Wirrda Well

South Australia, SA, Australia

Main commodities: Cu Ag Au
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The Wirrda Well iron oxide copper-gold mineralised system, which is located within the Olympic IOCG Province on the eastern rim of the preserved Gawler craton in northern South Australia, is ~25 km SSE of Olympic Dam, ~17 km ESE of Acropolis and 530 km NNW of Adelaide (#Location: 30° 38' 55"S, 136° 57' 02"E).

Wirrda Well, Acropolis, Olympic Dam, Carrapateena, Prominent Hill and Hillside, and all of the significant known IOCG mineralised systems of the Gawler craton, are hosted within Palaeo- to Mesoproterozoic rocks, and are distributed along the eastern edge of the currently preserved craton to define the Olympic IOCG Province.

See the Carrapateena record for a summary of the geological setting of the Olympic IOCG Province.

Hayward and Skirrow (2010) note that the Olympic Dam, Wirrda Well and Acropolis mineralised systems are found within an ENE-trending fault-bounded ~40 x 100 km block that partially cuts second order NNW-trending faults, and is characterised by a broad magnetic anomalism that is interpreted to represent widespread magnetite alteration. This block is bounded by ENE- to NE-trending faults, 10 to 15 km to the NW of Olympic Dam and a similar distance to the SE of Wirrda Well, and by major regional NNW-trending faults systems, one of which is the Elizabeth Creek Fault Zone just to the SW of Acropolis. Within this block, there is a cluster of ENE- to NE-elongated Hiltaba Suite plutons, including the Roxby Downs Granite (which hosts Olympic Dam) and the Burgoyne Batholith (which is host to the eastern extremities of both Acropolis and Wirrda Well). The lopolithic Burgoyne Batholith has a base at ~5 km depth, above interpreted Hutchison Group metasediments (Lyons and Goleby, 2005).

The Wirrda Well mineralised system is reflected by a near-circular ~4 km diameter magnetic anomaly with a ~1800 nT peak, and a near-coincident, but more diffuse gravity response of ~6 mGal above regional background (Vella and Cawood, 2006). Modelling suggests that the source is a vertical pipe, several hundred metres in diameter, with three apophyses radiating to the NW, SE and SW (Vella, 1997). These anomalies are overlain by a ~330 m cover sequence of Mesoproterozoic (post 1424 Ma) Pandurra Formation, Neoproterozoic and younger sedimentary rocks.

The immediate geological setting of the Wirrda Well mineralised system comprises Hiltaba Suite granites of the Burgoyne Batholith to the NE, bounded by a NE-dipping, NW-trending reverse fault separating the intrusives from 1591 10 Ma (U-Pb zircon determinations) Gawler Range Volcanics (GRV) to the south, which in turn overlie ~1850 Ma Donington Suite granitoids to the NW across a NE-trending contact (Hayward and Skirrow, 2010).

The Wirrda Well mineralisation comprises two main zones of ENE-trending hydrothermal breccias and iron oxide replacement systems centred on steeply NNW-dipping, ENE-trending faults located near intersection zones with second-order NW-trending faults. The western and eastern hematite altered breccias are ~3.5 x 0.8 and 2 x 0.5 km in size respectively. The eastern third of the latter is hosted within the Burgoyne Batholith, with the remainder within Donington Suite granitoids and partially within GRV to the south. A large 2 x 2 km mass of magnetite alteration (the probable main source of the magnetic response) occurs in an uplifted block along a northwest-trending fault immediately to the north of the main hematite mineralised zones (Hayward and Skirrow, 2010).

Fe-Cu (U-Au) mineralisation occurs as magnetite-hematite vein networks and alteration zones in sericitised, brecciated and hematite altered GRV, and in the underlying granites of the Hiltaba Suite Burgoyne Batholith and Donington Suite. Within the granites, massive granite breccia is developed with pervasive and vein magnetite and hematite, and various combinations and proportions of siderite, quartz, K feldspar, sericite, chlorite, barite, fluorite, apatite, phlogopite, sulphides (pyrite-chalcopyrite) and uraninite, with bornite more spatially confined to local zones.

Brecciation and hematite development are more widespread than at Acropolis, more closely resembling that at Olympic Dam. However, unlike at Olympic Dam, many of the breccias contain clasts derived from host deformed (Donington Suite) granite and Hutchison Group metasediments.

The best reported intersection from the mineralised hematite breccias is 248 m @ 0.86% Cu, 4.6 g/t Ag from 419 m (WMC Limited unpublished memoranda, 1985).

The most recent source geological information used to prepare this summary was dated: 2010.    
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.

  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Hayward N and Skirrow R,  2010 - Geodynamic Setting and Controls on Iron Oxide Cu-Au (ħU) Ore in the Gawler Craton, South Australia: in Porter T M, (Ed),  2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.3 pp. 119-146

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