Proceedings of the Tomsk Polytechnic Institute
awarded the Order of the October Revolution and the Order of the Red Banner of Labor
named after S. M. Kirov

Volume 281　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1976

MINERALOGICAL COMPOSITION OF TERRIGENOUS DEPOSITS OF THE CHINGASAN SERIES IN THE AREA OF THE UVOLZHSKY GRABEN

(YENISEI RIDGE)

V. A. Gavrilenko, I. F. Brednikhin

(Presented by Professor A. M. Kuzmin)

In the study of sedimentary formations, especially those not characterized faunistically, much attention is currently being paid to the mineral assemblage of the heavy fraction [1—6]. Mineralogical studies show that, from the set of typomorphic minerals, it becomes possible, with considerable justification, to subdivide even ancient barren strata, since rocks belonging to one or another member or suite are often characterized by quite definite mineralogical associations that reflect, to a significant degree, the primary composition of the rocks subjected to erosion. The composition of accessory-mineral assemblages, as well as the nature of its variation along section and laterally, contributes to solving a number of the most important questions of lithology, stratigraphy, and paleogeography.

The question of stratigraphic correlation of the deposits of the Chingasan Series in the northeastern Yenisei Ridge, owing to their considerable facies variability, is rather complex and poorly developed. Correlation is usually carried out on the basis of similarity in the lithological composition and structure of individual strata. The works of B. B. Puchkova and N. S. Podgornaya [4] in the basin of the Tei and Chapa rivers established that deposits of the named series, “belonging to one or another suite, have a constant mineralogical composition,” which makes it possible, with sufficient confidence, to correlate sections of the Chingasan Series within the northeastern part of the Yenisei Ridge by minerals of the heavy concentrate.

Similar studies were carried out by us for deposits of the Chingasan Series composing the Uvolzhsky graben (the basin of the Uvolga River).

The structure of the Uvolzhsky graben includes carbonate-terrigenous deposits grouped into five suites (from bottom to top): the Lopatinskaya, Kar’ernaya, Suktal’minskaya, Suvorovskaya, and Pod’emnaya. A brief characterization of them is given below.

The Lopatinskaya Suite, with a deep erosion surface and angular unconformity, overlies formations of the Tei or Sukhopit Series. In its lower part the suite is composed of variegated terrigenous rocks (450—500 m), represented predominantly by gravelites and sandstones; siltstones and conglomerates among them are of subordinate significance. In the upper part a member (350—400 m) of terrigenous-carbonate rocks is distinguished.

The Kar’ernaya Formation, which overlies the Lopatinskaya, is subdivided into two members: the lower—quartzite-like sandstones—and the upper—argillite-sandstone. The member of quartzite-like sandstones consists of beds of uneven-grained quartz sandstones, separated by thin, discontinuous interbeds of argillites or clay shales; the argillite-sandstone member consists of quartz, glauconite-bearing sandstones alternating with siltstones, argillites, and, in places, brecciated dolomites. The thickness of the formation is about 600 m.

Stratigraphically above the deposits of the Kar’ernaya Formation lies the flysch-like Suktal’minskaya Formation (800 m), composed of beds of bluish- or greenish-gray polymictic sandstones alternating with packages of rhythmically interbedded sandstones, siltstones, and argillites. Brecciated carbonate rocks with traces of slumping appear in individual rhythms.

Still higher lie the terrigenous deposits of the Suvorovskaya Formation, represented by variegated, heterogranular quartz and feldspar-quartz sandstones containing thin interbeds of siltstones and argillites. Conglomerates and gravelites are observed in the lower and upper parts of the formation. The total thickness of the formation is about 300 m.

The Pod”emnaya Formation, which completes the section of the Chingasan Series, is clearly subdivided into two members: the lower—dolomitic (250–300 m), composed of cherry-red silty-clayey dolomites, and the upper—sandstone-limestone (300–350 m), represented by alternating variegated sandstones, oncolitic limestones, and siltstones.

The results of the mineralogical analysis of the terrigenous deposits of the Chingasan Series and their principal lithological features are given in the table.

The most widespread accessory minerals of the heavy fraction are zircon, tourmaline, leucoxene, rutile, and apatite. Garnet, staurolite, anatase, epidote, sphene, cassiterite, magnetite, pyrite, pyrrhotite, malachite, fluorite, corundum, monazite, amphibole, ilmenite, and xenotime are present in subordinate amounts and by no means in all samples.

For the Lopatinskaya Formation, a characteristic feature is the constant presence in crushed samples of tourmaline and titanium minerals: leucoxene, rutile, and anatase.

Tourmaline is represented by prismatic or rod-shaped crystal fragments, brown, dark brown to black in color; more rarely, light-brown crystals with uneven, mottled coloration occur. Tourmaline grains, as a rule, are not rounded or are only weakly rounded. Strong pleochroism is characteristic: along No—dark brown and black, along Ne—pinkish yellow.

Leucoxene forms irregularly shaped lumps or grains of light-gray color and cryptocrystalline structure. As a rule, it develops over rutile and anatase or, together with the latter, over titanium minerals of tabular and cubic form.

Anatase is observed as irregularly shaped, unrounded or partly rounded fragments and, more rarely, in aggregates of small grains and crystals of bipyramidal and platy habit, usually brown, grayish-pink, and bluish-gray in color.

Rutile is represented by fragments of prismatic, columnar appearance, yellowish-brown to reddish-brown and brownish-red in color; more rarely, subrounded grains are observed.

Zircon occurs as subrounded and well-rounded

Table

Principal lithological features of the terrigenous deposits of the Chingasan Series in the area of the Uvolzhsky graben

colorless or pink grains and, rarely, as practically unrounded fragments of dark-brown crystals of prismatic-dipyramidal habit.

In addition to the above-mentioned minerals, well-rounded colorless apatite, isolated grains of brownish-brown cassiterite, blue corundum, and yellowish sphene are present in insignificant amounts. In concentrates from conglomerates of the sources of the Bolshoi and Maly Itul rivers, a significant amount (up to 20% of the weight of the fraction) of well-rounded grains of pink garnet has been noted.

On the whole, the terrigenous deposits of the Lopatina Formation are characterized by a zircon–leucoxene–tourmaline association of minerals.

The terrigenous deposits of the Kar’ernaya Formation, in the qualitative composition of the typomorphic minerals of the heavy concentrate, do not differ from similar formations of the Lopatina Formation, but differ noticeably in the set of secondary minerals and in the quantitative content of the principal ones.

As in the Lopatina Formation, tourmaline is the characteristic mineral of the heavy fraction. The mineral is represented for the most part by unrounded fragments of prismatic form with characteristic striation along the prism edges, a cross section in the form of a spherical triangle, and pleochroism from light green, almost colorless in No, to dark green, almost black in Ne. The color of the mineral is black, brown, or light brown, unevenly spotted, more rarely greenish-brown to light green. Isolated, well-rounded tourmaline grains of ovoid or nearly spherical form are observed, pleochroic in bluish and/or pinkish tones. The content of tourmaline in the Kar’ernaya Formation, in comparison with the Lopatina Formation, is somewhat lower, but noticeably higher than in the overlying deposits of the Suktal’ma Formation.

In terms of zircon content, the Kar’ernaya Formation differs rather sharply from the Lopatina Formation. In individual concentrates its amount reaches 15–20%. On the basis of morphological features, two varieties of zircon are distinguished. The first, most widespread (cyrtolites), is represented by unrounded fragments and prismatic-dipyramidal grains, red-brown and gray-brown to black in color. The prisms are mostly elongated, their faces well expressed, the apices of the pyramids slightly smoothed. In individual concentrates, grayish-brown, strongly shortened, semitransparent or completely opaque (metamict) crystals of tetragonal-short-prismatic habit have been encountered.

Brown and dark-brown metamict zircons of the first variety are distinguished by B. B. Puchkova and N. S. Podgornaya [4] as diagnostic for the deposits of the Kar’ernaya Formation of its Tey and Chap reserves.

The second, less widespread variety of zircon is represented by colorless, transparent or pink, well-rounded or semirounded, somewhat elongated grains, alongside which, though much more rarely, prismatic and prismatic-dipyramidal unrounded fragments of zircon crystals of the same color are encountered.

The total amount of titanium minerals in the Kar’ernaya Formation, in comparison with their content in the Lopatina Formation, decreases somewhat. Their quantitative ratios also change. For example, the content of leucoxene decreases almost 20-fold and, conversely, the amount of rutile increases 2-fold, thereby determining the face of the typomorphic mineralogical association. The concentrations of anatase remain practically unchanged. Rutile is observed in the form of rounded

or weakly rounded fragments, and occasionally twinned grains of yellowish-brown, brownish-red, or brownish-brown color, preserving deep striation along the prism faces.

Anatase is represented by various fragments of crystals of dipyramidal, tabular, or platy form, colored grayish-green, grayish-blue, and brownish hues.

Leucoxene forms yellow, yellowish-white, and yellowish-brown cryptocrystalline aggregates, which together preserve the form of platy or tabular protocrystals. It probably develops after rutile and anatase.

Among other features of the mineralogical composition of the deposits of the kar'ernaya suite, one may note the saturation of the sandstones of its upper horizons with authigenic glauconite, which sometimes amounts to as much as 15–16% of the weight of the fraction, and with partly limonitized pyrite (up to 25–30%).

Among the minerals present in subordinate amounts are colorless, transparent apatite, occurring as small fragments of prismatic grains; light-green to dark-violet detrital fluorite; orange and reddish-orange monazite; isolated signs of minerals of the amphibole group; epidote; and strongly magnetic pyrrhotite.

The rutile–zircon–tourmaline mineralogical association is characteristic of the suite.

The deposits of the suktal'minskaya suite are characterized by a sharp predominance of zircon in the composition of the heavy-mineral concentrate (from 30 to 80% of the weight of the fraction). Two morphological types of zircon are distinguished. The first, which is diagnostic for the deposits of the suktal'minskaya suite, is represented by pink, colorless transparent or translucent, well-rounded or semi-rounded grains that preserve their original prismatic (tetragonal-prism) or dipyramidal habit. The second type, which is in a sharply subordinate position, occurs as weakly rounded, almost unrounded fragments of crystals of brown metamict zircon.

The second most widespread mineral is tourmaline. Two of its varieties are distinguished. The first, predominant, occurs as well-rounded greenish-brown and dark-brown grains, while the second occurs as unrounded fragments of crystals of prismatic form, possessing an uneven mottled coloration, distinct longitudinal striation, and well-expressed spherical triangles in cross section.

Apatite is represented by well-rounded milky-white or, more often, colorless fragments, sometimes showing distinct separateness.

The total content of titanium minerals is noticeably reduced. In isolated occurrences, malachite, bottle-green epidote, angular fragments of pink garnet, strongly magnetic small fragments of pyrrhotite, and pyrite are identified.

The apatite–tourmaline–zircon mineralogical association is characteristic of the suktal'minskaya suite.

The mineralogical composition of the heavy fraction of the suvorovskaya suite differs little from that of the underlying kar'ernaya suite, being distinguished only by a sharply increased (almost tenfold) concentration of apatite. The amount of zircon and tourmaline remains practically unchanged; the content of leucoxene and rutile increases somewhat.

Apatite occurs most often as well-rounded colorless, transparent, or milky-white opaque grains with weakly pronounced [[unclear: continuation cut off at bottom of page]].

of linear or oval shape, more rarely in the form of fragments of hexagonal prisms or barrel-shaped crystals with slightly smoothed edges.

Zircon. Two varieties of the mineral are distinguished. The first, most widespread, consists of light-colored, weakly pinkish, reddish or colorless, semirounded, elongated or well-rounded isometric grains. Practically unrounded fragments of prismatic pink crystals occur very rarely. The second variety, clearly subordinate in occurrence, is represented by unrounded and slightly rounded fragments of prismatic, dipyramidal crystals of light-brown, brown, and dark-brown metamict zircon.

Tourmaline is observed in the form of well-rounded grains of greenish and brownish-brown color, more rarely as fragments of prismatic crystals.

A very characteristic feature of the mineralogical composition of the heavy concentrate of the Suvorov Formation is the rather high contents of titanomagnetite (0.002–0.032%) observed in practically all pan concentrates (possibly oxidized ilmenite). The mineral is represented by weakly magnetic, rounded grains, ellipsoidal lumps, and rounded plates of black color, with a reddish-brown streak. Among other titanium minerals there occur light-yellow, yellowish-red, reddish-brown and brownish-black semirounded and rounded prismatic grains of rutile, whitish-gray rounded loose lumps and tabular grains of leucoxene, and platy gray crystals with a faint greenish tint of anatase.

In individual pan concentrates, single grains of magnetite, irregularly shaped fragments of pink garnet, and staurolite were encountered; partially limonitized pyrite is present in insignificant amounts in practically all samples.

A tourmaline–apatite–zircon association of minerals is characteristic of the Suvorov Formation.

The mineralogical composition of the terrigenous deposits of the Pod’emnaya Formation has not been studied.

The material presented above, it seems to us, permits the following conclusions:

1. Study of the mineralogical composition of the heavy fraction made it possible to distinguish definite associations of minerals related to specific parts of the series section and regularly replacing one another through time.

2. The deposits of the formations, in terms of their suite of typomorphic and a number of secondary minerals, differ little from one another as a whole, but are rather sharply distinguished by their quantitative relationships.

3. The principal suppliers of clastic material were granitoid rocks (tourmaline, zircon, apatite) and only partly metamorphic rocks (garnet, staurolite).

4. The similarity of the mineralogical composition of the heavy fractions of the deposits of the Chingasan Series, the granitoids of the Teya and Uvolzhsky massifs (apatite, zircon, sphene, monazite, fluorite, cassiterite), and also the formations of the Teya and Sukhopit series (magnetite, garnet, staurolite, pyrrhotite) indicates that the formation of the deposits proceeded through denudation and redeposition of destruction products, mainly of local rocks and only partly from distant source areas.

1. The mineralogical composition of the terrigenous deposits of the Chingasan Series in the area of the Uvolzhsky graben, in terms of the assemblage of typomorphic minerals, practically does not differ from that of the sections of the series along the Chapa and Teya rivers [4]. Certain qualitative and quantitative differences may be explained by the specific conditions under which the deposits were formed.

2. The investigations carried out fully confirm the conclusion [4] that sections of the Chingasan Series in the northeastern Yenisei Ridge can be correlated by terrigenous minerals.

REFERENCES

1. V. P. Baturin. Petrographic Analysis of the Geological Past Based on the Terrigenous Component. Moscow, Publishing House of the Academy of Sciences of the USSR, 1947.

2. N. N. Gavril’ev. Mineral associations of terrigenous deposits of the Riphean and Vendian of the southeastern Siberian Platform. Doklady AN SSSR, No. 3, vol. 195, 1970.

3. M. T. Orlova. Accessory minerals of the ancient black shales of the western slope of the Southern Urals. Geology and Mineral Resources of the Urals. Collection of VSEGEI, issue 28, 1960.

4. B. B. Puchkova, N. S. Podgornaya. On the characterization of the mineralogical composition of Upper Cambrian and Lower Cambrian deposits of the northeastern part of the Yenisei Ridge. Geology and Geophysics, No. 11, 1966.

5. N. Ya. Tikhomirova. Correlation of Upper Precambrian and Lower Cambrian deposits of the Irkutsk Amphitheater by clastogenic minerals. Author’s abstract of Candidate of Sciences dissertation, Leningrad, 1964.

6. A. Poldervaart. Zircons in sedimentary rocks. Amer. J. Sci., vol. 253, 1955.