Big Bell

Western Australia, WA, Australia

Main commodities: Au
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The Big Bell gold deposit is hosted by an Archaean greenstone belt sequence within the Murchison Province of the Yilgarn Craton in Western Australia, some 30 km WNW of the township of Cue and is approximately 250 km to the west of the Norseman-Wiluna Greenstone belt.

At Big Bell the greenstone belt is narrow, steeply dipping, strongly attenuated and locally overturned, forming the western limb of a north plunging regional antiform. The greenstones are subdivided into: i). A lower mafic sequence of flow basalts, intercalated ultramafics, graphitic sediments and banded iron formation, with thin cross-cutting porphyry dykes. ii). A felsic volcanic sequence that gradationally overlies the lower mafics, and includes andesite, dacite, rhyodacite and rhyolite with minor sediments and gabbroic to doleritic intrusions. iii). An upper mafic sequence of basaltic flows, with lesser ultramafics and sediments. The greenstones are bounded by granites.

At Big Bell the volcano-sedimentary package is 1500 m wide and structurally over turned, striking at 30 degrees and dipping at 75 degrees to the east. To the east, the mine sequence is structurally overlain by 600 m of amphibolites, while to the west there is chlorite schists (with garnet, biotite, cummingtonite and amphibole) and amphibolite.

The mineralisation is associated with a distinctive lode horizon which corresponds to the highly deformed felsic sequence. The Big Bell lode is mainly a highly altered and metamorphosed quartz-muscovite and potash feldspar rich schist. The lode itself is up to 50 m thick, has a length of 450 m and has been tested to 1400 m down plunge. Mineralisation is associated with sulphides, particularly pyrite, which constitutes up to 10% of the lode zone. A wide variety of other sulphides are also present but in lesser volumes. The lode zone is enveloped by biotite and cordierite rich schist, which to the south hosts lower grade mineralisation.

To the north the mine sequence is less altered and is a 200 m thick quartz-feldspar porphyry with amphibole, biotite and numerous garnet-biotite bands. Visible gold is rare. It is found both in silicates (mostly quartz and K-feldspar) and in sulphides (mainly as discrete 5-10 micron blebs within pyrite).

The historical Big Bell mine produced 22.7 t of contained gold @ an average grade of 4.04 g/t Au between 1904 and 1955. Following closure the mine remained dormant until exploration recommenced in the 1980s.

Measured and indicated resources in 1990 were 23.6 Mt @ 3.4 g/t Au.
In mid 1999 the measured and indicated resources were 8.47 Mt @ 3.6 g/t Au.
Approximately 2 to 2.8 Mt of ore was being treated per annum from 1992. The mine, which was operated by Harmony Gold was closed in 2002-03.

Big Bell was purchased by WestGold Resources Limited in 2011 and became part of the MetalsX/WestGold Central Murchison Gold Project, which has subsequently been divided into the Meekatharra Gold Operations and Cue Gold Operations. Big Bell falls into the latter with the Cuddingwarra, Day Dawn and Tuckabianna deposits. From July 2018, the ore from all four mines was being treated at a central processing plant at Tuckabianna, near the town of Cue.

Remaining Ore Reserves and Mineral Resources at Big Bell only as at 31 December 2018 were (Western Resources Limited Annual Report, 2018)
  Indicated + Inferred Resource - 23.977 Mt @ 2.75 g/t Au for 66 t of contained gold;
  Probable Reserve - 11.829 Mt @ 2.89 g/t Au for 34 t of contained gold.

The most recent source geological information used to prepare this summary was dated: 2001.    
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
   Selected References:
Anonymous  1998 - Normandy Mining Limited: in   Extracts from the Normandy Mining Limited 1997 Annual Report    pp 12-14, 17, 26-28.
Handley G A, Cary R  1990 - Big Bell Gold deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 211-216
Mueller A G, Campbell I H, Schiotte L, Sevigny J H, Layer P W  1996 - Constraints on the age of granitoid emplacement, metamorphism, Gold mineralization, and subsequent cooling of the Archean Greenstone terrane at Big Bell, Western Australia: in    Econ. Geol.   v91 pp 896-915
Mueller, A.G. and McNaughton, N.J.,  2018 - Mineral equilibria and zircon, garnet and titanite U-Pb ages constraining the PTt path of granite-related hydrothermal systems at the Big Bell gold deposit, Western Australia: in    Mineralium Deposita   v.53, pp. 105-126.
Wilkins C,  1993 - A post-deformational, post-peak metamorphic timing for mineralization at the Archaean Big Bell gold deposit, Western Australia: in    Ore Geology Reviews   v7 pp 439-483

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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