NEW DATA ON THE GOLD-BEARING CHARACTER OF THE NORTHERN PART OF THE KUZNETSK ALATAU

A. I. Goncharenko (TSU)

The Kuznetsk Alatau is the most important gold-bearing province of the Altai–Sayan folded region. Within this region, in addition to numerous quartz-vein gold-ore deposits [7], promising deposits of the skarn type are known [8, 9].

Recently, within the northern part of the Kuznetsk Alatau, the author identified a new type of gold mineralization associated with apohyperbasite metasomatically altered rocks (listvenites).

Gold-bearing listvenites in association with hyperbasites are known in a number of regions of the Soviet Union [3, 4, 5, 6, 12, 16, 17] and abroad [13]. Industrial concentrations of gold are often associated with formations of this type. The gold mineralization in the listvenites of the northern part of the Kuznetsk Alatau is also of practical interest.

The gold-bearing listvenites occur in the endocontact of the northern part of the hyperbasite massif of the Severnaya–Zelenaya Mountains, which has been studied by V. A. Kuznetsov (1940), G. V. Pinus [15], E. D. Shpaikher (1963), O. G. Konovalova (1963), and the author.

The hyperbasite massif is an acmolith-like body, steeply dipping to the west, elongated in the meridional direction, and occurring among deeply metamorphosed Proterozoic rocks. Along the line of the western contact, the hyperbasites are cut by a series of small granitoid intrusions, while their eastern contact is complicated by the emplacement of intrusive bodies of gneissic gabbro. In the petrographic composition of the ultrabasic intrusion, the leading place belongs to dunites serpentinized to varying degrees. Harzburgites, pyroxenites, and serpentinites are subordinate in development. The latter usually gravitate toward tectonically weakened zones, where they are often connected by gradual transitions with listvenites.

Gold mineralization in the listvenites was established by us during a detailed petrographic study of the eastern contact zone of the hyperbasite massif with the enclosing amphibolites. The listvenites are exposed here along the wall of an ancient cirque in the form of a belt about 80 m wide, having a submeridional strike. According to the composition of the original rocks, two types of formations are distinguished in the indicated zone: ortho- and epilistvenites [12]. Ortholistvenites, as products of metasomatic alteration of hyperbasites, are the most widespread rocks and compose the endocontact part of the massif. Directly adjacent to the ortholistvenites

Adjoining the crumpling zone are epilistvenites, which arose as a result of metasomatic alteration of the enclosing amphibolites.

The sequence of formation of the distinguished types of listvenites may be represented as a column of metasomatic zonation. During alteration of amphibolites the following series of metasomatic formations arises: quartz–carbonate–mica rocks—quartz–albite–carbonate–mica rocks—mica–carbonate–chlorite rocks—epidotized amphibolites.

The apohyperbasite type of listvenites differs sharply in composition from the epilistvenites. The outer zone of these formations is composed of carbonatized serpentinites, which, through talc–carbonate–serpentine and talc–carbonate rocks, gradually pass into quartz–talc–carbonate and quartz–carbonate listvenites. Chromespinellides and magnetite are constantly present in these rocks. The structural-textural aspect of the listvenites is quite varied. Most often they are characterized by fine-grained composition and massive textures. An exception is formed by the widely developed talc–carbonate rocks, which not infrequently prove to be finely schistose. At the same time, the quartz–carbonate type of listvenites is distinguished by the presence of a characteristic network of quartz veinlets (up to 1–2 cm wide), clearly standing out against the background of the fine-grained groundmass. The microstructure of the listvenites varies from microlepidoblastic to granoblastic.

The character of the metasomatic zonation of the rocks described changes substantially in the near-contact zone of a dike of Alaskite granites that cuts the listvenites. In this case, intensive recrystallization of the listvenites is manifested. The zonation is expressed very clearly and has the following form (with increasing distance from the contact with the granites): micaceous rocks—quartz–mica–carbonate rocks—quartz–mica–talc–carbonate rocks—talc–carbonate rocks. Not infrequently the granites themselves undergo metasomatic alteration, passing in this case into quartz–mica beresite-like rocks.

The process of metasomatic alteration of the hyperbasites of the Mount Zelenaya area appears very complex and multistage. The sequence of superposed phases of listvenitization leads to the formation of at least three genetic types of metasomatic formations. Talc–carbonate rocks usually develop after the original alloserpentinites. As a result of deeper transformations, quartz–carbonate rocks arise (listvenites proper), among which a special type of potassic listvenites is distinguished.

The listvenites of the types noted differ from one another in mineralogical composition, peculiarities of chemism, and the behavior of individual petrogenic elements. At the same time, the iron content of the carbonates changes regularly from an almost pure magnesite variety in the talc–carbonate rocks to breunnerite in the potassic listvenites, which is a consequence of changes in the carbon-dioxide regime at individual stages of metasomatism.

The gold content of the listvenites is established in connection with mineralized zones of crumpling and brecciation. Gold is concentrated in the selvage zones of quartz veins, which themselves very often prove to be gold-bearing. Gold mineralization is accompanied by sulfide mineralization, which is manifested in the form of discontinuous veinlets ranging in thickness from fractions to 2–5 mm, small nests, and scattered accumulations. The sulfides are represented by galena, sphalerite (Fig. 1), pyrite, chalcopyrite, arsenopyrite, and pyrrhotite. Native gold occurs in close intergrowth with galena, more rarely together-

Fig. 1. Replacement of sphalerite (1) by galena (2) in listvenite. Polished section 3278/6, magnification 250×.

Fig. 2. Gold (1) and galena (2) in quartz. Polished section 3250/5, magnification 500×.

with pyrite and sphalerite, and also in quartz without visible connection with sulfides (Figs. 2 and 3). The form of the gold grains is rounded, droplet-like; their size ranges from 0.001 to 0.5 mm. It should be emphasized that gold is very closely associated with galena. Spectral analysis of the galena revealed nickel, copper, zinc, molybdenum, bismuth, tin, arsenic, gold, antimony, silver, calcium, manganese, and barium.

Fig. 3. Intergrowth of gold (1) with galena (2) at the boundary of sphalerite (3) with non-ore minerals (black). Polished section 3280/5, magnification 600.

Gold in an association similar to that described above is noted in listvenites of the Maralikha deposit in southern Altai [5], and also in the group of deposits of the Miass district of the Urals [6]. The Bluebell deposit in the USA [13] is distinctive, where mineralization of gold associated with pyrite, galena, chalcopyrite, and other sulfides “is localized in serpentinite formed during the hydrothermal alteration of peridotite under the influence of a granodiorite intrusion.”

The gold mineralization of Mount Zelenaya, being superimposed with respect to the listvenites, reveals a close genetic connection with them. The parent intrusion consists of leucocratic granites and granite-aplites, which are often spatially coincident with the listvenites. It is important to note here that gold has been established not only in the listvenites and in the quartz veins occurring among them, but also in the granites themselves, which have not undergone metasomatic alteration.

Gold-bearing granites form small stock-like bodies and dikes cutting the hyperbasites. The granites have a clearly expressed leucocratic character and consist of quartz, oligoclase, lattice microcline, biotite, hornblende, apatite, magnetite, and secondary minerals—sericite, epidote, and chlorite. The content of mafic components does not exceed 3–5%. The structure of the rocks is porphyritic with a granitic, more rarely granophyric and micropegmatitic, groundmass.

Intrusions of similar granites form a discontinuous chain along the line of the western contact of the ultrabasic massif of the Northern—

Zelenaya. The age of the intrusions is determined by their cross-cutting position relative to the diorites and gabbro-diorites of the Martaiga complex. Taken together with the features of the geological setting, petrographic composition, and chemistry of the granites (table), this makes it possible to regard them as an independent petrological association of rocks. There are grounds to suppose that the granites described are part of the formation of Devonian subvolcanic granites distinguished in the territory of the Kuznetsk Alatau by V. I. Bognibov, A. N. Distanova, and V. N. Dovgalev [2]. Apparently, the young Devonian epoch of gold mineralization in the northern Kuznetsk Alatau is connected with this formation, which must be taken into account in assessing the gold-bearing potential of the region as a whole.

Table

Chemical composition of granites of the Mount Zelenaya area

Numerical characteristics according to A. N. Zavaritsky

Listvenitization as a complex of metasomatic changes was widely manifested in the central part of the Kiya structural-facies zone of the Kuznetsk Alatau, which represents a large geoanticlinal uplift [1]. The internal structure of this zone is very complex [14]. Listvenites and listvenitized rocks are usually developed along the endocontacts and tectonically weakened zones of hyperbasite massifs. The geological-tectonic position of the hyperbasites is determined by their confinement to structures of long-term development, where manifestations of magmatism of different ages are recorded. At the same time, formations of younger intrusive complexes, with which various manifestations of hydrothermal metamorphism and metasomatism, including listvenitization, are associated, are often superposed on plutons of the hyperbasite complex. At the same time, in individual cases phenomena of autometamorphic listvenitization of hyperbasites are established [10].

Thus, there is every reason to regard listvenites and other products of metasomatic alteration of rocks as heterogeneous formations, and clarification of their role in connection with their gold content is of importance in the practice of geological prospecting work. In this respect, zones of listvenitization may constitute an interesting target for gold exploration. But listvenites are not always gold-bearing, and their evaluation as potential concentrators of gold must be carried out with due regard for the study of the intrusive formations of the area. As is known, the gold-bearing intrusions in the northern part of the Kuznetsk Alatau are those of the Martaitiga and Kundustuyul complexes, and recently the opinion has been expressed (B. D. Vasil’ev, 1966) that gold mineralization is genetically related to the Kiya gabbro-syenite complex. The data obtained by us make it possible to distinguish, within the territory of the northern part of the Kuznetsk Alatau, a gold-bearing intrusion of leucocratic granites, which is correlated with the granites of the Devonian subvolcanic formation [2].

Analysis of the features of the geological structure, the character of the distribution of magmatic complexes, and the processes of listvenitization and gold mineralization associated with them makes it possible to raise the question of the presence in the northern part of the Kuznetsk Alatau of a gold-bearing zone extending for about 80 km from the mouth of the Severnaya River (the basin of the N.-Ters’ River) to the headwaters of the Kundustuyul River, with a possible continuation to the north. The data of heavy-mineral sampling for gold agree well with the materials presented. Thus, an elevated gold content characterizes a large number of heavy-mineral samples from the alluvium of the headwaters of rivers and brooks that originate in the area of development of ultrabasic rocks. In the watershed part of the Gorelaya and Talanovaya rivers, where serpentinites and gold-bearing listvenites, cut by small bodies of granitoids and gabbro, are exposed, gold is contained in significant quantities in the deluvium of mining workings. In the alluvial deposits of the left tributaries of the Talanovaya River, osmian iridium and platinum occur together with gold. According to I. P. Beresnevich (1910), about 2 tons of placer gold were extracted in the area of the Semenovsky mine. This investigator considered favorable factors for discovering the primary source of the gold to be “the location of the placer high on the mountain, the roughness and rockiness of the gold, and also the character of the rocks (peridotites, serpentines).”

The establishment of gold-bearing listvenites in the northern part of the Kuznetsk Alatau significantly broadens the prospects of this region for gold and makes it possible to raise the question of the possibility of discovering primary gold-ore deposits of a special genetic type, related to the processes of listvenitization.

REFERENCES

1. Alekseev P. V. and Gorelov G. F. Geological results of the work of the ZSGU for 1963. Bulletin of the West Siberian and Novosibirsk Geological Administrations, issue 1, 1964.

2. Bognibov V. I., Distanova A. N., Dovgal’ V. N. Formation of Devonian subvolcanic granites of the Kuznetsk Alatau. Geologiya i geofizika, 1966, No. 9.

3. Borodaevsky N. I. and Borodaevskaya M. B. The Berezovsky Ore Field. Metallurgizdat, Moscow, 1947.

4. Borodaevskaya M. B. On the origin of berezites and some other metasomatic rocks of the Berezovsky gold-ore deposit in the Middle Urals. Transactions of the All-Union Mineralogical Society, issue 2–3, 1944.

5. Borodaevsky N. I. and Panova V. V. Gold-bearing listvenites of the Maralikha deposit in Southern Altai. Transactions of the TsNIGRI Institute, issue 25, 1958.

6. Borodaevsky N. I. Materials on methods for studying structures and for geological prognostic evaluation of gold deposits. Transactions of the TsNIGRI Institute, issue 35, 1960.

7. Bulynnikov A. Ya. Gold-ore formations and gold-bearing provinces of the Altai-Sayan mountain system. Transactions of Tomsk State University, geological series, vol. 102, 1948.

1. Budynnikov A. Ya., Vrublevsky V. A. On contact gold deposits of the Altai–Sayan mountain region. In: The Basic Ideas of M. A. Usov in Geology, Academy of Sciences of the Kazakh SSR, 1960.

2. Vasiliev B. D. Gold in the skarns of the Natalievskoye deposit (Mariinsk taiga). Materials on the Geology and Mineral Resources of Western Siberia, Tomsk, 1964.

3. Goncharenko I. A. Hyperbasites of the Barkhatny massif (Kuznetsk Alatau). Materials on Mineralogy, Petrography, and Mineral Resources of Western Siberia and Krasnoyarsk Krai, issue 4, 1967.

4. Gorevanov E. A. An ancient gold-bearing intrusion of the Kuznetsk Alatau. Bulletin of the Western Siberian Geological Exploration Trust, issue 1, 1934.

5. Kashkai A. M., Allakhverdiev Sh. I. Listvenites, Their Genesis and Classification. Baku, 1965.

6. Connolly J. Mesothermal gold deposits. In: Geology of Ore Deposits of the Western States of the USA, 1937.

7. Kortusov M. P. Paleozoic intrusive complexes of the Mariinsk taiga (Kuznetsk Alatau), vol. 1, Tomsk, 1967.

8. Pinus G. V., Kuznetsov B. A., Volokhov I. M. Hyperbasites of the Altai–Sayan folded region. Moscow, 1958.

9. Rabinovich K. R. Geological-genetic features of the listvenites of Southern Altai. Proceedings of the Altai Mining and Metallurgical Research Institute, Academy of Sciences of the Kazakh SSR, vol. 16, 1963.

10. Selimkhanov N. M. On the gold content of listvenites and other hydrothermally altered rocks of Azerbaijan. Scientific Notes of S. M. Kirov State University, no. 2, 1961.