- Email: [email protected]
Water-rock-ore Interaction (on Example: Major Bakchar Iron-ore Deposit – Western Siberia, Russia)
Available online at www.sciencedirect.com
ScienceDirect Procedia Earth and Planetary Science 17 (2017) 690 – 693
15th Water-Rock Interaction International Symposium, WRI-15
Water-rock-ore interaction (on example: major Bakchar iron-ore deposit – Western Siberia, Russia) Lepokurova Olesya E.a,c, Ivanova Irina S.b,c,1 a
Tomsk Division of Trofimuk Institute of Petroleum-Gas Geology and Geophysics of the Siberian Branch of the RAS, 4, Academichesky ave., Tomsk 634021, Russia b Institute of Ecological Problems of the North, Ural Branch of the RAS, Nab. Severnoi Dviny, 23, Arkhangelsk 163000, Russia c National Research Tomsk Polytechnic University, Lenin Avenue, 30, Tomsk 634050, Russia
Abstract The paper includes data of the enclosing sediment, iron ore and groundwater composition within Bakchar iron ore cluster. Based on the water chemical composition analysis the thermodynamic equilibrium was calculated for enclosing sediment–groundwater– secondary sediments system, and being correlated to existing geological data. According to thermodynamic calculations, water is non-equilibrium to primary enclosing rock aluminosilicate minerals in which they dissolve and, consequently, are enriched by these chemical elements: Fe, Ca, Mg, K, Na, Si, Al, Mn and others. These accumulated elements in the solution provide claywater equilibrium, carbonate-water equilibrium, Fe oxides and hydrooxides-water equilibrium. 2017Published The Authors. Published by Elsevier B.V. © 2017 by Elsevier B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of WRI-15. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 Keywords: iron, groundwater, water-rock-ore system, Bakchar deposit, Western Siberia
1. Introduction Since 2008 the authors have been studying the specific formation conditions of iron-bearing groundwater via thermodynamic calculations of the processes in the water-rock system within Tomsk Oblast (Western Siberia)1,2. The most challenging area is Bakchar iron ore cluster, one of the major global iron ore deposit. This paper gives a detailed description of a one-stage investigation – data correlation of enclosing sediment composition (including iron ore composition) to thermodynamic equilibrium (in water-rock system) calculation results based on water chemical composition.
*Corresponding author. Tel.: +7-913-888-6969; fax: +7-382-249-2163. E-mail address: [email protected]
1878-5220 © 2017 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2016.12.155
E. Lepokurova Olesya and S. Ivanova Irina / Procedia Earth and Planetary Science 17 (2017) 690 – 693
2. Research object Research target is upper aquifer groundwater within Bakchar ore cluster at a depth of 400 m. Bakchar cluster is the foremost investigated area within Western Siberia iron ore basin (fig. 1). This iron ore deposit, located in Bakchar region, Tomsk Oblast (within Andarma and Iksa interstream area, Chaya River tributary), is the major one not only in Russia but also in the world. This cluster is confined to Upper Cretaceous and Paleogene sediments superposed by Neogene-Quaternary series (160-200 m.). Productive layers range from 2 to 40 m. Iron-bearing layers include coastal-marine sediments – gritstone, oolite ore, sandstone, aleurolite and clays. Iron content varies from 34.7 to 53 %, whereas the average iron content is 40 %3. Industrial ores leptochlorite and/or oolite hydrogeothite. According to the oolite iron ore mineral composition, the basic minerals are goethite, hydrogeothite, siderite and lepthochlorite. Based on the latest X-ray fluorescence analysis and electron microscopy results4 the following minerals were observed in oolite aggregates: quartz, feldspar, sphalerite, rutile, ilmenite, zircon, magnetite, calciphosphates (anapaite) and REE phosphates (clarite). Some authors indicate the possible occurrences of sulfides (pyrite), glauconite and chlorite5,6. These ores formed in highly permeable sand sediments overlying and underlying between less permeable clay and aleurolite layers. It should be noted that, originally, sands were quartz-iron including glauconite, magnetite, ilmenite, feldspar, biotite, muscovite, pyroxene, sphene, hornblende and other aluminosilicates. Enormous amounts of water filtered through the above-mentioned horizons at their early formation stages. This hydrogeological setting even exists today.
Fig. 1. Location map and geologic-hydrogeochemical cross-section of Bakchar iron ore cluster: 1 –boundaries of Western Siberia; 2 – Western Siberia oolite-iron ore basin; 3 – geological cross-section contour; 4 – tested wells; 5 – clay rocks (nearly non-aquiferous); 6 – ferruginous sandstones (Fе = 20 – 30 %); 7 – iron ores (Fе = 30 – 45 %); (8 – 10) – areal water distribution with differently mineralized (g/l) ion salt composition: 8 – up to 0.7 (НСО3-Сa and НСО3-Сa-Mg рН 6.8 – 7.8); 9 – 0.6 – 1.2 (НСО3-Сa and НСО3-Na рН 6.8 – 8.6); 10 – > 2.5 (ClНСО3–Na and Cl–Na pH > 8)
The hydrogeological cross-section of Bakchar region indicates intensively water-encroached sediments (fig. 1). These ore horizons could be also related to aquifers, although they are intermittently interstratified with weakly water-permeable glauconite-leptochlorite-clay ore horizons and marine clays. The upper first three aquifer horizons are Quaternary and Paleogene sand sediments (Q II-P2–3). The fourth horizon is confined to Gankin suite sediments (K2 gn), formed from water encroached sediments with a thickness of 25-30 m. There is no confining layer in this aquifer so it merges directly into the iron ore thickness. At the hydrological cross-section base, underlying the iron ore thickness, fifth aquifer is located confined to sand sediments in the lower Ipatovian suite (K 2 ip). All horizons include artesian water which indicates the presence of possibly only one remote catchment basin. 3. Experimental data 29 groundwater samples from 23 wells were selected and analyzed. Average chemical composition is depicted in tab. 1. Detailed description can be found in1,2. Groundwater, circulating over the iron ore deposits in Quaternary and Paleogene sediments, contains highly increased Fe ion concentrations, i.e. up to 10 ppm, however, this concentration is not the highest in this region (up to 40 ppm). Under the iron ore deposits in the water of Ipatovian suite sediments (at a depth of 390 m.) the Fe concentrations decrease 6 times to the average value. This fact could show that Fe from groundwater precipitates into secondary sediments during its filtration through the rocks.
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E. Lepokurova Olesya and S. Ivanova Irina / Procedia Earth and Planetary Science 17 (2017) 690 – 693 Table 1. Average groundwater chemical composition in iron ore cluster, within Bakchar territory. Component Depth, m рН TDS, ppm HCO3–, ppm СО2, ppm SO42–, ppm Cl–, ppm Ca2+, ppm Mg2+, ppm Na+, ppm Fetot, ppm Si4+, ppm Mn2+, ppm DOC, mgO/l Al, ppb P, ppb B, ppb Sr, ppb Number of analysis
Aquifer sediments QII –Р2-3 К2 concentration (av) concentration (av) 20–160 (94) 130–392 (200) 6,8 – 7,8 (7,3) 6.9 – 8.6 (7.6) 410 – 740 (621) 594 – 2652 (1241) 305 – 549 (455) 359 – 817 (548) 2 – 35 (14) 2 – 58 (22) 0.1 – 3.2 (1.3) 0.1 – 11.3 (3.5) 0.6 – 35.5(4.5) 1.7 – 1266.6 (319.5) 82 – 126 (103) 2 – 138 (83) 8 – 32 (20) 1 –40 (23) 6 – 31 (17) 43 – 900 (273) 0.2 – 9.8 (4.5) 0.3 – 10.3 (3.2) 8 – 16 (12) 4 – 15 (9) 0.1 – 0.5 (0.2) 0.1 – 0.6 (0.3) 2.1–5.4 (3.8) 1.0–5.3 (3.5) 8 – 982 (202) 11 – 143 (68) *210 – 813 (446) *58 – 461 *23.7 – 95.9 (62.6) *107.7 – 2331.2 *480 – 757 (630) *1034 – 1322 18 (*5) 11 *2)
4. Results and discussion The HydroGeo program designed by7 was applied for the equilibrium calculations. This program is based on the equilibrium constant method. Water chemical analysis results, including organic substance concentrations, solution temperature, Eh and pH are implemented into the program. Chemical compound activity (i.e. in the solution itself) was obtained on the basis of time-consuming hydrogeochemical calculations. If compared to reference values (high or low values), saturated and / or unsaturated solutions (saturation parameter) are relevant to this or that mineral. The following investigation included those minerals that are found in the rocks of the above-mentioned crosssection: carbonates (calcite, magnesite, dolomite, siderite, rhodochrosite) and aluminosilicates (quartz, feldspar, clays and others). The investigation results are depicted in tab. 2. The obtained data showed that the water is in nonequlibrium with primary water-bearing rock minerals: feldspar, muscovite, biotite, pyroxene, hornblende, epidote, chlorite and others. Moreover, the Upper sediment groundwater (Quaternary, Neogene and Paleogene) are more understaurated relevant to initial aluminosilicate minerals due to low mineralization values and pH. In this case, under such conditions above-mentioned minerals actively dissolve, especially, pyroxene, epidote and hornblende which are Ca, Mg, Na, Fe, K, Si, Al sources. Some elements precipitate from the solution into secondary sediments: oxides and hydrooxides (Fe, Mn и Al), clays (kaolinite, montmorillonite, excluding potassium), carbonates (rhodochrosite, calcite, siderite, dolomite) which do not dissolve under these conditions. Table 2. Saturation parameter values of groundwater in basic rocks. Aquifer Calcite Siderite Dolomite Magnesite Rhodochrosite Albite Anorthite Muscovite Chlorite (Mg) Daphnite Fe-sepiolite Са-montmorillonite Nа-Mt Mg-Mt Illite Kaolinite Quartz Gibbsite Geothite
Paleogene-Quaternary -0.7–2.6/0.8 -1.1–2.9/1.5 -4.1–1.8/-0.9 -3.6–(-0.5)/-1.9 1.1–4.3/2.7 -3.2–(-1.8)/-2.4 -5.2–(3.3)/4.2 -2.4–(-1.3)/-1.8 -11–4.8/-0.5 -12.0–3.1/-4.0 -0.2–1.9/1.0 -0.8–0.7/0.1 -0.9–0.5/0.1 0.5–2.2/1.4 -1.3–(-0.3)/-0.1 0.3–1.1/0.8 1.7–2.6/2.2 13–25/18 28–39/32
Cretaceous -0.5–2.4/1.0 -0.2–4.1/1.9 -2.9–2.8/0.1 -2.6–0.4/-1.1 0.1–7.4/2.1 -2.1–0.1/-1.2 -5.0–(-3.2)/-4.1 -1.8–(-0.3)/-1.2 -6.4–5.2/2.2 -13.0–4.6/-3.5 -0.1–3.6/1.2 -0.3–1.3/0.4 0.2–2.7/1.4 1.1–3.0/1.9 -0.8–0.8/-0.1 0.5–1.1/0.9 1.0–2.5/1.8 14–28/20 29–42/35
Water in Cretaceous sediments are more alkaline and mineralized, but, at the same time, rather undersaturated relevant to endogenous minerals. However, they are more saturated to secondary aluminosilicates (forming illinite, Fe-sepiolite, daphnite, Mg-chlorite, and even albite) and carbonates (forming magnesite). At depth, water composition changes from HCO3-Ca to HCO3-Na, which is associated with secondary mineral formation.
E. Lepokurova Olesya and S. Ivanova Irina / Procedia Earth and Planetary Science 17 (2017) 690 – 693
Carbonates bond (precipitate from water) Ca, Mg, Fe, C; clay minerals- Al, Si, Ca, Mg, Fe, partially, Na and K, oxides and hydrooxides-Fe, etc. Na is fewer bonds with secondary sediments, as water remains in non-equilibrium to sodium minerals. Thus, sodium continues to accumulate in the water; in this case, the water composition changes to sodium – HCO3-Na. Consequently, filtrating water primarily dissolved feldspar and other minerals in terrigene enclosing rocks. In this case, a geochemical environment developed including allied common parameters (pH, Eh, O2, CO2, Fe2+, Fe3+, Si, salinity, etc.) of today’s environment. The most similar features of this environmental are gley, more or less neutral environment, slightly brackish water and increased Fe concentration. Such an environment furthered the formation of Fe hydrooxides and carbonates: hydrogoethite and siderite, where Si and Al are as usually bonded with clays. However, the increased Fe and Mg concentration in water provided such conditions that montmorillonite was substituted by iron-chlorite (leptochlorite) and possibly glauconite. Partially, other minerals formed (illinite, montmorillonite), as well as calcite which is always in equilibrium with above-mentioned groundwater. 5. Conclusion Although groundwater within major Bakchar iron ore cluster embraces increased Fe concentration (up to 10 ppm), it is not the highest in this territory (up to 40 ppm). Besides iron ore concentrates within the water of upper pre-ore horizons and lower ore deposits, where iron ore concentration sharply increases in the water of Cretaceous sediments. This indicates the fact that iron ore concentration precipitates from water into secondary sediments progressively as it filtrates through the rocks. According to thermodynamic calculations, water is non-equilibrium to primary enclosing rock aluminosilicate minerals (feldspar, muscovite, biotite, pyroxene, epidote and others) in which they dissolve and, consequently, are enriched by these chemical elements: Fe, Ca, Mg, K, Na, Si, Al, Mn and others. These accumulated elements in the solution provide clay-water equilibrium (kaolinite, montmorillonite, partially, chlorite), carbonate-water equilibrium (rhodochrosite, calcite, dolomite, siderite), Fe oxides and hydrooxides-water equilibrium. Such “equilibrium” according to 8 is equilibrium-non-equilibrium: water is always non-equilibrium to primary aluminosilicates, while under specific geochemical conditions it could be equilibrium to secondary ones. Water in Cretaceous ore and pre-ore sediments is equilibrium to Fe clay minerals (daphnite and sepiolite), hydromica and, partially, with magnesite and albite. In other words, secondary minerals are formed which could be observed in enclosing rocks of the above-described deposit, including ores and sediments. Acknowledgements The authors thank Professor Stepan L. Shvartsev for his contribution in the publication of this paper. The research was supported by the Russian Foundation for Basic Research, projects No.16-35-00002, 16-05-00155. This work was supported under the state assignment of the Ministry of Education and Science of Russia “Nauka” № 5.1931.2014/К. References 1. Ivanova I.S., Lepokurova O.E., Pokrovsky O.S., Shvartsev S.L. Iron-containing groundwater in the upper hydrodynamic zone in the central part of west-siberian artesian basin. Water Resources Journal; 2014; 41 (2); 164–179. 2. Lepokurova O.E., Ivanova I.S. Geochemistry of underground waters of the Bakchar iron ore deposit area (Tomsk region). Tomsk State University Journal; 2011; 353; 212–216 3. Mazurov A.K., Bojarko G.O., Ananev A.A., Emeshev V.G. Development potentialities of iron-ore deposits in the Tomsk Oblast. Mineral Resources in Russia. Economics and Management; 2005; 5; 16 – 20. 4. Rudmin M.A., Mazurov A.K., Ruban A.S. Mineral and elemental composition of iron ores in Bakchar iron ore cluster (Tomsk oblast). Fundamental Research; 2014; 11; 1323–1327. 5. Asochakova E.V., Bukharova O.V. Mineral inclusions of iron ores of Bakchar deposit (Western Siberia). Tomsk State University Journal; 2013; 369; 168–172. 6. Lepokurova O.E., Ivanova I.S. Ravnovesija podzemnyh vod rajona Bakcharskogo zhelezorudnogo mestorozhdenija (Tomsk Oblast ) s mineralami vmeshhajushhih porod. Materialy Vtoroj Vserossijskoj konferencii s mezhdunarodnym uchastiem «Geologicheskaja jevoljucija vzaimodejstvija vody s gornymi porodami». Vladivostok: Dalnauka Publishing House. 2015; 106–109. 7. Bukaty M.B. Software engineering for the solution of hydrogeological problems. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering; 2002; 305 (6); 348 – 365. 8. Shvartsev S.L. Geochemistry of fresh groundwater in the main landscape zones of the earth. Geochemistry International; 2008; 46 (13); 12851398.
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ScienceDirect Procedia Earth and Planetary Science 17 (2017) 690 – 693
15th Water-Rock Interaction International Symposium, WRI-15
Water-rock-ore interaction (on example: major Bakchar iron-ore deposit – Western Siberia, Russia) Lepokurova Olesya E.a,c, Ivanova Irina S.b,c,1 a
Tomsk Division of Trofimuk Institute of Petroleum-Gas Geology and Geophysics of the Siberian Branch of the RAS, 4, Academichesky ave., Tomsk 634021, Russia b Institute of Ecological Problems of the North, Ural Branch of the RAS, Nab. Severnoi Dviny, 23, Arkhangelsk 163000, Russia c National Research Tomsk Polytechnic University, Lenin Avenue, 30, Tomsk 634050, Russia
Abstract The paper includes data of the enclosing sediment, iron ore and groundwater composition within Bakchar iron ore cluster. Based on the water chemical composition analysis the thermodynamic equilibrium was calculated for enclosing sediment–groundwater– secondary sediments system, and being correlated to existing geological data. According to thermodynamic calculations, water is non-equilibrium to primary enclosing rock aluminosilicate minerals in which they dissolve and, consequently, are enriched by these chemical elements: Fe, Ca, Mg, K, Na, Si, Al, Mn and others. These accumulated elements in the solution provide claywater equilibrium, carbonate-water equilibrium, Fe oxides and hydrooxides-water equilibrium. 2017Published The Authors. Published by Elsevier B.V. © 2017 by Elsevier B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of WRI-15. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 Keywords: iron, groundwater, water-rock-ore system, Bakchar deposit, Western Siberia
1. Introduction Since 2008 the authors have been studying the specific formation conditions of iron-bearing groundwater via thermodynamic calculations of the processes in the water-rock system within Tomsk Oblast (Western Siberia)1,2. The most challenging area is Bakchar iron ore cluster, one of the major global iron ore deposit. This paper gives a detailed description of a one-stage investigation – data correlation of enclosing sediment composition (including iron ore composition) to thermodynamic equilibrium (in water-rock system) calculation results based on water chemical composition.
*Corresponding author. Tel.: +7-913-888-6969; fax: +7-382-249-2163. E-mail address: [email protected]
1878-5220 © 2017 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of WRI-15 doi:10.1016/j.proeps.2016.12.155
E. Lepokurova Olesya and S. Ivanova Irina / Procedia Earth and Planetary Science 17 (2017) 690 – 693
2. Research object Research target is upper aquifer groundwater within Bakchar ore cluster at a depth of 400 m. Bakchar cluster is the foremost investigated area within Western Siberia iron ore basin (fig. 1). This iron ore deposit, located in Bakchar region, Tomsk Oblast (within Andarma and Iksa interstream area, Chaya River tributary), is the major one not only in Russia but also in the world. This cluster is confined to Upper Cretaceous and Paleogene sediments superposed by Neogene-Quaternary series (160-200 m.). Productive layers range from 2 to 40 m. Iron-bearing layers include coastal-marine sediments – gritstone, oolite ore, sandstone, aleurolite and clays. Iron content varies from 34.7 to 53 %, whereas the average iron content is 40 %3. Industrial ores leptochlorite and/or oolite hydrogeothite. According to the oolite iron ore mineral composition, the basic minerals are goethite, hydrogeothite, siderite and lepthochlorite. Based on the latest X-ray fluorescence analysis and electron microscopy results4 the following minerals were observed in oolite aggregates: quartz, feldspar, sphalerite, rutile, ilmenite, zircon, magnetite, calciphosphates (anapaite) and REE phosphates (clarite). Some authors indicate the possible occurrences of sulfides (pyrite), glauconite and chlorite5,6. These ores formed in highly permeable sand sediments overlying and underlying between less permeable clay and aleurolite layers. It should be noted that, originally, sands were quartz-iron including glauconite, magnetite, ilmenite, feldspar, biotite, muscovite, pyroxene, sphene, hornblende and other aluminosilicates. Enormous amounts of water filtered through the above-mentioned horizons at their early formation stages. This hydrogeological setting even exists today.
Fig. 1. Location map and geologic-hydrogeochemical cross-section of Bakchar iron ore cluster: 1 –boundaries of Western Siberia; 2 – Western Siberia oolite-iron ore basin; 3 – geological cross-section contour; 4 – tested wells; 5 – clay rocks (nearly non-aquiferous); 6 – ferruginous sandstones (Fе = 20 – 30 %); 7 – iron ores (Fе = 30 – 45 %); (8 – 10) – areal water distribution with differently mineralized (g/l) ion salt composition: 8 – up to 0.7 (НСО3-Сa and НСО3-Сa-Mg рН 6.8 – 7.8); 9 – 0.6 – 1.2 (НСО3-Сa and НСО3-Na рН 6.8 – 8.6); 10 – > 2.5 (ClНСО3–Na and Cl–Na pH > 8)
The hydrogeological cross-section of Bakchar region indicates intensively water-encroached sediments (fig. 1). These ore horizons could be also related to aquifers, although they are intermittently interstratified with weakly water-permeable glauconite-leptochlorite-clay ore horizons and marine clays. The upper first three aquifer horizons are Quaternary and Paleogene sand sediments (Q II-P2–3). The fourth horizon is confined to Gankin suite sediments (K2 gn), formed from water encroached sediments with a thickness of 25-30 m. There is no confining layer in this aquifer so it merges directly into the iron ore thickness. At the hydrological cross-section base, underlying the iron ore thickness, fifth aquifer is located confined to sand sediments in the lower Ipatovian suite (K 2 ip). All horizons include artesian water which indicates the presence of possibly only one remote catchment basin. 3. Experimental data 29 groundwater samples from 23 wells were selected and analyzed. Average chemical composition is depicted in tab. 1. Detailed description can be found in1,2. Groundwater, circulating over the iron ore deposits in Quaternary and Paleogene sediments, contains highly increased Fe ion concentrations, i.e. up to 10 ppm, however, this concentration is not the highest in this region (up to 40 ppm). Under the iron ore deposits in the water of Ipatovian suite sediments (at a depth of 390 m.) the Fe concentrations decrease 6 times to the average value. This fact could show that Fe from groundwater precipitates into secondary sediments during its filtration through the rocks.
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E. Lepokurova Olesya and S. Ivanova Irina / Procedia Earth and Planetary Science 17 (2017) 690 – 693 Table 1. Average groundwater chemical composition in iron ore cluster, within Bakchar territory. Component Depth, m рН TDS, ppm HCO3–, ppm СО2, ppm SO42–, ppm Cl–, ppm Ca2+, ppm Mg2+, ppm Na+, ppm Fetot, ppm Si4+, ppm Mn2+, ppm DOC, mgO/l Al, ppb P, ppb B, ppb Sr, ppb Number of analysis
Aquifer sediments QII –Р2-3 К2 concentration (av) concentration (av) 20–160 (94) 130–392 (200) 6,8 – 7,8 (7,3) 6.9 – 8.6 (7.6) 410 – 740 (621) 594 – 2652 (1241) 305 – 549 (455) 359 – 817 (548) 2 – 35 (14) 2 – 58 (22) 0.1 – 3.2 (1.3) 0.1 – 11.3 (3.5) 0.6 – 35.5(4.5) 1.7 – 1266.6 (319.5) 82 – 126 (103) 2 – 138 (83) 8 – 32 (20) 1 –40 (23) 6 – 31 (17) 43 – 900 (273) 0.2 – 9.8 (4.5) 0.3 – 10.3 (3.2) 8 – 16 (12) 4 – 15 (9) 0.1 – 0.5 (0.2) 0.1 – 0.6 (0.3) 2.1–5.4 (3.8) 1.0–5.3 (3.5) 8 – 982 (202) 11 – 143 (68) *210 – 813 (446) *58 – 461 *23.7 – 95.9 (62.6) *107.7 – 2331.2 *480 – 757 (630) *1034 – 1322 18 (*5) 11 *2)
4. Results and discussion The HydroGeo program designed by7 was applied for the equilibrium calculations. This program is based on the equilibrium constant method. Water chemical analysis results, including organic substance concentrations, solution temperature, Eh and pH are implemented into the program. Chemical compound activity (i.e. in the solution itself) was obtained on the basis of time-consuming hydrogeochemical calculations. If compared to reference values (high or low values), saturated and / or unsaturated solutions (saturation parameter) are relevant to this or that mineral. The following investigation included those minerals that are found in the rocks of the above-mentioned crosssection: carbonates (calcite, magnesite, dolomite, siderite, rhodochrosite) and aluminosilicates (quartz, feldspar, clays and others). The investigation results are depicted in tab. 2. The obtained data showed that the water is in nonequlibrium with primary water-bearing rock minerals: feldspar, muscovite, biotite, pyroxene, hornblende, epidote, chlorite and others. Moreover, the Upper sediment groundwater (Quaternary, Neogene and Paleogene) are more understaurated relevant to initial aluminosilicate minerals due to low mineralization values and pH. In this case, under such conditions above-mentioned minerals actively dissolve, especially, pyroxene, epidote and hornblende which are Ca, Mg, Na, Fe, K, Si, Al sources. Some elements precipitate from the solution into secondary sediments: oxides and hydrooxides (Fe, Mn и Al), clays (kaolinite, montmorillonite, excluding potassium), carbonates (rhodochrosite, calcite, siderite, dolomite) which do not dissolve under these conditions. Table 2. Saturation parameter values of groundwater in basic rocks. Aquifer Calcite Siderite Dolomite Magnesite Rhodochrosite Albite Anorthite Muscovite Chlorite (Mg) Daphnite Fe-sepiolite Са-montmorillonite Nа-Mt Mg-Mt Illite Kaolinite Quartz Gibbsite Geothite
Paleogene-Quaternary -0.7–2.6/0.8 -1.1–2.9/1.5 -4.1–1.8/-0.9 -3.6–(-0.5)/-1.9 1.1–4.3/2.7 -3.2–(-1.8)/-2.4 -5.2–(3.3)/4.2 -2.4–(-1.3)/-1.8 -11–4.8/-0.5 -12.0–3.1/-4.0 -0.2–1.9/1.0 -0.8–0.7/0.1 -0.9–0.5/0.1 0.5–2.2/1.4 -1.3–(-0.3)/-0.1 0.3–1.1/0.8 1.7–2.6/2.2 13–25/18 28–39/32
Cretaceous -0.5–2.4/1.0 -0.2–4.1/1.9 -2.9–2.8/0.1 -2.6–0.4/-1.1 0.1–7.4/2.1 -2.1–0.1/-1.2 -5.0–(-3.2)/-4.1 -1.8–(-0.3)/-1.2 -6.4–5.2/2.2 -13.0–4.6/-3.5 -0.1–3.6/1.2 -0.3–1.3/0.4 0.2–2.7/1.4 1.1–3.0/1.9 -0.8–0.8/-0.1 0.5–1.1/0.9 1.0–2.5/1.8 14–28/20 29–42/35
Water in Cretaceous sediments are more alkaline and mineralized, but, at the same time, rather undersaturated relevant to endogenous minerals. However, they are more saturated to secondary aluminosilicates (forming illinite, Fe-sepiolite, daphnite, Mg-chlorite, and even albite) and carbonates (forming magnesite). At depth, water composition changes from HCO3-Ca to HCO3-Na, which is associated with secondary mineral formation.
E. Lepokurova Olesya and S. Ivanova Irina / Procedia Earth and Planetary Science 17 (2017) 690 – 693
Carbonates bond (precipitate from water) Ca, Mg, Fe, C; clay minerals- Al, Si, Ca, Mg, Fe, partially, Na and K, oxides and hydrooxides-Fe, etc. Na is fewer bonds with secondary sediments, as water remains in non-equilibrium to sodium minerals. Thus, sodium continues to accumulate in the water; in this case, the water composition changes to sodium – HCO3-Na. Consequently, filtrating water primarily dissolved feldspar and other minerals in terrigene enclosing rocks. In this case, a geochemical environment developed including allied common parameters (pH, Eh, O2, CO2, Fe2+, Fe3+, Si, salinity, etc.) of today’s environment. The most similar features of this environmental are gley, more or less neutral environment, slightly brackish water and increased Fe concentration. Such an environment furthered the formation of Fe hydrooxides and carbonates: hydrogoethite and siderite, where Si and Al are as usually bonded with clays. However, the increased Fe and Mg concentration in water provided such conditions that montmorillonite was substituted by iron-chlorite (leptochlorite) and possibly glauconite. Partially, other minerals formed (illinite, montmorillonite), as well as calcite which is always in equilibrium with above-mentioned groundwater. 5. Conclusion Although groundwater within major Bakchar iron ore cluster embraces increased Fe concentration (up to 10 ppm), it is not the highest in this territory (up to 40 ppm). Besides iron ore concentrates within the water of upper pre-ore horizons and lower ore deposits, where iron ore concentration sharply increases in the water of Cretaceous sediments. This indicates the fact that iron ore concentration precipitates from water into secondary sediments progressively as it filtrates through the rocks. According to thermodynamic calculations, water is non-equilibrium to primary enclosing rock aluminosilicate minerals (feldspar, muscovite, biotite, pyroxene, epidote and others) in which they dissolve and, consequently, are enriched by these chemical elements: Fe, Ca, Mg, K, Na, Si, Al, Mn and others. These accumulated elements in the solution provide clay-water equilibrium (kaolinite, montmorillonite, partially, chlorite), carbonate-water equilibrium (rhodochrosite, calcite, dolomite, siderite), Fe oxides and hydrooxides-water equilibrium. Such “equilibrium” according to 8 is equilibrium-non-equilibrium: water is always non-equilibrium to primary aluminosilicates, while under specific geochemical conditions it could be equilibrium to secondary ones. Water in Cretaceous ore and pre-ore sediments is equilibrium to Fe clay minerals (daphnite and sepiolite), hydromica and, partially, with magnesite and albite. In other words, secondary minerals are formed which could be observed in enclosing rocks of the above-described deposit, including ores and sediments. Acknowledgements The authors thank Professor Stepan L. Shvartsev for his contribution in the publication of this paper. The research was supported by the Russian Foundation for Basic Research, projects No.16-35-00002, 16-05-00155. This work was supported under the state assignment of the Ministry of Education and Science of Russia “Nauka” № 5.1931.2014/К. References 1. Ivanova I.S., Lepokurova O.E., Pokrovsky O.S., Shvartsev S.L. Iron-containing groundwater in the upper hydrodynamic zone in the central part of west-siberian artesian basin. Water Resources Journal; 2014; 41 (2); 164–179. 2. Lepokurova O.E., Ivanova I.S. Geochemistry of underground waters of the Bakchar iron ore deposit area (Tomsk region). Tomsk State University Journal; 2011; 353; 212–216 3. Mazurov A.K., Bojarko G.O., Ananev A.A., Emeshev V.G. Development potentialities of iron-ore deposits in the Tomsk Oblast. Mineral Resources in Russia. Economics and Management; 2005; 5; 16 – 20. 4. Rudmin M.A., Mazurov A.K., Ruban A.S. Mineral and elemental composition of iron ores in Bakchar iron ore cluster (Tomsk oblast). Fundamental Research; 2014; 11; 1323–1327. 5. Asochakova E.V., Bukharova O.V. Mineral inclusions of iron ores of Bakchar deposit (Western Siberia). Tomsk State University Journal; 2013; 369; 168–172. 6. Lepokurova O.E., Ivanova I.S. Ravnovesija podzemnyh vod rajona Bakcharskogo zhelezorudnogo mestorozhdenija (Tomsk Oblast ) s mineralami vmeshhajushhih porod. Materialy Vtoroj Vserossijskoj konferencii s mezhdunarodnym uchastiem «Geologicheskaja jevoljucija vzaimodejstvija vody s gornymi porodami». Vladivostok: Dalnauka Publishing House. 2015; 106–109. 7. Bukaty M.B. Software engineering for the solution of hydrogeological problems. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering; 2002; 305 (6); 348 – 365. 8. Shvartsev S.L. Geochemistry of fresh groundwater in the main landscape zones of the earth. Geochemistry International; 2008; 46 (13); 12851398.
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