RELATIONSHIP OF GOLD MINERALIZATION TO MAGMATISM IN THE KUZNETSK ALATAU

B. D. Vasil’ev (TPI)

The northern part of the Kuznetsk Alatau—the Mariinskaya taiga—has long been considered an area in which mineralization of the gold–arsenic formation developed, genetically associated with a batholithic granitoid intrusion. However, in 1955 we discovered here the Natal’evskoe gold deposit in skarns, belonging by type of mineralization to the gold–bismuth–copper formation, according to A. Ya. Bulynnikov—a formation that had previously been contrasted with the gold–arsenic formation, was considered characteristic of the eastern slope of the Kuznetsk Alatau, and there was genetically associated with older intrusive bodies.

For purpose-oriented prospecting for new gold-ore deposits in the Mariinskaya taiga, it was necessary to determine the genetic affiliation of the already known deposits and to identify the factors controlling the position, within the structure of the region, of different types of gold-ore mineralization. Work in this direction, carried out by the author in 1957–1966 with active support from the Zapsibzoloto trust, led us to the conclusion that in the northeastern part of the Mariinskaya taiga—the Berikul’ block—deposits and ore occurrences not only of the gold–bismuth–copper formation but also of the gold–arsenic formation cannot be genetically linked with the Martaiga complex of batholithic granitoids: they are not older than the intrusive bodies of the younger post-batholithic Kiisk gabbro–alkaline-syenite complex, which cuts the volcanogenic Devonian, and are probably genetically associated with this intrusive complex. Moreover, it became clear that almost every intrusive complex in the Mariinskaya taiga is accompanied, to one degree or another, by gold mineralization; however, from the standpoint of industrial development, the most interesting are the deposits of the postgeosynclinal stage of the region’s development.

These conclusions, which are of fundamentally important significance and require a reorientation of gold prospecting within the Mariinskaya taiga, deserve discussion and careful substantiation.

According to V. A. Kuznetsov’s scheme of tectonic zoning, the area under consideration is part of the Martaiga massif of the Altai–Kuznetsk folded-block zone of Salair age. It has a block structure, caused by the development of regional faults of northeastern and northwestern strike, and is divided by the latter into large blocks (Fig. 1).

Fig. 1. Scheme of the distribution of mineralization and intrusive formations of the Kiya complex in the Berikul block

1—base of the Palatninskaya Formation; 2—axis of the Makarak syncline; 3—zones of distribution of gabbroids of phase I of the Kiya complex; 4—western boundary of the distribution of dikes of alkaline and nepheline syenites; 5—large disjunctive faults; 6—known deposits of the gold-arsenic formation; 7—the same, inferred; 8–9—known deposits and ore occurrences of the gold-bismuth-copper formation; 10—the same, inferred; 11—ore occurrences of the polymetallic (sulfide) formation; 12—ore occurrences of native lead. The numbers on the scheme indicate deposits and ore occurrences: 1—Staro-Berikulskoye, 2—Komsomolskoye, 3—Kazanskoye, 4—Natalyevskoye, 5—Kamennyi, 6—Medyanka, 7—Strelka, 8—Sosnovka, 9—Ponomarevskoye, 10—Denisovskoye, 11—Madrichenkin Klyuch.

In vertical section, two structural stages are clearly distinguished: the pre-Devonian geosynclinal-folded stage and the Devonian, transitional stage, whose formation corresponds to two major stages in the history of the geological development of the region.

The sedimentary and volcanogenic strata of the Late Precambrian, Lower and Middle Cambrian, which compose the pre-Devonian structural stage in the Mariinsk taiga, belong to formations of the geosynclinal class (according to N. S. Shatsky and N. P. Kheraskov), while the presence among them of greenstone volcanogenic strata and large bodies of the “formation of granitoid batholiths of variegated composition” (according to Yu. A. Kuznetsov) indicates eugeosynclinal conditions of development of the region in the Late Precambrian and Cambrian. All the strata of the Late Precambrian and Cambrian within the region are dislocated in a single plan, gathered into large folds of submeridional strike with limb dips of 50–70° and complicated by narrow “near-fault” folds of northeastern strike. The lower boundary of the geosynclinal-folded stage within the region has not been exposed; the upper boundary is the surface of the Lower Devonian regional angular unconformity, separating the overlying transitional structural complex, composed of formations of another class and possessing a different structural plan.

During the geosynclinal stage of development of the region, two intrusive complexes formed in the northern part of Martaiga:

1) the Kundustuyul complex of avgitic diorites, and 2) the Martaiga complex of batholithic granitoids of variegated composition.

The Kundustuyul complex of the Late Precambrian includes greenstone gabbros, gabbro-diorites, and gabbro-diabases, forming a series of small linear bodies in anthraconite marbles of the oldest sedimentary sequence in the basin of the Kashkadak River. Directly in the gabbro-diorites of one of the left tributaries of the Kashkadak River, small gold-bearing quartz veins are exposed; through their destruction a short gold-bearing placer was formed. Since there are no other intrusive bodies within a radius of 5–6 km, it is natural to suppose that the connection of the gold-bearing quartz veins with the gabbro-diabases is not only spatial but also genetic. The gold content of this intrusive complex in the Kuznetsk Alatau was described by E. I. Gorevanov using the examples of Kundustuyul and the Usinsk district, situated farther south.

The Martaiga complex of batholithic granitoids is most widely distributed within the northern part of the Kuznetsk Alatau and unites the intrusive bodies of the Dudetsky, Kozhukhovsky, and other massifs, as well as a number of small stocks. All of them are characterized by a variegated petrographic composition with a predominance of diorites, syenites, quartz diorites, and, in larger bodies, granodiorites, granites, and plagiogranites. The intrusive bodies of the complex form chains of northeastern strike, cutting diagonally across the folds of the pre-Devonian structural stage and adjoining in the northeast the Dudetsky batholith, which is probably emplaced at the junction of basement faults of northwestern and northeastern strike.

The presence of xenoliths of intrusive rocks, the spatial separation of certain rock types within individual plutons, and facts of contact influence of some intrusive rocks on others make it possible confidently to distinguish three principal intrusive phases: gabbro, diorite-monzonite, and granite. The identified phases have the following features: a) within each subsequent phase, the more basic rocks are close in composition (or analogous) to the most acidic representatives of the preceding phase; b) the distribution of the products of all phases:

is controlled by the same structures; all phases are combined in the same massifs. This may indicate an insignificant time gap between the phases and the absence of abrupt changes in the tectonic setting during the formation of the individual phases.

The diversity of the petrographic composition of rocks within individual massifs, with the widespread development of hybrid varieties; the fine- and medium-crystalline, 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 exposures—all this indicates a shallow erosional level, exposing only the apical parts of intrusive bodies formed under conditions of intermediate depths. The geological age of the complex is determined in the northeastern part of Martaiga by the breakthrough of Middle Cambrian deposits and by the direct overlap of the eroded intrusive bodies of the complex by red-colored deposits of the Koblenets.

Many researchers still associate a large part of the gold-ore deposits of the Mariinsk taiga with the Martaiga batholithic granitoid complex, which seems to us to be erroneous. The fact is that in areas where intrusive rocks only of the Martaiga complex are distributed, gold mineralization is, as a rule, absent—for example, in the area of the weakly eroded Dudet batholith and the Ust-Kundat and Kozhukhov massifs. Conversely, in the fields of gold-ore deposits, in addition to derivatives of the Martaiga complex, as will be shown by us below, there are always small intrusive bodies of young gabbroids and alkaline syenites, upon which the gold mineralization is superimposed.

Therefore, at present it is very difficult to indicate a gold-ore deposit whose genetic connection with the Martaiga complex would be obvious. Probably genetically related to the Martaiga complex are the weakly gold-bearing quartz veins of the Bogotuyul copper-molybdenum deposit, described by D. V. Nikitin and N. N. Dingelshtedt in the endocontact of the Kozhukhov massif, as well as similar small veins with molybdenite and chalcopyrite in the central part of this same massif opposite the mouth of the Maly Ilov.

After the main folding and the emplacement of batholithic granitoids, the Kuznetsk Alatau entered a new, transitional stage of geotectonic development, characterized by the formation of specific red-colored sedimentary and volcanogenic formations and by the intrusion of post-batholithic intrusive complexes of increased alkalinity. As a result of this stage of development, a transitional structural complex (stage) was formed, which is composed of terrigenous and volcanogenic formations of the transitional class and is subdivided into two substages, separated by a major angular unconformity.

The lower substage is represented by the red-colored molasses of the Koblenets, preserved mainly in grabens, where their thickness reaches 2 km. The upper substage is represented by the complex volcanogenic formation of the Eifelian; it lies both on dislocated red-colored molasses of the Koblenets and directly on various formations of the older geosynclinal-folded stage, and in different parts of the region has a variable thickness on the order of 1–2 km.

The structure of the Devonian (pre-Givetian) stage is fold-block: along with horsts and grabens 10–12 km wide, open broad folds with dips of 30–40° are developed in the structure of the stage. The formation of the folded structures of the Devonian stage is closely connected with the development of zones of regional faults: the main folds of the stage are parallel

toward the boundaries of large blocks, near which the folds become smaller and more compressed, even overturned. Some synclinal folds at depth pass into grabens; the formation of these grabens is associated with the overturning of small folds and with intensive volcanism.

The considerable thicknesses of Devonian continental deposits, the fold-block structure of the Devonian stage, formed with the leading role of block movements and intensive volcanism in intrusive and extrusive forms—all this permits the northern part of the Kuznetsk Alatau to be regarded as a siberetine structure (after M. A. Usov).

The transitional stage in the development of the northern part of the Kuznetsk Alatau is associated with the formation of two intrusive complexes, gold-bearing to one degree or another: 1) the Kiya complex of gabbro and alkaline syenites, 2) the Chebulin complex of alkaline granites.

The youngest, Chebulin intrusive complex includes small stocks of alkaline granites arranged in a chain along the eastern boundary of the Palatninskii graben. The absolute age of the granites, determined in the TPI laboratory by R. M. Gold using the uranium-lead method on pyrochlore, is 327–350 million years. In the granites of the Chebulin complex there are small quartz-molybdenite veins, weakly gold-bearing.

The Kiya gabbro–alkaline-syenite multiphase complex is a comparatively young association of rocks widely distributed in the Mariinsk taiga. The complex consists of titan-augite gabbros and gabbro-pyroxenites (phase I), alkaline syenites and nordmarkites (phase II), nepheline syenites (phase III), microgranites and aplite-pegmatites (phase IV). In the regional plan, all intrusive bodies of the Kiya complex are confined to a single meridional zone 70 km long (from Makarak in the north to Mt. B. Taskyl in the south). The intrusive bodies of the different phases of the complex within the single belt of their distribution are oriented differently, which is clearly observed in the Berikul block (see Fig. 1). Elongated bodies of gabbroids of phase I are arranged along narrow zones of northwestern and sublatitudinal strike, marking deep faults, partly concealed. The later phases of the complex are represented by typical fissure bodies of alkaline syenites (northeastern strike), nepheline syenites (northwestern strike), microgranites and aplite-pegmatites (sublatitudinal strike), as a whole creating a complex “lattice.”

The age of the Kiya complex is determined as Eifelian (Vasiliev, Kartusov, 1964) on the grounds that the gabbroids of phase I of the complex near Makarak cut the volcanogenic rocks of the Palatninskaya Formation, while effusive analogues of nepheline syenites (bereshites) are localized in the upper parts of the Lower Eifelian Byskarskaya Series on the Uryup River. The close spatial connection, the presence of mutual transitions between intrusive and effusive formations, the same geological age, common features of chemism, and a similar trend in the evolution of the composition of the effusive formations of the Palatninskaya Formation and the intrusive formations of the Kiya complex make it possible to raise the question of the comagmatic nature of these formations. Genetically associated with the Kiya complex are titanomagnetite mineralization (phase I), rare-earth mineralization (phase II), nepheline raw material (phase III), and gold content.

The gold-ore deposits of the region, genetically associated with the Kiya complex, according to the features of the chemism of their typomorphic mineral associations, belong to two ore formations (after A. Ya. Bulynnikov): gold-bismuth-copper and gold-arsenic.

Thus, the known manifestations of essentially gold–bismuth–copper mineralization at Medyanka, Natalyevka, and in the headwaters of Kamenny Creek are spatially associated with thick dikes of gabbroids of phase I of the Kiysky complex; moreover, at the Natalyevskoye deposit this mineralization is superimposed on gabbroids and on dikes of alkaline syenites of phase II of the Kiysky complex, i.e., it definitely cannot have a genetic connection with the older Martaiginsky complex.

Typical representatives of the gold–arsenic formation within the district are the Berikul deposits. At the Staro-Berikul deposit, the Prokopyevskaya, Magistralnaya, and Krugobaikalskaya veins, with their northeastern ends, occur in gabbro-norites of phase I of the Kiysky complex, while veins No. 39 (horizon 232) and No. 49 (horizon 510) displace dikes of granite-aplites of phase IV of the Kiysky complex. At Novy Berikul the Komsomolskaya vein occurs partly in gabbroids of the Novo-Berikul massif (phase I), while the Leningradskaya vein is confined to an aplite-pegmatite dike. Consequently, the gold-ore deposits and ore occurrences of the gold–arsenic and gold–bismuth–copper formations within the district are not genetically related to the Martaiginsky complex of batholithic granitoids, as had been believed before the independent Kiysky intrusive complex was distinguished. They may be genetically related only to the post-batholithic Kiysky gabbro–alkali-syenite complex of Eifelian age (as a whole), since the younger Chebulinsky complex of alkaline granites is restricted in its distribution to only the western part of the district and has a different metallogenic specialization, although quartz–molybdenite veins in the intrusive bodies of this complex are weakly auriferous.

Spatially, the gold-ore deposits are controlled by the zones of occurrence of gabbroids of phase I of the Kiysky complex (see Fig. 1), but they are definitely formed after the emplacement of the alkaline syenites of phase II (gold–bismuth–copper) and even after the microgranites of phase IV (gold–arsenic).

Along the zones of occurrence of gabbroids of phase I, a distinct horizontal zonality is manifested in the distribution of hydrothermal formations of different types relative to the axis of the Devonian Makarak syncline (Fig. 2). This horizontal zonality is expressed in a successive change (with increasing distance from the syncline axis) not only of mineral associations, but also of ore-localizing structures. It is a reflection, at the present erosion level, of vertical facies (depth) zonality and depends on the depth of formation of the deposits relative to the base of the volcanogenic Eifelian, or, more correctly, relative to the land surface at the time the deposits formed. Thus, deposits of the gold–arsenic formation are localized in the form of persistent suites of quartz veins at depths of 1.5–2.5 km below the base of the volcanogenic Devonian (Fig. 3), whereas deposits of the gold–bismuth–copper formation occur as lens-shaped and pipe-shaped bodies of quartz–carbonate composition at depths of 0.8–1.0 km, respectively. Higher upward, gold mineralization is replaced by polymetallic mineralization, localized in thick crush zones, cemented mainly by carbonates and cutting not only the underlying Devonian, but also the Devonian formations proper.

The ore formations that were previously contrasted with one another (gold–arsenic and gold–bismuth–copper) have elements of compositional similarity (minerals, trace elements, isotopic composition of lead, etc.), show mutual transitions within a single deposit, and, participating in the struс—

or of a single facies column, are members of one genetic series of formations.

Thus, of the four intrusive complexes considered, the post-batholithic Kiia gabbro–syenite complex has the greatest ore-bearing capacity.

Taking into account the revealed regularity in the spatial distribution of gold mineralization, prospecting and exploration for gold within the northern part of the Kuznetsk Alatau should be carried out along the zones where gabbroids of phase I of the Kiia complex occur (see Fig. 1). At the same time, in the area of the village of Sosnovka one should expect mineralization of the gold–bismuth–copper formation, and in the headwaters of the Kazanka River—mineralization of the gold–arsenic formation (Berikul type).

Fig. 2. Generalized scheme of the distribution of deposits and ore occurrences of various formations in a folded structure
relative to the axis of the Makarak syncline

I — present-day erosional surface; II — base of the volcanogenic Devonian; III — axial line of the Makarak syncline. For other conventional symbols see Fig. 1.

Fig. 3. Scheme of vertical zonality