Phu Bia - Phu Kham, Long Chieng Track, Ban Houayxai


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The Phu Bia gold project comprises three gold deposits, the Phu Kham Gold Cap, Long Chieng Track and Ban Houayxai, and the larger Phu Kham Copper-Gold porphyry style deposit, all of which are located approximately 150 km north of Vientiane in the Xaisomboun Special Zone of Laos.

The geology in Laos is dominated by two volcano-sedimentary belts, the Louang Prabang and the Truongson Belts which converge in the Phu Bia district in north-central Laos. The two belts host all of the known gold and base metal deposits within Thailand and Laos. The Louang Prabang Belt contains the Chatree gold, Mae Sot zinc and Puthep copper deposits, while the Troungson Belt contains the Sepon gold and copper-gold deposits. All of these deposits are interpreted to be directly related to the emplacement of acid to intermediate intrusions into the Palaeozoic host rocks.

The Phu Bia gold project comprises three deposits, with oxide resources in all three and lesser primary ore in two. The known mineralisation is hosted by Palaeozoic sediments, tuffs and volcaniclastics, which are intruded by Permo-Triassic porphyry bodies believed to be the source of the gold mineralisation. The oxide zone of each of the deposits typically starts close to the surface and persists to depths of 20 to 60 m. The deposits are:

The Phu Kham Gold Cap deposit is the leached 'oxide cap' of the Phu Kham copper-gold deposit, in the outer zone of a porphyry-style hydrothermal copper-gold system, from which virtually all of the copper has been leached. The underlying hypogene copper-gold deposit comprises skarn and stockwork style mineralisation. The oxide gold cap predomiantly occurs as gossans formed after various types of skarn. Minor stockwork-disseminated style mineralisation occurs in the host rocks enclosing the gossans.

The Long Chieng Track stockwork vein style deposit appears to represent the high level expression of a conventional porphyry copper-gold system and includes both oxide and primary resources. The oxide zone ranges from 50 to 60 m in thickness, with the primary zone persisting to depth of at least 100 m, with a minimal supergene enrichment zone.

The Ban Houayxai deposit is a combination of stockwork vein and disseminated mineralisation interpreted to represent the distal expression of a porphyry copper-gold system. Gold predominantly occurs within the veins, although significant amounts are disseminated in the altered host rock. The ore zone comprises a 40 to 50 m thick oxide layer, overlying supergene enriched and primary mineralisation that persists to depths fo 50 to 100 m or more.

In addition, resources and reserves have also been outlined in the Phu Kham supergene enrichment and hypogene porphyry style mineralisation below the Phu Kham Gold Cap. The hyogene mineralisation comprises two styles, as follows:

i). Stock-work-disseminated sulphides - which comprises predominantly bornite and covellite with a relatively low associated content of chalcopyrite and averages around 0.5% Cu.
ii). Banded massive sulphides - which occurs as planar zones within the mineralised mass and is predominantly chalcopyrite rich, containing in excess of 1% Cu.

Published resource and reserve figures in 2005 at a 0.5 g/t Au cut-off include:

Measured + indicated + inferred oxide gold resources,
    Phu Kham Gold Cap - 7.82 Mt @ 1.0 g/t Au
    Long Chieng Track - 1.35 Mt @ 0.9 g/t Au
    Ban Houayxai - 3.60 Mt @ 1.1 g/t Au
    Total - 12.80 Mt @ 1.0 g/t Au
Measured + indicated + inferred supergene/hypogene sulphide copper-gold resources,
    Phu Kham Copper-Gold - 277 Mt @ 0.51% Cu, 0.21 g/t Au (at a 0.2% Cu cut-off)
    Phu Kham Copper-Gold - 131 Mt @ 0.75% Cu, 0.28 g/t Au (at a 0.4% Cu cut-off)
Measured + indicated + inferred hypogene gold resources,
    Long Chieng Track - 2.31 Mt @ 0.9 g/t Au
    Ban Houayxai - 2.34 Mt @ 1.2 g/t Au
    Total resources - 4.65 Mt @ 1.1 g/t Au
The resources includes the following proved + probable reserves
    Phu Kham porphyry Copper-Gold supergene/hypogene sulphide copper-gold reserves - 144 Mt @ 0.56% Cu, 0.25 g/t Au
    Phu Kham Gold Cap oxide gold reserves - 6.60 Mt @ 1.0 g/t Au
    Long Chieng Track oxide gold reserves - 0.62 Mt @ 1.0 g/t Au
    Ban Houayxai oxide gold reserves - 1.33 Mt @ 1.3 g/t Au
    Total oxide gold reserves - 8.55 Mt @ 1.1 g/t Au

Published mineral resource and ore reserve figures at 31 December, 2012 (PanAust Limited, 2013) were:

  Ban Houayxai Gold Deposit - Measured + indicated + inferred resources for,
      Oxide (0.25 g/t Au cut-off) - 12 Mt @ 0.66 g/t Au, 3.2 g/t Ag;
      Transitional (0.35 g/t Au cut-off) - 16 Mt @ 0.93 g/t Au, 9.5 g/t Ag;
      Primary (0.4 g/t Au cut-off) - 37 Mt @ 1.01 g/t Au, 7.4 g/t Ag;
      TOTAL - 65 Mt @ 0.93 g/t Au, 7.2 g/t Ag;

  Phu Kham Porphyry Deposit - Measured + indicated + inferred resources for,
    TOTAL (0.25 g/t Au cut-off) - 227 Mt @ 0.48% Cu, 0.22 g/t Au, 2.0 g/t Ag.

The most recent source geological information used to prepare this summary was dated: 2006.    
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:
Soysouvanha, V., Ariffin, K.S. and Wantanabe, K.,  2015 - Ore Mineralogy and Geochemistry of the Phu Kham Porphyry Copper-Gold Deposit, Hosted within NE Fault Zone, Lao PDR: in    Procedia Chemistry   v.19, pp. 961-968

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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