and the composite diorite-granodiorite intrusive. The ore zone here is 600 x 250 x 30 m, dipping east at 25°. The third zone, Windich, was another 800 m to the south, on the south-eastern corner of the intrusive-sediment contact. It was blind and lay within a partially oxidised granodiorite, with dimensions of 400 x 150 x 30 m dipping north-east at 10°.

Gold is present as discrete interstitial grains, blebs and clusters locked in late quartz and minor ankerite filled micro-fractures. Visible gold is rare. There is a close relationship between gold and the quartz-diorite body, while the gold was intimately associated with carbonate.

The Childe Harold and Phoenix deposits lie within the north-south Childe Harold fault, which separates a suite of argillaceous metasediments and felsic volcanic rocks to the east from an assemblage of basalt, dolerite, gabbro, ultramafic rocks and minor thin banded BIF to the west. The gold mineralisation in these two satellite deposits occurs within an east dipping brecciated chert unit within sheared metasedimentary rocks, and is found within en echelon quartz veins that are up to several metres thick, enveloped by a much wider selvedge of quartz-white mica-pyrite carrying economic gold mineralisation (Tully et al., 2017).

The Jubilee deposit is located to the 34 km SSE of Granny Smith, in the north-south Barnicoat Fault. It occurs within strongly magnetised greenschist facies basalt flows intruded by a NNW trending, steeply west dipping granite porphyry. Two alteration phases are recognised. The first is related to the granite intrusion which forms a core to and envelope of chlorite-magnetite, whilst the second phase, comprising carbonate-white mica-pyrite ± silica is associated with the gold mineralisation. Mineralisation occurs as stacked shear zones along 30°E dipping basalt flow contacts. The highest grades are within west dipping tension veins formed by fault splays that typically carry coarse gold in basalt or granite porphyry (Tully et al., 2017).

The Keringal deposit also lies within the Barnicoat Fault, 14 km SE of Granny Smith, hosted by a sequence of greenschist facies metamorphosed pillowed tholeiitic basalt, ultramafic rocks and minor aplitic porphyry dykes. Gold occurs along the deformed contacts between ultramafic rocks and basalts, and is particularly well developed at the apex of a gently north plunging wedge of mafic rock, and along shears that define the eastern and western margins of that wedge. Gold is predominantly found in association with quartz veins and white mica-albite-carbonate-pyrite ±pyrrhotite alteration of basalt and quartz-carbonate-fuchsite-pyrite ±white mica in ultramafic rocks. There is a zonation from proximal to distal alteration, represented bya cahnge from siderite and a and ankerite to calcite and a decrease in pyrite (Tully et al., 2017).

The Wallaby deposit and its northern continuation, Just in Case, are some 11 km to the west of Granny Smith. See the separate Wallaby record.

The initial resource within the Granny-Goanna-Windich bodies, when the mine commenced operation, was ~27 Mt @ 1.6 g/t Au.

The most recent source geological information used to prepare this summary was dated: 2017.     Record last updated: 5/9/2019
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.


Granny Smith

Wallaby

  References & Additional Information
   Selected References:
Hall G C, Hoyland P W  1990 - The Granny Smith Gold Deposit: in Hughes FE (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   v1 pp 519-524
Mueller, A.G., Hall, G.C., Nemchin, A.A., Stein, H.J., Creaser, R.A. and Mason, D.R.,  2008 - Archean high-Mg monzodiorite-syenite, epidote skarn, and biotite-sericite gold lodes in the Granny Smith-Wallaby district, Australia: U-Pb and Re-Os chronometry of two intrusion-related hydrothermal systems: in    Mineralium Deposita   v.43, pp, 337-362,
Ojala V J, Ridley J R, Groves D I, Hall G C  1993 - The Granny Smith Gold Deposit - the Role of Heterogeneous Stress Distribution at an Irregular Granitoid Contact in a Greenschist Facies Terrane: in    Mineralium Deposita   v28 pp 409-419
Tully, R.B., Platt, H.K., Chirnside, A.R. and Murray, A.L.,  2017 - Gold deposits of the Granny Smith - Wallaby District: in Phillips, G.N., (Ed.), 2017 Australian Ore Deposits, The AusIMM, Melbourne,   Mono 32, pp. 255-259.


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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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