Queensland, Qld, Australia

Main commodities: Au
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The Kidston open pit gold mine was situated some 280 km WNW of Townsville in northern Queensland, Australia.

The deposit occurred as a trapezoid-shaped breccia pipe with surface dimensions of 1100 x 900 m which is located on the northern edge of a NW trending Permo-Carboniferous rhyolite dyke swarm which connects the Lochaber ring complex to the south and the Newcastle Range volcanic complex to the north, and overlies a Permo-Carboniferous batholith at depth.   Several generations of rhyolite dyke are recognised.   The earliest is cut by the breccia pipe, while another is synchronous and yet another post dates the brecciation.   It appears that the orebody was formed at a depth of 3500 m below surface and that the breccia pipe did not reach the surface.

The breccia pipe is hosted by the Palaeo- to Mesoproterozoic Einasleigh Metamorphics and the Siluro-Devonian Oak River Granodiorite.   The former are represented by multiply deformed upper amphibolite facies biotite gneiss, migmatite and amphibolite with subordinate biotite schist and quartzite.   The Oak River Granodiorite occupies the SW portion of the pipe.

The breccia pipe extends to depths of more than 300 m and has generally inward (but locally outward) sloping margins dipping at more than 80° and usually has a sharp contact with the adjacent un-brecciated country rock.  

Brecciation and mineralisation took place in three phases, all associated with magmatic and hydrothermal processes.   The multistage breccia has a number of different clast styles and morphologies, from an early series of dyke like breccia zones with tubular clasts of rhyolite, through the main breccia phase with 1 to 20 cm (to 100 m) angular to sub-angular clasts (which have not been transported far and reflect the original stratigraphy), set in a matrix of fine chip sized clasts and smaller fragments, to the final stage where the clasts are mainly of the igneous rocks containing veining not found in stage 2 clasts.

Pre-breccia mineralisation occurs as stockwork quartz veins (commonly with molybdenite, pyrite±arsenopyrite±chalcopyrite) within rhyolitic breccia clasts, while in the multi-stage post breccia ore occurs as veins cutting the breccia and infilling breccia cavities.   The economic grade mineralistion is of post breccia age and is confined to an inverted funnel shaped zone of quartz-carbonate-sulphide veining and cavities referred to as the sheeted vein zone.   This funnel shaped zone has a barren core, with the orebody having an annular shape, near the breccia pipe margin on any level, with the diameter decreasing downwards.

Production to 1990 totalled 23.7 Mt @ 2.08 g/t Au, with an estimated remaining mineral resource of 42.6 Mt @ 1.43 g/t Au, 1.85 g/t Ag and a further inferred resource of 11.7 Mt at similar grades.

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.

  References & Additional Information
   Selected References:
Baker E M, Andrew A S  1991 - Geologic, fluid inclusion, and stable isotope studies of the Gold-bearing breccia pipe at Kidston, Queensland, Australia: in    Econ. Geol.   v86 pp 810-830
Baker E M, Tullemans F J  1990 - Kidston 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 1461-1465

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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