Northern Territory, NT, Australia

Main commodities: Au
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The Woolwonga gold deposit, which is located 175 km south of Darwin, lies within the Archaean to Palaeoproterozoic Pine Creek Inlier which covers an ENE elongated area of 400x150 km immediately to the south and east of Darwin in the Northern Territory, Australia.

The Pine Creek Inlier is composed of 2200-1870 Ma Palaeoproterozoic supracrustal meta-sediments and volcanics that are around 10-14 km thick, overlying Archaean crystalline basement exposed as three separate domal highs surrounded by the supracrustals.   The sequence commences with the Namoona Group conglomerates, meta-arkose, gneiss, schist and dolomite, which were metamorphosed to amphibolite facies from 2100 to 2000 Ma, then overlain by further sediments, the Mount Partridge Group of principally fluviatile sandstone, dolomitic siltstone and mudstone.   These were then unconformably followed by the South Alligator Group of carbonaceous mudstone, iron formation, greywacke and acid tuff which passed up into the greywackes and mudstone of the Finniss Group.   All of these sequences were intruded by Zamu dolerite.

Deformation at 1800 Ma produced greenschist facies metamorphism and a series of tight, non-cylindrical folds with considerable associated brittle deformation and extensive axial plane slaty cleavage in pelite.   Granite intrusion is dated at 1760 Ma.

The Woolwonga deposit lies on the axis of the Woolwonga Anticline, a continuous 8 km long structure, and falls within the Mount Bonnie Formation, the upper member of the East Alligator Group.   Outcrop in the mine area is exposed on two parallel 310° trending ridges and comprises interbedded siltstone, mudstone and greywacke.   The eastern of these ridges follows the Woolwonga Anticline axis for 1.2 km.   The Mount Bonnie Formation overlies the Gerowie Tuff, and is in turn overlain by greywackes of the Burrell Creek Formation (Finniss River Group).

The axis of the Woolwonga Anticline is near vertical, trending at 290 to 310° with a plunge of 30 to 35° SE.   The fold is cut by a series of en echelon 325 to 335° shears which are largely developed within the dominant mudstone-siltstone units and host the bulk of the mineralisation as vertical to steeply NE and SW dipping zones up to 30 m thick that cut across the fold crest.   Gold is associated with quartz-sulphide veins within this fracturing and is present on the margins of these veins and accompanying vein breccias, and oxidised equivalents near surface.   Colluvial and alluvial accumulations shed from the vein system into the adjacent valleys and flats.   Mineralisation is present as 1 to 500 mm thick sub-vertical sheeted quartz-sulphide veins to stockworks with pyrite and arsenopyrite bearing quartz making up 70% of the ore zone.   A second style is massive auriferous quartz saddle reefs up to 1.5 m thick developed at the contact between contrasting lithologies and comprise the remaining 30% of the ore.

The in situ geological resource in 1988 was: - 2.48 Mt @ 3.34 g/t Au, (0.737 Mt @ 2.98 g/t Au Oxide and 1.741 Mt @ 3.5 g/t Au sulphide),
    with a recoverable mining reserve of 2.1 Mt @ 2.78 g/t Au.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1990.    
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:
Kavanagh M E, Vooys R A  1990 - Woolwonga 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 747-750
Nicholson P M, Eupene G S  1990 - Gold deposits of the Pine Creek Inlier: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 739-742

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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