ON GEOCHEMISTRY OF OOLITIC AND SWAMP IRON ORES OF TOMSK REGION

The largest iron ore reserve of Tomsk region is found in the Bakcharsky deposit, the oolitic ores of which are relative to the coastal-marine type of sedimentary ores. The ores selected from a well of the Polynyansky section are represented by brown-cemented oolitic goethite-hydrogoethite iron ores, green-grey clay-chlorite microlithic and dark-brown types, and transitive types between oolitic goethite-hydrogoethite and clay-chlorite ones as well. According to the most recent information, the established two types of ores (the green-grey clay-microlithic and dark-brown, and the brown-cemented oolitic goethite-hydrogoethite iron ores) are the original genetic types of the iron ore deposit, with intermediate (transitive) types or subtypes between them. The X-ray fluorescent analysis of oolitic iron ores shows that the average content of Fe2O3 is 42.52%. Another source of iron ores in Tomsk region is continental shows of swamp ores on the Ob right riverside. Ores are deposited in sediments of a terrace above the flood plain in the form of lenses and veins of two mineral types: the limonite and siderite ones. At the Kireevsky show, the layer of sectional siderite ore is tracked from 0.2 to 0.5 m, according to the X-ray fluorescent analysis, the content of Fe2O3 varies from 43.62% to 50.85%. Based on the thermal X-ray phase, and the emission spectrum analysis, the mineral and geochemical structure of sedimentary iron ores from the Bakcharsky deposit and shows of the Ob riverside was studied. The main minerals of ores are goethite and hydrogoethite, siderite is mainly found in swamp ores, and leptochlorite is found in sea oolitic ores. For iron ores, typomorphic elements are the elements from the iron group of Cr, Ti, Ni, Mn, and V, as well as Zn, Sr, and La. High content of Mn, Zr, and La is typical for continental ores, and high content of Pb, V, Ni, Ti, Ba, and Sc is typical for coastal oolitic ores. The basic elements possessing distinctive peculiarities in both types of ores are the following: Mn, V, Ti, Ni, Cr, and Ba. The distribution of impurities in different types of ores reflects their features of the mineral structure and conditions of the formation. Continental siderite and limonite ores were formed within swamp systems. The acid swamp waters, formed in the bottom part of peat swamps, flushed out a large quantity of ferrous iron ions and iron-organic compounds with a delayed runoff in streams and small channels. Now, this phenomenon is observed not only for the Ob terraces, but also for other Siberian rivers such as the Tom, the Yaya, and the Chulym. Sea oolitic hydrooxide-chlorite-siderite ores are concentrated in distant swamp areas, where there are river valleys and shallow marine areas.

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