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Maldon |
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Victoria, Vic, Australia |
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Au
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Super Porphyry Cu and Au
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The Maldon gold field is centred on the town of Maldon, approximately 120 km north-west of Melbourne in Victoria, Australia.
Maldon has been an important historic gold producer with continuous reef mining having taken place from 1857 to 1926 during which time 58 tonnes of gold were produced from around 20 reefs. In 1988 small scale open pit mining and CIL treatment was undertaken on a resource initially of 0.7 Mt @ 3.6 g/t Au.
The deposit lies within the Bendigo tectonic zone of the Lachlan Fold Belt.
The host sequence is composed of Ordovician marine clastic sediments, mainly greywackes with lesser shales, adjacent to the Devonian Harcourt Granite, a granodiorite which has contact metamorphosed the sediments in the gold field area to produce a hard hornfels composed of varying proportions of quartz, biotite, cordierite and andalusite. The sediments are tightly folded with parallel axes trending at 345° and spaced at 225 m intervals, having frequently overturned western anticlinal limbs, producing steep easterly dips throughout the field.
Quartz reefs are generally concordant in strike with the enclosing sediments, but may cross fold axes, with the richest, thickest reefs occuring where they cut across bedding. The granite has truncated the reefs indicating mineralisation was at least earlier than the last phase of granodiorite emplacement.
One of the principal vein systems was the Eaglehawk Reef, a 2 to 10 m wide vein striking roughly parallel to the hosts but dipping 67°W, crosscutting the easterly dipping hosts. The reef rolled over at depth to parallel bedding where it thinned and was less productive. The reefs are generally massive milky white quartz with minor (1%) sulphide which are in decreasing order of abundance - pyrite, arsenopyrite, sphalerite, galena, pyrrhotite and marcasite. Gold occurs as visible free native gold and as sub-micron gold within the sulphides, particularly arsenopyrite.
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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Selected References:
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Arne D C, Bierlein F P, McNaughton N, Wilson C J L and Morand V J, 1998 - Timing of gold mineralisation in western and central Victoria, Australia: New constraints from SHRIMP II analysis of zircon grains from felsic intrusive rocks: in Ore Geology Reviews v13 pp 251-273
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Morgan B D, Woodland J G 1990 - Union Hill Gold deposit, Maldon: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1279-1280
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Phillips, G.N. and Hughes, M.J., 1998 - Victorian gold province: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp. 495-506.
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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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