Tymalyk Phosphorite Occurrence

(Kuznetsk Alatau)

A. K. Mkrtchyan

(Presented by Professor A. M. Kuzmin)

As a result of large-scale geological surveying carried out in 1960–62 under the author’s direction by a party of the Western Expedition of KGU in the upper reaches of the Tom and Terensu rivers, primary sedimentary-stratal and epigenetic-karst phosphorites were identified within Upper Proterozoic and Lower Cambrian deposits.

The basin of the upper reaches of the Tom and Terensu rivers forms a substantially carbonate massif, elongated in a northeastern direction, and in tectonic terms represents an uplifted saddle between the Shor and Batenevka intrageosynclinal horst uplifts. The geological structure of the area includes Upper Proterozoic and Lower Cambrian sedimentary-metamorphosed formations, folded into linear brachyform folds of northeastern strike. The section of the strata, from bottom to top, is as follows.

Yenisei Formation. The deposits of the formation are distributed along the right and left banks of the upper reaches of the Tom and Terensu rivers and make up the cores of the Tom-Karatash and Terensu anticlinal structures. The formation is essentially carbonate in composition. On the basis of lithological features and stratigraphic position, the formations of the suite are subdivided into three members: the lower member—black crystalline limestones, the middle member—light-colored dolomites, and the upper member—dark-gray phosphatic limestones.

The member of black crystalline limestones is most fully exposed on the left side of the Tom River, above the mouth of the Biskamzha River. It consists mainly of black massive fine-grained, more rarely bedded crystalline limestones with interbeds and lenses of dark-gray dolomites and dolomitic sedimentary breccias. In the upper part of the member, weakly phosphatic limestones are noted (1% \(P_2O_5\)). The thickness of the member in the area is about 700 m. It is correlated with the Kabyrza Formation of Mountain Shoria.

The member of light-colored dolomites has a wide distribution in the area. It is represented by light, more rarely light-gray massive fine-grained dolomites with interbeds of algal dolomites and rare interbeds and lenses of siliceous shales and silicilites. In the middle and upper parts of the member, lenses and interbeds of carbonate phosphorites are noted (6–9% \(P_2O_5\)). Its age, on the basis of the fossil flora assemblage, is determined as Late Precambrian (determinations by A. G. Sivov, 1962). The thickness of the member is 800 m. It is correlated with the West Siberian Formation of Mountain Shoria.

The sequence of dark-gray phosphate limestones is represented by gray, dark-gray bedded, more rarely massive limestones and dolomitic limestones with interbeds and lenses of dolomites, carbonate-phosphate sedimentary breccias, siliceous-carbonaceous shales, and silicilites. The main feature is the increased phosphatic character of the rocks of the sequence—from 0.2 to 6% \(P_2O_5\). The thickness of the sequence is extremely variable because of the unconformable occurrence upon it of the sedimentary-volcanogenic formations of the Tamalyk Formation. The maximum thickness reaches 900 m. It is correlated with the Belka Formation of Mountain Shoria.

The sequences distinguished within the Yenisei Formation can be traced rather clearly along strike, have consistent thicknesses, with the exception of the upper one, and a quite definite stratigraphic position. Therefore, in the future, with a more detailed study of the relationships between the sequences, they may be distinguished as independent formations. The thickness of the Yenisei Formation in the area reaches 2.4 km. Its age is determined as Upper Proterozoic.

Tamalyk Formation*). On the carbonates of the Yenisei Formation, with a break, lie the sedimentary-volcanogenic formations of the Tamalyk Formation. The nature of the break is apparently a stratigraphic unconformity, since both formations occur in a single structural plane. The formation is represented by siliceous-carbonaceous, clayey-carbonaceous shales, silicilites, siltstones, limestones, porphyrites, tuffs of porphyrites and quartz porphyries, dolomites, beds of siliceous, carbonate-siliceous phosphorites, and manganiferous limestones. The formation has a lithologically variegated composition, which changes rather rapidly both vertically and horizontally. Not only the lithological but also the geochemical features of the formation sharply distinguish it from the essentially carbonate section of the Upper Proterozoic and Lower Cambrian. The Tamalyk Formation is phosphorite-bearing and manganese-bearing. Along the right bank of the Terensu River, within the Tamalyk phosphorite occurrence, two phosphorite-bearing members with four beds of phosphorites are distinguished within it, with an average total thickness of 40–45 m and an average \(P_2O_5\) content of 12 to 24%. In the interfluve of Bagzas–Kuzku-zyur (right tributaries of the Terensu River), within the formation, a bed of carbonate-manganese rocks up to 20 m thick is distinguished, with a manganese content from 8 to 18%, and within the Tamalyk phosphorite occurrence lenses of manganiferous limestones up to 30–40 m thick are noted, with a manganese content from 2 to 10%. In addition, elevated contents of vanadium, molybdenum, titanium, chromium, nickel, and cobalt are noted in the siliceous-carbonaceous and clayey-carbonaceous shales of the formation. The vanadium-bearing shales of the formation not infrequently show increased radioactivity, which in individual areas is anomalous. The thickness of the formation in the area is 300–550 m. Its age is established as Lower Cambrian, since the formation is conformably overlain by carbonates of the Usin Formation, at the base of which abundant archaeocyathid fauna of the upper Bazai and Sanashtykgol horizons of the Lower Cambrian is noted (determinations by I. T. Zhuravleva, 1961). The Tamalyk Formation is correlated with the Mrass Formation of Mountain Shoria, within which archaeocyathid and trilobite fauna has been found, characterizing the lower parts of the Lower Cambrian.

Usin Formation. It is represented by gray, dark-gray massive and bedded fine-grained limestones with interbeds of dolomites and siliceous-carbonaceous shales. In the lower parts of the formation occur dark—

*) Distinguished by the author in the area in 1962.

gray limestones with archaeocyathan fauna of the Lower Cambrian. The thickness of the formation in the area reaches 1200 m.

The Tamalyk phosphorite occurrence is situated in the interfluve of the Terensu–Assuk, 3 km northwest of the settlement of Tamalyk. Geologically, the area is composed of sedimentary–volcanogenic formations of the Tamalyk Formation and carbonates of the Yenisei and Usa formations. Beds of primary sedimentary phosphorites are confined to the formations of the Tamalyk Formation, which constitutes the northwestern limb of the Terensu anticlinal structure, complicated by additional folding and by faults of northeastern, submeridional, and northwestern strike (Fig. 1). The phosphorite beds have been traced over a belt up to 6 km long. Here the deposits of the Tamalyk Formation are subdivided, from bottom to top, into three members: lower, middle, and upper.

The lower member is represented by black and dark-gray silicilites, siliceous–carbonaceous vanadium-bearing shales with lenses of dirty greenish porphyrites, porphyrite tuffs and quartz porphyries, dolomites, dark-gray manganiferous limestones, and beds of siliceous and carbonate–siliceous phosphorites. The thickness of the member is 120–220 m.

The middle member is represented by dark-gray and black limestones with interbeds and lenses of siliceous–carbonaceous shales, porphyrites, and their tuffs. In the upper part of the member, lenses of manganiferous limestones and a bed of siliceous phosphorites are noted. The thickness of the member is 35–180 m.

The upper member consists of schistose porphyrites and their tuffs, interbedded with siliceous–carbonaceous and clayey–carbonaceous shales. The thickness of the member is 130–150 m.

Thus, the phosphorites and manganiferous limestones are confined to the lower and middle members of the Tamalyk Formation. The lower member is the most persistent and productive. It contains three beds of primary sedimentary phosphorites, separated from one another by enclosing rocks, the thickness of which ranges from 20 to 50 m. The thickness of the phosphorite beds varies from 3 to 12 m, with their total thickness in the member being 19–30 m. The average content of phosphorus pentoxide in the beds is from 13.1 to 19.7%. In addition to the three principal phosphorite beds, two more lenticular beds, 0.5–2 m thick, are noted in the lower phosphorite-bearing member. The middle phosphorite-bearing member contains one phosphorite bed, the thickness of which ranges from 4 to 14.2 m, and the average content of phosphorus pentoxide is 26.7%. The average chemical composition of the phosphorites of the principal beds is given in Table 1.

The F content ranges from 1.22 to 3.1%; S, recalculated as SO₃, is 1–1.2%. The content of lemon-soluble phosphorus in bedded phosphorites is 4–5%, and in karst phosphorites up to 7% P₂O₅.

The bodies of primary phosphorites generally have a bedded, lens-shaped form with swells and pinches in individual areas. The beds are usually represented by massive siliceous or carbonate–siliceous rocks. Sometimes thin interbedding of siliceous phosphorites with clayey–carbonaceous, siliceous–carbonaceous weakly phosphatic shales and limestones is observed, the latter often being manganiferous. The contacts of the phosphorite beds with the enclosing rocks are sharp in some cases (ditches Nos. 32, 25), and gradual in others (ditches Nos. 11, 70, borehole 7). Siliceous phosphorites have the greatest distribution in the deposit. Within one and the same bed, the predominance of a definite type of phosphorite is usually noted—

Fig. 1. Schematic geological map of the Tamalyk phosphorite occurrence.
1—Quaternary deposits; 2—Upper Proterozoic, Yenisei Formation—dolomites, limestones, interbeds and lenses of siltstones; 3—Upper Proterozoic, Yenisei Formation—interbeds of siltstones; 4—Lower Cambrian, Tamalyk Formation—siltstones, siliceous-carbonaceous shales, siliceous shales, lenses of porphyrite tuffs, tuff-porphyrites and quartz porphyries, dolomites, manganiferous limestones, phosphorite beds; 5—Lower Cambrian, Usa Formation—limestones, dolomitic limestones with interbeds of dolomites; 6—phosphorite beds traced by mine workings; 7—presumed phosphorite beds; 8—intrusive formations; 9—geological boundaries; 10—faults; 11—sites of finds of fossil fauna; 12—sites of finds of fossil flora; 13—attitude elements of rock bedding; 14—core-drilling boreholes; 15—line of geological section.

tov. Thus, for example, bed III is represented mainly by carbonate–siliceous phosphorites, whereas beds I, II, IV are siliceous (Table 1).

Siliceous phosphorites are dark-gray to black, fine-grained massive, more rarely thin-bedded, very dense rocks. The bedding is due to the lenticular-layered distribution of carbonaceous material. Under the microscope the structure is determined as microgranoblastic and, owing to the presence of muscovite, lepidogranoblastic. The rock consists of quartz micrograins (45–70%), phosphate grains (25–50%), muscovite (up to 3–4%), pyrite, and carbonaceous matter. The amount

Table 1

of the latter increases sharply (to 10–15%) below the groundwater level. The phosphate substance is often recrystallized to apatite in the form of grains and aggregates. Grain sizes are 0.01–0.05 mm, aggregates up to 0.2–0.4 mm. Carbonate–siliceous phosphorites differ from the siliceous ones only in their higher carbonate content. Somewhat different from those described are the so-called “coprolite-like” siliceous phosphorites of bed IV, which occurs in the upper parts of the middle member. These are dark-gray to black rocks with an uneven texture and structure. The texture is brecciated, and the structure ranges from fine- to small-grained. The rock consists of fragments, “coprolite-like” phosphate concretions, and cement. Fragments up to 4–6 mm in size are represented by siliceous shales and angular siltstones. Their content in the rock is up to 20–25%. “Coprolite-like” phosphate concretions, ranging in size from 0.5 mm to 2.5 mm and rounded or oval in shape, are represented by a finely dispersed intergrowth of phosphate and carbonaceous matter, usually bordered by a thin (0.01 mm) crustification rim of pure phosphate. The dark-gray cement is represented by a finely dispersed intergrowth of chalcedony, phosphate, carbonaceous matter, and pyrite. Among newly formed minerals, individual grains of diopside, muscovite, actinolite, quartz, and plagioclase are noted. A preliminary study of the coprolite-like formations showed that they are fossilized remains of sponge spicules and radiolarians (determinations by V. A. Shipitsyn, 1964).

In the northern part of the occurrence, primary-sedimentary phosphorites, as a result of contact metamorphism, have been transformed into apatite, quartz–apatite, and carbonate–apatite rocks (trenches 64). Their formation is associated with the contact effect of a granitoid intrusion on the primary-sedimentary phosphorites. The apatite and quartz–apatite rocks are gray, yellowish-gray, massive or banded, ranging from fine-

to fine-grained ones. Under the microscope the structure is determined as microgranoblastic. The banding is due to the alternation of thin interlayers (up to 2 mm) consisting of micrograins of quartz and apatite. The apatite grains are in the form of hexagonal plates measuring 0.05–0.01 mm. Quartz occurs as irregularly shaped grains up to 1 mm in size, and diopside as aggregates of small grains. Carbonate-apatite rocks are distinguished by the presence in the rock of small xenomorphic carbonate grains and by a sharp decrease in the amount of quartz.

The bedded phosphorites at the occurrence are accompanied by residual-metasomatic brecciated phosphorites and karst phosphorites, the formation of which is connected with the development of an ancient weathering crust of the linear-infiltration type. Brecciated phosphorites form on the “heads” of primary sedimentary beds as talus deposits 20 to 40 m thick. Karst phosphorites fill cavities in the carbonate formations of the Tamalyk, Usinsk, and Yenisei suites near—and, as a rule, hypsometrically below—the beds of primary phosphorites, forming, in plan, elongated bodies 50–60 to 200 m long. The depth of distribution of the brecciated and karst phosphorites is controlled by the groundwater level (90–230 m). According to textural-structural features, the karst phosphorites are divided into phosphorite breccias, clayey, loose, and opoka-like phosphorites.

Phosphorite breccias are gray, greenish-gray, brownish dense rocks. They consist of fragments and cement. The fragments, from angular to rounded, are represented by siliceous, carbonate-siliceous phosphorites, silicilites, siliceous shales, hornfelsed porphyries, brown ironstones, vein quartz, and, more rarely, dike rocks. The fragments range in size from fractions of a millimeter to 1–3 cm, rarely to the first tens of centimeters. The phosphate cement is yellow-green-gray, more rarely—owing to iron hydroxides—brown. Sericite is noted in the cement. The ratios of fragments and cement are highly varied. Repeated redeposition of phosphate material is often observed in the rock. Clayey phosphorites fill karst cavities and are a light-yellowish or dirty-greenish sandy-clayey mass. Opoka-like phosphorites—yellow and light-gray cryptogranular dense rocks—are noted as rubble among clayey and loose phosphorites, and also fill cracks in brecciated phosphorites.

The phosphate substance of the primary and secondary phosphorites, according to the determination of N. A. Krasilnikova, is represented by fluorapatite.

A study of the technology for beneficiating the phosphorites, carried out by the research laboratory of the Krasnoyarsk plant “Sibelektrostal” on two samples weighing 60 kg each, gave positive results. The chemical composition of the technological samples is given in Table 2.

Table 2

From sample No. 1, taken from the primary carbonate-siliceous phosphorites of bed IV, a concentrate was obtained by flotation with a content of

phosphorus pentoxide content of 27.3%, with a recovery of 97.5%. From sample No. 2, taken from brecciated phosphorites of the same bed, flotation yielded a concentrate with a phosphorus pentoxide content of 26.9%, with a recovery of 98.7%. These concentrates meet the requirements for phosphorite meal and for phosphorites used in the production of superphosphate and thermal phosphates.

In addition to the phosphorites described above, which are confined to deposits of the Tamalyk Formation, two further horizons with primary phosphate accumulation have been identified in the area. Lenses and beds of phosphorites are noted in the sequence of light-colored dolomites (the Karatash occurrence) and in the sequence of gray phosphatic limestones (the Verkhne-Tom occurrence) of the Yenisei Formation. The upper level of phosphate accumulation corresponds, in our opinion, also to a number of deposits and ore occurrences of phosphorites in Gornaya Shoria: Belkinskoe, Mrasskoe, Kolzasskoe, Oingolskoe, and others. A distinctive feature of the phosphorites identified within the Yenisei Formation is their carbonate composition and their confinement to members of weakly phosphatic limestones and dolomites (0.2–3% \(P_2O_5\)). The thickness of lenses and beds of phosphorites is from 15 to 40 m, their extent from 50 to 500 meters, and the phosphorus pentoxide content is 6–9%. These phosphorites usually have a brecciated or layered texture. In the first case they are sedimentary breccia composed of small, up to 1.5 cm in size, angular fragments of dark-gray to black carbonate phosphorites, cemented by gray and light-gray weakly phosphatic dolomite. The layered carbonate phosphorites are represented by gray phosphatic dolomitic limestones and dolomites with thin interbeds and small lenses of dark-gray carbonate phosphorites.

Thus, in the area of the headwaters of the Tom and Terensu rivers, three levels of phosphate accumulation are established, two of which are confined to the Yenisei Formation of the Upper Proterozoic, and one to the Tamalyk Formation of the Lower Cambrian. The phosphorites of the first two levels are associated with the carbonate type of section and are represented by carbonate rocks, whereas the phosphorites of the third level are associated with a substantially siliceous type of section and are represented mainly by siliceous rocks.

REFERENCES

1. M. K. Vinkman, A. B. Gintsinter, L. I. Egorova. Reference sections of the Lower Cambrian and Sinian of Gornaya Shoria and Gorny Altai. Sov. Geol., No. 12, 1962.

2. V. K. Radugin. Elements of the stratigraphy and tectonics of Gornaya Shoria. Materials on the Geology of the West Siberian Region, issue 37, 1936.

3. G. I. Spanderashvili. Phosphorites of Gornaya Shoria. Sov. Geol., No. 5, 1962.

4. A. A. Chetyrkina. Prospecting for phosphorites in Gornaya Shoria. Agronomic Ores of the USSR, vol. V, 1939.