The Belogorsk Deposit of Refractory Clays

P. G. Usov and S. S. Il’enok

This clay deposit is well known under the name “Voronovskoye deposit”; it is located 25 km to the southwest of the city of Tomsk, in the area of the Kashtak siding of the Tomsk–Taiga railway branch, and lies between the railway line and the village of Voronovo.

The clays we studied from the areas explored by the geological-prospecting party of the “Sibgeolnerud” trust have been called the Belogorsk deposit. These areas are situated directly near the village of Voronovo and at a distance of 300 m from it, in a northwestern direction. The areas occupy a small area and form a single whole with the Voronovo deposit—its western and northwestern part.

The area east of the Belogorsk areas, north and northeast of the village of Voronovo, has been studied by the chemical laboratory of the West Siberian Geological Administration. The materials we report on the study of the clays of the Belogorsk areas are of definite value for characterizing the clays of the Voronovo deposit as a whole and expand its reserves.

Exploration and study of the clays were carried out in two areas, shown on the sketch under the names “area No. 1” and “area No. 2,” Fig. 1. At the same time, six clay samples were examined from an area located 1.5 km east of area No. 2.

Fig. 1. Sketch map of the location of the explored areas of deposits of white and gray clays in the vicinity of the village of Voronovo, Tomsk District. Ocular survey.

The sketch map of the location of the studied areas is shown in Fig. 1, and the arrangement of the workings is given in Figs. 2 and 3.

In both areas, on the basis of lithological features, the following clays have been distinguished:

1) clays of brown and chestnut-brown coloration, occurring predominantly as the upper layer, except for borehole 18, where they were encountered at a depth of 6 to 8 m in a bed of blue clays;

2) blue clays, occurring as the second layer, beneath the brown clays;

3) clays of white, light-gray, gray, and dark-gray color, occurring in various alternations without any noticeable regularity.

The brown and blue clays, despite their different natural coloration, according to laboratory investigations constitute a single group—low-melting clays. Both have the same composition and, upon firing,

Fig. 2. Diagram of detailed exploration of the Belogorsk deposit of refractory and low-melting clays (area No. 1) in Tomsk Oblast

Fig. 3. Diagram of detailed exploration of the additional Belogorsk deposit of refractory and low-melting clays (area No. 2)

yield an identically colored red shard. The brown and especially the blue clays of the areas studied swell during firing and form a porous shard. Clays of the same coloration in the northern part of the deposit do not exhibit swelling during firing. The brown and blue clays have high plasticity and may be used for the production of building brick and roofing tile.

The clays of white, light-gray, and gray color are of considerably greater industrial value. The various degrees of coloration of these clays in gray tones are due to the presence in them of different amounts of carbonaceous substances, which are readily detected by microscopic examination and by calcination. After firing, the shard from these clays has a color ranging from gray or yellowish to yellow and is comparatively uniform for all varieties. The white and variously tinted gray clays are less constant in chemical and even in grain-size composition than the brown and blue clays. The most variable component in them is silica \((\mathrm{SiO}_2)\), which indicates varying degrees of sandiness. The mineralogical composition of the fine fractions of these clays is the same and differs noticeably from the mineralogical composition of the clayey part of the brown and blue clays. The white and variously tinted gray clays contain smaller amounts of fluxing oxides and iron oxides than the brown and blue clays. They have a higher alumina content and, in composition, constitute one group—semi-acid clays, while in terms of refractoriness—

—predominantly obtuse-angular. The nature of occurrence of the clays and the arrangement of the workings are shown in the sections in Figs. 4, 5, 6, and 7.¹)

The grain-size composition of the clays, by workings and sections, is given for each lithological variety in Table 1.

Section along line V–V

[Figure: geological section along line V–V, with elevation scale and workings Sk. 35, Sk. 25, Sk. 30, Sk. 23, Sk. 14, Sk. 15.]

Legend:
- Soil–vegetative layer
- Loam
- Sand
- Blue clay
- Useful bed

Fig. 4

In grain-size composition, the rocks of brown and blue coloration form one group—heavy loams containing clay fractions from 8 to 25% and considerable quantities of particles of colloidal sizes.

Section along line VII–VII

[Figure: geological section along line VII–VII, with elevation scale and workings Sk. 1, Sk. 2, Sk. 3, Sk. 32, Sk. 31, Ok. 4.]

Legend:
- Soil–vegetative layer
- Brown loams and brown clays
- Blue clay
- Sand
- White and light-gray clays
- Lower series of useful bed

Section along line I–I

[Figure: geological section along line I–I, with elevation scale and workings Sk. 1, Sk. 10, Sk. 25, Sk. 33.]

Fig. 5

Rocks of white color and of various shades of gray (light gray and dark gray) are finer in their general mass, except for several

¹) Plans of the explored areas and their sections were compiled by the geologist of the East Siberian Trust of Nonmetallic Minerals “Sibgeolnerud,” comrade Perevalov.

samples, they belong to the group of clays with a content of fractions finer than 0.005 mm of about 50–60%, and reaching 80% in individual samples.

The mineralogical composition of the coarse-dispersed part of the white clays and of the clays of various shades of gray shows no substantial difference. It differs markedly from the mineralogical composition of the coarse-dispersed part of the brown and blue clays, chiefly in the content of dark-colored minerals. The heavy fraction of the brown clays is predominantly fine-grained, with individual grains up to 0.3 mm². Under the microscope plagioclase is established, being

Section along line III–III

Legend:

• Sod-vegetation layer
• Brown loams
• Brown clays
• Sand
• Blue clay
• White and light-gray clays
• Lower boundary of the reserve calculation

Fig. 6

Section along line I–I

Legend:

• Sod-vegetation layer
• Loams
• Brown clay
• Bluish-gray clay
• Sand
• White and light-gray clays
• Lower boundary of the reserve calculation

Section III–III

Section II–II

Fig. 7

the principal mineral of the heavy fraction. The amount of feldspar in the heavy fraction reaches 75%. In grain size, plagioclase varies from the very

Table 1

Plot No. 1

Section V—V (boreholes Nos. 24, 35, 25, 30, 23, 14, 15 and 16)

Section VI—VI (boreholes Nos. 9, 10, 11, 12, 39)

Section VII—VII (boreholes Nos. 1, 2, 3, 32, 31, and 4)

Section III—III (boreholes Nos. 42, 7, 12, 14, 37, and 18)

Section I—I (boreholes Nos. 1, 10, 25, and 38)

Wells located on the boundaries of the plot, not included in the sections (Nos. 33, 36, 41, 27, and 34)

Plot No. 2

Section I—I (wells Nos. 44, 46, 52, and 51)

Section II—II (wells Nos. 45, 46)

Section III—III (borehole No. 50, pit 6, pit 7, and borehole 51)

Bronovskoe deposit

Note. The abbreviations in the table in column 5 denote: brown—brown, blue—blue, white—white, gray—gray, light gray—light gray, and dark gray—dark gray.

ranging from small to grains of tenths of a mm and, as a rule, colored brownish and brown. Distinct polysynthetic twins are sometimes observed.

Quartz constitutes about 15% of the schlich and, in grain size, does not differ from feldspar. In smaller quantities there occurs green hornblende, observed either as small pyramidal grains or as larger pleochroic prisms.

Apatite occurs as single grains, as do rare greenish and brown flakes of chlorite and biotite. Particles of carbonaceous matter are present, more often occurring as rounded grains.

The schlich of the blue clays is uneven-grained and coarser than that of the white and even the brown clays; it is colored dark gray. The dust-like material has an increased quartz content, reaching 18%; the main mass of the schlich in this variety as well is composed of feldspar—plagioclase—which occurs as grains, often strongly kaolinized and in places almost entirely transformed into clayey matter. The configuration of the grains does not differ from that in the other schlichs. Large grains of feldspar and quartz often occur in ovoid or rounded form. In addition to feldspar and quartz, rare grains of green hornblende, flakes of biotite, and carbonaceous matter occur.

The fine fractions (smaller than 0.001 mm) of these clays differ in composition from the fine fractions of white clays and clays with various shades of gray color. They contain a high percentage of iron oxides and a high percentage of oxides of alkali and alkaline-earth metals. The chemical compositions of the fractions smaller than 0.001 mm of the brown and blue clays are given in Table 2.

Table 2

Taking the water split off at temperatures above 400° as chemically bound, and that removed up to a temperature of 400° as bound zeolitically, the chemical compositions of the fine fractions, assuming the iron oxides to be present as hydrates, are expressed by the following formulas:

fine fraction of brown clays

\[ 0.063R_2O \cdot 0.134(\mathrm{Mg},\ \mathrm{Ca})O \cdot Al_2O_3 \cdot 2.5SiO_2 \cdot 0.85H_2O + 2.0H_2O, \]

fine fraction of blue clays

\[ 0.0284R_2O \cdot 0.266(\mathrm{Mg},\ \mathrm{Ca})O \cdot Al_2O_3 \cdot 2.58SiO_2 \cdot 0.84H_2O + 2.42H_2O. \]

When determining the mineralogical composition of the fine fractions of the clays by the staining method, montmorillonite and kaolinite are established in samples of brown clay in approximately equal quantities. In samples of blue clay, montmorillonite is established as the principal mineral, and hydromicas are present as an admixture.

The differential heating curves and weight-loss curves for fractions smaller than 0.001 mm are given in Fig. 8.

The blue clays are designated by number 1 and the brown clays by number 2.

Clays of gray, light-gray, and white color

The concentrate of the gray clays is mainly fine, with a small number of coarse grains, up to \(0.4\) sq. mm in size. The color of the concentrate is yellowish gray. Under the microscope feldspar—plagioclase—is identified, making up the main mass of the concentrate (up to 60%). In shape the grains vary from rounded and ovoid to irregular and prismatic, and in size from the smallest to one, more rarely to \(3—4\) tenths of a mm. Usually they are strongly

Fig. 8. Heating and weight-loss curves of the fine fractions of the clays of the Belogorsk deposit.

kaolinized and under the microscope have a color ranging from brownish to dark brown. Potassium feldspar may also be present, but because of the strong degree of weathering of the grains, twinning structure is not observed, with the exception of \(2—3\) grains with polysynthetic twins of plagioclase.

Quartz is the second most abundant mineral. It makes up about 20% of the concentrate and, in grain size and shape, is analogous to the feldspar. Green hornblende occurs in the form of elongated grains, little prisms, and sometimes rounded grains ranging in size from the smallest to \(0.1—0.2\) mm in length, with distinct pleochroism. Carbonaceous particles and plant remains are fairly widely developed in the concentrate. They are observed as opaque black grains, \(0.01\) to \(0.06\) mm in length, often elliptical or rounded in form. Plant remains usually have an elongated form, resembling prisms with serrated edges.

edges and in transmitted light reddish-brown. In total, organic substances in the schlich amount to about 15%.

The schlich of the light-gray clays is fine- and uniformly grained. Under the microscope, feldspar is identified, making up the principal mass of the schlich. The feldspar grains have a fresher appearance than in the preceding samples and do not give a dark-brown coloration. On average, the grain sizes are on the order of 3–4 hundredths of a sq. mm. Polysynthetic twins are found rather often. Quartz is present in smaller quantity than in the preceding schlichs. The presence of carbonaceous particles is noted, about 3–5% of the schlich. Individual grains of green hornblende and brown hornblende are encountered, and more rarely grains of rare minerals.

The schlich of the white clays is yellowish-gray, for the most part fine-grained. The dust-like material consists, as in the preceding samples, of the finest and coarser, strongly kaolinized feldspar grains. Individual grains are completely destroyed and transformed into a clayey substance. Among the other components, rare quartz grains are observed, the larger of which show cloudy extinction. Within the schlich one scale of plant material with serrated edges was encountered, as well as rare grains of carbonaceous material.

The coarse-dispersed part of the clays of the deposit is predominantly composed of feldspars—plagioclase; the second mineral in abundance is quartz. In the brown and blue clays, green hornblende is present in significant quantities. In these clays rare grains of apatite, chlorite, and biotite are also found. In the gray clays hornblende occurs in smaller quantities, and in the light-gray and white clays it was not found at all. In these clays the minerals apatite, chlorite, and biotite, which occur in the brown and blue clays, were also not found.

The chemical compositions of the fine fractions of the white and variously tinted gray clays are given in Table 3.

Table 3

In the form of chemical formulas these compositions take the following expressions.

\[ \begin{aligned} \text{White clay:}\quad &0.075(\mathrm{Mg},\ \mathrm{Ca})\mathrm{O}\cdot \mathrm{Al}_2\mathrm{O}_3\cdot 2.1\,\mathrm{SiO}_2\cdot 1.6\,\mathrm{H}_2\mathrm{O} + 0.95\,\mathrm{H}_2\mathrm{O} \\ \text{Light-gray:}\quad &0.09(\mathrm{Mg},\ \mathrm{Ca})\mathrm{O}\cdot \mathrm{Al}_2\mathrm{O}_3\cdot 2.15\,\mathrm{SiO}_2\cdot 1.7\,\mathrm{H}_2\mathrm{O} + 0.8\,\mathrm{H}_2\mathrm{O} \\ \text{Gray:}\quad &0.094(\mathrm{Mg},\ \mathrm{Ca})\mathrm{O}\cdot \mathrm{Al}_2\mathrm{O}_3\cdot 2.2\,\mathrm{SiO}_2\cdot 1.65\,\mathrm{H}_2\mathrm{O} + 0.85\,\mathrm{H}_2\mathrm{O} \\ \text{Dark-gray:}\quad &0.09(\mathrm{Mg},\ \mathrm{Ca})\mathrm{O}\cdot \mathrm{Al}_2\mathrm{O}_3\cdot 2.2\,\mathrm{SiO}_2\cdot 1.7\,\mathrm{H}_2\mathrm{O} + 0.9\,\mathrm{H}_2\mathrm{O} \end{aligned} \]

When determining the mineralogical composition by the staining method, in the fine fractions of the white and variously tinted gray clays only kaolinite is detected.

The heating curves and weight-loss curves of the fine fractions from these clays are given in Fig. 8 and are designated for the white clays by number 3, for the light-gray clays—4, for the gray clays—5, and for the dark-gray clays—6.

Table 4

Chemical composition and refractoriness of clays

Area No. 1
Section V—V

Section VI—VI

Section VII—VII

Section III—III

Section I—I

In discussing the mineralogical composition of the clays it was indicated that the fine fractions of the white clays and of clays with various shades of gray are composed of kaolin, while the coarse-disperse part consists mainly of residues of the parent rocks—feldspars and quartz—which reduce the refractoriness and plasticity of the clays. With such a composition, enrichment of them is obviously possible. Kaolin separated from these clays will have a higher industrial value and will find wide application.

The chemical composition and refractoriness of the fine-disperse part separated by elutriation are given in Table 5.

Table 5

Owing to the presence of feldspars in the composition of the clays, they sinter at a low firing temperature (in the range from 1100 to 1200°C) and have a large sintering interval, corresponding to 350–420°. This property of the clays is very valuable for their technological processing.

The sinterability of white clays and of clays with various shades of gray separately is given in Table 6, under numbers 1 through 6 inclusive; under numbers 7 and 8 is shown the sinterability of their mixtures, composed in proportion to the thickness of the beds.

Table 6

White clays and clays with various shades of gray, despite the considerable fine-dispersity of their composition, contain small amounts of particles of colloidal size. Therefore, when plasticity is determined by the method of establishing the rolling and flow limits, they belong to the high classes of plasticity—the first and second. And in terms of the shrinkage value during drying of articles formed plastically, they are characterized as very lean and lean clays, having drying shrinkage of from 5 to 7%. The low content of colloidal particles in the clays is also indicated by their very

low cohesiveness. Products made from them have a tensile strength in the dry state of from 4 to 7.5 kg/cm².

Owing to the small shrinkage during drying, products made solely from white clays and from gray clays of various shades, manufactured by the plastic forming method, have increased porosity in the dry state, as a result of which shrinkage during firing is high, reaching 18%.

With the plastic method of processing, such clays are better used in a mixture with brown and blue clays that do not exhibit bloating during firing. Brown and blue clays are low-melting; their fine-dispersed fraction is composed of montmorillonite and hydromicas, minerals with more sharply expressed colloidal properties than kaolin. Specimens made solely from brown and blue clays give drying shrinkage of up to 10%. Therefore, by adding them in small quantities to white and gray clays, it is possible to increase the drying shrinkage of the products and reduce it during firing.

Masses made from white and gray clays in the semi-dry state are formed into products quite normally and develop a structure with normal porosity.

At a mass moisture content of 9%, depending on the pressure, the porosity has the following values:

Table 7

And after firing to sintering at a temperature of 1150°C with a holding time of one hour, they have quite permissible shrinkage, given in Table 8.

Table 8

Conclusions

1. White clays and gray clays of various shades are suitable for manufacturing floor and facing tiles by the method of semi-dry pressing.

2. In a mixture with brown and blue clays that do not exhibit bloating during firing, sewer pipes can be made from white clays by plastic forming.

3. Brown and blue clays that do not bloat during firing are suitable for manufacturing building brick and roofing tile.