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 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 Currawong deposit occurs near the base of the Gibson's Folly Formation and comprises two stratabound, concordant, massive sulphide lenses that are dissected by sub-vertical late faults.   Each lens has a concordant stringer zone in the footwall of the massive sulphides and is hosted by subaqueous rhyodacitic to andesitic breccias and coherent volcanic rocks, and equivalent epiclastics, which all interfinger with the enclosing turbidites.

Mineralisation has been divided into six types:  1). Pb-Zn,  2). pyrite-Zn,  3). massive pyrite,  4). pyrite-magnetite,  5). footwall stringer zones and  6). overprinting veins and breccias resulting from structural remobilisation.

Wilga is a single massive sulphide lens in the Gibson's Folly Formation, just above the contact with the Thorkidaan Volcanics.

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.

The Wilga deposit was partially mined from October 1992 to July 1996. It is to be ressurrected as the Stockman project, with 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 summary 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
 References to this deposit in the PGC Literature Collection:
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

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