PATTERNS OF DISTRIBUTION AND FORECASTING OF GOLD ORE DEPOSITS IN THE NORTHERN PART OF THE KUZNETSK ALATAU

B. D. Vasil'ev

(Presented by Prof. Dr. A. M. Kuzmin)

At the present time it is considered almost generally accepted that the principal gold content of the Mariinsk taiga is connected mainly with the Devonian intrusion of granodiorites and, to a lesser degree, with Devonian alkaline syenites (Dembo et al.). Below, another point of view is set forth concerning the age, genetic affiliation, and patterns of spatial distribution of the gold ore deposits of the district, and an attempt is made to forecast new deposits.

The northern part of the Kuznetsk Alatau has a block structure, caused by long-developing regional disjunctives of two principal trends: 330–340° NW and 20–40° NE. At the end of the Early Cambrian, within the territory of the area there existed a zone of uplift of northeastern strike (the Central'ninsko-Berikul'skaya zone), bounded by regional disjunctives, and associated zones of subsidence.

In the zones of subsidence, sequences of volcanogenic (Chumai Formation) and terrigenous rocks with limestone horizons containing Sanashtykgol'-Obruchevka fauna (Karacharovo Formation) were formed, cut by dikes of hydrothermally altered quartz albitophyres. Correlating these formations respectively with the Pecherkino and Ancheshevo formations of the Salair, we obtain stratigraphic and magmatic criteria for substantiating the possibility of discovering in Martaiga polymetallic and gold-barite deposits of the Salair type. The presence here of small placers, in which the gold content is 3–5 times higher than in the placers of Berikul' and Natal'evka, together with the presence of barite and pebbles of limonite, indicates that these placers were formed through erosion of oxidation zones of sulfide deposits. Thus, in Martaiga, in the subsidence zones of the end of the Early Cambrian epoch, and first of all in the Chumai basin, there is a real possibility of discovering Lower Cambrian deposits analogous to those of the Salair.

The Central'ninsko-Berikul'skaya uplift zone, within which the principal gold ore deposits of Martaiga are concentrated, differs sharply from the subsidence zones in the degree of gold content and, what is especially important, in the age and type of gold mineralization. It is precisely in this zone that bodies of the pre-Devonian granodiorite complex are widely distributed, with which Dembo and others genetically associate the principal gold ore deposits of the district. It seems to us that these deposits are of younger age. The younger intrusive activity is represented by the Kiisk gabbro–alkaline-syenite complex.

of Eifelian age (Vasil'ev and Kortusov, 1964). Within the latter, the following phases have been distinguished: I—titanium-augite gabbro; II—alkaline syenites with a subphase of nepheline syenites; and III—microgranites and aplite-pegmatites. The rocks of the complex form bodies in a belt of meridional strike north of Taskyl over a distance of up to 70 km. Within the general belt, the bodies of the individual phases of the complex have different orientations. Thus, the distribution of gabbroids of phase I is controlled in the northern part of the region by concealed basement faults: the Natal'evka (340°) and Berikul' (330°) faults, and by the exposed Makarak fault (60–70°). Along the two latter zones, from east to west in the modern erosion section, there is a change in facies from hypabyssal to subeffusive. The alkaline syenites of phase II form fissure bodies striking 20–30° NE, while the microgranites of phase III form bodies of sublatitudinal strike.

At the Natal'evka, Komsomol'sk, and Berikul' deposits, the ore bodies sometimes occur in gabbroids of phase I of the Kiya complex. In addition, at Natal'evka the mineralization is also superposed on alkaline syenites of phase II, while at Berikul' the quartz veins cut microgranites of phase III. On this basis, we genetically relate the gold mineralization of the Natal'evka, Komsomol'sk, and Berikul' deposits not to the pre-Devonian granodiorite intrusion, but to the Kiya gabbro–alkaline-syenite complex of Eifelian age. It is younger than phase III of the complex, but spatially it is controlled by the zones in which the gabbroids of phase I are emplaced. Being Devonian in age, the gold-ore deposits of the district are regularly situated with respect to the folded structure of the Devonian structural stage, which as a whole is characterized by open folds with axes striking 30° NE. Thus, the deposits and ore occurrences of the Au–Cu–Bi formation (Natal'evka, Medyanka, Kamennyi) are located on the limbs of the Devonian Makarak syncline, at approximately the same distance from the axis of the latter, where sharply hypabyssal dike bodies of gabbroids occur. Deposits of the Berikul' type (Berikul', Komsomol'sk), in which most of the gold was deposited with galena and sphalerite, are situated at a greater, but equal, distance from the axis of this syncline, where the gabbroids form relatively large hypabyssal bodies and accordingly were formed at greater depths.

The dependence between the type of mineralization, the facies character of the intrusive bodies, and the definite position of both with respect to the folded structure of the Devonian indicates that the observed zonality is determined by the depth at which the intrusions and mineralization formed. Thus, the spatial position of the gold-ore deposits of Mariinskaya taiga is controlled, on the one hand, by the emplacement zones of gabbroids of the Kiya complex (NW structures) and, on the other hand, by their position in the folded structure of the Devonian stage (NE structures). The regularities established make it possible to forecast gold-ore deposits of particular types within the territory of the Mariinskaya taiga. For example, in the headwaters of the Kazanka, the discovery of a deposit of the Berikul' type is possible, and east of Makarak, an ore cluster with Au–Cu–Bi mineralization. Establishing vertical zonality in the distribution of deposits opens prospects for forecasts at depth within ore fields.