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The Kuldur deposit was found and explored in sixties of the 20th century by a geologistV. Uspensky. It includes two brucitite deposits — the Main and Southern.

The Kuldur deposit

The Kuldur deposit

About deposit

All industrial reserves of brucite mineral are concentrated in the main deposit, which is represented as coming out on the surface, little elongated lens 600x450m in sizeand with capacity of to 100m in the central part of it.


The brucitite lense is inclined from northwest to southeast; also, there are calciphyres and ophicalcites in its near-contact area including ore — hosting low Cambrian slates. An mineral body is dissected by numerous bostonite dikes (the alkaline rocks of medium composition) and dioritic porphyries of upper Paleozoic age. Besides, deweylite bodies, which are the product of brucite minerals weathering along of outcrop low tectonical zones (the hypergenesis zone) are widely spread and developed at the deposit. The late Cretaceous age crouans, which have played a role of a source of heat at primary magnesites reconversion into magnesium hydroxide (brucite), underlay from below, in direct nearness from the brucitite lense. Low Cambrian slates played the role of the thermal screen between crouans and primary underplayed magnesites.

Mining and processing of mineral

The deposit is mined by the open pit method under explosion with external stacking. The operating cut height is 10 m.; the subbench height is 5 m.

Stages of production

During all technological mining cycle and brucite mineral processing, its chemical composition control studying at such parameters as MgO, CaO, SiO2 and Fe2O3 content is carried out in the factory’s laboratory.

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Brucite mineral

Natural mineral magnesium hydroxide which compose the base of brucite mineral is named after the American mineralogist A. Bruce (1777-1818).

The chemical formula is Mg(OH)2. The structure of pure mineral consists 69,12% of MgO and 30,88% of H2O.Amongst the industrial magnesium minerals, it takes the leading place at Mg content:

Main industrial magnesium minerals

  Mg, % MgO, % Mineral Chemical formula
1 41,68 69,12 Brucite Mg(OH)2
2 34,5 57,3 Forsterite (olivine series) Mg2SiO4
3 30,0 49,7 Olivine (Mg-Fe) (Mg,Fe)2SiO4
4 28,8 47,8 Magnesite MgCO3
5 26,3 43,6 Serpentine 3(Mg,Fe)O 2SiO2 2H2O
6 11,96 19,83 Bischofite MgC12·6(H2O)
7 8,75 14,51 Carnallite (K,Mg)Cl36(H2O)

Its color could be white, light grey, grey and it gets a brownish tint at iron content of more than 0,5–0,8%. The luster at cleavage plane is nacrous, at other places it turns from waxy to vitreous. It shines through and is translucent sometimes.

Its hardness at Maos scale is 2,02,5; its density is 2,372,42 gr./cm3.

It consists of dust (the smallest crystals) and flakes. Crystals are mainly thick  tabular.

It has a layered structure and the anions function is fulfilled by ()1- group with the ion radius of 1,33 A. The ion groups are set on the principle of the most dense hexagonal packing. Each layer consists of two parallel flat sheets (0001), combined by () groups, and the layer of Mg2+ atoms located between them, which occupy all octahedral vugs between () sheets; each Mg2+ atom spaces between six ()1- sheets, connecting three ()1- of one sheet with three ()1- of another. The perfect cleavage passes between the triple layers, linked together by weak residual bonding force.

It does not conduct electricity. At heating up to 350° it starts evolving water, the peak is at temperature range of 400450. It is easily dissolved in acids; also in fine grinded form it is well dissolved in water (less than 200 microns).

As an incidental mineral, brucite is commonly found in metamorphized dolomites and dolomite limestones, marbles, serpentinites, magnesium skarns, in iron-ore and chromite deposits sometimes or in chlorite slates. (the Satkinskoe magnesite deposit, the Akhmatovskaya mine, some serpentinites of Buryat Autonomous Republic, the Shorginskoe chrome iron ore deposit (Armenia), the Saiginsky area of alkali-ultrabasic rocks, etc.).

Deposits. As a rock-forming mineral, brucite is found in brucite marbles (Kusinskoe, Lespromkhoznoe deposits) and brucitits (Savkinskoe, Kuldur deposits). The brucite ore of Kuldur deposit is unique because of its high whiteness (up to 98%) and low Fe2O3 content.