Mt Lyell

Tasmania, Tas, Australia

Main commodities: Cu Au Ag
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The Mt Lyell copper deposits are located adjacent to the town of Queenstown, 25 km east of the west coast of Tasmania, Australia, ~175 km NW of Hobart and ~120 km south of Burnie.
(#Location: 42° 3' 51"S, 145° 35' 2"E).

The deposits are hosted by the Central Volcanic Complex of the 250 km long, middle to late Cambrian Mt Read Volcanic Arc on the west coast of Tasmania, Australia. To the south-east of the Henty Fault this complex is composed of rhyolitic to dacitic acid lavas and pyroclastics with some andesites and minor shale and is the host to mineralisation. The Central Volcanic Complex is unconformably overlain by the keratophyric tuffs, massive agglomerates, conglomerates, sandstones, shales and limestones of the Tyndall Group. The predominantly volcanic sequence is unconformably overlain by a thick Ordovician succession progressing from red conglomerate, to red sandstone and finally to a widespread limestone. The volcanic sequence is unconformably overlain by a thick Ordovician succession progressing from red conglomerate, to red sandstone and finally to a widespread limestone.

In the mine area the sequence is composed of (from the base):
• 800 m of plagioclase-amphibole porphyritic lavas with minor siltstone and pyroclastics,
• 0 to 200 m of feldspar porphyritic silicic lavas,
• 0 to 600 m of mainly coarse grained silicic pyroclastics,
• 250 to 800m of predominantly pyroclastics, lavas, volcanic breccias, minor intermediate tuff and intrusives,
• 0 to 800 m of mainly silicic pyroclastics,
• 0 to 350 m of dacitic to intermediate pyroclastics and lavas.

The last unit is the main host mine sequence. Some 10 km strike length of this sequence has undergone pervasive feldspar destructive alteration to quartz-sericite, sericite-quartz-chlorite-carbonate and albite-sericite-chlorite schists.

Mineralisation is present in three main transgressive hydrothermal replacement forms, namely:
• Disseminated pyrite-chalcopyrite - representing the bulk of the ore and including the Prince Lyell, Royal Tharsis, A Lens, Razorback, Crown Lyell, I & III, Western Tharsis and Cape Horn. The ore generally contains 10 to 20% total sulphide with grades of 1.5 to 2% Cu, 0.4 g/t Au, 3 g/t Ag. Massive sulphide lenses 15 to 20 cm thick persist for tens to hundreds of metres in the disseminated ores.
• Massive pyrite-chalcopyrite - represented by the Mt Lyell (The Blow) and South Lyell deposits. The first 1.5 Mt at Mt Lyell assayed 2.85% Cu, 2.8 g/t Au, 80 g/t Ag. In general however, this style averages 0.4% Cu, 0.3 to 0.4 g/t Au, 30 to 100 g/t Ag over a 200 m vertical interval as massive silicified pyritic lenses with 80% sulphide.
• Chalcopyrite-bornite - occurring as coarse grained masses of bornite in bodies of pyritic cherty quartz below steeply dipping, faulted chert-conglomerate contacts. These were the richest orebodies on the field with 5 to 7% Cu, 0.3 to 0.4 g/t Au and 30 t0 40 g/t Ag. Deposits included North Lyell, Crown Lyell II, Lyell Tharsis, Lyell Comstock and Twelve West.
• Banded pyrite-sphalerite-galena - found as small concordant lenses of massive sulphide on the northern end of the field,
• Native copper-cuprite - as clays within argillaceous sediments at the Orovician unconformity.

Production and reseve figure were quoted as follows in 1990:
  Production - 102.68 Mt @ 1.18% Cu, 7 g/t Ag, 0.4 g/t Au.   Resources - 18 Mt @ 1.91 % Cu, 2.72 g/t Ag, 0.62 g/t Au.

Alternatively, the total ore system is quoted as having contained:   312 Mt @ 1% Cu, 0.3 g/t Au (Large, et al., 2001). For more detail see the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1990.    
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 Lyell

  References & Additional Information
   Selected References:
Corbett K D  1981 - Stratigraphy and mineralization in the Mt Read volcanics, western Tasmania: in    Econ. Geol.   v76 pp 209-230
Corbett K D  2001 - New mapping and interpretations of the Mount Lyell Mining District, Tasmania: a large hybrid Cu-Au system with an exhalative Pb-Zn top: in    Econ. Geol.   v96 pp 1089-1122
Corbett K D  1992 - Stratigraphic-volcanic setting of massive sulphide deposits in the Cambrian Mount Read Volcanics, Tasmania: in    Econ. Geol.   v87 pp 564-586
Cox S F  1981 - The stratigraphic and structural setting of the Mt Lyell volcanic-hosted sulfide deposits: in    Econ. Geol.   v76 pp 231-245
Eastoe C J, Solomon M, Walshe J L  1987 - District-scale alteration associated with massive Sulfide deposits in the Mount Read Volcanics, western Tasmania: in    Econ. Geol.   v82 pp 1239-1258
Hills P B  1990 - Mount Lyell Copper-Gold-Silver Deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v2 pp 1257-1266
Huston D L, Kamprad J  2001 - Zonation of alteration facies at western Tharsis: implications for the genesis of Cu-Au deposits, Mount Lyell field, western Tasmania: in    Econ. Geol.   v96 pp 1123-1132
Large R R  1992 - Australian volcanic-hosted massive sulfide deposits: features, styles, and genetic models: in    Econ. Geol.   v87 pp 471-510
Large R R, McPhie J, Gemmell J B, Herrmann W, Davidson G J  2001 - The spectrum of ore deposit types, volcanic environments, alteration halos, and related exploration vectors in submarine volcanic successions: some examples in Australia: in    Econ. Geol.   v96 pp 913-938
Large R, Doyle M, Raymond O, Cooke D, Jones A and Heasman L,  1996 - Evaluation of the role of Cambrian granites in the genesis of world class VHMS deposits in Tasmania : in    Ore Geology Reviews   v10 pp 215-230
Raymond R L,  1996 - Pyrite composition and ore genesis in the Prince Lyell copper deposit, Mt Lyell mineral field, western Tasmania, Australia: in    Ore Geology Reviews   v10 pp 231-250
Reid K O  1975 - Mount Lyell copper deposits: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 5 pp 604-619
Solomon M  1981 - An introduction to the geology and metallic ore deposits of Tasmania: in    Econ. Geol.   v76 pp 194-208
Solomon M, Eastoe C J, Walshe J L, Green G R  1988 - Mineral deposits and Sulfur isotope abundances in the Mount Read volcanics between Que River and Mount Darwin, Tasmania: in    Econ. Geol.   v83 pp 1307-1328
Solomon M, Vokes F M and Walshe J L,  1987 - Chemical remobilization of volcanic-hosted sulphide deposits at Rosebery and Mt. Lyell, Tasmania: in    Ore Geology Reviews   v2 pp 173-190
Walshe J L, Solomon M  1981 - An investigation into the environment of formation of the volcanic-hosted Mt Lyell copper deposits using geology, mineralogy, stable isotopes and a six-component chlorite solid solution model: in    Econ. Geol.   v76 pp 246-284

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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