North Urals Bauxite - Severouralsk, Cheremoukhovskaya - Gloubokaya, Krasnoturyinsk, Krasnaya - Shapochka, Ivdel, Karpinsk
Sverdlovsk Oblast, Russia
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The North Urals bauxite deposits include the historic mines and known resources in the Krasnaya-Shapochka district, Krasnoturyinsk, Ivdel along the Talitza River to the north, and Karpinsk to the south. The major new mine, Cheremoukhovskaya-Gloubokaya which commenced operation in 2015, is at Severouralsk, in the Sverdlovsk Oblast, is on the eastern slopes of the Urals Mountains, ~375 km north of Yekaterinburg.
The discovery of the North Urals deposits is credited N. Korzhavin in 1831. They are located on the eastern slopes of the Northern Urals Mountains, and are on the western limb of the Shegul'tan Syncline of the Tagil Synclinorium. The bauxite-bearing mineralisation strikes near north-south and dips at 20 to 30°E. The lateral limits of mineralisation within individual deposits are defined by a gradual thinning-out of the ore horizon. The western boundary is marked by the outcrop, while the eastern, down dip limits of the deepest deposit have been traced by exploration drilling to depths of as much as 2000 m (Smirnov, 1977). The Cheremoukhovskaya-Gloubokaya mine is an underground operation working to depths of 1550 m below the surface (Rusal, 2015).
Remaining Measured + Indicated + Inferred Mineral Resources at the North Urals mines as at 31 December 2020 were 351.0 Mt of bauxite (Rusal Annual Report, 2020).
The Northern Urals group of deposits have been offset by east-west faults and are separated by barren to low grade intervals to produce a string of deposits and sub-economic occurrences. The northern and southern extent of the cluster is represented by the Ivdel and Karpinsk deposits respectively that are 65 km NNE and 45 km SSW of Severouralsk. This group of bauxite deposits is controlled by a north-south elongated palaeo-depression, bounded on the west by a pre-Uralian ridge, which mainly comprises mafic eruptives, specifically andesitic-basalt and dolerite porphyries, cut by intrusions of gabbro and granodiorite. To the east, there is a corridor of low palaeo-ridges composed of andesitic-basalt porphyries (Bol'shun, 1971; Gladkovsky and Sharova, 1951).
The stratigraphy within the North Urals has been summarised as follows, from the base upwards (after Rodchenko, 1964 and Smirnov, 1977):
Silurian - Wenlockian
Pokrovsk Group - Andesitic-basalt porphyries.
Voskresensk Group - and pink massive limestone;
Kolonga Group - Dark-grey, bedded limestone;
Sos'va Group - Porphyrites, diabases, conglomerate, tuff-breccia, tuff-shale, and seam of grey limestone;
Late Silurian to Lower Devonian - Gedinnian and Ludlovian;
Sarainaya Group - Dark-grey, bituminous limestone, shale, sandstone, and conglomerate;
Petropavlovsk Group - Pink and light-grey, reefal limestone;
Mid Devonian - Eifelian
Subrov'sk ore horizon
Vagransk Group - Dark-grey, bituminous, bedded limestone with Amphipora;
Light-grey, massive, reefal limestone;
Dark-grey, platy, and finely-platy limestones with seams of clay and clay-siliceous shale;
Light-grey, massive reefal limestone;
Dark-grey, bituminous, bedded limestone;
Grey and light-grey, massive, reefal limestone;
Late Devonian - Frasnian
Slates, with lenses of dark-grey and platy limestone;
Light-grey, massive, reefal limestones.
The bauxite unit is early Eifelian in age, although similar mineralisation of late Eifelian age is also known, but is not of economic .
Within the bauxite-bearing belt, there is extensive fault dislocation, predominantly steeply-dipping and shallower reverse faults, with varying degrees of displacement. The largest of these are near east-west, oblique to the regional strike, with vertical throws of ~200 to 400 m. Such structures control the extent of the deposits, and are generally interpreted to be largely pre-ore fractures (Gutkin and Rodchenko, 1965). At least 11 such pre-ore faults have been recognised, dislocating the basin that hosts the mineralised unit into a series of depressions and uplifted blocks at the time of sedimentation. The pre-ore depressions within this basin appear to be the most favourable sites of bauxite accumulation. Barren sectors of the Subrov'sk ore horizon have irregular outlines, and are confined to the pre-ore rises, on which bauxite was either not precipitated or was removed. In addition to these structure, more than 240 post-ore faults have affected the continuity of the deposits (Smirnov, 1977).
The economic mineralisation of the Subrov'sk Horizon, occurs in association with the underlying Devonian Eifelian limestones. The base of the mineralised unit comprises reefal massive limestones of the Gedinnian Petropavlovsk Group, which has a very irregular karst surface. The mineralised horizon is overlain by bituminous limestones, and Eifelian clay, in places including carbonaceous shales of the Vagransk Group. The ore horizon has been subdivided into two sub-horizons: i). a lower unit composed of red high-grade, low-grade and jasper-like bauxites; and ii). an upper unit, of mottled pyritic bauxites. The red high-grade bauxites fill depressions in the basement, whilst the red low~grade and jasper-like bauxites are concentrated on the slopes of the depressions, with the mottled bauxites distributed throughout the depression and basin. Most of the bauxite is pisolitic (Patterson, 1967), but has been fully lithified allowing large scale underground mining. A 0.2 to 0.5 m thick limestone-bauxite breccia occurs at the base of the deposit in places, distinguished by its low alumina content and is not of economic interest (Smirnov, 1977).
During the formation of bauxites, erosion was taking place from the west, where the principal source of the bauxite-forming detritus was the weathering crust of basement massifs/basement ridges of Upper Silurian eruptive and clastic rocks. The bauxite outlines of the individual deposits are both very irregular in plan, and variable in thickness, being confined to the karst profile of faulted depressions within the underlying Palaeozoic limestones. Their structure is further complicated by the interfingering of the different bauxite varieties. The ore fields have been subdivided into three types based on their geometry: i). discontinuous mineralisation, with generally small barren zones which occur sporadically, with small dimensions that range from a few up to several hundred square metres; ii). transitional, where the barren zones occupy 20 to 30% of the mineralised area; and iii). discontinuous mineralisation, where the barren zones occupy >30% of the total ore block, occurring as elongate belts or areas of different aspect and of significant dimensions (Smirnov, 1977).
According to Smirnov (1977), the red bauxites constitute the principal economic mineralisation, comprising 85 to 97% of the total resource. The red bauxites are the diaspore type; the jasperoid and mottled types are diaspore-boehmite; and the bauxite-pyrite mineralisation is composed of pyrite-diaspore-boehmite. The red bauxites are characterised by the following composition: 53 to 55 wt.% Al2O3; 2 to 6 wt.% SiO2; 23 to 25 wt.% Fe2O3; 2.0 to 2.5 wt.% Ti02; and 1.6 to 2.5; wt.% CaO; 1.9 to 3.6 wt.% CO2; and 1.6 to 2.5; wt.% S.
In 1977, the high-sulphur pyritic and mottled bauxites, containing from 1 to 15 wt.% of S (on average 5.4 to 7.3 wt.%), comprise 5% of the total reserves (Smirnov, 1977).
The North Urals operation is 100% owned by the Russian company, United Company RUSAL.
The geological information in summary is drawn from Smirnov, V.I., (Ed.), 1977 - The Ore Deposits of the USSR; Pitman Publishing, v.1, pp. 295-299.
The most recent source geological information used to prepare this summary was dated: 1977.
This description is a summary from published sources, the chief of which are listed below.
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