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Kimpersay |
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Kazakhstan |
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Ni Co
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Kimpersay lateritic nickel deposit is located near the southern end of the Ural Mountains in north-western Kazakhstan.
The ore deposit is a sheet like and developed over serpentinites on the eastern contact between the ultramafic massif and rocks of gabbroic composition. The Kimpersay Ultramafic Massif that hosts this deposits, also contains the bulk of the CIS chromite reserves, 80 km to the south.
The Kimpersay ultramafic massif lies within the Uraltau Anticlinorium, flanked by Proterozoic and lower Palaeozoic sediments. It is 82 km long, from <1 to 32 km in width, covering an area of 920 sq km, and is elongated in a north-south direction, parallel to the axis of the Uralian Fold Belt. The massif is tear shaped, with large chromite deposits being localised in the broad, bulbous southern end. The lateritic Ni deposits are to the north. The attitudes of the northern and southern sections of the massif are markedly different. In the north it is basically conformable with the schistosity of the Proterozoic in the hangingwall, and with the Ordovician sediments of the footwall. The eastern footwall contact is, in many cases, tectonic. The northern part of the massif is a homoclinally dipping body, up to 2.5 km thick, with a dip to the west of 40 to 60° (Smirnov, 1977).
The serpentinites at Kimpersay are mainly after dunite, and are of the chrysotile variety, with lesser ex-peridotitic (harzburgite and lherzolite) serpentinites. The ore field is cut by gabbro-dolerite dykes from 5 to 15 m thick, which may be traced for 2 km. These dykes attract thicker and more Ni rich pockets within the ore sheet (Smirnov, 1977).
The sheet-like, or blanket deposits consist of mottled clays of Tertiary age and Quaternary loams. Their thickness varies from 1 to 15 m, although they are absent in places. An early Mesozoic weathering crust formed on both serpentinites and gabbroids. The weathering crust developed on serpentinites comprises two profiles, a complete cerolite-nontronite-ochreous and a cerolite-ochreous-siliceous type. The thickness of the complete crust, including the leached serpentinites, is very variable, from 5 to 30 m, with a number of substantial hollows (Smirnov, 1977).
The lower ore bearing leached serpentinites are made up of jointed lumpy bleached rocks from 10 to 20 m thick. This zone carries 0.7 to 1.3% Ni in its upper sections. Higher in the sequence the zone of leached serpentinites passes into nontronitised serpentinite. This portion of the sequence is the principal ore-bearing zone, comprising dark green clay like formations, often with the original rock texture preserved. Its thickness varies from 3 to 7 m, and in the ore pockets reaches 10 to 20 m. The predominant nontronites in this zone have 0.7 to 1.3% Ni, with restricted pockets of up to 2.5% Ni. In most of the pure varieties of nontronites the content of the principal components lies within the following limits (in wt%): SiO2 = 34 to 42%; Fe2O3 = 19 to 35%; MgO = 4 to 12% (Smirnov, 1977).
The zone of nontronitised serpentinites passes gradually upwards through a zone of ochreous nontronitised serpentinite into an ochreous siliceous band. The transition is frequently sharp. The upper siliceous zone is 0.5 to 3.0 m thick with Fe and Mn hydroxides, relict minerals such as magnetite and spinel, and yellow, high Fe clays. Only 15 to 20% of this zone is ore grade.
Two sectors of ore grade have been mapped in the deposit. In each the ore is sheet like with an extremely uneven lower surface, an intensely variable thickness and uneven mineralisation. The average thickness of barren overburden is 7 m. The average composition of the ores is 1.15% Ni; 0.054% Co; 20.6% SiO2 ; 47.2% Fe2O3 ; 9.3% MgO ; 3.4% Al2O3 (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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