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Benambra, Wilga, Currawong, Stockman
Victoria, Vic, Australia
Main commodities: Zn Cu Pb Ag Au

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The Currawong and Wilga Zn-Cu-Pb-Ag(-Au) deposits are located 16 km south-east of the town of Benambra in north-eastern Victoria, Australia.   The two deposits are 3.5 km apart along strike.

The Benambra deposits were discovered by a WMC Resources/BP Minerals joint venture in 1978 and 1979. The Wilga deposit was partially mined from October 1992 to July 1996 by Denehurst Ltd., before all mining operations ceased. In June 2007, it was ressurrected as the Stockman Project when it was acquired by Jabiru Metals Ltd following a competitive tender conducted by the Victorian Government. Jabiru Metals was later acquired by Independence Group (IGO) in June 2011, and IGO discovered the Eureka and Big Foot lodes in close proximity to the Currawong deposit in 2012 and 2013 respectively. Round Oak Minerals Pty Ltd, then CopperChem Pty Ltd, acquired the project from IGO in December 2017. Round Oak Minerals plans to operate two underground mines – the historic Wilga Mine which previously operated in the 1990s, and a new mine to be developed at Currawong. Annual production of ~1 Mtpa is planned from the operation (Round Oak Minerals website, viewed Feb, 2022).

The Wilga and Currawong deposit occurs within the middle to upper Silurian Cowambat Rift, the most southerly of a series of Silurian depo-centres in the Palaeozoic Lachlan Fold Belt of south-eastern Australia.   The Cowambat Rift has undergone strong deformation and only three fault bounded remnants remain un-eroded, with both deposits in the same remnant, the Limsetone Creek Graben.

The deposits are hosted by the volcanic rich Enano Group which locally overlies Ordovician to Silurian turbiditic sediments with lesser basaltic to andesitic volcanic components.   Most contacts between the following units which make up the Enano Group are faulted.

• The middle to upper Silurian Thorkidaan Volcanics - 2 to 3 km in thickness of massive porphyritic rhyolites (interpreted to be either welded and non-welded ignimbrites or lavas and intrusives) with lesser stratified volcaniclastics and pumiceous breccias.
• Cowombat Siltstone - up to 500 m thick of grey, black & green siltstone with lesser limestone, conglomerate and sandstone.
• Gibson's Folly Formation - more than 500 m of lenticular dacitic, andesitic and basaltic units enclosed within monotonous fine grained turbidites, with local massive rhyolites.   The Currawong and Wilga deposits are found in the southern part of this unit, while dioritic intrusives and serpentinite lenses cut its northern extension.

The Enano Group is overlain by the Lower Devonian welded ignimbrites of the Snowy River Volcanics and the limestones of the Buchans Group and are intruded by upper Silurian to upper Devonian granites.

The Wilga and Currawong deposits are both located near the footwall of the NE-SW trending Indi Fault. Wilga is a single massive sulphide lens in the Gibson's Folly Formation, just above the faulted contact with the Thorkidaan Volcanics. Currawong is also located towards the base of the Gibson's Folly Formation, ~3 km to the NE. It is more structurally complex, comprising five lenses separated by the Currawong Fault. The lenses are hosted within a distinct horizon of strongly altered volcanic and sedimentary rocks that comprise subaqueous rhyodacitic to andesitic breccias, coherent volcanic rocks, and equivalent epiclastics, which all interfinger with the enclosing turbidites. The mineralised lenses at both deposits are stratabound, concordant and composed of massive sulphides. They are dissected by sub-vertical late faults and have stringer zones in the footwall of the massive sulphides. The dominant sulphides include pyrite, sphalerite, chalcopyritine, galena, minor arsenopyrite and pyrrhotite.

Mineralisation has been divided into six types:  i). Pb-Zn,  ii). pyrite-Zn,  iii). massive pyrite,  iv). pyrite-magnetite,  v). footwall stringer zones and  vi). overprinting veins and breccias resulting from structural remobilisation.

Pre-mining resources were as follows:
    Currawong - 9.5 Mt @ 4.33% Zn, 1.65% Cu, 0.86% Pb, 38 g/t Ag, 1.3 g/t Au.
    Wilga - 3.97 Mt @ 6.2% Zn, 3.0% Cu, 23 g/t Ag.

Remaining resources as at June 2012 (Independence Group NL, 2013) of:
    indicated resource - 9.548 Mt @ 4.2% Zn, 2.0% Cu, 0.8% Pb, 42 g/t Ag, 1.2 g/t Au.
    inferred resource - 0.781 Mt @ 2.2% Zn, 1.4% Cu, 0.3% Pb, 23 g/t Ag, 0.5 g/t Au.
    indicated + inferred resource - 10.329 Mt @ 4.0% Zn, 2.0% Cu, 0.8% Pb, 40 g/t Ag, 1.1 g/t Au.
    indicated resource - 2.987 Mt @ 4.8% Zn, 2.0% Cu, 0.5% Pb, 31 g/t Ag, 0.5 g/t Au.
    inferred resource - 0.670 Mt @ 5.5% Zn, 3.7% Cu, 0.4% Pb, 34 g/t Ag, 0.4 g/t Au.
    indicated + inferred resource - 3.657 Mt @ 4.9% Zn, 2.3% Cu, 0.5% Pb, 32 g/t Ag, 0.5 g/t Au.
  TOTAL indicated + inferred resource - 13.986 Mt @ 4.3% Zn, 2.1% Cu, 0.7% Pb, 38 g/t Ag, 1.0 g/t Au.

For detail see the reference(s) listed below.

The most recent source geological information used to prepare this decription was dated: 2012.     Record last updated: 2/10/2013
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:
Allen R L  1992 - Reconstruction of the tectonic, volcanic, and sedimentary setting of strongly deformed Zn-Cu massive sulfide deposits at Benambra, Victoria: in    Econ. Geol.   v87 pp 825-854
Allen R L, Barr D J  1990 - Benambra Copper-Zinc deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v2 pp 1311-1318
Bishop J R, Lewis R J G  1992 - Geophysical signatures of Australian volcanic-hosted massive sulfide deposits: in    Econ. Geol.   v87 pp 913-930
Bodon S B, Valenta R K  1995 - Primary and tectonic features of the Currawong Zn-Cu-Pb(-Au) massive Sulfide deposit, Benambra, Victoria: implications for ore genesis: in    Econ. Geol.   v90 pp 1694-1721
Large R R  1992 - Australian volcanic-hosted massive sulfide deposits: features, styles, and genetic models: in    Econ. Geol.   v87 pp 471-510

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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