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Aleksandrinka |
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Russia |
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Cu Zn Au Ag
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Super Porphyry Cu and Au
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The Aleksandrinka massive sulphide Cu-Zn deposit is located 25 km to the northeast of Magnitogorsk in the central Urals Mountains of Russia (53° 31'N and 59° 22' E).
For details of the regional setting, see the Regional Setting section of the 50 Let Oktyabrya record.
The Aleksandrinka ore field is within the Uchaly-Aleksandrinka Zone of the Devonian Eastern Magnitogorsk island arc and unlike the other deposits of this same zone has elevated Au and Ag contents.
The deposit contained 9.8 Mt @ 4.4% Cu, 5.5% Zn, 1.1 g/t Au, 37 g/t Ag, and 118 g/t Cd.
The Aleksandrinka deposit is hosted in a linear, NW trending rift-like structure, containing ore-bearing volcanoclastic facies and associated limestones which can be traced over a distance of 10 km. All 23 of the known orebodies are localised at the southeastern slope of the rift.
Three stratigraphic units are recognised in the Middle Devonian (Givetian) host Karamalytash Formation:
i). Footwall rhyolite-dacite unit which is >100 m thick and hosts a halo of stockwork ore which pinches out with depth,
ii). Ore-bearing volcanosedimentary rocks containing rhyodacite with small phenocrysts, which is 100 to 200 m thick and is characterised by extensive developments of quartz-sericite alteration and related sphalerite-galena-tennantite and chalcopyrite stockwork mineralisation and
iii). Hangingwall basalt-rhyolite unit containing silicic volcanics rich in large phenocrysts, which is 100 m thick and is overprinted by alteration characterised by epidote, illite, chlorite and hematite.
The Karamalytash Formation is overlain by limestone, hornblende-plagioclase andesite, dacite, basaltic andesite and flyschold terrigenous rocks. Late diabase dykes and a dacitic subvolcanic sill are exposed to the southeast of deposit.
The main orebody is localised within the volcanosedimentary member at the contact between overlying basalt and underlying acid volcanics. Host volcanosedimentary unit is composed of disintegrated aphynic and porphyritic dacites with small phenocrysts and by volcanoclastic rocks (xenolith-bearing lavoclastites) containing fragments of basalt, rhyolite, dacite, silicified volcanics, Jasper, chloritolite, sulphide mineralisation and miscellaneous intrusive rocks. Rare interlayers of pink and greenish-grey argillites, dolostone, chloritolite, sulphidic siltstone, sandstone and oxidised quartz-siderite-hematite rock are also recorded.
The Aleksandrinka orebodies are localised within an area of 1.0 x 1.5 km on the northeastern slope of a palaeo volcanic depression.
The largest of these orebodies is the poly-cyclic No. 1 Lode, which has a plan area of
0.7 sq. km with maximum length and width of 400 and 330 m respectively and thickness of 0.5 to 25 m, occuring at depths of from 34 to 270 m. This lode consists of semi-connected southern, northern and eastern segments. The dip of the lode increases southward from 20 to 60°. To the north, it is bounded by a fault, while to the south it is cut by dacite and dolerite dykes and a sill-like intrusion of hornblende-plagloclase andesite.
The Northern Orebody, which is exposed in the open pit, comprises several cycles of ore development. Massive chalcopyrite-pyrite ore occurs in the northern part of the orebody, while fine-grained banded ore dominate in the remainder orebody. Several small banded and densely disseminated bodies are found at the southern and southwestern pinch-outs of the Northern Orebody. The No. 5 Orebody is composed of densely disseminated ore.
The main mineral assemblages within the orebodies principally comprise pyrite, chalcopyrite, sphalerite and bornite, with lesser galena, tetrahedrite-tennantite, chalcocite and covellite and rare pyrrhotite, enargite, wuertzite, stannite, renierite and native gold.
Alteration has produced quartz-pyrite and barite-pyrite products by acid leaching, while secondary sulphide enrichment produced pyrite-chalcopyrite, bornite-pyrite, pyrite-bornite-tennantite-sphalerite assemblages. Siderite-quartz-hematite products of complete sulphide oxidation are occasionally developed in the upper parts of mineralisation cycles.
The main economic ores include: i). massive pyrite-chalcopynite-sphalerite containing >2% Zn, ii). massive chalcopyrite-pyrite ore containing <2% Zn and 1 to10% Cu, and iii). polymetallic massive galena-sphalerite-barite-chalcopyritc-pyrite ore with 4-10% Pb. Bornite occurs in all ore types. Disseminated pyrite with an insignificant admixture of chalcopyrite and sphalerite occurs beneath the No. 1 Lode and contains around 0.7% Cu.
The most recent source geological information used to prepare this decription was dated: 2000.
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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Selected References:
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Maslennikov V, Koroteev V, Prokin V, Yazeva R, Bochkarev V and Fershtater G, 2000 - Massive sulfide deposits of the Central and Southern Urals: in Seltmann R, Koroteev V, Fershtater G and Smirnov V, 2000 The Eroded Uralian Paleozoic Ocean to Continent Transition Zone; Granitoids and Related Ore Deposits IUGS/UNESCO, IGCP Project 373, International Field Conference in the Urals, Russia, 18-30 July, 2000, Excursion Guidebook, Publication #14, IGCP Project 373, Natural History Museum, London, pp 69-98
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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.
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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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