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SWAN, Mt Elliott
Queensland, Qld, Australia
Main commodities: Cu Au

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The SWAN and Mount Elliott deposits are located within the Eastern Fold Belt of the Mount Isa Inlier in northwest Queensland, approximately 90 km south of Cloncurry and 20 km north of the Selwyn deposits (#Location: 21° 32'S, 140° 30'E).

For geological background on the setting, see the Cloncurry IOCG Province record.

These two deposits are part of the same mineralised system in which host rock chemistry and rheology control mineralisation style within the same low grade envelope. The two deposits are separated by a major steep fault zone.

The Eastern Fold Belt comprises a sequence of 1890 to 1610 Ma metasediments and volcanics that have been intruded by three main phases of igneous rocks. On a local scale, the SWAN and Mount Elliott deposits are situated close to the contact of the Kuridala and Stavely Formations. Mount Elliott occurs within the phyllite, schist and black shale of the Kuridala Formation at the base of the Soldiers Cap Group, which in the deposit area comprises a package of intensely skarn-altered (clinopyroxene ±actinolite, magnetite, scapolite and apatite) phyllites, schists and metadolerites. SWAN is hosted within a breccia that has been emplaced into a package of banded and brecciated calc-silicates and calcareous sediments of the Stavely Formation, a younger unit which has been correlated with the Mount Norna Quartzite. The structural (overturned) footwall lithology to mineralisation at SWAN is a massive calc-silicate (coarse-grained calcite, tremolite, albite, scapolite, actinolite, muscovite and chlorite), layered calc-silicates (1 to 10 cm interlayered and boudinaged bands of very fine-grained siliceous material, commonly hematite-stained and albite-altered, alternating with coarse-grained calcite, tremolite, albite, scapolite, actinolite, muscovite and chlorite) and intensely altered and sheared metasediments (Brown, Lazo, Kirwin and Corlett, 2009).

A 200 to 400 m wide body of metadiorite/metagabbro lies within the southern portion of SWAN, comprising medium- to fine-grained actinolite, plagioclase, biotite, quartz, tremolite, magnetite, epidote and calcite. It has a relatively unaltered core, although the margin adjacent to the SWAN breccia is strongly hematite-stained, albite altered and brecciated (Brown, Lazo, Kirwin and Corlett, 2009).

The majority of the SWAN mineralisation is hosted by the SWAN breccia, which is crackle- to matrix-supported, with angular to rounded, strongly albite-altered calc-silicate and metadolerite fragments set in a fine- to coarse-grained matrix of hematite-stained albite, clinopyroxene, actinolite, magnetite, calcite, pyrite and chalcopyrite. The fragments are from centimetres to metres across. A 30 to 100 m thick banded calc-silicate unit forms the eastern margin of both the SWAN breccia and the massive calc-silicates, and comprises regular 0.5 to 3 cm thick bands of hematite-stained albite, magnetite, clinopyroxene, actinolite, epidote and calcite, which are commonly mineralised on margin of the breccia (Brown, Lazo, Kirwin and Corlett, 2009).

The banded calc-silicates grade, over a 10 to 30 m interval, into a quartz, muscovite, and chlorite schist to the east.

The SWAN deposit is cross-cut by several narrow, 1 to 30 m thick, ~30° SE dipping, late-stage, pink to grey felsic (plagioclase, K-feldspar, quartz, chlorite after biotite, titanite, magnetite, pyrite and chalcopyrite) dykes with chilled margins. These dykes cut the mineralised breccias and pre-date late-stage mineralised veins. A 5 to 30 m wide, commonly mineralised, steeply dipping, dominantly sinistral strike-slip fault separates the SWAN and Mount Elliott deposits. Numerous smaller anastomosing faults cut the main mineralised breccia and appear to have channelled late-stage fluids, dissolving the carbonate gangue of the breccia leaving friable highly porous ore (Brown, Lazo, Kirwin and Corlett, 2009).

Four main styles of primary Cu-Au mineralisation are recognised within the Mount Elliott and SWAN deposits: i). The Mount Elliot breccia, ii). the SWAN breccia, iii). banded/replacement mineralisation and iv). late vein hosted mineralisation. These styles are manifested as follows. At Mount Elliott, mineralisation is dominantly within the Mount Elliot breccia, with 0.1 to 20 m wide clasts set in a very coarse-grained, open spaced matrix containing voids up to tens of metres wide. The fragment within the SWAN breccia are much smaller than in the Mt Elliot breccia, and mineralisation at the former is considered to have formed some time after the development of the breccia which created a large porous and chemically suitable trap. Mineralisation permeated, replaced and altered the banded calc-silicate on the eastern margin of the SWAN breccia, forming banded mineralisation of magnetite, hematite-stained albite, chalcopyrite, pyrite, clinopyroxene, actinolite and epidote. Late-stage, 1 to > 200 cm thick veins of coarse-grained calcite, chalcopyrite, pyrite and molybdenite represent an event that crosscuts all of these mineralisation styles (Brown, Lazo, Kirwin and Corlett, 2009).

Mt Elliot mine was earlier (Shiqi Wang and Williams, 2001) described as containing 2.9 Mt @ 3.33% Cu, 1.47 g/t Au, hosted by carbonaceous meta-pelites and amphibolites, occurring in two zones controlled by NW trending, NE dipping brittle faults in a 200 m wide zone of intense post peak metamorphic alteration. It was interpreted as comprising an older, outer, system of albitised meta-sediments (bleached by the loss of biotite and carbonaceous material), over-printed by a "skarn" zone of diopside-hedenbergite veins and replacement features with abundant scapolite, apatite and calcite. Sulphides and magnetite (from outer pyrrhotite-pyrite to chalcopyrite-pyrrhotite-pyrite to chalcopyrite-pyrite-magnetite to magnetite-pyrite±andradite in the core) occur within the skarn, veining and replacing clinopyroxene and intergrowing with calcite.

Brown, Lazo, Kirwin and Corlett (2009) quote a resource at SWAN and Mt Elliot of:

    475 Mt @ 0.5% Cu, 0.38 g/t Au at the cut-off grade of 0.25% eCu, still open at depth, including a high grade resource of:
      62 Mt @ 1.01% Cu, 0.4 g/t Au at a cut-off of 1.0% eCu.

The most recent source geological information used to prepare this decription was dated: 2010.    
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.

Mt Elliott

  References & Additional Information
   Selected References:
Babo, J., Spandler, C., Oliver, N.H.S., Brown, M., Rubenach, M.J. and Creaser, R.A.,  2017 - The High-Grade Mo-Re Merlin Deposit, Cloncurry District, Australia: Paragenesis and Geochronology of Hydrothermal Alteration and Ore Formation: in    Econ. Geol.   v.112, pp. 397-422.
Brown M and Porter T M,  2010 - The Mount Elliott IOCG System, Eastern Fold Belt, Mount Isa Inlier, Northwest Queensland: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.3 pp. 219-232
Duncan RJ, Stein HJ, Evans KA, Hitzman MW, Nelson EP and Kirwin DJ,  2011 - A New Geochronological Framework for Mineralization and Alteration in the Selwyn-Mount Dore Corridor, Eastern Fold Belt, Mount Isa Inlier, Australia: Genetic Implications for Iron Oxide Copper-Gold Deposits : in    Econ. Geol.   v106 pp. 169-192
Fortowski D B, McCracken S J A  1998 - Mount Elliott copper-gold deposit: in Berkman D A, Mackenzie D H (Eds),  Geology of Australian and Papua New Guinean Mineral Deposits The AusIMM, Melbourne    pp 775-782
Shiqi Wang and Williams P J  2001 - Geochemistry and origin of Proterozoic skarns at the Mount Elliott Cu-Au(-Co-Ni) deposit, Cloncurry district, NW Queensland, Australia: in    Mineralium Deposita   v36 pp 109-124
Shiqi Wang, Williams P J  1996 - The alteration and mineralisation styles of a skarn hosted Mount Elliott Cu-Au deposit and adjacent SWAN prospect, Cloncurry district: in Baker T, et. al. (Eds),  MIC 96, New Developments in Metallogenic Research, The McArthur-Mt Isa-Cloncurry Minerals Province EGRU Contribution 55 (Townsville, Qld)    pp 139-142

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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