Mt Todd, Yimuyn Manjerr

Northern Territory, NT, Australia

Main commodities: Au Ag
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The Mount Todd gold mine ( also known as Yimuyn Manjerr ) is located within the Palaeoproterozoic Pine Creek Inlier of the Northern Territory, Australia, approximately 40 km north-west of Katherine and 220 km south-east of Darwin.   The operation comprises a series of pits, including Batman (the largest), Tollis, Golf and Quigleys distributed over a north-east trending interval of approximately 6 km.

The Mt Todd operation comprises several discrete orebodies striking NNE within a broad NE trending corridor of gold mineralisation in the central domain of the Inlier.   The ore is hosted by the Palaeoproterozoic Burrell Creek Formation which is principally composed of greywacke, siltstone, sandstone and shale of delta to pro-delta facies.   In the mine area greywackes are massive and blocky with beds from 0.2 to more than 1.5 m in thickness, siltstones are fine to massive as beds from a few mm to more than a metre thick, while the shales are commonly graphitic and occur as interbeds in the greywacke and siltstones.   These sediments are conformably overlain by the 1890 Ma volcaniclastics and volcanolithic sediments of the Tollis Formation.

Between 1870 and 1780 Ma the region was subjected to three compressional events that together make up the Top End Orogeny.   The first, the Nimbuwah Event or D1, corresponds to the Barramundi event seen right across northern Australia.   It produced tight NE to N to NW trending asymmetric folds and continuous axial plane cleavage and is associated with the development of conjugate buck-quartz veins.   These were formed prior to the emplacement of the Yenberrie Leucogranite which contact metamorphosed the Burrell Creek Formation to hornblende hornfels facies at much the same time a the peak regional metamorphism.   The second deformation, D2, was the Maud Creek Event at 1850 Ma producing open westerly trending folds and a spaced disjunctive to fracture cleavage.   This was preceded by the emplacement of the Tennyson Leucogranite phase of the 1835 to 1820 Ma Cullen Batholith which further contact metamorphosed the sediments and Yenberrie Leucogranite.   The D3 Shoobridge Event deformation from 1780 to 1770 Ma is characterised by the reactivation of mostly sinistral strike slip faults and shears (such as the important NW trending Pine Creek Shear Zone), a steeply dipping foliation and mesoscopic en echelon folds.   This was followed by the emplacement of shallow lopoliths of Oenpelli Dolerite at 1688 ±13 Ma.

Each of the first two compressional events was followed by extension, the development of shallow rift grabens which were the centres of deposition for clastics, volcanics and volcano-sediments.

Five main types of veining are recognised at Mt Todd, namely:  i). Buck-quartz veins - early barren veining associated with D1,  ii). Quartz-tourmaline veins - follow the buck quartz, but closely precede the sulphide veining,  iii). Quartz-sulphide veins & lodes - which carry the gold mineralisation and predominantly strike NNE as zones of structurally controlled (in cataclasite zones) sheeted veining and anastomosing stockworks ranging from a mm to 10 cm in thickness and hosted by greywacke or siltstone dominated sections of the host sequence. Sulphides include pyrrhotite, chalcopyrite, arsenopyrite, pyrite, marcasite, löellingite, cubanite, galena, sphalerite, bismuth, bismuthinite, other related sulphides and gold. They define a zone that passes through the Batman, Golf and Tollis pits.   This veining and mineralisation apparently post dated D1, but accompanied the emplacement of the Tennyson Leucogranite of the Cullen Batholith, following the peak metamorphism, but preceded D2.  iv). Calcite-base metal veins - a set of NW striking veins occuring near faults and range from <1 mm to 3 cm in thickness with cockscomb and colloform calcite, carrying galena, sphalerite, pyrite, arsenopyrite and chalcopyrite and are of no economic interest,  v). Epithermal style quartz veins - several late, large unmineralised quartz veins.

Greisen type W-Mo-Sn-Bi-Cu mineralisation in the carapase of the early, D1, Yenberrie Leucogranite suggests an earlier discrete mineralising event before the main gold phase.

The ore deposit at Batman has a length of 1500 m and has been delineated to a depth of 500 m.   It has a central thickness of 150 m tapering towards either extremity and dips at 75° E.   The main ore envelope strikes at 10°, while the host lithologies strike approximately NW and dip at around 45°SW.

Open pit mining commenced at Batman in 1993 with a total production to the end of 1996 of 13 Mt @ 1.0 g/t Au.
At the end of 1995 reserves at Batman were 97.6 Mt @ 1.07 g/t Au.
Production in 1996, included Tollis and Golf also and amounted to 8 Mt.
The mine was closed in 1997.   Total production over the period was 13.7 tonnes of gold.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2003.    
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:
Hein K A A  2003 - The Batman and Quigleys gold deposits of the Mt Todd (Yimuyn Manjerr) Mine, Australia: structural, petrographic and mineralogical investigations of coeval quartz sulphide vein and lode/stockwork systems: in    Ore Geology Reviews   v23 pp 3-33
Hein K A A  2003 - Relative timing of deformational, metamorphic and mineralisation events at the Mt. Todd (Yimuyn Manjerr) Mine, Pine Creek Inlier, Northern Territory, Australia: in    Ore Geology Reviews   v22 pp 143-175
Hein K A A, Zaw K and Mernagh T P  2006 - Linking mineral and fluid inclusion paragenetic studies: The Batman deposit, Mt. Todd (Yimuyn Manjerr) goldfield, Australia: in    Ore Geology Reviews   v28 pp 180-200
Ormsby W R, Olzard K L, Whitworth D J, Fuller T A, Orton J E  1998 - Mount Todd 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 427-432

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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