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Cheremshan, Sinara |
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Russia |
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Ni
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Cheremshan and Sinara lateritic nickel deposits are located near the town of Yekaterinburg (Sverdlovsk) in the central Urals of the Russian Federation, and is just to the south of the Rogozha Ni-Co and Volkovo Cu deposits (see separate records). Cheremshan is an inclined sheet within a zone of fracturing, sandwiched between un-lateritised serpentinites.
At Cheremshan the geology of the underlying bedrock comprises a 300 to 500 m thick sequence of Silurian marble and carbonaceous-argillaceous-siliceous slates, interstratified with chlorite-quartz and sericite-quartz schists and hornfels, which have been intruded by serpentinites, principally between the lower marble and upper slate units. These are overlain by elluvium developed on the serpentinite and shales, and by a layer of Oligocene argillaceous sands and lignite, followed by Miocene and Quaternary clays (Smirnov, 1977).
The Cheremshan serpentinite massif has a layered form, generally conformable with the Silurian country rock, and is 6.3 km long by 0.5 km wide, splitting into a series of apophyses to the south. It is composed of antigorite and chrysotile-antigorite serpentinites in which relict minerals are not preserved. Only locally are peridotitic serpentinites or serpentinised dunites encountered. This massif and the enclosing Silurian sequence, are squeezed between two larger mafic and ultramafic bodies. The un-weathered Cheremshan massif serpentinite averages 0.19% Ni (Smirnov, 1977).
During the Hercynian/Variscan a series of large fractures and feathering zones of crushing and mylonitisation formed in the Palaeozoic complex, between the two larger intrusive masses, being largely responsible for the serpentinisation of the massif and adjacent marbles (Smirnov, 1977).
The weathered serpentinite ore zone is steep dipping following a zone of fracturing. In the north-western part of the deposit the weathered zone is controlled by the zone of fracturing only, although over the remainder the residual weathering zone it is underlain by karst developments in the underlying marble which dips below the serpentinite. The north-western portion of the deposit has been investigated to a depth of 150 to 200 m, and the leached serpentinites are shown to thin out at 70 to 100 m. The central and south-eastern sections have been drilled to depths of between 250 and 400 m without encountering the base of the weathered zone. One hole continued in friable, leached serpentinites to a depth of 416 m, while another intersected 423 m @ 2.62% Ni (Smirnov, 1977).
The residual weathered zone consists of ochreous-siliceous material after serpentinite, leached serpentinite, disintegrated serpentinite and sand-clay and rubble after weathered slates. In the upper sections there are sometimes layer-like bodies of nontronitised serpentinite, which thin out at 30 to 50 m. Within the ore sheet the ochreous-siliceous zone is 40 to 50 m thick and continues to a maximum depth of 160 to 200 m in the north-west and south-east. The metal content of this zone varies from 0.2 to 3% Ni. The ochreous-siliceous zone is flanked by leached serpentinites, including friable-leached, intensely ochreous serpentinites adjacent to the ochreous-siliceous zone; friable-leached, cerolotised serpentinites, affected by nontronitisation; and relatively compact leached, silicified serpentinites. The first two of these types usually have commercial Ni contents. The total thickness of the zone of leached serpentinites within the ore zone of the fault varies from 20 to 80 m. The Ni content of the leached serpentinites varies from 0.4 to 3.5% Ni. Adjacent and underlying karst developments are usually filled with friable formations, and exhibit some brecciation from collapse (Smirnov, 1977).
The leached serpentinites account for around 60% of the ore, with 37% in the karst marble and 3% in lignites at the base of overlying Oligocene sands and clays. The orebodies dip at 50 to 70° to the east, are 1 to 35 m thick and are mined at an ore:waste stripping ratio of 1:25 (Smirnov, 1977).
Sinara, is in the same district as Cheremshan and is a very similar deposit.
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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