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Mt Rawdon |
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Queensland, Qld, Australia |
| Main commodities:
Au
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Super Porphyry Cu and Au
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Mt Rawdon is an open pit mine exploiting a bulk tonnage, low grade reserve, located 80 km SW of Bundaberg and 520 km NNW of Brisbane in central Queensland.
The deposit is hosted within a late Triassic diatreme that cuts meta-sediments of the Carboniferous Curtis Island Group, and the Palaeozoic Briggs Creek Granodiorite. Andesites, trachytes and rhyolites of the late Triassic Arabanga Volcanics outcrop 500 m to the west, while swarms of trachyte and rhyolite dykes cut the diatreme. The host volcaniclastic rocks strike northeast and have a shallow to moderate dip to the southwest. The diatreme is filled with polymict, poorly sorted, matrix supported fragmentals dominated by clasts of variably altered dacite porphyry, meta-sediments and granodiorite. This fragmental grades out into a marginal breccia, that forms a steeply dipping pipe-like structure related to the emplacement of a dacite porphyry plug. The diatreme is in turn cut by a central dacite plug and numerous dykes.
Phyllic and propylitic alteration was pre-mineral and was associated with the intrusion. These alteration phases are overprinted by silica-pyrite and chlorite, with gold being intimately associated with the latter. The gold mineralisation takes the form of finely disseminated pyrite within the host rocks as well as more discrete sulphide veinlets. It post-dates the dacites and trachy-andesites intrusives and occurs as disseminations in the matrix of the fragmentals, as replacements patches and stringers. Gold grades are generally sympathetic to the pyrite alteration and density of veining.
There are three main stages of mineralisation. The first is volumetrically the largest with pyrite, arsenopyrite, sphalerite, galena, native bismuth and gold, with a gangue mineralogy of chlorite, Mn-calcite, epidote, tremolite-actinolite and apatite. Stage 2 and 3 are similar. Gold is present as electrum with a fineness of 350-880 as inclusions in pyrite, but also has a close association with sphalerite and minor minerals.
The orebody has a surface exposure as a roughly ovoid area of some 200 x 300 m on a 0.7 g/t Au cutoff and in 2000, an indicated + measured resources totalling 37.9 Mt @ 1.0 g/t Au, 4 g/t Ag., mineable at a 1.2:1 waste to ore stripping ratio. The mineralisation continues below the bottom of the optimised pit.
Remaining open pit resources and reserves as at June 30, 2012 (Evolution Mining, 2012), were:
Measured + indicated + inferred underground resources, 52.5 Mt @ 0.7 g/t Au for 37.14 t Au.
Proven + probable ore reserves, 36.2 Mt @ 0.8 g/t Au for 28.43 t Au.
The most recent source geological information used to prepare this decription was dated: 2001.
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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Brooker M, Jaireth S 1995 - Mount Rawdon, southeast Queensland, Australia - a diatreme-hosted Gold-Silver deposit: in Econ. Geol. v90 pp 1799-1817
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Gallo J B, Mustard H, Taylor S 1990 - Mount Rawdon Gold deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1505-1507
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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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