BORON MINERALIZATION IN THE AREA OF THE IZEKIYUL RIVER

(Kuznetsk Alatau)

S. S. Il’enok

(Submitted by Professor Doctor Yu. A. Kuznetsov)

The area of the Izekiyul River, a right tributary of the Chernyi Iyus River, on the eastern slope of the Kuznetsk Alatau, is composed of ancient, sufficiently dislocated formations constituting a synclinal fold of northeastern strike. Within them there is distinguished a thick sequence of marbled limestones, overlain by a spilite–keratophyre formation with thin horizons of limestones, shales, and sandstones. The first is correlated with the Filippovka suite of Proterozoic marbles of the Sarala district, while the second represents a characteristic volcanogenic–sedimentary complex of the Middle and partly Upper Cambrian, widely developed in the Kuznetsk Alatau. These formations are cut by an intrusion of complex composition, probably of Upper Cambrian age.

The early phase of the intrusion, in the form of quartz and quartz-free augite–hornblende and hornblende diorites and microdiorites, which are accompanied by dikes of plagiaplite, malchite, and diorite-porphyrites, composes the massifs of the Spasskii and Kuznetskii Belki. A later phase of the intrusion forms the massifs of the Bel’skii and Nikol’skii Belki. They are composed of monzonites and syenites of various composition, and in places, in the endocontact part, of diorites. Among the rocks of the vein facies there are observed quartz monzonite-porphyrites, syenite-porphyries, granite-porphyries, and aplites. The rocks are grouped under the name of the Bel’skii intrusive complex and were described by the author earlier (1950).

In the area of the Izekiyul River, in spatial and genetic association with the intrusive massifs noted above, diverse mineralization is manifested. Quartz veins with sulfides of various composition—auriferous to one degree or another—with hematite, scheelite, and carbonates are widely developed. Boron mineralization, with the occurrence of the minerals axinite and tourmaline, attracts attention. Ferruginous tourmaline (schorl) forms part of the quartz veins of the central part of the district. Quartz–tourmaline veins are widely developed in the area of Rozhdestvenskii Belok, 2.5–3.0 km from the contact of the monzonite intrusion. Here the veins are characterized by small size—2.0–3.0 m in length and 0.10–0.25 m in thickness. The quartz is gray, coarse-grained, and to a considerable degree cataclastic.

Tourmaline in the vein is concentrated near the selvages, more often growing in bunches from the walls into the inner part of the body. The color of the mineral is black, the habit is acicular, and the size of the crystals ranges from several

from millimeters to 2–3 cm. In the form of rare grains, tourmaline occurs in quartz veins situated along a broad zone of folding near the contact with the intrusion.

In the area of the immediate contact, axinite is developed; here it is associated with epidote and quartz. This type of boron mineralization is of greatest interest, since it is associated with areas of significant accumulations of axinite, which may have industrial significance. Along the southern endocontact of the intrusive massif of Bel’skii Golets

Fig. 1. Exposure of fine-grained diorites—1, cutting diabase porphyrites—2. In the exocontact zone—quartz-epidote-axinite veins—3.

lenses and small veins of quartz-epidote-axinite composition are observed (Fig. 1). Their thickness is small, usually about 0.15 m, rarely greater. Veinlets a few centimeters thick are very frequent. The densest mass of lenses and veinlets is observed near the contact. Rare veinlets are observed at distances of up to 200–300 m from the contact. The texture of the mineral mass is usually banded or veinlet-like. This is connected with the distinct segregation of axinite in the form of independent bands and veinlets cutting the quartz-epidote aggregate (Fig. 2), which indicates its later deposition. This feature of axinite is manifested everywhere. In its morphological character, the quartz is massive, coarse-grained and subhedral, strongly cataclased and cut into fragments. Epidote has a yellow-green color, is coarse-grained and long-prismatic. Its accumulations are confined to the selvages of the veins. Large crystals of this mineral grow in bunches from the walls toward the inner part of the vein. Epidote often penetrates into the wall rocks, forming spots of a metasomatic fine-grained aggregate.

Axinite has a brownish-violet color. The habit of the individuals is everywhere platy. Well-formed wedge-shaped crystals are often visible. Striation is clearly expressed on the faces \(p\), \(n\), \(r\). The size of the crystals reaches 2.5 cm. Under the microscope, thin crystals of actinolite are noticeable in the axinite. In a thin section of normal thickness, axinite has barely perceptible pleochroism. Other properties are: \(Ng = 1.680\), \(Nm = 1.676\),

\(N_p = 1.670,\; N_g - N_p = 0.010,\; 2V = /--/73^\circ,\) specific gravity 3.35—indicate the ferruginous character of the mineral.

In the area of Spasskii Golets, along the eastern contact of the diorite massif, there occurs a zone of epidotized rocks about 35 m thick with a high content of axinite. The intrusive diorites here are situated among Cambrian plagioclase porphyries. The latter, in the contact area with the diorites, have been replaced by a fine-grained aggregate of epidote, albite, actinolite, and quartz, which is cut by abundant veinlets of epidote and axinite. In addition, in places there are joined to them

Fig. 2. Relationship of axinite—a—with a quartz-epidote aggregate—k; b—country rock, strongly replaced by fine-grained chlorite and epidote.

very thin veinlets of hornblende asbestos with quartz. The thickness of the axinite veinlets is small and rarely reaches 1.5–2 cm. It is interesting that axinite spreads widely from the walls of a veinlet outward, replacing albite. In this process, areas of axinite-actinolite composition are formed. In thin veinlets, axinite dies out over a considerable distance as a single crystal, while in areas of replacement of the country rocks it forms large grains containing inclusions of actinolite.

It should be noted that later epidote of two generations is also present here, cutting axinite in the form of veinlets. The epidote of the first generation is greenish-yellow in color and, judging from its optical properties, corresponds to a mineral with an iron-oxide content of about 9%. The second generation of epidote is pale-colored and still more depleted in iron, which also corresponds to its observed association with calcite.

The appearance of asbestos was preceded by the formation of cracks and the crushing of minerals. The cracks are filled with white calcite with a small admixture of quartz, and along the walls—with flattened strands of actinolite-asbestos fibers. The color of the asbestos is greenish-yellow to silky-white; the fiber is brittle, reaching 1–2 cm in length. In such areas axinite proves to be strongly crushed and under the microscope resembles patchy quartz.

Actinolite asbestos in the field of contact-metamorphosed rocks in the described area is not uncommon. Farther north, on the left bank of the Shiplinskii spring and near the settlement of the same name, actinolite asbestos is observed in veinlets of fibrous quartz, forming a beautiful aggregate—“cat’s eye.”

The occurrence of axinite in the Kuznetsk Alatau was first noted by S. M. Kurbatov (1941, 1946). He discovered this mineral in skarns

of the “Yuliya” deposit together with diopside, garnet, and epidote. In this connection the author draws attention to the paragenetic association of axinite with coarse-crystalline segregations of epidote, which corresponds to the features of the occurrence of axinite in our area. In a later work, S. M. Kurbatov (1946) relates the appearance of epidote and axinite to secondary hydrothermal replacement processes.

V. M. Klyarovskii described axinite from the Telbes deposit (1953), where it forms nests and fillings of cavities in garnet-pyroxene skarns, being a later formation. In this case the garnet proves to be crushed, and a considerable part of it is replaced by axinite. In association with the latter, epidote, quartz, chlorite, calcite, and an ore mineral are noted.

The author of the latter paper considers the occurrence of axinite among skarns to indicate that the skarns developed at the expense of carbonate-bearing (dolomitized) rocks. One cannot agree with this proposition of the paper, for the researcher himself points to a later development of axinite in relation to the skarns, as do S. M. Kurbatov’s works and our own, which is connected with the stage of hydrothermal activity following the skarns. This association is especially clearly visible in the material described by us.

Moreover, axinite mineralization may be widely developed in the field of altered effusives, as occurs in the area of the Izekiyul River, and the presence of this mineral in skarns cannot serve as proof that the latter formed at the expense of carbonate rocks.

Thus, in the sector of the Izekiyul River there is broad development of boron mineralization with a clearly expressed zonality of deposition. In the area of immediate contact with outcrops of intrusive diorites and monzonites, abundant veinlets of axinite and epidote occur, not infrequently with metasomatic development of these minerals, passing into quartz veins and lenses with axinite and epidote. With increasing distance from the contact, both axinite and epidote in the quartz veins rapidly disappear, giving way to quartz veins with tourmaline.

The considerable content of axinite, especially near the diorites of Spasskii Golets, may be of practical interest.

LITERATURE

Il’enok S. S.—The Bel’skii intrusive complex. Izv. Tomsk Polytechnic Institute named after Kirov, vol. 65, no. 2, pp. 145–173, 1950.

Kurbatov S. M.—Axinite from the “Yuliya” mine, Khakass Oblast. DAN SSSR, no. 5, 1941.

Kurbatov S. M.—The role of aqueous solutions in the formation of pegmatites and contact deposits. Transactions of the Jubilee Scientific Session of the Leningrad State Order of Lenin University, 1946.

Klyarovskii V. M.—Axinite from the Telbes deposit of Gornaya Shoriya. Proceedings of the All-Union Mineralogical Society, second series, vol. 82, no. 1, 1953, pp. 62–64.