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Moline Dam, Northern Hercules, Southern Hercules |
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Northern Territory, NT, Australia |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Moline and Northern and Southern Hercules gold deposits, which are located 50 km NNE of Pine Creek and 200 km SSE of Darwin, lie 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.
Following a break the sequence was subjected to deformation and greenschist metamorphism from 1870 Ma to produce a series of tight, non-cylindrical folds with considerable associated brittle deformation and extensive axial plane slaty cleavage in pelite. This was followed by intrusion of the 1835-1800 Ma Cullen and Mt Davis Granites.
The Moline Dam gold deposit occurs near the top of the 200 m thick Mount Bonnie Formation, the uppermost unit of the East Alligator Group, while Northern Hercules, a few hundred metres stratigraphically higher is apparently within the Burrell Creek Formation of the Finniss Group. The hosts are folded through several phases into a tight, tilted, but gently southeast plunging, 18 km long anticlinorial structure between the late to post tectonic Cullen and Mt Davis Granites. The structure has been subjected to faulting and shearing which influences the emplacement of veining.
At Moline Dam the hosts are silicate and sulphide facies banded iron formation, chert, silicified shale and quartz veins. Gold is associated with banded and network veined pyrite ±pyrrhotite, sphalerite, galena, arsenopyrite and bismuthinite in micro and mesofolded, disrupted, laminated chert/BIF and shale that are variably sericitic, carbonaceous, silicieous, chloritic, feldspar-albite-adularia and tourmaline altered and pyritic/pyrrhotitic. The sulphides are finely disseminated as well as coarse and layered in a quartz-albite gangue, and are in part original and redistributed, with the associated gold mineralisation being generally stratabound. Mineralisation is present in four lodes individually up to 23 m wide and cumulatively up to 50 m in width, persisting down dip for 30 to +100 m and along strike for 1100 m.
At Northern Hercules mineralisation is associated with steeply dipping quartz-pyrite ±arsenopyrite, chalcopyrite, sphalerite, galena veining in multiple, sub-parallel lodes cutting the host sandstone-greywacke-siltstone-shale sequence cutting obliquely across strike over a length of 800 m. There are up to 4 such lodes with individual widths of up to 23 m and a cumulative width of 45 m within an 80 m wide shear zone. Southern Hercules is virtually continuous with Northern Hercules, but is hosted by the Mount Bonnie Formation and similar in character to Moline Dam.
Reserve figures in 1990 were:
Moline Dam measured and indicated to 75 m depth - 1.984 Mt @ 2.46 g/t Au
Northern Hercules measured and indicated to 75 m depth - 1.043 Mt @ 3.71 g/t Au
For a total of 3.027 Mt @ 2.89 g/t Au.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription 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.
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Miller G C 1990 - Moline Gold deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v1 pp 763-768
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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
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