ON A NEW ORE OCCURRENCE OF ZINC AND LEAD IN THE NORTHWESTERN PART OF KEMEROVO OBLAST

P. N. Parshin

(Presented by the seminar of the Research Institute of Hydrogeology)

The northwestern part of Kemerovo Oblast (the Yashkino and Yurga administrative districts) is located at the junction of two geological structures: Kuzbass and the Kolyvan-Tomsk folded zone. Since 1963, hydrogeochemical investigations have been carried out here by the Problem Geological Laboratory of the Tomsk Polytechnic Institute.

In the autumn of 1965, on the right-bank part of the Tom River, 2 km north-northeast of the village of Krylovo (right bank of the Tom River, 25 km upstream from Yurga station), we encountered an interesting ore occurrence represented by pyrite, sphalerite, and galena. The good preservation of the sulfide minerals makes it possible to clarify certain features of the manifestation of sulfide mineralization in the area.

The geology of the area has been studied very poorly because of the poor exposure of the Paleozoic rocks, which are overlain by an almost continuous cover of Meso-Cenozoic sediments.

The geological structure of the area includes effusive-sedimentary marine formations, certain horizons of which, to the east, within Kuzbass, pass facially into red-colored continental sandy-clayey deposits.

The oldest formation in the area is an effusive-sedimentary sequence exposed along the left bank of the Tom River near the village of Mitrofanovo and previously assigned by some researchers (Matveevskaya, 1965; Nuvar’eva, 1964, and others), together with the Mitrofanovo member, to the Mitrofanovo suite of the Middle Devonian. The sequence is represented by interbedding of sandstones, chlorite-sericite schists, silicified limestones, felsite porphyries, albitophyres, and tuffs of acidic and intermediate composition. Their thickness ranges from a few meters to tens of meters. The total thickness of the sequence is more than 1 kilometer. The sequence dips westward at angles from 70 to 90°. We accept the age of the sequence as \(D_1—2\), by analogy with the Telbes Formation of Kuzbass; the possibility of a Lower Paleozoic age for the described formations is not excluded.

South of the section described, at the southwestern outskirts of the village of Mitrofanovo, rocks of the Mitrofanovo member (sequence; Tyzhnov, 1931) are exposed, represented by conglomerates, sandstones, clayey shales with Middle–Upper Devonian fauna, quartzites, and albitophyres. The total thickness of the member is 400–600 m. Its age is Middle–Upper Devonian (more precisely, the upper part of the Givetian—the lower part of the Frasnian). The mutual—

the relations of the rocks of the suite with the above-described rocks of the section on the left bank of the Tom River are unclear; however, the dip angles in the Mitrofanovo member do not exceed 40°, which is a factor allowing one to suppose that they rest unconformably upon the underlying steeply dipping Lower–Middle Devonian (?) formations.

To the north, in the area of Yashkino Station, the rocks of the Mitrofanovo member pass facially into the reefal limestones of the Yashkino member of Givetian–Frasnian age. The latter are underlain and overlain by clayey shales, distinguished by A. V. Tyzhnov under the name of the Pachino suite (thickness). Thus, it is most probable that the effusive-sedimentary formations of the Mitrofanovo member and the Yashkino limestones occupy a stratigraphic position within the Pachino suite. The age of the latter is dated by us as Middle–Upper Devonian; its total thickness is on the order of a kilometer.

The deposits of the Pachino suite are overlain, without visible unconformity, by the sandy-shale Yurgino suite, with a total thickness on the order of a kilometer. Apparently the upper part of the Yurgino suite includes effusive-sedimentary formations with lead-zinc mineralization, known in the area of the village of Baranovo. The age of the latter, according to the fauna collected by us here, is determined, in the conclusion of L. N. Kraevskaya, as Upper Devonian, possibly even Etroeungtian (the faunal determinations were made by L. N. Kraevskaya and Yu. A. Dubatolova).

The Paleozoic section is completed by sandy-clayey shales of the Lower Carboniferous, with a thickness of more than one kilometer.

The Paleozoic formations are folded mainly into folds of northeastern strike, are strongly schistose, and are affected by faults of submeridional and sublatitudinal directions. Associated with the latter are diabase dikes, presumably of Late Hercynian age, most widespread north of the area described.

At the expense of the Paleozoic rocks a Mesozoic weathering crust has developed, almost everywhere overlain by loose sediments of Quaternary (and outside the area—Cretaceous and Paleogene) age. The development of the weathering crust is selective in character and depends on the Paleozoic relief and the lithological composition of the rocks. Thus, over secondary quartzites and strongly silicified sandstones and shales, which form positive relief forms of the Paleozoic basement, no weathering crust is formed.

The host rocks of the ore occurrence described by us are quartzites and strongly silicified carbonaceous (?)-clayey shales with a clearly expressed subparallel banding due to light and dark-gray varieties, with the former predominating. Dark-gray varieties also occur as individual lenses. Almost all of them contain fine sulfide dissemination, represented by pyrite, sphalerite, and more rarely galena. Sphalerite crystals up to 2 mm in size are sometimes arranged as separate chains along thin fractures healed by quartz. In one of the samples, a sphalerite crystal 3 mm in size is located in a nest-like cluster of pyrite crystals 8 mm in diameter. Such facts allow one to suppose that the precipitation of sulfides occurred after the main processes of hydrothermal mineralization, in particular after the silicification of the rocks, and that the crystallization of sphalerite preceded the pyritization of the rocks.

The age of the ore-hosting rocks is apparently Upper Devonian. They can be correlated with those faunistically characterized 6 km north of the point described, at the western margin of the village of Baranovo. In this connection it is an interesting fact that in the western part of the village of Baranovo the bed of secondary quar-

...cites developed here at the expense of sandy-silty sediments, do not contain even traces of sulfide mineralization. However, already 200 m east of the indicated point, secondary quartzites and quartz albite-porphyries contain lead-zinc mineralization. Here, too, it is possible to trace a gradual increase in the degree of albitization of clayey and chlorite-sericite schists up to the formation of albite-porphyries. On the flanks of the Baranovo ore occurrence, the clayey schists contain almost no sulfide mineralization and have rather gentle (20–40°) dip angles. This indicates their possible role as ore-screening rocks along the flanks of fault disturbances during the manifestation of hydrothermal mineralization.

Silicification and albitization of rocks in the district are confined to major faults and often reach the formation of secondary quartzites and albite-porphyries, which cannot be strictly stratified. The main zones of sulfide mineralization are situated on the flanks of zones of intense silicification and, apparently, are connected with some rejuvenation of deep-seated faults. Morphologically, the most silicified zones form positive relief features with outcrops of bedrock at the surface, whereas the parts of the zones most enriched in sulfide mineralization are subject to intense chemical and physical weathering and thus form negative relief features in comparison with the former. In the latter, the ore-bearing rocks are overlain to a considerable extent by later Cenozoic deposits. This fact greatly facilitates the mapping of zones prospective for mineralization and, to a significant degree, explains the distribution of hydrogeochemical anomalies in the district. The latter prove to be displaced in plan from the zone of mineralization, and for their more precise interpretation it is necessary to carry out drilling, with study of the character and thickness of the unconsolidated deposits and with hydrogeochemical sampling.

Ore occurrences of lead and zinc, in addition to the two points described, are known in the areas of the villages of Mitrofanovo and Orlovka, along the Popovka, Iskitimka, Nikolskaya, and Nizhne-Yashkino rivers. Thus, at present a whole series of manifestations of sulfide mineralization is known in the district. The most interesting at present are four promising sites identified from data of integrated hydrogeochemical studies: Baranovo, Mitrofanovo, Kungurskii, and Dolgorechenskii (Udodov et al., 1965). In addition, several interesting (according to preliminary data, smaller) sites are being outlined, in particular 4 km north of Yashkino station, in the middle course of the Iskitimka River, in the lower course of the Lebyazhya River, and a number of others. Of interest is the nickel-cobalt ore occurrence encountered by us in 1963 in the middle course of the Vlaskovo River, at the northwestern edge of the Vlaskovo limestone quarry, on the tectonic contact of the Yashkino limestones and the clayey schists of the Pachino Suite. The content of nickel and cobalt in one sample, according to spectral analysis, reaches 1%. At this same point, in dumps of brown iron ores, native copper was discovered under the microscope by B. M. Levashov.

V. V. Borodin also notes a significant gold content in the oxidation zone of the Baranovo ore occurrence.

It is important to note the presence of bauxites in the district, associated with the Yashkino limestones (Vardanyants, 1931, and others).

Thus, from the facts presented it is clear that this district is promising for mineral resources, and that further geological investigations must be undertaken to identify them.

References

L. A. Vardanyants. On a bauxite deposit in the vicinity of the Yashkino cement plant. Bulletin of ZSGRU, No. 3, 1931.

A. L. Matveevskaya, E. F. Ivanova. Geological structure of the southern part of the West Siberian Lowland in connection with questions of oil-and-gas potential. Publishing House of the Academy of Sciences of the USSR, 1960.

Yu. A. Nuvar’eva. On the spatial and genetic relationship of polymetallic mineralization of the Kolyvan–Tomsk zone with Devonian volcanism. In: Geology and Metallogeny of Effusive-Sedimentary Formations of Siberia. Nedra Publishing House, 1964.

A. V. Tyzhnov. Materials on the stratigraphy and tectonics of the Devonian deposits of the Kuznetsk Basin. Bulletin of ZSGU, vol. XI, issue 1, 1931.

A. V. Tyzhnov. On the study of Devonian limestones of the northwestern margin of the Kuznetsk Basin. Bulletin of ZSGT, No. 3, 1931.

P. A. Udodov, V. M. Matusevich, N. V. Grigor’ev. Hydrogeochemical prospecting under conditions of the semi-closed structures of the Tom–Ya interfluve. TSU Publishing House, Tomsk, 1965.