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Captains Flat, Lake George Mine |
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New South Wales, NSW, Australia |
| Main commodities:
Zn Pb Cu Ag 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 Captains Flat (or Lake George mine ) VMS / VHMS volcanic hosted massive sulphide zinc-lead-copper deposit is located in the Lachlan Fold Belt in south-eastern New South Wales, Australia, 50 km south-east of Canberra.
The Captain's Flat host sequence is confined to a well defined north-south trending graben some 2 to 8 km wide, bounded by horsts of contorted Ordovician metasediments and Siluro-Devonian granitoid batholiths. The hosts comprise tightly folded Middle to Upper Silurian felsic pyroclastics, volcanogenic sediments and shales in the following succession, from the base: i). Copper Creek Shale - 60 to 150 m of sediments with subordinate tuffs. ii). Kohinoor Volcanics - 50 to 850 m of coarsely porphyritic andesitic to dacitic to rhyolitic lavas, tuffs, volcanic breccias, tuffaceous shales and volcanic cherts. This unit hosts the orebodies. iii). Captains Flat Formation - 850 to 1200 m of predominantly shales and siltstones with lesser volcanic flows and tuffs.
Ore is present in three overturned shoots which dip at 80 to 87° W and plunge north at 60 to 70°, known as Elliots, Central and Keatings. The ore ranges from <1 to 20 m in thickness. The interconnected Elliots and Central shoots had a combined strike length at surface of 500 m while Keatings 250 m to the north was 300 m long. Ore was continuous down dip/plunge for 800 to 1000 m. The rhyolitic crystal tuff (to quartz schist) that forms the immediate footwall is a zone 80 to 100 m thick, which also defines the pyritic halo to the orebody. This envelope of pyrite continues for 500 m north of Elliots and for 1200 m south of Keatings.
The ore at Captains Flat is composed of the following, in order of decreasing abundance: pyrite, sphalerite, galena, chalcopyrite, tennantite (tetrahedrite), arsenopyrite, gold, rare pyrrhotite and very rare stannite. The gangue is of quartz, chert, occassional carbonates, chlorite and sericite. The orebody has a sharply defined geologic hangingwall and diffuse footwall, grading into stringer mineralisation. The highest grades of Zn & Pb are in the eastern (geological hangingwall) side of the orebody, while copper in excess of 0.5% is only in the western (geological footwall) side. The ore varies from an upper layer of massive, banded sphalerite-galena in the geological hangingwall, stratigraphically downwards to banded pyrite-sphalerite, then to massive to semi-massive pyrite with occassional chalcopyrite and rare sphalerite, which in turn merges down into a zone up to 90 m thick of stringer and disseminated pyrite and rare chalcopyrite at the top.
Total production from 1882 to 1962 when the mine closed was:
4 Mt @ 0.67% Cu, 6% Pb, 10% Zn, 56 g/t Ag, 1.7 g/t Au.
The mine and dumps, which are in the catchment of the river that flows through Canberra, have been completely rehabilitated.
For more detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1975.
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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Davis L W 1975 - Captains Flat lead-zinc orebody: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne Mono 5 pp 694-700
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Davis L W 1990 - Silver-Lead-Zinc-Copper mineralisation in the Captains Flat-Goulburn synclinorial zone and the Hill End synclinorial zone: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1375-1384
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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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