Mt Leyshon

Queensland, Qld, Australia

Main commodities: Au
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The Mt Leyshon gold deposit, is located 24 km south of Charters Towers in northeast Queensland, Australia (#Location: 20°17'31"S, 146°16'15"E)

The deposit is hosted by the Permian Mt Leyshon Intrusive and Breccia Complex (a subvolcanic porphyry-breccia complex) which occurs within an ~100 km-long northeast-trending corridor of sub-volcanic Permo-Carboniferous rock scharacterized by anomalous magmatism, veining, and brecciation, which on the basis of coincident aeromagnetic anomalies has been proposed as a zone of magnetite-destructive alteration. It is formed at the contact of a Cambro-Ordovician volcano-sedimentary sequence with the Ordovician to Devonian Ravenswood Granodiorite Complex batholith.

The basement to the Mount Leyshon intrusive complex comprises four major units:  (i) The Cambrian Puddler Creek Formation to the south dominated by hornfelsed siltstones, intruded to the north by the  (ii) Ordovician Fenian Granite, a medium-grained to aplitic granite; both units are crosscut by  (iii) dykes and stocks of rhyolitic Basement Porphyry and  (iv) a later set of northnortheast-trending dolerite dykes. All of these basement lithologies are found as breccia clasts within the Mount Leyshon intrusive complex.

The Mount Leyshon intrusive complex is roughly circular (although NE elongated), with a diameter of 1.6 km, and contains a diverse sequence of early breccias and tuffs related to a suite of rhyolitic to andesitic porphyries. Multiple phases of porphyry intrusion have been identified, namely the:  (i) Main Pipe Breccia;  (ii) Southern Porphyry, a rhyolite to dacite stock;  (iii) early porphyry dykes and associated small porphyry bodies;  (iv) the rhyolitic Wallaby Tail Porphyry which is coeval with the Southern Porphyry;  (v) Mine Porphyry and Mount Hope Breccia;  (iv) Mount Leyshon Breccia (possibly coeval with (iii));  (v) tuffisite breccia dykes;  (vi) late dykes and associated breccias.

The principal host to ore is a ~400 x 300 m diameter breccia pipe with a minimum vertical extent of 650 m, localised in the NW of the diatreme/Main Pipe Breccia which is otherwise generally barren.

The host breccia is polymict and matrix supported, with sub-rounded to angular clasts varying from large blocks >1 m in diameter, through predominantly cobble sized fragments to abundant pebble sized clasts.   The clasts are set in a grey-green to black-green matrix that constitutes 30% of the rock.

Gold mineralisation is predominantly within the breccia, but also occurs in adjacent wall rocks.   In general it is spatially associated with small scale fracture patterns, fracture density and other permeability controls, typically occurring as cavity fill and matrix replacement in the breccias, or disseminated in the porphyries with less common high grade veining.

The mineralogy comprises sulphides (pyrite, chalcopyrite, galena and sphalerite) with free gold and electrum, predominantly in the 1 to 600 µm range. The principal gangue comprises chlorite, carbonate, micas and quartz.

In 1995 the total resource was 48.3 Mt @ 1.27 g/t Au.  In the same year production totalled 6.77 t Au from 5.34 Mt of milled ore averaging 1.44 g/t Au and 0.49 t Au from heap leaching, as well as 7.5 t Ag.

The mine produced ~100 t of gold from 70 Mt of ore averaging ~1.4g/t Au between 1986 and 2000 (Allan et al., 2011)

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:
Allan, M.W., Morrison, G.W. and Yardley, B.W.D.,  2011 - Physicochemical evolution of a porphyry-breccia system: a laser ablation ICP-MS study of fluid inclusions in the Mount Leyshon Au deposit, Queensland, Australia: in    Econ. Geol.   v.106 pp. 413-436
Anonymous  1998 - Normandy Mining Limited: in   Extracts from the Normandy Mining Limited 1997 Annual Report    pp 12-15, 26-28
Anonymous  1998 - Mt Leyshon: in    Register of Australian Mining 1997/98    p 192
Anonymous  1998 - Normandy Mining Limited: in   Extracts from the Normandy Mining Limited 1997 Annual Report    pp 12-14, 17, 26-28.
Orr T H  1994 - The Mount Leyshon Gold Mine: geology and mineralisation: in Henderson R C, Davis B K (Eds),  New Developments in Geology and Metallogeny: Northern Tasman Orogenic Zone, Townsville, 21-22 Feb, 1994, James Cook University of North Queensland, Townsville, Australia,   EGRU Contribution 50, pp. 29-35
Orr, T.H. and Orr, L.A.,  2004 - Mt Leyshon gold deposit, Charters Towers, Queensland: in   CRC LEME 2004 www.crcleme.org.au/RegExpOre/Pajingo.pdf    pp. 1-4
Paull P L, Hodkinson I P, Morrison G W, Teale G S  1990 - Mount Leyshon Gold deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v2 pp 1471-1481
Teale G S and Lynch J E  2004 - The discovery and early history of the Mt Leyshon gold deposit, North Queensland: in   Hi Tech and World Competitive Mineral Success Stories Around the Pacific Rim, Proc. Pacrim 2004 Conference, Adelaide, 19-22 September, 2004, AusIMM, Melbourne,    pp 385-389
Wormald P J, Orr T O H and Hodkinson I P  1993 - The Mount Leyshon Gold Mine (NE Queensland), an intrusive breccia and igneous complex: in   Field Excursion Guidebook, Charters Towers, 12-14 June, 1993 Geol. Soc. Aust., Qld Div.    pp 61-74

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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