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Orlovo, Orlovsky |
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Kazakhstan |
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Cu Zn Pb
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Super Porphyry Cu and Au
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Orlovo or Orlovsky, is in the Rudnay-Altai District of eastern Kazakhstan, ~165 km NW of Ridder, 90 km NE of Semey [Semipalatinsk], and within 5 km SW of the border with Russia (#Location:50° 55' 55"N, 81° 21' 51"E).
It lies within a Carboniferous to Devonian volcanic arc, and was discovered in 1959. It is a pyritic, stratabound, volcano-sedimentary, copper-zinc deposit, with associated gold, hosted by middle Devonian rocks (Smirnov, 1977). The deposit is composed of two separate orebodies, the Osnovnyi [Main], and the Novyi [New] (Mukoseev, 1989). Mining commenced in 1977.
In 1990, annual production amounted to 0.88 Mt @ 3.44% Cu, 2.1% Zn, 0.51% Pb.
The host sequence comprises, from the structural base:
Middle Devonian
Berezovo Group - a 500 m thick middle Devonian succession of cherty clay-siltstones with bands of 'quartz-albitophyre', tuffaceous sandstone, tuffites and sandstones; overlain by the,
Talovo Group, comprising mainly 'quartz-albitophyre', their lava-breccia, tuffs and tuffites, and lesser sediments. The orebodies are restricted to the contact between the two groups (Smirnov, 1977). According to Mukoseev (1989) the orebodies are confined to the contact between an underlying Eifelian basalt-rhyolite volcanic unit and the overlying Givetian rhyolite of the basalt-rhyolite complex. Both are middle Devonian. The former is mainly represented by sedimentary deposits of the Losishinskii Formation (presumably of the Berezovo Group), while the latter is composed of volcanogenic rocks of the Talovskii Formation. The ores are also structurally controlled, corresponding to the location of the overlying Givetian centre of volcanism (Mukoseev, 1989).
Upper Devonian, composed of three groups, as follows,
Lower - siltstone, limestone, conglomerate and acid to intermediate volcanics;
Middle - quartz-feldspar sandstone; and
Upper - tuffs and tuffites of mixed composition, porphyrites and tuffaceous sandstone.
Unconformity
Middle Carboniferous - conglomerate, sandstone and carbonaceous-clay siltstone.
Berezovo Thrust
Lower Palaeozoic - metamorphic schists has been thrust over the upper Devonian rocks from the west, above sections of the orebody (Smirnov, 1977).
The sequence is cut by four sets of intrusives, namely i). middle Devonian sub-volcanic quartz-albite porphyry stocks and dykes; ii). early Carboniferous pre-batholithic quartz-albite porphyries; iii). post middle Carboniferous batholithic gabbro, granodiorite, plagiogranite and granite bodies; and iv). small later intrusives of diorite, dolerite and micro-granodiorite porphyry, occurring as dykes and sills (Smirnov, 1977).
The Orlovo ore deposits are confined to the south-western limb of a horst-anticline, occurring between the steep Eastern Fault zone to the east and the shallow, west dipping Berezovo thrust to the west. The orebodies occur at the contact between the Berezovo and Talovo Groups. This contact is complex, with local downwarping, domes, flexures and tectonic breakup. Within the Orlovo ore field there are two groups of ore lenses. These are the 'Main' which includes three orebodies, the 'First', 'Second' and 'Third', and the 'New' which comprises two major orebodies (Smirnov, 1977).
IMC Group Consulting Ltd, 2011, in a Competent Persons Report to Kazakhmys Plc, report that the 'Main' orebody comprises an upper and lower part, with an irregular pod-shape, dipping at 20 to 30°SW, and an average thickness of 35 m, extending down dip for 600 m. An oxidised, refractory, 0.85 Mt cap is exposed at surface. Soe 350 m to the SW of the lower part of the Main orebody, is the 'New' orebody, which comprises a southern, up to 56 m thick portion, dipping at 10 to 15°SW, and a 5 to 20 m thick northern portion of very high grade ore. The combined New orebody has a strike length of ~250 m, an persists to a depth of ~150 m.
The orebodies are conformable and lensoid in shape, with strike and dip dimensions of hundreds of metres, and thicknesses of tens of metres. Each is surrounded by an alteration halo that is 1.5 to 2 times the dimensions of the ore. Alteration zoning, includes an upward progression from silicification, to quartz-sericite, quartz-chlorite, chlorite, carbonate and biotite (Smirnov, 1977).
At the base of the deposit there are massive ores, comprising 60 to 65% of the total orebody. Veinlet-segregated ores are usually developed in hydrothermally altered rocks and are mainly confined to the footwall of the orebodies, occurring as veinlet-phenocryst chalcopyrite-pyrite within a zone of intense silicification, passing upwards into more massive-uniform chalcopyrite with subordinate pyrite, accompanied by strong chlorite alteration. The 'uniform ores' exhibit massive, banded, streaky, brecciated and colloform fabrics. The principal sulphide minerals are pyrite, which may constitute 10 to 90% of the ore, chalcopyrite, sphalerite and galena, with minor fahlore/tennantite, sooty iron-disulphide, magnetite and arsenopyrite. There is a tendency for a vertical mineral zonation from barite-pyrite, with subordinate sphalerite-chalcopyrite and galena mineralisation in the hangingwall, to barite-polymetallic ores, to polymetallic ores, to chalcopyrite at the base. The main gangue minerals are barite, quartz, fluorite and albite. In the massive and semi-massive sulphides the ratio of Pb:Zn:Cu is 1:4.1:4.8 (Smirnov, 1977; Mukoseev, 1989).
Mineral resources remaining as at 1 January, 2011 were (IMC Group Consulting Ltd, 2011. Competent Persons Report to Kazakhmys Plc):
Measured resource - 17.817 Mt @ 4.12% Cu, 3.67% Zn, 0.89 g/t Au, 40.76 g/t Ag, 1.26% Pb;
Indicated resource - 3.763 Mt @ 3.68% Cu, 3.94% Zn, 0.81 g/t Au, 36.22 g/t Ag, 0.94% Pb;
TOTAL resource - 21.580 Mt @ 4.05% Cu, 3.45% Zn, 0.84 g/t Au, 38.31 g/t Ag, 1.18% Pb;
Ore reserves (same date and source - included in resource)
TOTAL proved + probable reserve - 18.007 Mt @ 3.88% Cu, 3.45% Zn, 0.84 g/t Au, 38.31 g/t Ag, 1.18% Pb.
The most recent source geological information used to prepare this decription was dated: 2011.
Record last updated: 15/5/2013
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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