Redistribution of petrogenic elements under speleolithogenesis in Okhotnichiya cave (Baikal region, Irkutsk oblast)

Bazarova E.P. ¹, Markova Yu.N. ²

1 Institute of the Earth Crust sb ras; 2 Institute of Geochemistry sb ras, Irkutsk, Russia

bazarova@crust.irk.ru

Mineralogy and geochemistry of the caves are interconnected and relatively insufficiently known, new and recently developed scientific branch. The caves are represents the accessible for a man cavities in the upper part of the Earth crust, which are having unlighted parts and the length (the depth) bigger than two other dimensions. Cave mineral is recognizing as homogeneous solid substance with a definite chemical composition and well-ordered atomic structure normally founded in a cave. Cave minerals are often forms a different speleothems which are the secondary mineral formations, originated in the cave environment from the primary mineral as the result of physicochemical reactions. Well-known stalactites, stalagmites, draperies, cave pearls, moondmilch (lunar milk), flowstone cores and many others are relating to such formations. Cryomineral formations of the caves are also should be taking for the cave minerals, which are originated as a result of chemical equilibrium change of aqueous solution due to its supercooling which is giving rise to crystallization of earlier dissolved components. Cave minerals are allowed to judge about rock composition, which are forming the karsting massif and geochemical researches of secondary mineral formations provides the information about a little known for the present time processes of chemical elements loss and redistribution in natural underground cavities.

Discovered at 2006, Okhotnichiya cave is the third by the length cave of Baikal region at present time [4]. The cave located at oncolyt and stromatolite limestones and dolomites of uluntuiskaya strata of Late Proterozoic. Right away the entrance is a large grotto location of 15 – 20 m width and the height of 5 – 10 m in which for the moment of discovery there were long-term frazil with the area of 4 m².There is no the frazil at present time. The cave extension is 5700 m with the amplitude of 77 m [4]. The cave is representing the galleries system of a height nearly 25 m with the average of 8-10m and width of 1-15 m with the average of nearly 3 m. The secondary formations of a different genesis are widely spread in the cave, among them: residual, collapsed, aqueous mechanical, aqueous chemogenic, cave snow and ice (seasonal formations) and organogenic, the bones of ancient animals are referred to it [2]. Aqueous chemogenic formations of the cave are formed by calcite, aragonite, monohydrocalcite and gypsum. In the area of expansion of seasonal glaciations there were found the cryomineral formations, formed by the rare mineral ikaite (CaCO₃·6H₂O) [1].

It is known, that the composition of secondary minerals of the cave is controlling by the composition of bringing solution, which is, in it’s turn, depends on the composition of enclosing rocks. Moreover, the mechanism of mineral aggregate formation is of a high significance, and in a certain cases is of a decisive importance. The authors were used the classification of Stepanov-Maltsev [3, 5] based on the method of active solution feeding and operating with such the notions as cores, for the classification of aqueous chemogenic formations of Okhotnichiya cave. According to the classification, there are aggregates of gravitational, subaquatic, corallite and antolite cores are divided, and the mineral composition is given in [1].

The authors investigated the redistribution of petrogenic oxides under the secondary mineral formation in the cave. It was determined that under the formation of aggregates of gravitational cores occurs the loss of SiO₂, TiO₂, Al₂O₃, Fe₂O₃, MgO, Na₂O, K₂O and accumulation of SO₃, small accumulation of P₂O₅, and СаО and СО₂ are inactive. During the formation of aggregates of corallite’ cores occurs insignificant redistribution of SiO₂, TiO₂, Al₂O₃, Fe₂O₃, MgO and P₂O₃ and large accumulation of SO₃. The concentration of СаО and СО₂ is practically permanent, the concentration of К₂O in common is also corresponds to the enclosing rocks, and Na₂O is insignificantly caring out.

Thus, the aggregates, formed under more active inflow of solution are the most “pure” in a chemical term. The greatest number of impurities is observed in calcite of corallite cores, which formed under the less active feeding of solution and thin films motion of water under the influence of capillary forces. The presence of SiO₂, TiO₂, Al₂O₃, Fe₂O₃, MgO and P₂O₃ in corallites is also can be connected with clay admixture, trapped by the mineral aggregates during the growth process. The concentration of MgO in corallite composition is relatively increased in comparison with the enclosing rocks, which is confirm the author’s supposition about monohydrocalcite formation due to magnesium ions appearance in karst water.

References:

1. Bazarova E.P., Gutareva O.C., Kononov A.M., Uschapovskaya Z.F., Nartova N.V., Osintsev A.V. Minerals of the Okhotnichiya cave (Baikal region, Irkutsk oblast)// Speleology and karstology, 2011. №7. p. 5 – 14.

2. Klementev A.M., Korshunov E.O., Osintsev A.V. Okhotnichya cave - a new location of fossil fauna at Primorskiy range (Western PreBaikal’e) // Proceedings of the laboratory of ancient technologies. Irkutsk: ISTU Publishing. 2007. Ed. 5. p.146-153.

3. Maltsev V.A. Minerals of karst system of Kup-Kutan caves (south-east of Turkmenistan)//World of Stones, 1993, №2 <vl-maltsev.narod.ru> accessed 2011 May 31.

4. Osintsev A.V. Large caves of Baikalskiy region – newest researches// Speleology and spelestology: the development and interaction of the sciences. Abstract book of international scientific-practical conference. – Nabereznie Chelny:NGPI - 2010. p. 99 - 101.

5. Stepanov V.I. The periodicity of crystallization processes in karst caves// Fersman mineralogical museum proceeding/ - Ed. 20- Мoscow, 1971. p. 161 - 171