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Geological and structural controls on magnetism in the Tanami Mine corridor, Tanami Desert, N.T.


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Marsh, Scott 1996 , 'Geological and structural controls on magnetism in the Tanami Mine corridor, Tanami Desert, N.T.', Coursework Master thesis, University of Tasmania.

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Gold mineralisation was first discovered at the Tanami Mine in August 1900.
However, it was not until the late 1980's that large-scale open pit mining and
systematic gold exploration was carried out within and around the Tanami Mine. The
Tanami Mine Corridor, a 15 km long, NNE-striking arcuate package of magnetic
Mount Charles Beds on the western margin of the Frankenia Granite dome, is host to
more than 1 Moz. of contained gold in more than 30 individual deposits. Gold
mineralisation is hosted in 350-000°, 020-040° and 060-070°-striking, east- to SEdipping
brittle shear zones cross-cutting stratigraphy. Host rocks include subgreenschist
facies basalt and turbiditic sedimentary rocks which dip and face 30-70°
Regional-scale, low-magnetic alteration zones within the Tanami Mine Corridor are
the result of chlorite-carbonate hydrothermal alteration along syn-mineralisation shear
zones. Chlorite-carbonate alteration patterns delineated from detailed 1VD magnetic
images include: (i) regional alteration domains, which are 0.5-3 km long and up to
200 m wide haloes around strike-continuous (>10 km), 030-040°-striking, eastdipping
shear zones; (ii) stratabound haloes, which are 350-450 m long and up to 150
m wide within autoclastic and pillow basalt flows; and (iii) cross-cutting haloes which
have developed in brittle fracture zones adjacent to 060-090° trending shear zones.
The cross-cutting haloes are commonly 50-100 m wide and up to 600 m long.
Chlorite-carbonate alteration is the result of CO 2 -H20-rich hydrothermal fluids
channelling up brittle structures and causing alteration of titanomagnetite in basalt and
magnetite-bearing interflow sedimentary units to chlorite and sphene. The most
intensely altered zones have resulted in 100% replacement of titanomagnetite,
whereas weak to strongly altered zones have partial replacement of titanomagnetite of
between 10 and 90%.
Gold mineralisation and related sericite+quartz±pyrite alteration (SQ±P) overprints
chlorite-carbonate alteration and forms intense but restricted (<10 m), magnetitedepleted
alteration haloes around mineralised veins. SQ±P alteration haloes are not readily recognised from airborne or total magnetic intensity (TMI) magnetic profiles
as they are often too narrow and masked by the broader chlorite-carbonate lowmagnetic
haloes. SQ±P haloes are characterised by an inner halo (<5 m) of
leucoxene/anatase replacing sphene±ilmenite and pyrite replacing chlorite±-magnetite.
The outer halo (-5-10 m) consists of leucoxene/anatase replacing sphene±ilmenite,
and ankerite±dolomite replacing chlorite±magnetite.
Depth to the upper saprolite zone within the Corridor as depicted from 2D modelling,
and which is consistent with field data, varies between an average of 20 m to more
than 100 m down shear zones. The shallow depth to upper saprolite provides an ideal
environment for applying high frequency filters to detailed airborne magnetic data.
These filters allow for the enhancement, mapping and drilling of shallow geological
features such as syn-mineralisation, magnetite-depleted alteration haloes.

Item Type: Thesis - Coursework Master
Authors/Creators:Marsh, Scott
Keywords: Geomagnetism, Hydrothermal alteration, Gold ores
Copyright Holders: The Author
Copyright Information:

Copyright 1996 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

2 col. folded maps in pocket at back of vol. Library has additional copy on microfiche. Thesis (M.Econ.Geol.)--University of Tasmania, 1997. Includes bibliographical references

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