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Hill End Goldfield - Hawkins Hill, Reward |
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New South Wales, NSW, Australia |
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Au
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Super Porphyry Cu and Au
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The Hill End goldfield of central-western New South Wales is located within the Palaeozoic Lachlan Fold Belt in central-western New South Wales, Australia. It was the site of the first discovery of economic gold in Australia in 1851.
During the early years, the Hill End goldfield produced as much as 50 t of gold, together with the Holtermann Nugget, the largest non-alluvial nugget ever mined at 268 kg. Following the high gold grades in the early underground mines of the 1870s and 1880s, the bonanza grades were never replicated and mining declined after 1890, but continued through until 1920 with minor spurts of activity from 1950 to the present (Harper, 1918; Stevens, 1972).
It lies within the Hill End Trough, which contains a 7 km thick succession of late Middle Silurian to Middle Devonian ~425 to 385 Ma, deep-water, epiclastic and volcaniclastic sedimentary rocks. The trough is bounded by 367 to 363 Ma shallow-water deposits of the paleogeographic Molong and Capertee Highs to the
west and east, respectively (Packham, 1969, 1999, 2003). The Hill End Trough is 70 km wide and >200 km long, and is underlain by a basement of
Ordovician volcanic rocks that lie between the Molong and Rockley-Gulgong volcanic belts to the west and east respectively, both of which belong to the Ordovician Macquarie Arc in the Lachlan fold belt of eastern Australia (Fergusson, 2009).
The Hill End goldfield is noted for its coarse gold, both as alluvial nuggetts and as masses of gold and quartz in narrow quartz veins. The lodes are hosted on the flanks of the Hill End and adjacent anticlines within a deformed sequence of Silurian to Devonian turbidites. They have similarities to the Victorian deposits (eg Ballarat and Bendigo), also within the Lachlan Fold Belt, but some 650 km to the south-west.
The doubly plunging Hill End anticline is the highest amplitude fold in the district and has the structurally highest crest. The core of the anticline is occupied by the late Silurian Chesleigh Formation, which hosts the historic Hawkins Hill mine and adjacent Reward mine. The Chesleigh Formation comprises interbedded fine-, medium- and coarse-grained, quartz-rich or quartzo-feldspathic, lithic sandstones/greywackes, siltstones and slates. The upper part of the formation includes minor radiolarian chert and rhyolitic air-fall tuffs. Beds are generally 10 to 50 cm thick, with finer-grained units bedded at a cm scale and coarse units at 1 to 2 m scales. Graded bedding, soft-sediment deformation and Bouma A to E sequences suggest deep-water turbidity currents in a submarine
fan environment (Pogson and Watkins, 1998). The Formation is conformably overlain by the Early Devonian Cookman, Turondale, Waterbeach and Guroba Formations
that are composed of rhythmically bedded, turbiditic mass flow deposits. These are conformably overlain by the Merrions Formation which includes subaqueous mass flow explosive eruptive lavas and volcaniclastics deposited in a deep marine environment, and the Cunningham Formation, the final major unit of the Hill End Trough, comprising thin-bedded (1 to 5 cm), fine-grained, often pyritic, non-volcanic turbidites (Pogson and Watkins, 1998).
Gold occurs along the 25 km strike length of the Hill End Anticline. Historic mining at Hawkins Hill worked out a series of rich, gold-bearing veins over a strike length of 1 km and locally to a depth of 200 m on the east limb of the Hill End anticline. Most of the payable gold occurs on the east dipping limb, in small, rich, bedding plane parallel veins, while lesser deposits are found in the eastern limb and adjacent folds. These veins are <1 up to 15 cm thick on the limbs and up to 2 m wide on the crest. Gold also occurs in thin (1 to 20 mm) leader veins that are generally flat lying and merge with, but dont cut the main veins. In addition there are zones of brecciation and stockwork veining, locally over widths of up to 10 m. Veins are laminated or composite laminated and massive. Rich shoots in the main veins plunge almost horizontally and correspond to the intersection of the main and leader veins.
Primary native gold is encased in quartz, locally in contact with calcite or fine grained galena.
The field is reported to have produced 56 tonnes of gold in total.
Since 1994, exploration below the shallow historic mines by Hill End Gold Limited has apparently outlined to November 2010 a resource of 10.4 t of contained gold in the district, including 0.9 Mt @ 8.6 g/t Au in the Hawkins Hill - Reward deposit.
For detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2021.
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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Downes, P.M., 2003 - Mineralisation in and adjacent to the Hill End Trough: in Vassallo, J.J. and Glen, R.A. (Eds.), 2003 Evolution of the Hill End Trough: Hill End Trough Geological Survey of New South Wales, Sydney, Australia, CD Geoscience Data package, Report 2003/291 pp. 63-93.
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Wilkins, C. and Quayle, M., 2021 - Structural Control of High-Grade Gold Shoots at the Reward Mine, Hill End, New South Wales, Australia: in Econ. Geol. v.116, pp. 909-935.
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Windh J 1995 - Saddle reef and related Gold mineralization, Hill End Gold Field, Australia: evolution of an auriferous vein system during progressive deformation: in Econ. Geol. v90 pp 1764-1775
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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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