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Sakhara |
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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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All papers now Open Access.
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The Sakhara sheet like lateritic nickel deposit is located near Magnitogorsk, in the Russian Federation.
The underlying un-weathered rocks comprises volcanics and sediments of Silurian, Lower to Middle Devonian and Lower Carboniferous age which have been cut by basic to ultra-basic intrusions of gabbro-dunite-pyroxenite. These are in turn overlain by continental sediments of Oligocene, Miocene and Quaternary age (Smirnov, 1977).
The dunites have been intensely serpentinised, occurring as a 5 sq. km, north-south elongated body with satellites. They are separated from the gabbros by 20 to 300 m selvages of wehrlite and pyroxenite (Smirnov, 1977).
The weathering crust, which extends to depths of 15 to 70 m, covers all of the Palaeozoic rocks and is far more extensive than the ore deposit. The weathering crust in the majority of the deposit has a 'complete' cerolite-nontronite-ochreous profile. It is only represented by a cerolite-ochreous profile where the layer thins, mainly on the margins. The complete profile comprises the following, from the top down: i). ochreous-siliceous zone, 1 to 25 m thick; ii). nontronite and nontronitised serpentinite, 2 to 30 m thick; iii). leached serpentinite, 10 to 30 m thick; iv). disintegrated serpentinite, up to 45 m thick (Smirnov, 1977).
The upper boundary of the weathering crust is relatively smooth, while the lower margin is sinuous, with north-south elongated narrow hollows, and a vertical variation of up to 40 m, usually around 25 m. Three magnesite layers are found in the deposit. One is very irregular, while the other two are 0.3 to 3 cm thick, The upper layer is at the base of the ochreous-siliceous layer, the second is near the base of the nontronite zone, while the third is at the transition from leached to disintegrated serpentinites.
Three ore bands are present over most of the deposit, except where removed by erosion. The upper orebody is confined to the middle portion of the ochreous-siliceous zone. The middle orebody is localised in the upper portions of the zone of nontronite and nontronitised serpentinite; while the lower orebody is in the lower sections of nontronite. These three horizons and associated magnesite bands may relate to water table standstill levels (Smirnov, 1977).
The total thickness of the orebodies varies from 3 to 25 m, largely as a result of the variable removal of the upper and middle orebody layers on the margins of the deposit. About 95% of the reserve is above the current water table, with an average overburden of 25 m. The composition of the nontronitised serpentinite averages (from 165 samples): 0.89% Ni; 43.5% SiO2; 18.5% Fe; 7.6% MgO; 5.2% Al2O3; 1.9% Cr2O3. In comparison the fresh serpentinised dunite assays (from 22 samples): 0.15% Ni; 35.9% SiO2; 7% Fe; 40.7% MgO; 0.95% Al2O3; and 0.6% Cr2O3 (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.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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