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Achisay, Turlan |
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Kazakhstan |
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Zn Pb
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Achisay, or Turlan, deposit is hosted by Devono-Carboniferous limestones and dolomites within a belt of Proterozoic and Palaeozoic sediments developed along the major, north-west trending Talasso-Fergana fault zone.
The deposits have been known since at least the nineteenth century. Early mining from 1867 to 1915 and 1926 to 1964 removed galena, with oxidised zinc ore being subsequently mined. A systematic geological appraisal was carried out in 1926, prior to the commencement of the modern period of exploitation.
Annual mine production in 1990 amounted to approximately 2.03 Mt @ 4.47% Zn, 0.87% Pb. According to the USGS (pubs.usgs.gov/of/2009/1252/SedZn-PbEX2009.xls) the deposit contained 50 Mt @ 5% Zn, 1% Pb, 5 g/t Ag, 0.4 g/t Au.
The host Devono-Carboniferous sequence comprises:
1) Middle to Late Devonian Tyul'kubash Group, which is predominantly red arkosic sandstone with conglomerate lenses; this is followed by a mild unconformity, and
2) Late Devonian limestones and marls. The top of this unit is marked by a probable tectonic breccia and then the Carboniferous which commences with:
3) basal thin bedded, light grey limestone that has been tectonically brecciated at the contact with the late Devonian; overlain by the
4) Iskristyi unit of thin bedded and platy black dolomite;
5) Turlan horizon containing limestone, often dolomitised, with seams of argillised, finely laminated and in places brecciated dolomite; followed by the
6) Rudnichnyi horizon which is composed of fine grained, interstratified, dark grey limestone and dolomite; capped by the
7) Bel'mazar horizon composed of massive and thick bedded limestone with rare dolomite seams (Smirnov, 1977).
Some 64 orebodies have been identified over a length of 2 km within the Iskristyi, Turlan, Rudnichnyi and Bel'mazar horizons. Approximately 50% of the total ore has come from the Iskristyi unit. Although no mention is made of it in the text of the source literature, the accompanying plan implies a relationship between brecciation within the host carbonates and the localisation of ore. Brecciation within the hosts is also facilitated by faulting, with zones of 20 to 250 m width recorded for one major fault, while another separating the upper Devonian and Carboniferous sediments ranges from 0.5 to 40 m (Smirnov, 1977).
The orebodies average 0.5 to 3 m in thickness, but are locally up to 30 m wide in zones of intersecting joints, and are complex and very irregular in shape. They are composed of short ribbon like veins, of impersistent thickness, which are often mutually connected by apophyses. These veins are both concordant and discordant, with sharp contacts between ore and wall rock. The primary ores are 60 to 90% pyrite with veinlets of sphalerite and galena. Other sulphides, which are only present in very small quantities, are marcasite, chalcopyrite, hematite and magnetite. The sulphide ores exhibit massive, banded, streaky, colloform and breccia like textures and structures. The ore is said to display features of an intense, post ore "dynamometamorphism", as do the country rocks (Smirnov, 1977).
Oxidation is complete to depths of 200 to 250 m, while oxide minerals have been found as deep as 400 m. Oxide lead minerals have replaced sulphide ore, while zinc oxides have been re-deposited in the footwall rocks of the ore where stratified layers of zinc ores are found. The oxide ores consist of cerussite and smithsonite, with associated hydrohematite, goethite, hydrogoethite, anglesite, plumbojarosite, calamine, hydrozincite, psilomelane and gypsum. The ratio of Pb:Zn is 1:1.5 in the sulphide ore, and 1:17 in oxidised zinc ore (Smirnov, 1977).
Approximately 500 km to the north in the Dzhezkazgan Cu district, the equivalent of the 'basal member' of the host Carboniferous sequence at Turlan contains minor Pb/Zn mineralisation. The Carboniferous carbonate sequence at Dzhezkazgan occurs immediately below the lower Permian host unit of the Cu deposits.
The most recent source geological information used to prepare this decription was dated: 1997.
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.
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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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