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Lady Loretta
Queensland, Qld, Australia
Main commodities: Zn Pb Ag

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The Lady Loretta stratabound zinc-lead-silver deposit is located ~120 km NNW of Mount Isa in the Mt Isa Inlier of Northwest, Queensland, Australia (#Location: 19° 46'S, 139° 03'E)

The Lady Loretta deposit lies within the regionally north-trending Proterozoic Paradise Graben which was developed in the Lawn Hill Platform, and is ~30 km west of the Mount Gordon Arch. Within this graben there are a number of folded and faulted anticlines and synclines. The structure in the Lady Loretta area comprises two NE-trending synclines, the 'Big Syncline' to the SW, and the smaller, 1300 m long 'Small Syncline' to the NE, separated by an anticline and the 'Syncline Dividing Fault'.

Lady Loretta is a stratabound massive to semimassive sulphide deposit located in the keel of the 'Small Syncline'. It is hosted by the late Palaeoroterozoic Lady Loretta Formation, part of the McNamara Group, which is equivalent in age to the 1670 Ma Mt Isa Group, but older than the Lawn Hill Formation that hosts the Century orebody. The Lady Loretta Formation is composed of siltstone, carbonaceous and pyritic shale, carbonate, sandstone and minor tuff.

The bulk of the mineralisation occurs over a strike length of 300 m and is best developed in the keel of the syncline, where it attains a thickness of up to 50 m. The ore lens is composed of finely banded sphalerite, pyrite and galena, while distinctive barite-chert-sphalerite lenses are found as two wings to the massive sulphide (75% sulphide) ore zone. The ore zone is progressively underlain by a more regionally extensive 15 to 40 m thick massive to banded pyrite-black shale unit and then by sideritic sediments.

Published reserve and resource figures include:
  Resource, 1990 - 8.3 Mt @ 18.4% Zn, 8.5% Pb, 125g/t Ag, (12% Zneq, cutoff, Hancock & Purvis, 1990);

JORC compliant Mineral Resources and Ore Reserves as at 31 December 2011 (Glencore Annual Report, 2012) were:
  Measured + indicated resource - 13.3 Mt @ 16.4% Zn, 5.7% Pb, 93 g/t Ag;
  Inferred resource - 2 Mt @ 14% Zn, 6% Pb, 92 g/t Ag
    Proved + Probable Ore Reserves - 12.7 Mt @ 14.2% Zn, 4.8% Pb, 84 g/t Ag.

JORC compliant mineral resources as at 31 December 2016 (Glencore Annual Report, 2017) were:
    Measured resources - 5.28 Mt @ 16.3% Zn, 6.4% Pb, 104 g/t Ag;
    Indicated resources - 3.9 Mt @ 14% Zn, 4.6% Pb, 86 g/t Ag.
    Measured + indicated resources - 9.2 Mt @ 15% Zn, 5.6% Pb, 96 g/t Ag;
    Inferred resources - 0.3 Mt @ 11% Zn, 5% Pb, 90 g/t Ag.
    Proved + probable reserves - 8.5 Mt @ 13% Zn, 5.1% Pb, 87 g/t Ag.

The most recent source geological information used to prepare this decription was dated: 1996.    
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:
Betts P G, Giles D, Lister G S  2003 - Tectonic environment of shale-hosted massive sulfide Pb-Zn-Ag deposits of Proterozoic northeastern Australia: in    Econ. Geol.   v98 pp 557-576
Betts, P.G., Giles, D., Mark, G., Lister, G.S., Goleby, B.R. and Ailleres, L.,  2006 - Synthesis of the Proterozoic evolution of the Mt Isa Inlier: in    Australian J. of Earth Sciences   v.53, pp. 187-211.
Duffett M L  1998 - Gravity, magnetic and radiometric evidence for the geological setting of the Lady Loretta Pb-Zn-Ag deposit - a qualitative appraisal: in    Econ. Geol.   v93 pp 1295-1306
Gibson, G.M., Hutton, L.J. and Holzschuh, J.,  2017 - Basin inversion and supercontinent assembly as drivers of sediment-hosted Pb-Zn mineralization in the Mount Isa region, northern Australia: in    Journal of the Geological Society   v.174, pp. 773-786.
Hancock M C, Purvis A H  1990 - Lady Loretta Silver-Lead-Zinc deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 943-948
Loudon A G, Lee M K, Dowling J F, Bourn R  1975 - Lady Loretta silver-lead-zinc deposit: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 5 pp 377-382
Polito, P.A., Kyser, T.K., Southgate, P.N. and Jackson, M.J.,  2006 - Sandstone Diagenesis in the Mount Isa Basin: An Isotopic and Fluid Inclusion Perspective in Relation to District-Wide Zn, Pb, and Cu Mineralization: in    Econ. Geol.   v.101, pp. 1159-1188.

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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