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Mt Morgans - Westralia, Jupiter

Western Australia, WA, Australia

Main commodities: Au
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The Mount Morgans group of gold deposits are located within an area of ~20 x 10 km in the North-Eastern Goldfields Province of the Archaean Yilgarn Craton, and 30 to 40 km WSW to SW of Laverton and ~750 km NE of Perth in Western Australia.

The deposit area straddles the core and western limb of the Mt. Margaret anticline that plunges moderately to the south and has a NNW trending fold axis. Dominant rock types are mafic volcanics, mafic intrusives, minor ultramafics and metasediments, and a narrow, <100 m wide band of a regionally continuous banded iron formation (BIF). All of these primary rock types are been intruded by concordant and discordant felsic porphyry dykes and sills as well as local thin lamprophyre dykes. The hinge zone of the Mt Margaret Anticline/Dome, as well as late structures throughout the district, are intruded by syenite stocks. All rocks have been subjected to regional greenschist facies metamorphism. Large granitic intrusions form the core of the Mt Margaret anticline.

A number of styles gold mineralisation are recognised. The bulk of the historic production has come from BIF-hosted replacement style mineralisation (e.g., the Westralia deposit) where extensive sulphide replacement and silicification of the magnetite has occurred forming large tonnage moderate to high grade mineralisation. This deposit is situated within the Archaean greenstone succession, ~3 km east of the Celia Lineament, a major deformation zone. Tholeiitic basalts and lenticular BIF horizons are intruded by concordant and subconcordant quartz-feldspar porphyries, while ultramafic rocks are the dominant wallrocks.

Syenite related gold mineralisation occurs at the Jupiter deposit where the total pre-mined resource inventory was ~45 t of gold. The geology and mineralisation at Jupiter, which is 15 km ESE of Westralia, is very similar to that at the nearby >210 t Au Wallaby deposit, 8 km to the SE. The Jupiter mineralisation lies within the Jupiter Corridor, defined by a 2 km long north-south trend containing three main syenite intrusive bodies, from south to north known as Ganymede, Heffernans and the Doublejay which together have been historically mined as the Jupiter Open Pit. Several smaller syenite dykes and intrusive bodies are found proximal to the three main syenites, and all are contained within the Jupiter Corridor.

A large and anomalous syenite complex occurs at Cameron Well, between Westralia and Jupiter, whilst basalt hosted shear zone related mineralisation is also extensive, with sericite-silica-carbonate-sulphide alteration zones forming medium to high grade orebodies at the Transvaal and Ramornie bodies.

Deposits are situated in dilational jogs, at the intersection of a major NNW-trending sinistral shear zone and later, also sinistral, NNE-striking shear and fault zones. Moderate to steeply SE-plunging high-grade ore shoots occur in the BIF unit at these structural intersections. Other smaller, splay shear hosted vein arrays in mafic and ultramafic rocks also host gold mineralisation.

Known resources in 1998 were: 5.4 Mt @ 3.9 g/t Au for 21 t of contained gold.

The Westralia and Jupiter deposits respectively had pre-mined endowments of >77 and ~45 t Au.

The Mt Morgans group of deposits at 28 July 2016 (Dacian Gold website, viewed March, 2018) had:
  A Mineral Resource of 44.7 Mt @ 2.3 g/t Au for 102 t Au, comprising
      Measured Resources - 5.236 Mt @ 1.5 g/t Au;
      Indicated Resources - 28.287 Mt @ 2.1 g/t Au;
      Inferred Resources - 11.138 Mt @ 3.1 g/t Au.
  An Ore Reserve at 21 November 2016 of: 18.6 Mt @ 2.0 g/t Au for 37 t Au, including
      Proved Reserves - 1.110 Mt @ 2.4 g/t Au;
      Probable Reserves - 17.475 Mt @ 2.0 g/t Au.

The most recent source geological information used to prepare this summary was dated: 2016.     Record last updated: 6/3/2018
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.


  References & Additional Information
   Selected References:
Vielreicher R M, Groves D I, Ridley J R and McNaughton N J,  1994 - A replacement origin for the BIF-hosted gold deposit at Mt. Morgans, Yilgarn Block, W.A.: in    Ore Geology Reviews   v9 pp 325-347


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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