KOLODZHUL ADAMELLITE MASSIF (KHAKASSIA)

G. A. IVANKIN, E. V. VLADIMIROVA, R. M. GOLD, A. D. GLAZUNOVA

(Presented by the general faculty seminar of the Geological Prospecting Faculty of TPI)

In recent years much attention has been given to the study of intrusive rocks of the Kuznetsk Alatau and its eastern part in particular, which is justified by the established connection of a number of types of mineral raw materials with certain complexes or formational types of these rocks. However, different researchers propose sharply divergent schemes for the development of magmatism in this territory; the correlation of specific intrusive formations is carried out ambiguously. The main reason for the disagreements in correlation and in establishing the genetic affinity of the intrusive formations of the Kuznetsk Alatau is the insufficient, and often one-sided, study of specific plutons. We have undertaken attempts to carry out a comprehensive study of a number of massifs. Below is a brief account of the results of studying the Kolodzhul granitoid stock, taking into account the data of other researchers. In processing the material, besides the authors, V. G. Zvyagin and L. A. Sukhanova took part.

The Kolodzhul massif of granitoid rocks, exposed in the area of the river of the same name south of the Shira–Kommunar road and 5 km southwest of the settlement of Marchengash, was distinguished as a separate body as early as by Ya. S. Edelshtein. Later researchers assigned it either to the Beloiussky or to the Tigertysky intrusive complexes.

The massif is small in size (about 13 sq. km) and, in the present erosional section, is a stock of oval shape. The regular rounded outline of the massif in plan is disturbed only on the northwestern side, where it is overlain by younger Devonian and Quaternary formations. When mapping the boundaries of the stock at a large scale, their strong dissection is often revealed, caused by the presence of numerous apophyses extending from the main body into the enclosing rocks. The apophyses often pass into typical dikes. Far from the contact, within the enclosing strata, a number of dike bodies have also been noted, composed of rocks quite analogous to those of the massif. These bodies represent a dike facies and are synchronous with the formation of the stock. In addition, an integral part of the Kolodzhul massif is made up of aplite and aplite-pegmatite dikes, located mainly within the area of its outcrop.

The massif is exposed chiefly among the rocks of the Koshkulak effusive sequence, lying on the eroded surface of faunistically characterized, essentially carbonate deposits of the Middle ...

Cambrian. In the north it is in contact (and intrudes them) with Tarzhul stromatolitic dolomites, which underlie carbonate, carbonate-effusive, and carbonate-terrigenous sequences with Lower Cambrian fauna. In the ENE, on the eroded surface of the massif, there lies an effusive sequence, the age of which is considered Lower Devonian, and proluvial-alluvial Quaternary deposits.

The massif is composed of adamellites, whose macroscopic appearance is distinctive and makes it easy to distinguish them from rocks of similar composition of the neighboring Belonosskii pluton. The adamellites of the massif are medium-grained rocks with a characteristic variegated, generally pink or red coloration. The variegation of the color is due to the sharp separation of white plagioclase grains against the general background of an aggregate of grains of potassium feldspars and quartz. The structure of these rocks varies from weakly porphyritic (southern part of the massif) to clearly porphyritic (its northern part).

Under the microscope the following mineralogical composition of the rocks has been established: orthoclase, microcline, plagioclase, quartz, biotite, hornblende. Among accessory minerals, sphene, apatite, magnetite, zircon, and orthite have been identified; among secondary minerals—chlorite, sericite, epidote, leucoxene, and a pelitic aggregate.

Attention is drawn to the constancy of the mineralogical composition of the rocks of the massif, which was established by counting, on an integration stage, the quantitative ratios of the principal rock-forming minerals (Table 1).

Table 1

Percentage ratios of rock-forming minerals in the Kolodzhul adamellites

Let us give a brief characterization of the minerals composing the adamellites.

Orthoclase and microcline constitute on average 33.4% of the total volume of the rock and occur in approximately equal amounts. At the same time, microcline rarely displays a grating structure; more often it is represented by a non-grating variety and in this case differs from orthoclase mainly in the value of \(2V\), which, according to measurements on the Fedorov stage, ranges from \(-74^\circ\) to \(-86^\circ\) (in orthoclase \(2V\) varies around \(-60^\circ\)). The minerals form grains up to 2–3 mm in size (often smaller). In a number of cases perthitic and microperthitic structure of orthoclase grains is noted. An abundant development of pelitic products along grains of potassium feldspars is characteristic, especially for the red varieties of adamellites of the northern part of the massif.

Plagioclase is represented by oligoclase-andesine (Table 1) and forms comparatively large (up to 5 mm) grains, sometimes displaying-

...having a zonal structure (these grains are often completely replaced by sericite and epidote, especially in their central parts) and small grains. The latter are composed of more acidic plagioclase (Nos. 26–28) and are fresher. In the most strongly altered varieties of adamellites, the development of an albite-oligoclase rim around plagioclase grains is sometimes observed. The angle of the optical axes of the plagioclases ranges from \(+80^\circ\) to \(+86^\circ\).

Quartz usually occurs as small grains (up to 1 mm); it sometimes penetrates orthoclase grains and contains small inclusions of biotite, feldspars, and accessory minerals.

Biotite is the principal mafic mineral and forms platy grains up to 2–3 mm in size, distinctly pleochroic from brown and reddish-brown (along \(Ng\)) to light yellow (along \(Np\)); \(Ng—Np = 0.049\). Usually the biotite is replaced, to one degree or another, by chlorite, sometimes completely. A characteristic feature of the biotite is that accessory minerals, in the overwhelming majority of cases, occur as inclusions in its grains.

Hornblende occurs only as isolated grains; it is green, \(2V\) ranges from \(-66^\circ\) to \(-82^\circ\), \(CNg = 10—17^\circ\), \(Ng—Np = 0.030—0.033\); it is pleochroic from light green with a slightly noticeable bluish tint (along \(Ng\)) to light yellow (along \(Np\)). The absorption scheme is direct: \(Ng > Nm > Np\).

Chlorite, sericite, and epidote are common secondary minerals in the adamellites described. Chlorite develops after biotite and hornblende, epidote and sericite after plagioclase. At the same time, a regular increase is observed in the degree of replacement of primary minerals by secondary ones in the direction from south to north within the massif.

The texture of all rock varieties is granitic, hypidiomorphic-granular, weakly porphyritic. Grains of potassium feldspars and plagioclases possess approximately the same degree of idiomorphism; quartz is sharply xenomorphic relative to them. From south to north within the massif, regular changes in the texture of the rocks are noticeable, from equigranular (generally coarser-grained) to more fine-grained porphyritic.

To study the qualitative composition and quantitative proportions of the accessory minerals contained in the rocks of the massif, 56 crushed-rock samples and one heavy-mineral concentrate sample were prepared, the latter obtained by washing \(1.5\ \text{m}^3\) of eluvial grus of the adamellites. For the preparation of the crushed-rock samples, specimens weighing about 1 kg were taken from the outcrop area of the massif. After processing and separation into fractions, the crushed-rock samples were subjected to mineralogical study under a binocular microscope. In carrying out these investigations, a number of typical accessory minerals and minerals whose formation is probably connected with the postmagmatic stage of development of the pluton were identified in the rocks of the pluton (Table 2).

Thus, the principal accessory minerals of the adamellites of the Kolodzhul pluton are magnetite, ilmenite, zircon, and orthite. In this respect, magnetite and, in part, ilmenite quantitatively greatly predominate over the other minerals; their amounts determine the magnitude of the total “yield” of accessory minerals from the crushed-rock samples. Sphene, apatite, monazite, and others occur in very small quantities and, in most cases, in a limited number of samples. Noteworthy is the virtual absence of sphene in the rocks and the appreciable content of orthite in all samples.

In general, the composition and quantitative ratios, as well as the percentage of the total yield of the heavy fraction, are maintained over the entire area of the massif. However, accessory minerals occur in somewhat greater amounts in samples from the southern sector and in the smallest amounts in adamellites near the contact with dolomites.

Table 3 presents the results of chemical analysis of samples of adamellites of the Kolodzhul massif taken from its different sectors. As is evident from the table mentioned, the pluton is composed of rocks whose chemical composition is practically constant (analyses

Table 2

Content of dispersed minerals in the adamellites of the Kolodzhul massif

1—6). The exceptions are analyses 7 and 8. The first of these (sample G-129) characterizes the composition of the adamellites near their contact with dolomites and shows an elevated content of CaO and MgO in the rock, an increased percentage of loss on ignition, and a reduced amount of SiO₂, which can probably be explained by the influence of the process of assimilation of the enclosing rocks by the magma. The second (sample G-153) reflects the composition of strongly beresitized rocks.

In order to determine the composition of dispersed elements and trace elements, spectral analyses of rocks and monomineral fractions were carried out. All samples were analyzed for a large suite of elements (Pb, Ba, Be, As, Cu, Zn, Ni, Co, V, Mn, Ti, Zr, Sn, Mo, Cr, Cd, Hg, Sc, Sb, Bi, W, Au, Ag, Ce, Y, Yb, Nb, Ta, In, Ge, Tl, Sr, Re, Pt, Os), although Table 4 gives the results of analyses only for those elements whose presence was recorded in a significant number of samples.

In addition to Table 4, we note that cobalt was found in 44 samples (out of 51) of biotite; its average content is about 0.001%. Of the large number of spectral analyses (about 300 in all) of other monomineral fractions (and of rocks as a whole), a low cobalt content was established in only two cases. An interesting fact is the association (although in very small amounts) of silver with orthoclase and plagioclase, tin with orthite and ilmenite, chromium with magnetite and ilmenite, zirconium (up to 0.1%) with biotite, nickel (up to 0.01%) with biotite, magnetite, and ilmenite, and arsenic (up to 0.03%) with biotite. The other elements listed earlier were not detected, or were detected in single samples. At the same time, the greatest number of trace elements was established in biotite, which is probably explained not only by the properties of this mineral itself, but also (possibly chiefly) by the fact that biotite contains microscopic inclusions of other minerals, mainly accessory ones.

We also note that our materials concerning the association of a number of trace elements with particular carrier minerals (for example, lead with orthoclase, zinc with biotite, etc.) agree well with the data of other investigators (Tauson L. V., 1959)* and supplement them.

The physical properties of the rocks of the Kolodzhul massif, given mainly according to the data of P. V. Tokarev, are as follows.

The density of the overwhelming majority of samples is determined as 2.5–2.6 g/cm³.

Magnetic susceptibility varies from \(200 \cdot 10^{-6}\) to \(2300 \times 10^{-6}\) CGSM; its average value is \(1003 \times 10^{-6}\) CGSM. The value of residual magnetization ranges from \(40 \times 10^{-6}\) to \(31000 \times 10^{-6}\) CGSM, the average being \(4313 \times 10^{-6}\) CGSM. We determined the ratios \(\frac{Jr}{Ji}\), which for most samples vary from 1 to 2.

An emanation survey established an increased (from 10 to 20 eman) concentration of radioactive emanations in soils developing on rocks of the Kolodzhul massif.

The composition, structure, and properties of the adamellites composing the dike bodies essentially do not differ from those of the rocks of the massif (especially its northern part).

The later differentiates, represented by dikes of aplite and aplite-pegmatite, play a very modest role in the structure of the massif. These dikes have very small thicknesses (usually up to 10 cm, more rarely up to 0.5–1 m) and occur extremely rarely. The aplites and aplite-pegmatites are ordinary; the presence in them of orthite as an accessory mineral strengthens the affinity of these rocks with the rocks specifically of the Kolodzhul massif. The age of the rocks of the massif, determined by the potassium-argon method on biotite, proved to be 420 million years.

* Geochemistry of rare elements in connection with the problem of petrogenesis. Publishing House of the Academy of Sciences of the USSR, 1959.

Table 3

Chemical composition of rocks of the Kolodzhul, Karlygan, and Goltsovy massifs

In the morphology of the bodies, external appearance, mineralogical and chemical composition (Table III), texture and structure of the rocks, and geological position, the Kolodzhul massif is readily comparable with the Karlygan and Galtsov massifs, which are located at the headwaters of the Tom River.

In conclusion, we note that, on the basis of comparison of the rock properties of the Kolodzhul massif presented here with those of the rocks of the multiphase Ulen–Tuim intrusion, we arrive at the conclusion that the described massif has no genetic connection with the latter—its formation is associated with the development of a later deep-seated magmatism.

Table 4

Summary table of the results of spectral analysis of monomineral fractions from rocks of the Kolodzhul massif

Quantity of samples with element contents

Continuation of Table 4

Continuation of Table 4