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Tarmoola

Western Australia, WA, Australia

Main commodities: Au
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The Tarmoola (or King of the Hills) Archaean greenstone belt hosted gold deposit lies close to the eastern margin of the Kalgoorlie Terrane within the Eastern Goldfields Superterrane of the Archaean Yilgarn Craton of Western Australia.   It is located 29 km to the north-west of Leonora in the Eastern Goldfields, and is 265 km north of Kalgoorlie.

Prior to modern mining, the deposit was exploited as the King of the Hills Gold Mine. It was active from 1985 to 2004 as an open pit that produced ~50 t of gold, then went underground from 2011 to 2014 to produce ~7.5 t of gold (Mindat online record). Subsequent owners have reverted to referring to the deposit as the King of the Hills.

Tarmoola is the largest granitoid hosted gold deposit in the Yilgarn Craton.

The Leonora District has been sub-divided into three main geological domains, namely:  i). A Western Domain dominated by the Raeside Batholith composed of strongly deformed granodiorite, monzogranite, and granite gneiss;  ii). The Central Domain characterised by mafic and ultramafic supracrustal units with interbedded slate and ferruginous sediments, making up an eastward younging sequence;  iii). The Eastern Domain composed of strongly faulted mafic and felsic igneous rocks with abundant intercalated sandstone, shale, conglomerate and banded iron formations.   These are intruded to the NE by the undeformed Bundarra granitoid batholith, and are limited to the east at surface by the sediments of the Pig Well graben.

Three major NW striking deformation zones are recognised in the district, namely:  i). The normal Sons of Gwalia shear zone,  ii). The sinistral Mount George lineament; and  iii). The sinistral Keith-Kilkenny high strain zone.   These separate zones of distinct lithological, structural or deformational character.   Most gold mines in the district are related to the Sons of Gwalia shear.

The host at Tarmoola is predominantly a trondhjemite pluton which intrudes a shallow dipping (20 to 35°), north-west striking sequence of supracrustals, while several intermediate to acid dykes cut both.   The major ore zones are located within 80 m on either side of the supracrustal-trondhjemite contact, with pervasive hydrothermal alteration related to gold of all types.

Major ore zones, based on a 1 g/t Au cutoff, are found in the following situations:  i). within the trondjhemite as discontinuous WNW striking, steeply south-west and north-east dipping zones of conjugate quartz-carbonate veins containing pyrite, chalcopyrite, sphalerite, galena, gold and rare scheelite;  ii). along the steeply dipping eastern trondhjemite contact in the supracrustal and trondhjemite rocks; and  iii). subparallel to the shallow dipping, western trondhjemite margin within supracrustal hosts.   The veins in the supracrustals are similar to those from the trondhjemite.

There were three main deformational phases at Tarmoola, namely:  i). D1 which caused early, barren isoclinally folded quartz-carbonate veins and pervasive foliation during the early phases of the progressive east-west shortening.  ii). Gold mineralisation accompanied D2 when the the trondhjemite acted as a competent body within the ductile supracrustals during sub-horizontal NW-SE shortening, which produced the auriferous conjugate veining internally and reactivated foliation on the trondhjemites eastern contact causing low stress zones which focussed hydrothermal activity and ore vein formation.   Reverse movement between the trondhjemite and supracrustals on the western intrusive contact produced west dipping gold bearing shears in the supracrustals.  iii). D3 formed brittle-ductile shear zones, quartz-carbonate veins and brittle faults, displacing lithological contacts and auriferous veins.

Two main ore zone types are recognised.   The first is in the supracrustals adjacent to the trondhjemite contacts, with the most contimuous and widest zones in quartz-carbonate altered supracrustals adjacent to the northern and eastern contacts, and is generally in <2 m wide veins.   Ore within the trondhjemite occurs in ore zones that are <10 m wide, strike WNW and are discontinuous.

Open pit mining between 1985 and mid 1999 produced 16.5 tonnes of gold at a grade of 1.9 g/t Au.
The resource estimate in 1999 was 65.05 Mt @ 1.54 g/t Au, which includes
a reserve of 28.5 Mt @ 2.03 g/t Au (Duuring, et al., 2001).

Ore reserve and mineral resource estimates in June 2013 (St Barbara Ltd ASX release 22 August, 2013) were:
  Measured + indicated + inferred resource
    King of the Hills - 11.843 Mt @ 6.4 g/t Au (3.0 g/t Au cut-off)
  Proved + probable reserves (included in resources)
    King of the Hills - 2.572 Mt @ 3.7 g/t Au (3.0 g/t Au cut-off).

Remaining Mineral Resources at the King of the Hills deposit as of 30 June, 2018 were (Red 5 Limited 2018 Annual Report):
  3.904 Mt @ 5.2 g/t Au for 20 t of gold.

For more detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary 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.


  References & Additional Information
   Selected References:
Duuring P, Hagemann S G, Cassidy K F, Johnson C A  2004 - Hydrothermal Alteration, Ore Fluid Characteristics, and Gold Depositional Processes along a Trondhjemite-Komatiite Contact at Tarmoola, Western Australia: in    Econ. Geol.   v99 pp 423-451
Duuring P, Hagemann S G, Love R J  2001 - A thrust ramp model for Gold mineralization at the Archean Trondhjemite-hosted Tarmoola deposit: the importance of heterogeneous stress distributions around granitoid contacts: in    Econ. Geol.   v96 pp 1379-1396
Fairclough M C, Brown J C  1998 - Tarmoola gold deposit: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne   Mono 22 pp 173-178


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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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