Beaconsfield, Tasmania Reef

Tasmania, Tas, Australia

Main commodities: Au
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The Tasmania Reef gold deposit is located at Beaconsfield, 40 km north-west of Launceston in northern Tasmania, Australia.

The Tasmania Reef is hosted by an upwardly fining lower Palaeozoic (Cambrian to Ordovician) sequence of conglomerate, grit, sandstone and calcareous shale (overlain by Ordovician limestones) that has been thrust over a Proterozoic quartzwacke-siltstone-mudstone basement block to the west.   Close to the basement block the sequence has been intruded by a large, elongate NNW trending body of serpentinite, pyroxenite and gabbro.   All of these are unconformably overlain by little deformed Permian to Mesozoic sediments.

The Tasmania Reef is a gold bearing ankerite-quartz vein developed within the Cambro-Ordovician sequence which comprises:
i). a lower 100 m of siliceous sandstone, passsing down dip into a limestone-dolomite,
ii). 60 m of pebble conglomerate in a matrix of quartz, sericite and ankerite,
iii). 125 m of interbedded sandstone, grit and conglomerate, and
iv). an upper 240 m thick interbedded sequence of calcareous sandstone, silstone and shale with occassional limestone, becoming more calcareous as it approaches the overlying Gordon Limestone.   The sandstone has interstitial sericite and carbonaceous matter.

The reef strikes at 55° and dips at 60° SE, while the host strikes 325° and dips at 50 to 60° NE.   The gold orebody is restricted to the upper two units described above, known as the Transition Beds, producing a 400 m long ore panel that plunges steeply east with a maximum thickness of 5.4 m, but averages 1.96 m.   The reef thins and splits and does not persist into the overlying Gordon Limestone.   The quartz-carbonate reef contains variable sulphides (predominantly pyrite with subordinate arsenopyrite), with more carbonates and fine sulphides in the centre and is more quartz rich on the margins.   Gold is closely related to the pyrite.   The average grade from surface to depth of 120 m was 38 g/t Au, from 120 to 250 m it averaged 25 g/t Au, then dropping further by 410 m before improving to 20 g/t Au between 410 and the deepest level at 454 m.

Production and ore reserve figures at 1989 were:
  Historic production, 1877 to 1914 - 1.085 Mt @ 24.5 g/t for 26.581 t Au
  Resource to 440 m, 1986 - 0.670 Mt @ 24.0 g/t for 16 t Au.

In 2000 the total resource (including 1.2 Mt of reserves) was - 1.7 Mt @ 17.1 g/t for 29 t Au.

At the end of 2005, the ore reserve was:
    0.506 Mt @ 14.3 g/t Au at a 6 g/t Au lower cut-off, and an upper cut of 165 g/t Au.
    This reserve is included within the total resource of 0.889 Mt @ 16.1 g/t Au.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2003.    
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:
Hicks J D, Sheppy N R  1990 - Tasmania Gold deposit, Beaconsfield: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v2 pp 1225-1228
Hills P B  1998 - Tasmania gold deposit, Beaconsfield: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne   Mono 22 pp 467-472

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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