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Volkovo |
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Russia |
| Main commodities:
Cu V Ti Fe
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Volkovo copper deposit, is located on the eastern slopes of the central Ural Mountains in the Russian Federation, near the town of Yekaterinburg (Sverdlovsk). The annual production rate in the early 1990's was of the order of 1.10 Mt of ore @ 0.86% Cu head grade.
Geology
Volkovo lies in the platinum bearing belt of the gabbro-peridotite association of the Urals. This belt is composed of a number of lensoid bodies which form a roughly north-south, discontinuous chain of mainly gabbro, pyroxenite, dunites and lesser hornblendites. All are found cutting Ordovician to Silurian mafic volcanic accumulations. The largest is the Tagil Massif, which is 120 km long by up to 20 km in width. The Volkovo deposit is located in the most northern part of the Tagil Massif, in a zone that is known locally as the Volkovo Massif, and is characterised by the development of intensely segregated copper-sulphide mineralisation (Smirnov, 1977).
The Volkovo Massif is, overal,l a NNW elongated intrusive body composed of gabbro, gabbro-diorite, quartz-diorite and a complex of fine hornfelsed rock. The attitude of the gross lithological boundaries and the weakly defined banding in the different lithologies all varies from north to south, from north-south to almost east-west, while the dip changes over the same interval from gentle (30 to 35°) westerly, to steeply (75 to 80°) south-westerly. The majority of the complex is composed of a suite of gabbros, including: i). pyroxene (with both gabbroic and ophiolitic textures); ii). biotite-bearing; iii). olivine and olivine-bearing; and iv). hypersthene-bearing gabbros. All have a characteristic dark colour. There is also a systematic variation in the composition of plagioclase, from labradorite, through bytownite to anorthite (Smirnov, 1977).
A vertical zonation, or 'stratigraphy' is evident, with the more basic rocks being lower in the pile, represented by olivine and hypersthene-bearing types at the base, pyroxene gabbros in the middle, and quartz-diorite in the upper portions. There is also a lateral zonation, from quartz-diorites and diorites in the south, which are replaced on moving northwards, first by gabbro-diorites and labradorite gabbros with an ophitic texture, and then to labradorite gabbro with gabbroic textures, and finally in the northern portion by olivine- and olivine-bearing gabbro. A similar east-west zonation from the flanks of the massif towards its centre is evident, with the shape of a north-south trending antiform. Olivine- and olivine-bearing gabbro is found in the core of the structure, with dominant anorthite plagioclase. The overlying and flanking diorites are most deeply eroded to the north, exposing deeper sections of the body. These patterns also control the distribution of Cu-sulphide, titano-magnetite and apatite mineralisation found within the intrusive (Smirnov, 1977).
Mineralisation
Ore grade Cu-sulphides are mainly confined to the pyroxene gabbros with gabbroic textures and labradorite, and to a lesser extent bytownite plagioclase. These occur in the hangingwall section of the gabbroic massif. Mineralisation however, is unevenly distributed, with maximum accumulations recorded in *taxitic, melanocratic varieties of the gabbro. The boundaries of the ore are very gradational and gradual and may only be determined by assaying (Smirnov, 1977).
The ore zone that has been defined within the massif has a strike length of more than 3 km, and is conformable with the gross lithological strike and dip, varying from around 60° in the north to 38° further south. The ore occurs as a more or less parallel series of irregular lens like zones distributed through the thickness of, down dip and along strike within, the favourable gabbro. Over 200 orebodies that have been delineated. Most of the ore lenses comprise Cu-sulphides with vanadium bearing titano-magnetite and apatite, although independent Cu-sulphide orebodies are also encountered. However, although they are found together, there is a tendency for titano-magnetite to predominate lower in the 'sequence', particularly in the pyroxene, predominantly biotite gabbros, whereas Cu is best developed in the pyroxene, predominantly labradorite gabbros. This leads to two types of mineralisation, a vanadium-iron-copper zone higher in the pile, and vanadium-iron lower in the sequence. The Cu sulphides tend to be disseminated, while titano-magnetite is present as both disseminations and as schleiren. Rarely chalcopyrite veinlets are seen with epidote, chlorite and carbonate, forming a later stage development (Smirnov, 1977).
The principal commodity is Cu, with associated Fe, V, Ti and phosphorous. The iron content of both the vanadium-iron-copper and vanadium-iron mineralisation varies between 11 and 17.5% Fe. Au, Ag, Pd, Se and Te are present in trace amounts. The dominant copper minerals are bornite (75 to 80%) and chalcopyrite (20 to 25%), with insignificant primary chalcocite (2 to 3%). In addition, there is abundant titano-magnetite and apatite in the ore, with less frequent pyrrhotite and pyrite, and minor amounts of sphalerite and galena. The principal gangue minerals are 43 to 65% pyroxene and 30 to 38% clinopyroxene. The Cu-sulphides, titano-magnetite and pyrite occur in the interstices between the silicate minerals, suggesting a later formation. Titano-magnetite appears to be the earliest forming ore component, and is commonly replaced by bornite, and less frequently by chalcopyrite (Smirnov, 1977).
Bornite is usually associated with, and is commonly intergrown with chalcopyrite, and replaced by chalcocite. Bornite ranges from 0.001 to 10 mm (1 to 10 000 µm), predominantly 0.5 to 2 mm in diameter. Chalcopyrite varies from a powdery dissemination, up to 4 mm, generally not exceeding 1 to 2 mm. Chalcocite is found as graphic intergrowths with, rimming and occurring within cracks in bornite crystals (Smirnov, 1977).
Palladium is reported to have been concentrated in the chalcopyrite and bornite of the Cu-sulphide and titano-magnetite ores (Smirnov, 1977).
The most recent source geological information used to prepare this decription was dated: 1996.
This description is a summary from published sources, the chief of which are listed below.
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