PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
The experiments were carried out at iron-ore Severo-Peschanskaya mine in the North Urals [4]. The
Severo-Peschanskaya magnetite deposit represents a blind ore body of complicated form with maximum
dimensions by a course of pool of 1500 m, a dip of 600 m and capacity around 100 m. Series of large
crumpling and crushing zones I and II, which are placed in a direct vicinity from basic constructions of the
industrial site, are caused by intense tectonic activity in a deposit area. In (Fig.1) a schematic cut of the mine
and of a site of installation of geophysical observation stations at the horizon of 240 m are presented.
The observation stations, (Fig.2), were placed in such a way that during 5-8 years the two stations,
the first and the second one which are located close to the ore body should come close to the boundary of the
destruction zone, at the same time as the last station, the third one, in an area of the main trunk, should be
located in a «quiet» zone where effect of mining operations should remain a minimum one.
Rock massif broken by tectonically fractured zones was composed of diorite and porphyrites. The
observation points were located at distance of 700-800 meters away from the explosions and the ore body at
the depth of 450 meters. The measurements were made by means of four probes with ultrasonic transducers
working like electrodes for observations of electrical anisotropy parameters. At each station (Fig.2) four bore
holes were drilled at the depth of around of 4 m and from the wall of the rock production in a zone of natural
pressures four probes with ultrasound sensors were installed, the bodies of which were used as electrodes.
The distance between the holes reached about one meter. The holes were cemented which ensured steady
contact between sensors and the rock and constancy of measurement base. The base deformation is small [4,
5] and it may be ignored. This fact allowed to relate all the observed variations of elastic impulse
propagation time (the velocity of elastic wave propagation) between the sensors and also variations of
electric resistance, at the account of strain stress state of the massif. It also permitted to monitor temporal
variations of physical parameters (deformation, elastic wave velocity, electrical resistance etc.). Not only
variations of the stress state of the massif were evaluated but the deformation process as a single rapturecontinuous
process was also reconsidered.
The observations were carried out with intervals of longitudinal wave velocities which was included
in successive comparison of propagation times of elastic impulse for the base during the observation time.
The error of determination of elastic impulse propagation time reached ±0,5%.[5]. The electrical
anisotropy parameter (as analogy with coefficient of electrical anisotropy) K* was determined as difference
of potentials measured on mutually perpendicular installations in stabilized tone. De-energizing the mine in a
period of conducting mass explosions decreased noise interference and gave opportunity to observe
anomalous variations of K* by a value up to 0.06 % [6]. Thus, monitoring by geophysical methods was
realized with the use of the means of measurement and automating observations available at present. The
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