Horseshoe, Labouchere, Fortnum - Glengarry Sub-basin

Western Australia, WA, Australia

Main commodities: Au Cu Ag
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The Horseshoe (previously Horseshoe Lights) gold-copper-silver deposit is located 34 km north of Peak Hill and 150 km north of Meekatharra and is hosted within the Palaeoproterozoic Glengarry Basin sub-basin of the larger Nabberu Basin to the north of the Yilgarn Craton in Western Australia.

The deposit is hosted at the top of the Narracoota Volcanics (tholeiitic basalt grading up into Mg basalts), below the Thaduna Greywacke (a lower, 100 m thick greywacke with subordinate mudstone and an upper, thicker coarse sandstone, grit and conglomerate unit.   Both are members of the Glengarry Group, just to the south of the overlying Mesoproterozoic (1100 Ma) Bangemall Group.   At the top of the Narracoota Volcanics there are weakly metamorphosed volcaniclastics represented by quartz-chlorite schist, quartz-eye tuffs and altered volcanics, capped by a prominent 1 to 2 m thick, poorly bedded chert (BIF) with magnetite, specular hematite and pyrite which often contains significant gold associated with the pyrite.

The immediate host is a suite of green, fine grained quartz-chlorite schist, quartz-sericite, quartz-kaolin schist and quartz-eye schist, with scattered 1 to 10 cm thick chert bands.   The main orebody at Horseshoe is a series of lenses and pods (fragmented by shearing) of quartz-hematite-goethite gossan with an average width of 20 m, with lengths of 50 to 200 m and vertical extent of 50 m.   The gossan contains high gold, although below 100 m chalcocite (with digenite and covellite) mineralisation is developed above primary siliceous massive pyrite with lesser chalcopyrite.   To the east and west veins and blebs of chalcopyrite-pyrite are found in the footwall and hangingwall.   The overall dimensions of the primary + secondary ore zone is 300 m in strike by 300 m vertically and up to 50 m wide.

Production from the start of mining in 1984 to the end of 1987 was 1.513 Mt @ 4.2 g/t Au for 6.348 t of recovered Au from open cut operations.
  Reserves in March 1988 were:   2.7 Mt @ 2.8 g/t Au, 3.4% Cu, 27 g/t Ag.

The smaller Labouchere and Deep South gold deposits are also in the Glengarry Sub-basin and are in the Peak Hill goldfield with combined proven+probable reserves of 1.7 Mt @ 3.4 g/t Au.   These deposits are hosted by the Labouchere Formation which occurs in the hangingwall of the Horseshoe banded iron formation and the Narracoota Volcanics.   Labouchere is developed on two stratabound pyritic chert bands representing the same unit on two limbs of a fold.   The main lode is 200 m long, has a maximum width of 35 m and dips at 75° E.   The gold bearing pyrite is oxidised to a depth of 100 m.   The East lode is narrower and is sporadically mineralised adjacent to a shear zone.   Deep South is associated with silicified shales with abundant fine to course euhedral pyrite as laminae.

The Fortnum gold deposit is located within the Glengarry Sub-basin, 25 km to the west of Horseshoe.   Mineralisation is associated with a pyritic quartz-hematite jasperoid within the upper parts of the Narracoota Volcanics, which are locally overlain by a volcaniclastic sequence and the Thaduna Greywacke.   Two large structural breaks, the D34 Shear and Fortnum Fault cut the sequence in the mine area.   The former shear, which is up to 100 m wide, contains the bulk of the economic gold, in four styles, namely:  1). In sheeted quartz-pyrite-magnetite-hematite vein sets and replacements of mafic volcanics producing jasperoid bodies,  2). In quartz veins and sulphidic replacement bodies along bedding planes in sediments,  3). In quartz veins and intense sericite alteration in schists in the shear zone and  4). In the laterite profile.   Fortnum produced 6 Mt @ 3 g/t Au for 17.45 t of recovered gold between 1994 and 1999.

For detail consult 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.

  References & Additional Information
   Selected References:
Hanna J P, Ivey M E  1990 - Labouchere and Deep South gold deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 667-670
Hill A D, Cranney P J  1990 - Fortnum gold deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 665-666
Parker T W H, Brown T  1990 - Horseshoe Gold-Copper-Silver deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 671-675

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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