TECTONOPHYSICAL CRITERIA FOR FORECASTING THE LOCATIONS OF QUARTZ CRYSTAL DEPOSITS (CASE OF SUBPOLAR URAL)

Spatial reconstruction of tectonic stresses within the Subpolar Ural quartz crystal-containing province was conducted by the kinematic method [Gushchenko, 1973, 1979] based on the main indicators of tectonic stresses on slickensides. Local stress states (LSS) and general stress fields for large blocks were reconstructed by the method described in [Sim, Marinin, 2015]. In the blocks with numerous occurrences of quartz crystal (Pelingichey and Omega-Shor blocks), the general stress fields is characterized by a stress state close to uniaxial tension, i.e. the Lode-Nadai coefficient µ=–1. In these blocks, thick quartz veins are perpendicular to the tension axis of the general stress field. In the block without quartz crystal (West Saled), the general stress field is characterized by a triaxial stress state or pure shear state (–1˂µσ˂+1). The LSS of the quartz crystal deposits show the following: the stress state of µ=–1 is typical of quartz veins without quartz crystal nests, and a special kind of stress state is reconstructed near the nests with piezoelectric material. It is named a variation of the type of stress state (VTSS), which means that within one tectonic stage, the type of stress state changes approximately as follows: µσ=+1 (40 %), µσ=–1 (40 %), and –1˂µσ˂+1. It means that in the piezoelectric mineral deposits, pulsating tectonic stresses provided for a fluid flow of hydrothermal solutions at the intersection of ore-bearing and ore-controling faults when tension (µ=–1) was replaced with compression (µ=+1), while the orientations of compression and tension axes remained unchanged. Apparently, such a regime was caused by alternating activation of the above-mentioned faults. The tectonic stress reconstructions were performed for 33 mineral deposits and occur­rences of quartz crystal. VTSS was determined in 32 deposits; one mineral occurrence is characterized by uniaxial tension. Therefore, we propose using VTSS (variation of the type of stress state) as a criterion for predicting the locations of quartz crystal deposits.

Subpolar Ural, tectonic stress, variation of the type of stress state (VTSS), quartz vein, quartz crystal

1. Angelier J., 1994. Fault slip analysis and paleostress reconstruction. In: P.L. Hancock (Ed.), Continental deformation. Pergamon Press, Oxford, p. 53–100.

2. Bott M.H.P., 1959. The mechanics of obique slip faulting. Geological Magazine 96 (2), 109–117. https://doi.org/10.1017/S0016756800059987.

3. Bukanov V.V., Burlakov E.V., Kozlov A.V., Pozhidaev N.A., 2012. Subpolar Urals: minerals of quartz crystal-bearing veins. Russian Mineralogical Almanac 17 (2), 26–31 (in Russian).

4. Gerasimov N.N., Krivoshein A.A., 2013. Quartz mining at the Zhelannoe deposit. Russian Mining Journal (9), 71–72 (in Russian).

5. Gushchenko O.I., 1973. Analysis of the orientations of the slip on the fault plane and their tectonophysical interpretation during the reconstruction of palaeostresses. Doklady AN SSSR 210 (2), 331–334 (in Russian).

6. Gushchenko O.I., 1979. The method of kinematic analysis of destruction structures in reconstruction of tectonic stress fields. In: A.S. Grigoriev, D.N. Osokina (Eds), Fields of stress and strain in the lithosphere. Nauka, Moscow, p. 7–25 (in Russian).

7. Karyakin A.E., Smirnova V.A., 1967. Structures of Quartz Crystal-Bearing Fields. Nedra, Moscow. 240 p. (in Russian).

8. Lacombe O., 2012. Do fault slip data inversions actually yield “paleostresses” that can be compared with contemporary stresses? A critical discussion. Comptes Rendus Geoscience 344 (3–4), 159–173. https://doi.org/10.1016/j.crte.2012.01.006.

9. Osokina D.N., 1987. On the hierarchical properties of the tectonic field of stresses and deformations in the Earth’s crust. In: A.S. Grigoriev, D.N. Osokina (Eds), Fields of stresses and deformations in the Earth’s crust. Nauka, Moscow, p. 136–151 (in Russian).

10. Sim L.A., 2012. Some methodological aspects of tectonic stress reconstruction based on geological indicators. Comptes Rendus Geoscience 344 (3–4), 174–180. https://doi.org/10.1016/j.crte.2011.11.003.

11. Sim L.A., Marinin A.V., 2015. Methods of field tectonophysics for identification of paleostresses. In: Modern tectonophysics. Methods and results. Materials of the Fourth Youth Tectonophysical Workshop. IPE RAS, Moscow. V. 2. P. 47–76 (in Russian).

12. Sim L.A., Yurchenko O.S., Sirotkina O.N., 2005. Tectonic stresses in the northern Urals. Geophysical Journal 27 (1), 110–120 (in Russian).

13. Stephens T.L., Walker R.J., Healy D., Bubeck A., England R.W., 2018. Mechanical models to estimate the paleostress state from igneous intrusions. Solid Earth 9 (4), 847–858. https://doi.org/10.5194/se-9-847-2018.

14. Yamaji A., Sato K., 2011. Clustering of fracture orientations using a mixed Bing ham distribution and its application to paleostress analysis from dike or vein orientations. Journal of Structural Geology 33 (7), 1148–1157. https://doi.org/10.1016/j.jsg.2011.05.006.