Intrusive Formations of the Natalyevskoye Deposit Area in the Mariinsk Taiga

B. D. Vasiliev

(Presented by Professor A. M. Kuzmin)

The formulation of the problem is connected with the discovery and study, in the Mariinsk taiga, of the Natalyevskoye gold deposit in skarns.

Until quite recently, various researchers [1, 3, 4, 5] believed that all intrusive formations in the environs of B. Natalyevka belong to a single Martaiga intrusive complex of intermediate basicity, with which the gold mineralization was also associated.

In studying the Natalyevskoye deposit, we came to the conclusion that two intrusions of different ages occurred in the deposit area, each of which is characterized by definite types of intrusive rocks, skarns, and gold mineralization. Of greatest practical interest are the ores of the gold–bismuth–copper formation, associated with the young gabbro intrusion.

Below we attempt to characterize the intrusive formations of the Natalyevka area, in order to show the individual features of each of the magmatic complexes distinguished and to determine their place in the general history of magmatism of the Kuznetsk Alatau.

The area of the Natalyevskoye deposit is characterized by a highly complex geological structure, with widely manifested disjunctive tectonics. In the geological structure of the area the principal role belongs to carbonate, effusive, and effusive-sedimentary formations of the Late Cambrian, Lower Cambrian, and Middle Cambrian, which are cut by two intrusions of different ages, namely: the older granodiorite intrusion and the young gabbro intrusion.

Martaiga Intrusive Complex

The rocks of the Martaiga intrusive complex are of considerable extent, forming several small and medium-sized plutons, which we combine into the Natalyevka group of intrusive bodies. This group includes the Natalyevka, Belokamensky, and Severny plutons and a number of small stocks.

The intrusive bodies of the Natalyevka group have common features of petrographic composition and a linear form, clearly elongated in plan from south to northeast, and, subordinated to the general folded structure of the enclosing strata, are arranged in a chain north of the settlement of B. Natalyevka.

1. The Natalyevsky pluton is exposed over an area of about 0.3 km² near the settlement of B. Natalyevka; it has a complexly dissected and sharply elongated form, with average dimensions of 1.3 km by 0.25 km. The pluton is emplaced in a Lower Cambrian effusive-sedimentary sequence and is subordinate to the folded structure of the latter. Individual apophyses of the pluton, 50–60 m thick, lie parallel to the dip of the bedding of the enclosing rocks. The petrographic composition of the rocks within the pluton is uniform. These are mainly diorites, quartz diorites, monzonites, and, along the eastern margin, hybrid gabbroids appear. The contacts of the pluton generally dip steeply to the northwest and are accompanied by garnet and diopside-garnet skarns.

2. The Belokamensky pluton is exposed over an area of about 1.5 km² on the divide between the Belokamenka and Kashkadak rivers. It is an irregularly shaped body, elongated from south to north for 2.5 km, with uneven outlines in plan, and is emplaced in rocks of the Late Precambrian, Lower Cambrian, and Middle Cambrian.

The Belokamensky pluton contains a mass of large and small xenoliths and roof pendants and is characterized by considerable diversity in the rocks composing it. However, changes in the structural-textural features and composition of the rocks within this pluton occur so frequently that, within its contour, it is practically impossible to distinguish areas of distribution of different petrographic varieties. In the central and northern parts of the pluton, diorites and quartz diorites are predominantly distributed. Monzonites and quartz monzonites gravitate toward the southern and eastern parts of the pluton. Hybrid diorites and gabbroids are traced along the western margin of the pluton.

In the near-contact parts the rocks acquire a sharply expressed porphyritic structure. Skarn formations of garnet, diopside-garnet, and magnetite-garnet composition tend in their distribution toward the western part of the pluton. Dikes of spessartites are also concentrated here.

1. The Northern pluton, the largest, has not been completely contoured. Its central part is composed of fine-grained alaskite granites, which to the north are replaced by granodiorites, and to the south by quartz monzonites and diorites. The massif is cut by a series of steeply dipping disjunctives trending SSW and has almost no skarn rim.

In the petrographic study of the rocks of the Natalyevka group of intrusive bodies, the commonality of their mineralogical composition is established comparatively easily. All the rocks are characterized by an abundance of intermediate, sharply zoned plagioclase (andesine; in granites, oligoclase No. 23) and relative paucity of potassic feldspars. Quartz is almost always present in varying amounts. In all varieties of rocks the principal representative of the dark-colored minerals is green hornblende, and in the acidic varieties also biotite. Accessory minerals are represented by apatite, magnetite, sphene, and zircon. All the rocks are characterized by pink tones in coloration and a considerable degree of alteration.

The variegation of the petrographic composition of the rocks within individual plutons, the fine- and medium-grained, often porphyritic structures of the rocks, the presence of large roof pendants and xenoliths, skarn rims along the contacts, and the large number of small rock outcrops—all this indicates a shallow erosional level, which has exposed only the uppermost, apical parts of the intrusive bodies.

As already noted above, all bodies of the Natalyevka group are characterized by a linear form in plan; all the bodies are elongated in a northeastern direction and are arranged in a chain along the continuation of one another.

of one another. This gives grounds to suppose the presence of a single large intrusive massif, extending from the village of Natalyevka to the northeast for a distance of 8–10 km, but not yet fully exposed by erosion and denudation.

Fig. 1. Petrochemical diagram of intrusive rocks of the Natalyevskoye deposit area (after the method of A. N. Zavaritsky).
1–5 — intrusive rocks of the Kozhukhov massif (after A. R. Ananyev, 1950); 6–9 — intrusive rocks of the Kozhukhov massif (after L. V. Alabin, 1959); 10–14 — intrusive rocks of the Olginsky massif (after L. V. Alabin, 1959); 15–21 — rocks of the Natalyevka group of intrusive bodies; 22–26 — rocks of the gabbro complex of Medyanka, Natalyevka, Kamenny; 27–28 — average olivine and olivine-free gabbro according to Daly; 29–30 — average olivine and olivine-free gabbro of Patyn (after S. S. Ilyenko, 1960).

In terms of the petrographic composition of the rocks and their petrochemical characteristics (Fig. 1), as well as the spatial position and form of the bodies, the Natalyevka group is clearly correlated with the linear Kozhukhov granodiorite massif, located 10 km to the northwest. The affiliation of the latter with the Martayginsky intrusive complex was shown by L. V. Alabin (1959), A. R. Ananyev (1950), and T. M. Dembo (1952).

Gabbro intrusion

The gabbro intrusion at the deposit was identified by us as an independent one in 1958. It occurs in the area of the “Shakhta” elevation, north of the settlement of Bolshaya Natalyevka, in the form of a small body (400 × 80 m)

a dike-like linear body composed of olivine gabbro-norites, gabbro, and gabbro-diabases. The intrusive body has a broad strike; i.e., it is not subordinate to the folded structure of the Cambrian strata and cuts not only the porphyrites of the Middle Cambrian but also the monzonites of the Martaiga complex. The intrusive body is intersected by quartz veins with gold-copper-bismuth mineralization.

Gabbroic rocks are characterized by a dark-gray, almost black color with a lilac tint, a high degree of freshness and toughness, and the presence of spheroidal jointing upon weathering. They display a gabbro-ophitic texture passing into poikilo-ophitic, and rarely cryptic, texture. The principal minerals are fresh plagioclase (labradorite No. 5571), titanaugite, ferruginous olivine, more rarely hypersthene, and brown and green hornblende. Reaction relations between olivine and pyroxenes, and between pyroxene and hornblende, are characteristic. Pyroxenes almost always contain a mass of platy ilmenite inclusions forming a lattice. Among the ore minerals, ilmenite, magnetite, and pyrrhotite predominate. Biotite is rare in the gabbro and forms rims around ore minerals.

At the headwaters of Kamenny Creek, 5 km north of the settlement of B. Natalyevka, on the southern margin of the Northern pluton, in 1960 we established yet another body of specific gabbroic composition, situated partly within the effusive-sedimentary sequence and, in the form of narrow linear apophyses of sublatitudinal strike, cutting the diorites of the Northern pluton. The intrusive body is composed chiefly of pegmatoid varieties of ilmenite gabbro and is cut by albite veins. Copper mineralization and a gold-bearing placer along Kamenny Creek are spatially associated with it.

Seven kilometers south of the settlement of B. Natalyevka, in the area of the Medyanka River, gabbroic rocks analogous to those described compose thick dikes of northwestern strike, mainly in the southern part of the syenite-diorite massif of the Martaiga complex. The largest and most clearly expressed dike is exposed by the Kundat River 1 km above the mouth of the Medyanka River. Its thickness is about 100 m, and its length is up to 1 km. It is composed of olivine gabbro (often trachytoid), normal gabbro, and porphyritic quartz gabbro. Gold-copper mineralization is known in this area.

Fifteen kilometers southeast of the settlement of B. Natalyevka, as a result of detailed work in 1959 and 1960, we were able to subdivide the field of intrusive rocks south of N. Berikul. In so doing, the Novo-Berikul gabbro massif became clearly delineated, composed of olivine gabbro, amphibolitized gabbro, banded gabbro with primary magmatic banded ores of iron and titanium. Pyroxenites and plagioclasites are encountered rarely.

The new scheme for the sequence of formation of the various intrusive formations of the southern part of the Berikul area is as follows.

1. Diorites, syenites, monzonites, and hybrid gabbro of the Martaiga complex form bodies of northeastern strike.

2. The dike intrusion of diorite porphyrites cuts the rocks of the Martaiga intrusion and forms closely spaced dikes of northeastern strike.

3. The titaniferous gabbro intrusion cuts the rocks of the Martaiga complex and the diorite porphyrites; it forms lopolith-like large, weakly layered bodies of northwestern strike with banded ores of titanium and iron.

4. The intrusion of alkaline syenites forms linear bodies of northeastern strike with a mass of broad apophyses. It cuts

and intensely metamorphizes the rocks of the gabbro intrusion, accompanied by strong alkaline metasomatism.

1. The dike intrusion of spessartites, diabases, and porphyrites forms persistent bodies of northwestern strike.

2. The dike intrusion of microgranites, aplites, and pegmatites creates thick dikes of northeastern strike.

The material presented makes it possible to conclude that in the Berikul and Natalyevka areas of the Martaiga there is a comparatively young gabbro intrusion cutting through the rocks of the Martaiga complex, but itself cut by an intrusion of Devonian (?) alkaline syenites.

In the southeastern part of the area (St. Berikul, N. Berikul, Nikolka) it occurs in the form of large bodies. In the northwestern part of the area (Medyanka, Natalyevka, Kamenny) it occurs in the form of small linear dike-like bodies. Iron-titanium ores and gold-arsenic deposits are associated with the large bodies. Gold-copper-bismuth mineralization is associated with the small bodies. In future prospecting and mapping work in the Martaiga, attention must be focused on distinguishing the young gabbro intrusion, in view of its specific metalliferous character.

In petrochemical characteristics, the gabbro rocks of the area of B. Natalyevka are very close to the olivine and olivine-free gabbros of Daly (Fig. 1), and differ somewhat from the average olivine and olivine-free gabbros of Patyn [6] in their poverty in alumina and feldspathic lime.

REFERENCES

1. Alabin L. V. The Olginsky intrusive massif in the northwest of the Kuznetsk Alatau. Bulletin of the West Siberian and Novosibirsk Geological Administrations, issue 3, 1955.

2. Ananyev A. R. The Kozhukhovsky granite-diorite massif in the northwestern spurs of the Kuznetsk Alatau. Scientific Notes of TSU, No. 14, 1950.

3. Bulyannikov A. Ya. Gold-ore formations and gold-bearing provinces of the Altai-Sayan mountain system. Proceedings of TSU, vol. 102, 1948.

4. Burovsky V. A. Gold-bearing skarns of the Natalyevka deposit in the Mariinsk taiga. Scientific Notes of TSU, No. 36, 1960.

5. Dembo T. M. Geological structure and gold mineralization of the northern part of the Kuznetsk Alatau. Proceedings of Nigrizoloto, issue 19, 1952.

6. Ilyenok S. S. Principal features of the petrology of the Patyn massif. Geology and Geophysics, No. 4, 1960.