Geological review

Tomsk oblast occupies the south-eastern edge of the West-Siberian plate, framed in the south by the structures of Kuznetskiy Alatau and Kolyvan-Tomsk folded areas.

In the history of the geologic development of the oblast territory the following stages can be defined: Baikal-salairsky, Hercynian and Mesozoic geotectonic stages, which correspondingly formed lower, middle and upper structural layers. Two lower layers form fold basement of the plate and the upper layer constitutes the platform mantle.

The basement is folded by highly dislocated and metamorphized effusive- terrigenous rocks of Precambrian and Paleozoi, broken through by intrusions of different age and structure. The most ancient formations on the folded plate basement are baikalides. They constitute the Yenisey fold system in the north of the oblast, formed in the Early Precambrian on the crust of the continental type that appeared as a result of splitting of the Proterozoic fold systems.

The formations of the salair type build the soil-footing contact in the basin of the river Chulym in the Tym-Ket interfluve and present the northern extension of the Kuznetskiy Alatau. The Salair fold structures are presented by Pre-Cambrian and Lower Paleozoic metamorphic complexes. The segments of these structures form horst uplifts which separate depressions of superimposed type, made by sedimentary and volcanic-sedimentary deposits. In the west salairids are bordered by Beloyarsk and in the west by Verkhneketsk deep faults. The most ancient formations include Upper Riphean amphibolites and marbles of the Kirgislinsky complex, which crops in the erosive cut of the basement in the axial regions of the Yaysky horst in the south-east of the oblast. In the Lower Cambrian terrigenous- volcanic deposits the ore-bearing hydrothermal metasomatism is widespread, shown by the areas with sulfur-polymetallic mineralization.

During the Hercynian development stage of the territory in the conditions of its prevailing deflection the accumulation of the marine, marginal-marine, marginal-continental facies and vulcanites took place. Formed terrigenous, terrigenous-carbonate and volcanogenis thiknesses of Devonian and Carbonian lie with the cross bedding on the dislocated salair basement. Owing to the differences in facie conditions of sediment formation in the Pre-Tom region, two structural facie zones, which differ in the type of sections, can be chosen: the Kuznetsko-Alatausky zone in the east and the Kolyvan-Tom in the west.

Within the structure of the Kuznetsky-Alatausky zone the carbonate deposits of marginal-marine and marine facies of the Upper Devonian and Lower Carbonian form Tashmin and Usman synclines. The Hercynides section foundation is fold by lagoonal-continental red-coloured deposits of the Lower Devonian suite, overlapped by vulcanites, which earlier had been united with the Kolyvan-Tom zone vulcanites into one Lower-Middle Devonian volcanogenic rock mass. Intrusive bodies are very diverse and presented by ultrabasites, gabbrides, microdiorites.

Thicker (up to 7 km) Devon-carbonous rock mass in the Kolyvan-Tom zone is presented by volcanogenic and carbonic- terrigenous deposits of marginal-marine facies of the Tomsk downfold. The section of Lower Carbonous sediments is rich in crinoids, moss animals, and brachiopods. The sediments of the whole structural formational complex are united in submeridional folds. In the Late Hercynian tectogenesis cycle in the Kolyvan-Tom zone the intrusion of “Tomsk diabase” dikes. Zones of hydrothermal change of terrigenous rock masses include quartz-vein gold mineralization and separate ore outcrops, which give placer leakage fluxes and small gold placers.

From the east and south-east the Tomsk downfold is framed by Tomsk thrust, where Devonian sediments of the Kolyvan-Tomsk zone are pulled over younger sediments of the Kuznetskiy Alatau northern extension. The thrust is associated with numerous fracture zones and complex folded structures. In its rear areas the thick Urbeyskiy collapse zone that may contain gold, can be marked out.

Heightened tension in the plan of folded and tectonic structure of the Tomsk downfold was brought by the Kolarovo-Semiluzhensky thrust of the north-north-eastern strike. Within the latitudinal collapse zones which frame the thrust, antimony deposits with gold-antimonite mineralization were discovered.

The northern extension of the Kolyvan-Tomsk folded structure is presented by the Pyl-Karaminskiy composite anticline, which covers the Chulym-Ket-Tym interfluve. In the relief of the folded basement surface the composite anticline is shown by the uplift, made from the formations of Devonian-Carbonian terrigenous and carbonous sediments. The Ust-Tym median massif, which extends along the left bank of the river Ob northwards from the town of Kolpashevo, is considered to be the fragment of the Salair folded system, transformed by the Hercynian tectogenesis. Within the basement relief it is expressed by the downfold, which is represented by carbonate and carbonate-terrigenous rocks of mass of the same age as the the Tomsk downfold sediments.

The platform mantle was formed in the Mesozoe and Cainozoe as a result of the West-Siberian plate plunge that had started in the Jurassic period, the process was associated with the rocks of mass formation of marine, marginal-marine, marginal-continental and continental facies. Sediment formation didn’t affect only the Tomsk downfold, which had been transformed into the horst structure at the beginning of the Cainozoe named the Tomsk inlier (or Tomsk-Kamensiy inlier).

The position of most deep-water zones of the plunging plate was determined by the riftogenesis, which appeared in the west of the territory at the end of trias. In the paleorelief of the Pre-Jurassic surface the range of rifts appeared (Koltogorskiy, Ust-Tymsky and Chuzikskiy), which divided the paleorelief into inter-rift blocks – uplifts (Nizhnevartovkiy, Kaymysovskiy, Alexandrovskiy-Vasyuganskiy and Pudinskiy). The macrostructure development of the sedimentary cover was predetermined by the peculiarities of the basement block structure with the main trend of heritage structures smoothing. The positive forms of the relief – horsts comprise the large vaults, megabanks, inliers, the negative – grabens correspondingly have downfolds and depressions.

The Jurassic deposits present the leading oil-and-gas complex in the south-east of the West-Siberian plate. According to facies conditions of the Jurassic rock of mass formation the Ob-Tazovskaya and Ob-Irtyskskaya different facies areas are selected. The first area covers mostly bent plate parts in the north-west of the territory and is formed by marginal-marine and marine terrigenous deposits, which are rich in organic substances. The second comprises uplifted areas in the Jurassic paleorelief in the east of the territory. They are expressed in megs-banks, large uplifts, formed by carboniferous continental facies.

Cretaceous system in the territory of the oblast is represented by the marine, marginal-marine and continental deposits. Marine regression on the border of the Early and late cretaceous led to the continental regime establishment in the significant part of the territory, which was replaced by a new power transgression in the Late Cretaceous period. Marine facies are wipespread westwards from the meridian of the town of Kolpashevo, continental facies present eastwards from the settlement of Beliy Yar. The area between them is occupied by facies of transition type with the rapid change of the ancient coastline borders. In the Kolpashevsky region, where most complicated facies relations take place, the alternation in the section of transgressive and regressive packs together with continental deposits can be observed. Marginal-marine facies of the upper parts of the Ipatovskaya and lower parts of the Gankinskaya suites contain oolitic ores of Narymsky and Kolpashevsky horizons. The continental Kiyskaya suite in the south-east of the oblast includes allite deposits and sometimes bauxites, which belong to the Chulym-Yenisey bauxite province.

Within the paleogene system in the territory of the oblast the Paleocene, Eocene and Oligocene deposits were discovered. The Eocene deposits contain glauconitic sanstones, the Bakchar horizon of the sedimentary iron ores, which forms together with the Narym and Kolpashevo iron ore horizons the Bakcharsky, Kolpashevsky and Parabel-Chuziksky ore blocks. In the area of Tomsk inlier plunging to the marginal-marine facies of the Early-Middle Eocene, the industrial zircon-ilmenite deposits were explored.

Oligocene is widely presented by the alluvial and limnetic-alluvial sandy-argillaceous deposits, which contain lignites and brown coals aside from zircon-ilmenite mineralization. The coal-bearing Oligocene series are the raw base of brown coals of the Tomsk oblast.

Quaternary formations reflect the latest stage of the West-Siberian plate uplift and its folded frame. The formation of limnetic-alluvial deposits of the Kochkovskaya suite, which contains pebble basement acting as the key horizon, reached the regional level in Eopleistocene period. During the Early-Middle Neopleistocene stage the formation of limnetic-alluvial rock of mass deposits took place in the West-Siberian Plain. The fact that the considerable part of the territory belongs to the periglacial zone conditioned the eurhythmy of deposits: during interglacial periods the alluvial sediments were accumulating and during glacial periods – the limnetic deposits. From the end of the Late Pleistocene till present the elevation of the territory takes place with the parallel split process and formation of the modern river network and deposits of the valley complex.

Natural resources

Tomsk oblast is rich in different natural resources that comprise its resource potential: oil and gas, metal and non-metal minerals, brown coal, peat and sapropel, fresh drink, mineral, thermal, and industrial underground waters.

The most important energetic source is carbohydrates, which provide the highest level of budgetary recharge and investment inflow. Tomsk oblast is included into West Siberia oil-and-gas province and is one of the leading oil-and-gas producing regions of Russia. In the interiors of the perspective lands, divided into 5 oil-and-gas regions, 7.5 bn tons of carbohydrates are concentrated. Federal balance registered 103 oil and gas deposits. Proven deposits are situated mainly on the left bank of the river Ob in the territory of the Alexandrovsky, Kargasoksky and Parabelsky administrative regions within the borders of the Sredneobskaya, Kaymysovskaya and Paiduginskaya oil-and-gas regions. Perspectives of the right bank of the Ob (mostly gas deposits) are connected mainly with the exploration of Paleozoic deposits of the Predyeniseyskaya oil-and-gas region, which covers the north-east of the oblast.

Regarding metal resources the oblast territory has large reserves of sedimentary iron ores and zircon-ilmenite placers, which build the basis for the further development of the mineral resource and processing branches. The degree of metals exploration differs. Proven placer reserves of the Tuganskoye and Georgievskoye deposits were included in the Federal balance. Within the primary development stage of the Tuganskoye placers in the South-Alexandrovo area the experimental-industrial production was organized. The degree of iron ore exploration remains on the level the productive estimate of main ore blocks of the West-Siberian iron ore basin in the belt of cretaceous-palaeogene deposits with the width of 80-260 km. The basin area in the territory of the oblast totals to 80 000 km2 with total iron ore resources up to85.9 bn tons. For the industrial exploration the most promising are the ores of the Bakchar deposit. Their potential customers can be Kuznetskiy and West-Siberian metallurgical plants. The work on geological exploration and technological evaluation of the Bakchar iron ore deposit was launched in 2005.

In the south-east of the oblast within the Tomsk inlier the deposits of gold, antimony, zinc and bauxites were discovered. Their commercial evaluation, except for gold, is not high and limited by probable reserves of different validity. The main object for geological study out of this list of metals remains gold. In 1997 while performing revision works on the evaluation of mineral and raw materials base condition in the south of the oblast, the Tomsk potentially gold-field region was defined. Total forecast resources of gold within the defined gold-bearing blocks were evaluated according to the P3 category in the amount of 105 tons. Currently the work on exploration and evaluation of ore and alluvial gold in Khaldeevskaya and Tugoyakovkaya areas has been started.

Non-metal mineral resources, which form the raw base of processing industry enterprises, are presented by industrial, mining and chemical staff and construction materials. The deposits of industrial and mining-chemical minerals, registered by the federal balance, gravitate towards the areas with superficially plunged basement in the south-east of the Tomsk oblast. Main representatives of this group of natural resources are high-melting clays, kaolin and quartz glass-making sands. Deposits of construction materials, which form the group of generally used natural resources, are widespread in a greater degree.

Regarding peat resources the oblast ranks second in Russia. The reserves are almost not used as well as associated natural resources of bog genesis: phosphates, carbonates and limnetic sapropel. Brown coals are studied rather poorly and are practically non-demanded, although they are valuable chemical-technological and energetic source. The Talovskoye and Tuganskoye brown coal deposits are the objects of top priority industrial development.

Large reserves of fresh underground waters of the West-Siberian artesian basin and partially interstitial waters of the Proterozoic-Paleozoic basement bodies (in the south of the oblast) serve as the main source of the public water supply. In the territory of the oblast 31 fresh water reservoirs have been found; 21 of them belong to the artesian basin. In deep horizons of Mesozoic deposits of the platform mantle, the mineral and thermal waters are spread, including industrial waters of oil and gas deposits, which have elevated concentrations of the whole range of valuable components. For medical purposes 4 mineral water reservoirs were explored.

Material is prepared by OJSC "Tomskgeomonitoring"