50 Let Oktyabrya, Koktau, Priorskoe (Priorskoye)


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The 50 Let Oktyabrya (also known as Koktau) and Priorskoe (or Priorskoye) volcanic hosted massive sulphide (VHMS) copper, pyrite, zinc deposits are located ~130 km east of Aktobe and 50 km NE of the town of Khromtau in Aktyubinsk Region, northern Kazakhstan, and ~22 km south of the Russian border (#Location: 50° 28' 52"N, 59° 6' 20"E). Priorskoe is ~10 km NW of 50 Let Oktyabrya.

The 50 Let Oktyabrya deposit was discovered in 1964, whilst mineralisation was first discovered at Priorskoe in 1967, followed by delineation exploration from 1967 to 1972.

Regional Setting

The 50 Let Oktyabrya and Priorskoe deposits lie within the regional Tagil-Magnitogorsk Megaterrane within the Uralian Orogen. This orogen comprises a 2500 km long, north-south trending mountain belt that extends from the steppes of northern Kazakhstan to the Arctic ocean, and were formed as a result of the collision of the Baltica (largely the East European craton) and Siberia-Kazakh plates during the Late Carboniferous to Early Permian period. It is composed of a series of such terranes and megaterranes, that are, from west to east, the:
i). Preuralian foredeep which includes Late Devonian to Early Carboniferous rift basin sedimentary rocks deposited during extension, prior to the onset of Uralian orogenic activity (Snyder, et al, 1994), as well as Permian pre-flysch (deep-water condensed sediments), flysch and molasse deposited during and after orogenesis (Puchkov, 2009);
ii). West Uralian Megaterrane - predominantly composed of early Palaeozoic shelf and deep-water passive margin sediments deposited to the east of the East European craton prior to orogenesis (Puchkov, 2009);
iii). Central Uralian Megaterrane - representing exhumed crystalline basement of the Urals, predominantly Meso- and Neoproterozoic (Puchkov, 2009). The West and Central Uralian megaterranes occur in a pile of tectonic slices imbricated by intense fold-and-thrust deformation during the Late Devonian to Late Permian Uralian Orogeny. This imbricated pile also includes slices of Ordovician to Lower Devonian oceanic and Ordovician to Lower Carboniferous intraoceanic island arc volcanism of the Guberlya arc formed to the east of the passive margin sequence. These combined imbricated piles constitute the Sakmara Zone, the eastern margin of which is defined by the serpentinitic mélange that is the Main Ural Fault (Puchkov, 2009; Pushkarev et al, 2006);
iii). Tagil-Magnitogorsk Megaterrane - predominantly composed of Ordovician to Lower Carboniferous complexes of oceanic crust and intraoceanic island arc rocks, overlain by platformal carbonate and rift-related volcanic rocks (Puchkov, 2009). The Tagil volcanic arc to the north comprises Late Ordovician to Early Devonian intra-oceanic volcanic sequences evolving from tholeiitic through differentiated calc-alkaline to subalkalic shoshonitic compositions during westward subduction. During the Emsian (early Devonian), the Tagil terrane accreted to the Magnitogorsk oceanic arc to the south which formed due to eastward subduction and was active from Emsian to the Famennian (Late Devonian) Plotinskaya, 2017). These arcs of the Tagil-Magnitogorsk Megaterrane were then involved in an oblique arc-continent collision with the East European plate, being progressively accreted from south to north, commencing during the Late Devonian in the south and Early Carboniferous in the north, persisting to the Late Permian (Puchkov, 2009).
iv). East Uralian Megaterrane - comprises Proterozoic gneiss and schist overlain by weakly metamorphosed Ordovician to Devonian clastic sedimentary strata and tectonically emplaced sheets of Ordovician to Lower Carboniferous oceanic and island arc complexes. It was also intruded by voluminous Late Palaeozoic granite bodies which define the Main Granitic Axis of the Urals (Puchkov et al. 1986). The East Uralian and Tagil-Magnitogorsk megaterranes are separated by East Magnitogorskian mélange zone. To the east the former is bounded by the regional Kartaly (Troitsk) Fault.
v). Transuralian Megaterrane - which contains pre-Carboniferous complexes that include blocks of Proterozoic gneisses, crystalline schists and weakly metamorphosed sediment rocks, coarse Ordovician rift facies terrigenous and volcanic rocks and oceanic deposits, Silurian island-arc complexes and Devonian deep-water rocks overlain unconformably by Lower Carboniferous suprasubductional volcanogenic strata, which form a post-accretionary overstep complex (Puchkov, 2009).

The 50 Let Oktyabrya and Priorskoe deposits are part of the world's largest belt of volcanic hosted massive sulphide deposits, containing ~2.3 Gt of ore with about 70 Mt of base metals (Zaykov et al, 1998; Prokin and Buslaev, 1999; Franklin et al, 2005; Kontar, 2013). This belt of more than 45 deposits is at least 1200 km in length and is almost entirely restricted to the Tagil-Magnitogorsk Megaterrane. The deposits of the belt include the Cu-dominated Gaya, Yubileyno-Snegirikhinskoe, 50 Let Oktyabrya and Podolskoe deposits, and the Zn-dominated Uchaly, Novo-Uchaly, Uzelga, Sibay, Aleksandrinka, Yaman-Kasy, Degtyarsk, Shaimerden and Safyanovka.

The 50 Let Oktyabrya and Priorskoe deposits are situated on the eastern limb of the regional Magnitogorsk Synclinorium within the Tagil-Magnitogorsk Megaterrane (Smirnov, 1977).

Geology and Mineralisation

The main elements of the geology of the 50 Let Oktyabrya deposit area are:

Basic volcanics of the Mugodzhary and Milyasha groups which are of Middle Palaeozoic age (Smirnov, 1977). The Mugodzhary Group volcanics, which are of middle Devonian (Eifelian) age (Zonenshain, et al., 1990), are essentially lavas, and have been ubiquitously metamorphosed to amphibolite facies anthophyllite-biotite-cordierite hornfels (Smirnov, 1977).
Granitoids of the north-south elongated, 10 x 3 km, Sredneorsk Massif, which cuts the volcanics. The contacts with the volcanic rocks are steeply dipping, and either i). complex sinuously intrusive, with north-south elongated basaltic xenoliths near the margins, or ii).  rectangular tectonic. Three lithologic types are represented, namely an early gabbro and gabbro-dolerite, little of which remains, and later, more extensive granodiorite and leucogranite phases. The bulk of the granitoid massif is found along the western margin of the volcanic belt, although a north-south trending apophysis which splits from the main batholith in the north, forms the eastern margin also (Smirnov, 1977).
Sub-volcanic bodies of rhyodacite composition cut all of these rocks. These sub-volcanic bodies have complex, irregular shapes, with various dimensions, and are arranged in the form of a chain striking over several kilometres. These bodies are generally intensely altered and are interpreted to be related to the emplacement of ore (Smirnov, 1977).
Dykes of various compositions and ages cut these rocks. The oldest correspond to the end phase of volcanic emplacement, and comprise felsite-rhyolite and quartz-rhyolite porphyries, as well as discordant dykes of dolerite porphyry and microdiorite. Dykes of aplite accompanied the introduction of the Sredneorsk Massif. The last dykes are of granite-porphyry, granodiorite-porphyry and quartz-porphyry that cut all of the earlier bodies, and the sub-volcanic bodies (Smirnov, 1977).

The structure of the area is 'block like' with north-south, north-easterly and north-westerly faulting. The oldest of these faults determines the location of the sub-volcanic bodies. The position of the Sredneorsk Massif, and the form of its contacts are attributed to the location of pre-intrusive faults. Later faults control late dykes, while the last episode displaces all of the rocks described (Smirnov, 1977).

Three main ore accumulations are recorded, namely the:

i). Northern accumulation which, like the sub-volcanic rhyodacite dyke-like body in which it is hosted, has a marked north-easterly elongated lensoid shape. The ore lens has a steep, 70 to 85° dip to the south-east, and plunges to the south-west at 70 to 75° in the north and 45 to 60° in the south. The thickness varies from 10 to 80 m, averaging 35 m. On its flanks it splits into several apophyses of massive and segregated ore, with inclusions of altered rhyodacite in the latter (Smirnov, 1977).
ii). Central accumulation, which is confined to the gently sloping roof of a stock of rhyodacite which is cut by steeply dipping faults. It comprises a 10 to 12 m thick, flat lying body, complicated by outwardly and downwardly steep dipping apophyses (Smirnov, 1977).
iii). Southern ore accumulation, located in the upper part of a sub-volcanic body of rhyodacite. The morphology of the orebody is complex. It has a flat upper margin, which is conformable with the hangingwall contact with the altered extrusives. The lower margins however, are strongly contorted, with numerous downward apophyses and bulges. The thickness of the orebody averages 50 m, but in places is as much as 120 m. On its western flank there are a series of small lens and vein like bodies dipping eastward at 75 to 80°. These ore apophyses are within the dyke like sub-volcanic rhyodacite bodies, or are in the contact them, with individual rhyodacite dykes separated by band like layers of amphibolised basalts (Smirnov, 1977).

The ore at 50 Let Oktyabrya differs from many of the other VHMS deposits of the Urals, in that it has lesser sphalerite. The principal commodities are copper and sulphur, with traces of Co and Ni, as well as Cd, Se, Te, Ag, Ga, Rh, Zn, Pb, As, Mo and Bi. The major minerals are pyrite, chalcopyrite, pyrrhotite and magnetite. Minor and rare minerals are sphalerite, arsenopyrite, galena, cubanite, linnaeite, cobaltite and molybdenite. Quartz and anthophyllite are present in significant amounts as gangue minerals, while cordierite, biotite, spinel, quartz, garnet, andalusite, chlorite and carbonates are sometimes recorded. The ores have been subdivided into massive-uniform with an average 75%, and segregated with 25% sulphide (Smirnov, 1977).

The principal sulphide suites are: a). chalcopyrite-pyrite, b). chalcopyrite-pyrite-pyrrhotite, and c). pyrite (sulpho-pyrite). The ores are extremely heterogeneous in grain size, from very fine to crystals that are 1 to 2 cm across. This is apparently related to subsequent regional and contact metamorphism. In the massive ores the most widespread textures are massive-uniform and streaky structures, and less frequently porphyritic and breccia like banded ores. The segregated ores are characterised by segregated and veinlet fabrics (Smirnov, 1977).

No clear vertical mineral zonation is recorded, although essentially, copper as chalcopyrite-pyrite and chalcopyrite-pyrrhotite ores are located mainly in the upper parts of the sulphide accumulations, while the pyritic massive and segregated ores predominate lower in the deposit (Smirnov, 1977).

In addition to the amphibolite alteration of the basic volcanics described above, skarn veinlets of epidote, andradite, and sometimes prehnite and magnetite are also seen within these extrusives. Alteration to anthophyllite-quartz-albite, biotite-quartz-albite and quartzose varieties composed essentially of sericite, cordierite, anthophyllite, andalusite and spinel are developed within the sub-volcanic rhyodacite bodies. Zones of intense quartz-sericite are formed within the same sub-volcanic rhyodacite bodies below the sulphides and around the sulphide apophyses (Smirnov, 1977).

Production and Resources

Production from 50 Let Oktyabrya in 1993 totalled 1.26 Mt of ore at a head grade of 1.56% Cu.
Reserves at 50 Let Oktyabrya are estimated at 46 Mt @ 1.81% Cu (Russian Copper Company website, viewed January, 2020).
Pre-mining resources at Priorskoe were 38 Mt @ 1% Cu, 3.7% Zn, 0.1 g/t Au, 15.5 g/t Ag (USGS Mineral Resources database, viewed January 2020).
Reserves at Priorskoe are estimated at 36 Mt @ 1.02% Cu, 3.88% Zn (Russian Copper Company website, viewed January, 2020).

The most recent source geological information used to prepare this summary was dated: 1998.     Record last updated: 18/1/2020
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.

50 Let Oktyabrya

  References & Additional Information
   Selected References:
Prokin V A and Buslaev F P  1998 - Massive copper-zinc sulphide deposits in the Urals: in    Ore Geology Reviews   v14 pp 1-69
Vikentyev, I.V., Belogub, E.V., Novoselov, K.A. and Moloshag, V.P.,  2017 - Metamorphism of volcanogenic massive sulphide deposits in the Urals. Ore geology: in    Ore Geology Reviews   v.85, pp. 30-63.

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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